Controlling the melt rheology of linear entangled metallo-supramolecular polymers.

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Soft Matter View Article Online

DOI: 10.1039/C4SM02319F

H. Goldansaz1, Q. Voleppe1, S. Piogé2, C.A. Fustin1, J.F. Gohy1, J. Brassinne1, D. Auhl3, E. van Ruymbeke1 1: Bio and Soft Matter, IMCN, Université catholique de Louvain, Belgium 2: Institut des Molécules et des Matériaux du Mans, Département Méthodologie et Synthèse, CNRS, Université du Maine, France 3: Maastricht University, Faculty of Humanities and Sciences, Maastricht, Netherlands

Abstract

We study in the melt the linear viscoelastic properties of supramolecular assemblies obtained by adding different amounts of nickel ions into linear entangled poly(ethylene oxide) (PEO) building blocks end-functionalized by a terpyridine group. We first show that the elasticity of these supramolecular assemblies is mainly governed by the entanglements dynamics of the building blocks, while the supramolecular interactions delay or suppress their relaxation. By adjusting the amount of metal ions, the relaxation time as well as the level of the lowfrequency plateau of these supramolecular assemblies can be controlled. In particular, the addition of metal ions above the 1:2 metal ion/terpyridine stoichiometric ratio allows secondary supramolecular interactions to appear, which are able to link the linear supramolecular assemblies and thus, to lead to the reversible gelation of the system. By comparing the rheological behavior of different linear PEO samples, bearing or not functionalized chain-ends, we show that these extra supramolecular bonds are partially due to the association between the excess of metal ions and the oxygen atoms of the PEO chains. We also investigate the possible role played by the terpyridine groups in the formation of these secondary supramolecular interactions.

I. Introduction

These last years, stimuli-responsive polymers have gained a large interest, showing dramatic changes in their properties and state under the application of a stimulus that can be easily controlled. Stimulus can be of different nature, such as temperature, pH, shear, irradiation, or magnetic field.1-10 Possible applications based on this kind of “smart” materials are diverse and cover several fields such as food industry, construction, coating and biomedicine.11,12 1


Published on 27 November 2014. Downloaded by University of Western Ontario on 02/12/2014 02:56:43.

Controlling the melt rheology of linear entangled metallosupramolecular polymers

Soft Matter

Page 2 of 33 View Article Online

DOI: 10.1039/C4SM02319F

Among the stimuli-responsive polymers, supramolecular polymers, which typically consist of chains held together by weak reversible non-covalent interactions, represent a very promising class of systems since these reversible, non-covalent interactions allow the preparation of high polymeric network with those of low molecular weight molecules.13-15 Due to their reversible bonds, they can change dramatically their shape or phase under the influence of external parameters and are easy to process, re-use and recycle.16-18 They also show interesting selfhealing properties.11, 19-21

The properties of such self-assembled polymers depend on several factors such as the functionality of the building blocks,17,22 the concentration, or the localization, density and the lifetime of associating bonds.16-18,

23-27

Their dynamics can therefore be widely tailored by

playing with these parameters. In particular, the nature of the supramolecular interactions will largely influence the properties of the self-assembled structures. While many works have studied the influence of the presence of hydrogen bonds,17,22,28 supramolecular bonds based on metal-ligand coordination is becoming more exploited today.1,13,27 Metal-ligand coordination is particularly attractive since the coordinative bond is relatively strong (bond energy ca. 40 − 120 kJ/mol),27,29-30 highly directional,31 and the structure, dynamics, and thermodynamic stability of the complexes can be easily varied by choosing among a broad series of ligands and metal ions comprising nearly half the periodic table.1,32-37 Such associative bonds can therefore be of various strengths, from strong bonds that lead virtually to irreversible or static binding of the metal, to weak and labile interactions that allow for reversible and dynamic binding.38,39 Beside the intrinsic stability of metallo-supramolecular aggregates, external parameters also play an important role in the strength of the binding, such as the nature of the solvent1 and of the counter-ions.39 Indeed, the presence of coordinative species can change dramatically their dynamics by altering the dissociation/exchange mechanism between metal complexes.

Several strategies have been successfully applied in the rational design of metallosupramolecular polymer networks and gels,27,38,40 which have been classified in two distinct categories depending on the way cross-links are formed within the supramolecular network. The first category involves the combination of ditopic ligands and metal ions that can accommodate more than two ligands, leading to tris- or higher complexes. In this way, the metal ions act as branching points or as cross-linkers within the polymer network. A typical 2



molecular weight materials that combine the properties of typical covalent polymers or of a

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example of this approach is found in the work of Rowan and coworkers who combined lanthanoid and transition metal ions in conjunction with a ditopic oligomer to produce supramolecular gels that can exhibit thermo-, chemo- and mechano-responses, as well as

involves the combination of multitopic ligands and metal ions, leading to bis-complexes. A typical example of such a gel has been reported by Craig and co-workers.35-37 The coordination motifs were based on poly(4-vinylpyridine) and bifunctional palladium(II) or platinum(II) pincer complexes, which give access to metallo-supramolecular networks that can swell in organic solvents. The dynamic mechanical properties of these materials were tuned by the choice of the metal ion and the structure of the pincer used for coordination. While the influence of the functionality of the building blocks,17,22 the solution concentration, or the localization, density and lifetime of the associating bonds16-18,23-27 on the properties of the transient networks have been largely addressed in literature, only few works have investigated the role played by the own dynamics of the building blocks in the flow properties of such systems. Indeed, most of the supramolecular networks are based on short, non-entangled telechelic building blocks in solution,14,15,19,22 which leads to rheological properties fully governed by the dynamics and density of the associative bonds. However, as it has been shown in refs. [28, 42], considering entangled building blocks can considerably influence the dynamics of such supramolecular polymers, since the physical polymeric networks is created from both the associative bonds and the chain entanglements. Also, for supramolecular polymers in which the density of supramolecular bonds is small compared to the density of these entanglements, we expect that their elasticity will be mostly governed by these building block entanglements.42 In such a case, one should be able to describe their rheological properties by looking at the supramolecular assemblies as if they were entangled covalent polymers able to split into several entangled building blocks at the rhythm of the lifetime of the supramolecular bonds, while an unassociated building block is able to move only after the time needed to disentangle from its neighboring chains. This is the approach we would like to follow here, which differs from describing the properties of supramolecular gels made of short building blocks, which are usually investigated based on the rubber elasticity theory.

In this work, we focus on metallo-supramolecular assemblies based on endfunctionalized building blocks. Our main objective is to investigate how the dynamics of 3



light-emitting properties,4,5,41 and to produce thermoresponsive films.6 The second category

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metallo-supramolecular systems can be influenced by the building block architecture. To this end, relatively long building blocks have been selected to ensure that they are entangled with each other, and we focus on their dynamics in the melt state. In particular, we would like to

well-defined entangled mono-functional and/or bi-functional building blocks of poly(ethylene oxide) (PEO). These systems have been selected for the simplicity of the building block architecture, which should lead to the creation of linear polymeric assemblies. The rheological behavior of the corresponding supramolecular systems should therefore be interpreted without ambiguity, allowing us to point out any unexpected process.1 Due to its specific properties, such as its water solubility, biocompatibility, or high crystallinity, the PEO is an interesting polymer for various industrial and biomedical applications.43-45 By combining these properties with the peculiar dynamics of the reversible bonds, one can therefore expect to further extend its range of possible properties and applications. In order to create supramolecular interactions, the extremities of the PEO building blocks have been functionalized with terpyridine, while nickel ions (Ni++) have been chosen as metal ions, allowing the creation of terpyridine-nickel bis-complexes, as it has already been demonstrated in literature.27,39 The nickel ions have been chosen since the terpyridine-nickel bis complexes are known to be rather stable (with a logK2 value for the nickel(II) bis-complex of around 11.1 in aqueous solutions)39,46(on the contrary, for example, to complexes based on Zn ions). Also, contrary to metal ions such as cobalt, they remain stable at high temperature.

Our first aim is to understand how to control the dynamics of such systems by varying the proportion of metal ions present in the samples, below and above the 1/2 nickel/terpyridine stoichiometric ratio. Since the building blocks are linear and the ligands are localized at their extremities, we expect the creation of linear polymeric assemblies of various lengths, depending on the amount of metal ions added to the system. The addition of metal ions, while keeping their total amount below the 1/2 stoichiometric ratio, should increase the average length of the linear assemblies and thus their corresponding viscosity.47 On the other hand, the influence of an excess of ions on the dynamics of these systems could lead to a decrease of viscosity, compared to the 1/2 stoichiometric ratio, due to the creation of a larger ratio of mono-complexes.39 This assumption is tested in Section IV.4.

Our second objective is to understand how the viscoelastic response of such systems can be tuned, by playing with the relative proportion of mono- and bi-functional entangled 4



investigate the dynamics of metallo-supramolecular polymeric assemblies made from linear

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PEO building blocks. By incorporating mono-functional building blocks, we expect to vary the average length of the supramolecular linear assemblies, since they will act as chain stoppers (for the assemblies). It seems therefore important to understand how this ratio will

In order to analyze the rheological data of the different systems, we use a mesoscopic model based on the tube theory,48-50 which allows us to determine the molar mass distribution (MMD) of a linear polymer or supramolecular assemblies from its viscoelastic behavior.51-53 As detailed in refs. [54-57], tube models are usually used for predicting the rheology of polymer melts, knowing their composition. However, since we expect the polymeric assemblies to be linear, it can be used in the “inverse” way (i.e., from its rheology to its MMD).53,58,59

II. Materials: synthesis and preparation

The supramolecular systems studied are based on dihydroxy-terminated linear poly(ethylene oxide) and α-methoxy ω-hydroxy- linear poly(ethylene oxide) purchased from Aldrich (see Figure 1). These PEO have a weight averaged molar mass of 11 kg/mol and a dispersity of 1.1. Both were dried by azeotropic distillation with toluene before use. They were functionalized at the chain-end(s) by a terpyridine ligand following a reported procedure (see Supplementary Information).60,61

Figure 1: Structure of the mono- and bi-functional building blocks used in this study.

5



influence the elasticity and flow properties of these supramolecular systems.

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Nickel chloride has been added to the samples to promote supramolecular interactions. A typical procedure is described in the following: 200.46 mg (19.4 µmol) of terpyridine di-end

dissolved in 2 mL of methanol by stirring. 5.06 mg (39 µmol) of anhydrous nickel chloride salt (NiCl2, 99.99%) were dissolved in 1 mL of ethanol using sonication. 476 µL of this solution were then added to the PEO solution to reach a final concentration in polymer around 80 g/L. The mixture was then stirred overnight under argon atmosphere at 60˚C in a sealed vial. Finally, the solvent was removed under reduced pressure, and the obtained solid was further dried in a vacuum oven at 35°C for 15 hours. For measuring the viscoelastic properties, the obtained powder was then loaded in the rheometer at 70°C, in order to ensure that it melts easily, and allow to properly shaping the sample.

Several samples have been prepared and analyzed in this work, containing various amounts of metal ions and based on several ratios between mono- or bi-functional PEO. Their compositions are listed in Table 1. It must be noted that the ion concentration in the system is expressed in terms of equivalent with respect to the number of terpyridine end groups. This means, for example, that a supramolecular system with equimolar amounts of bi-functional PEO and ions will contain 0.5 ion equivalents with respect to the terpyridine. Expressed into weight proportions, these amounts are very small (it represents, for example, 0.56 wt% of Ni2+ for Bi_PEO_1eq)

Table 1: list of the samples Mono-functional PEO/ bi- Ni2+ concentration

PEO_11k 2+

PEO_11k_Ni

functional PEO [wt%/wt%]

[ion equivalent]

Non functionalized PEO

/

Non functionalized

Same proportion as in Bi-PEO_1eq

Mono-PEO_0.5eq

100/0

0.5

Bi-PEO_0.5eq

0/100

0.5

Mono-PEO_1eq

100/0

1

Bi-PEO_1eq

0/100

1 (= 0.56 wt%)

(10% Mono-PEO/90% Bi-PEO)_1eq

10/90

1

6



functionalized poly(ethylene oxide) (tpy-PEO-tpy; Mn = 10,800 g/mol; PDI = 1.12) were

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25/75

1


75/25

1

Bi-PEO_0.25eq

0/100

0.25

Bi-PEO_0.75eq

0/100

0.75

Bi-PEO_0.85eq

0/100

0.85

Mono-PEO_2eq

100/0

2

PEO_101k

Non functionalized

/

Non functionalized

/

Non functionalized

4.5 wt%

PEO_231k 2+

PEO_231k_Ni

In addition to these samples, non-functionalized linear PEO of molar mass of 101 and 231 kg/mol have been used as reference samples to determine the material parameters used in the tube model (see Section 4.2). Samples were kept in appropriate condition in order to prevent radical oxidative mechanism, which mainly takes place upon UV- irradiation.44

III. Experimental and Modeling tools

In order to determine the dynamics and structure of these samples, rheological measurements have been performed in the linear regime (see Section III.1), as well as Small Angle X-ray scattering (see Section III.2.). We then use a tube-based model (see Section III.3) to analyze the data and determine the average number of building blocks present in the polymeric assemblies. It must be noted that since the samples are in the melt state, we could not use NMR techniques in order to determine the molar mass of the supramolecular assemblies, as it has been proposed, for example, in ref. [62].

III.1. Rheology Measurements

Small Amplitude Oscillatory Shear (SAOS) measurements were conducted on a Rheometric Scientific strain controlled rheometer (ARES, TA instrument) equipped with parallel plate fixtures (8 mm – 25 mm diameter). The SAOS tests were performed at a temperature of 70 °C. Above the melting temperature (of around 50 °C), this temperature was low enough in order to minimize possible degradation of the sample.44 Dynamic time sweep tests were first 7



DOI: 10.1039/C4SM02319F

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performed to ensure the sample equilibrium (see Section IV.1). Then, strain sweep experiments were conducted to determine the linear viscoelastic region for the frequency sweeps. For non-functionalized PEO samples, the Time-Temperature Superposition (TTS)

samples within the rheometer was checked by looking at the evolution of the viscoelastic response during 30 days. It was found that once equilibrated (after few hours, see Section IV.1), the samples did not show further evolution with time.

III.2. Small Angle X-ray scattering (SAXS)

Time- resolved synchrotron small angle X-ray scattering (SAXS) measurements were carried out at the synchrotron beam line 10 of the PETRA III storage ring at HASYLAB (DESY, Hamburg, Germany). The operating wavelength was 0.154 nm. Data were taken every 8 s with exposure time of 2 s. The scattered intensities are recorded by a 2D detector (Pilatus 300k) positioned at a distance of 1.03-1.28 m above the sample. Custom-made polymeric (Kapton, Vespel®) cells, with 0.25 mm thickness, were used to hold the sample. Temperature was controlled using a convection oven, operating with nitrogen. The temperature accuracy is better than ±0.5 °C.

III.3. Tube-based model – Time Marching Algorithm (TMA)

Stress relaxation function G(t) In order to relate the molar mass distribution (MMD) of a sample to its linear viscoelastic properties, we use the time-marching algorithm (TMA) developed in previous works for predicting the LVE of linear, star,51,63-65 and complex polymers66,67. As described in Section III of the Supplementary Information, we apply it here to the specific case of linear chains.

Inverse problem: From LVE to MMD By adding metal ions to the bi-functional linear building blocks, linear supramolecular chains will be created from the association of several building blocks, which should significantly influence their rheological properties. In order to determine their average number, we use here the TMA model in the inverse direction: starting from the rheological response to determine the corresponding MMD of the supramolecular assemblies.

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principle was applied in order to build a master curve. The stability of the supramolecular

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Since this inverse problem is known to be ill-posed, this approach requires limiting as much as possible the number of unknown parameters to define the MMD of these assemblies. To this end, we start from the assumption that the probability for an end-group to become

considered as constant. Since we expect several linear building blocks to associate into a long, linear assembled chain, this assumption allows us describing the statistical MMD of these polymeric assemblies by a Flory distribution68-70:

n( x) = p a

x −1

(1 − p a ) =

N ( x) N tot

(1)

Where pa is the probability of a building block to be linked to the growing polymeric assemblies, N(x) and n(x) are the number and the number proportion of chains with a degree of polymerization equal to x, and Ntot represents the total number of chains. This last number depends on the initial number of monomers N0, being equal to N0 (1-pa). Knowing that x is equal to ratio between M(x), the molar mass of the chain of degree of polymerization x and

M0, the mass of one monomer, the weight fraction of chains of mass M, w(M), is defined as:

w (M ) =

N ( x )M ( x ) M ( x ) M ( x )−1 2 x −1 2 = p a M 0 (1 − p a ) = x p a (1 − p a ) N0M 0 M0

(2)

Assuming that the MMD of the linear assemblies are well represented by a Flory distribution, the number of unknown parameters to define their MMD is reduced to only one parameter, the weight average molar mass of the sample, Mw (with Mn=Mw/2=M0/(1-pa)). The dispersity of such distributions is, by definition, fixed to 2. The inverse problem can therefore be consistently solved: Mw is determined in order to minimize the relative error, ε(Mn) between the experimental relaxation moduli (G’exp and G”exp) and the moduli predicted, based on this

Mn, (G’theo and G”theo):

ε (M w ) =

1 2Nω

Nω

 (G 'exp (ω i ) − G 'theo (ω i , M n ))

i =1



∑ 

G ' exp (ω i )

+

(G" (ω ) − G" (ω , M ))  , exp

i

theo

G "exp (ω i )

i

with Nω, the number of frequencies at which the moduli have been measured. This method is used in Section IV.3.

9

n

 

(3)



associated via metal-ligand association does not depend on the length of the chain and can be

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IV. Results and discussion

As most of the supramolecular polymers, the assemblies studied here show thixotropic effects that need to be taken into account in the measurement protocol. This is illustrated in Figure 2,

the loading of the sample in the rheometer. It is observed that the rheological response of this sample becomes stable and reproducible only after several hours of measurement. This time evolution of the viscoelastic properties can be attributed to the reorganization of the system and to the formation of new supramolecular bonds, which takes place as soon as the sample is heated. The natural consequence of these new links is an increase of the zero-shear viscosity of the sample through time. As shown later in Section IV.4., this viscosity build-up is reversible, and the supramolecular junctions can be destroyed under large shear rates. 7

7

10

10 (1)

(a)

(2)

(3)

(b) (3) (2) (1)

t 6

6

10

10

(2)(3) (1) 5

10 -4 10

5

-3

10

-2

10

-1

10 ω [rad/s]

0

10

1

10

2

10

10

0

0.5

1

1.5 2 time [s]

2.5

3

Figure 2: (a) Evolution of the storage () and loss () moduli of sample (10% Mono-PEO/90% BiPEO) 1eq, through time, at 70 °C. (b) Storage and loss moduli versus time, corresponding to a frequency of oscillation of 0.1, 1 and 10 rad/s (related to the dashed lines (1), (2) and (3) in Figure 2.a).

Thus, in order to obtain reproducible data, all samples have been first equilibrated during several hours. In order to accelerate the sample equilibration, higher temperature could have been used. However, as it has been described in ref. [44], this could also affect the stability of the PEO chains, leading to their partial degradation. We therefore limited the measurement temperature to 70 °C. 10

4

x 10


which shows several successive frequency sweep measurements at 70°C, performed just after

G',G"(ω ) [Pa]


IV.1. Thixotropic behavior and sample equilibration

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IV.2. Rheological response of non-functionalized linear PEO chains and materials

In order to translate the viscoelastic response of the metallo-supramolecular polymers into their molar mass distribution, one needs first to determine the material parameters of the tube

used as reference samples, having a weight averaged molar mass of 11 kg/mol, 101 kg/mol and 231 kg/mol and respective dispersities of 1.14, 1.06 and 1.2. Their viscoelastic properties are shown in Figure 3. Based on these data, and assuming that their MMD are well represented by a log-normal distribution, the plateau modulus, the molar mass between two entanglements and the Rouse time of an entanglement segment have been fixed to 1.45 MPa, 2000 g/mol and 5 10-8s, respectively. As shown in Figure 3, the agreement between the experimental data and the storage and loss moduli predicted based on these parameters is indeed very good. Compared to the values proposed in literature,71 the value of the plateau modulus is identical, while the value of the molar mass of an entanglement segment, Me, is slightly higher than the one proposed in ref. [71], of 1700 g/mol.

6

10

4

10

2

10

0

10

-2

10

0

10

2

10

ω [rad/s]

4

10

6

10

Figure 3: Experimental storage (o) and loss () moduli of non-functionalized linear PEO samples, of weight averaged molar mass (and dispersity) equal to 11 kg/mol (PDI = 1.14) (blue curves), 101 kg/mol (PDI = 1.06) (red curves) and 231 kg/mol (PDI = 1.2) (grey curves). Continuous curves are predictions from the TMA model.

11


model (see Section III.3). To this end, three linear non-functionalized PEO samples have been

G',G"(ω ) [Pa]


parameters

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IV.3. Metallo-supramolecular chains based on a stoichiometric number of metal ions:

Rheological behavior:

chains should lead to long linear supramolecular chains containing several of these building blocks. On the other hand, the addition of these metal ions to a sample composed of 100 wt% of mono-functional PEO should lead to the creation of linear chains with a molar mass equal to twice the molar mass of the building blocks. This picture is validated in Figure 4, which presents the viscoelastic data of these samples, as well as the data corresponding to the nonfunctionalized PEO building blocks: the influence and efficiency of the metal-ligand interactions is clearly demonstrated by a large viscosity increase. In particular, the linear rheology of the assemblies based on the bi-functional PEO building blocks shows a much longer terminal relaxation time than the samples based on the mono-functional or the nonfunctionalized PEO building blocks, which corresponds to the larger average molar mass of the supramolecular assemblies. The assemblies based on the mono-functional building blocks also show a terminal relaxation time longer than the relaxation of the pure PEO chains.

6

10

1.5 dw(M) 1

dlog(M)

0.5

4

10

10

3

10

4

10

5

10

6

M [g/mol]

2

10

-2

10

0

10

2

10

ω [rad/s]

12

4

10

6

10


As already mentioned in the introduction, adding metal ions to the bi-functional linear PEO

G',G"(ω ) [Pa]


influence of the building block functionalization

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Figure 4: Experimental storage (o) and loss () moduli of the metallo-supramolecular PEO systems obtained by adding nickel ions to bi- (black), mono- (red) or non- (blue) functional PEO building blocks in stoichiometric amount. Continuous curves are predictions from the TMA model, considering

and a log normal distribution with Mw = 22 kg/mol and PDI=1.1 for the mono-functional PEO.

In order to quantify the degree of association of the bi-functional building blocks, the inverse model presented in Section III.3 is used. To do so, the material parameters determined in the case of non-functionalized linear PEO (see Section IV.2) are considered, and the MMD of the supramolecular assembly of bi-functional building blocks is assumed to be correctly described by a Flory distribution (see Equation 4). The only unknown parameter, Mw, is then fixed by best-fitting procedure, in order to minimize the relative error between predicted and experimental viscoelastic data (see Equation 5). Its value is found to be equal to 86 kg/mol, which correspond to a number averaged molar mass, Mn, equal to 43 kg/mol. As shown in Figure 4, the shape of the predicted storage and loss moduli is in good agreement with the experimental data, which allows us to conclude that a Flory distribution, with a fixed dispersity of 2, is indeed suitable to describe the molar mass distribution of this sample. On the other hand, the sample based on mono-functional building blocks can be reasonably well approximated by considering that the supramolecular assemblies are all built from the combination of two building blocks.

From the comparison between experimental and predicted viscoelastic data, we observe that at the timescale and temperature of the measurement, the metal-ligand associations seem to behave like permanent bonds, and the supramolecular assemblies relax similarly to covalent linear chains with same Flory distribution, i.e. mainly by reptation process. It is easier for the whole assemblies to diffuse in the melt in order to relax their stress, than for the supramolecular bonds to break. This result can be understood, based on the results found in previous publications, where it was shown that the lifetime of such bis-complexes is around 103.8 s at 70°C.72,73 Thus, in this case, the relaxation times of the supramolecular assemblies depends on their molar mass distribution, and cannot be represented by a single Maxwell element, as usually observed for supramolecular gels in which the relaxation is fully governed by the dynamics of the supramolecular bonds.1,74

Melt morphology: 13



a Flory molar mass distribution with Mw =86 kg/mol for the bi-functional PEO (see the inset figure),

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Planar aromatics such as pyridine derivatives with simultaneous possibility of pi-pi stacking and metal-ligand association can build up highly ordered columnar or discoid structures, as reported by several authors.75 Depending on the strength of the interaction between the planes

planar structures can lead to their phase separation from the soft polymeric phase into fibrillar or rod like assemblies, evidenced by X-ray scattering and transmission electron microscopy.7678

In such a case, linear chains can associate via pi-pi stacking and create a physical

network,76,77 which prevent or delay the relaxation of the system. From rheological data shown in Figure 4, one can conclude that such a network is not observed. Indeed, the supramolecular assemblies made of several bi-functional building blocks are still relaxing and the corresponding storage modulus does not show any second (low frequency) plateau. Same conclusion was drawn from SAXS measurements, which didn’t show any structure in the melt state (see Supplementary Information).

IV.4. Influence of the ions content on bi-functional PEO building blocks

By adding a lower amount of metal ions to the bi-functional PEO building blocks, compared to the 1:2 metal/terpyridine stoichiometric ratio, the probability to create metalligand bis-complexes able to bridge two functionalized building blocks is reduced. As a consequence, it is expected that the supramolecular assemblies of such samples are of smaller length, compared to sample Bi_PEO_0.5eq. This is tested in Figure 5, which presents the rheological response of sample Bi-PEO_0.25eq (see Table 1). This sample, which only contains 0.25 equivalent of ions, relaxes much faster than the reference sample BiPEO_0.5eq, which contains 0.5 equivalent of ions, while it relaxes much slower than the pure sample. Thus, this result confirms the ability to create shorter supramolecular assemblies by varying the metal ions content. Using our TMA model in the inverse direction (see Section III.3.), the weight-averaged molar mass of this sample is estimated to be equal to 25 kg/mol, i.e. slightly more than twice the molar mass of the building blocks. In the case of these bifunctional building blocks, it is thus possible to vary the average molar mass of the assemblies, (and consequently their viscosity,) from Mw = 11 kg/mol (in the case of the pure sample) to Mw = 86 kg/mol (in the case of the stoichiometric metal/terpyridines ratio).

14



and on their concentration, the crystalline ordering, rigidity and hydrophobicity of these

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6

Bi-PEO-1eq

4

10

Bi-PEO-0.85eq

2

Bi-PEO-0.25eq PEO-10k

Bi-PEO-0.5eq

10

0

10

-4

10

-2

10

0

10

ω [rad/s]

2

10

4

10

Figure 5: Storage (o) and loss () moduli of the metallo-supramolecular systems obtained by adding different equivalents of nickel ions to the bi-functional PEO building blocks. The amount of metal ions is either smaller than the stoichiometric amount of 0.5 eq. (as with 0.25 and 0 eq of ions), either larger (as with 0.85 or 1 eq. of ions).

On the other hand, adding a larger amount of metal ions to the bi-functional PEO building blocks, compared to the 1:2 metal/terpyridine stoichiometric ratio, leads to more surprising results, as illustrated in Figure 5 for samples containing 0.85 or 1 equivalent of ions: the supramolecular systems are not able to flow anymore, showing a gel-like behavior. This behavior differs from the results shown in previous solution studies for other metallosupramolecular systems, which have shown that a too large amount of metal ions, i.e. exceeding the stoichiometric ratio, usually leads to a large reduction of viscosity39,79 due to the creation of terpyridine-metal ion mono-complexes and thus to a reduction of the average length of the polymeric assemblies. In particular, it was shown that the complexation behavior in solution of terpyridine bi-functionalized PEO with several metal-ions such as Co(II), Cd(II) or Cu(II), leads to a viscosity decrease when adding excess of metal-ions. It must be noted however that by adding an excess of Ni(II) salt to the PEO solution, only a small viscosity decrease was observed, contrary to the effect observed with the other metal ions. Based on this result, the authors concluded that with Ni++ ions, the formation of bis-complexes is preferred compared to the creation of mono-complexes in agreement with the respective stability constants,46 which seems to be also the case here. However, while this fact could explain why long linear assemblies do not decompose into shorter assemblies, it does not 15


G',G"(ω ) [Pa]


10

Soft Matter


DOI: 10.1039/C4SM02319F

suffice to explain the network formation that we observe here in the melt for entangled PEO systems.

complexes involving the terpyridine groups and the metal ions since the building blocks are linear and the nickel ions allow the association of only two terpyridine ligands. In order to obtain such viscoelastic behavior with terminal relaxation time larger than 104s, the linear


assemblies should have, at least, a molar mass of 15.106 g/mol, which is not realistic. Based on Figure 5, one can therefore conclude that there is a second type of interaction that takes place, which allows the chains to associate in order to create a network, and that these interactions occur only if there is an excess of metal ions (compared to the stoichiometric amount) which are not trapped into terpyridine-metal complexes.

It is important to note that the network properties obtained by adding an excess of metal ions are reversible. This is illustrated in Figure 6 for sample BI-PEO-0.75eq: a supramolecular network is created through time (see Figure 6a), which can be destroyed under large shear deformation (see Figure 6b). The state of the network after destruction (see the red triangles of Figure 6a) corresponds to the moduli which have been reached at the largest amplitude of deformation, γmax = 200%. Then, starting from this new state, the system will again evolve through time in order to recover its equilibrium state.

6

6

10

10

(b)

(a) 5

G', G"(ω) [Pas]

10 G'(ω) [Pa]


The observed viscoelastic response cannot be only attributed to the creation of

4

10

3

5

10

10

time 2

10 -4 10

4

-3

10

-2

10

-1

0

10 10 ω [rad/s]

1

10

2

10

16

10 -2 10

-1

10

0

10

1

10 γ [%]

2

10

3

10

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Figure 6: (a) Evolution through time of the storage modulus of the metallo-supramolecular systems obtained by adding 0.75 eq. of nickel ions to the bi-functional PEO building blocks (black o), toward its equilibrium state (blue o). The data represented by the triangle symbols have been measured right supramolecular network. (b): Storage (o) and loss () moduli of the same sample, measured as a function of the amplitude of deformation, at a freq. of 10 rad/s. First from low to high, then from high to low amplitude of deformation.

Furthermore, one can observe on Figure 5 that the level of the elastic plateau of the sample containing 1 equivalent of nickel ions is nearly constant, and the value of the observed plateau is close to 1.45 MPa, i.e. close to the value of the plateau modulus of the covalent PEO systems (see Section IV.2). This suggests that adding a low amount of nickel ions (of around 1 wt%) is enough to freeze the motion of nearly 100 wt% of the PEO chains.

From these results, we conclude that this gel-like behavior is due to extra junctions, able to connect together the linear polymeric assemblies made of linear building blocks. Based on literature, we point out three different mechanisms which could lead to the observed gel-like behavior:

The first one is the fact that part of the metal ions in excess can be trapped by the PEO chains themselves, which are able to create coordination complexes with a wide variety of metal cations owing to their simple, regular chemical structure, to the presence of donating oxygen atom in each segment and to their high flexibility.44 Thus, in this case, while weaker than the terpyridine, the oxygen atoms are also expected to play the role of ligands, able to trap the extra cations and create loops of same size as the ion diameter.44,81,82. Such a process is, for example, exploited in electrolyte applications. In the case of the systems described here, this mechanism can indeed consistently explain the observed viscoelastic behavior if we assume that the metal ions can be surrounded by the oxygen atoms from at least two different chains. In this way, as proposed in the cartoon of Figure 7a, associations between the PEO chains are created, leading to the formation of a supramolecular network. The extra nickel ions play thus the role of bridges between different PEO chains, which leads to an important increase of the sample viscosity. This idea is further tested in Section IV.5 by adding metal ions to non-functionalized PEO.

17



after the strain sweep measurements (see Figure b), and show the partial breaking of the

Soft Matter


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As already mentioned, in the experimental conditions considered here, the lifetimes of the metal ion-terpyridine bonds between the PEO chains are long enough to be considered as stable during the measurement. Similarly, based on this picture, the lifetime of these

prevent the relaxation of the sample during the measurement.

(a)

(b)

Figure 7: Cartoon showing the possible interactions between the chains observed with bi-functional PEO building blocks, in presence of nickel ions in a proportion larger than the stoichiometric ratio. The metal ions are represented either by the symbol • or by the symbol Ni2+, while the terpyridines are represented by the symbol [. (a) Coordination complexes are created between the PEO chains and the nickel ions. (b) The extra uncoordinated Ni2+ ions react locally to generate covalent branching chains.

A second process which can lead to a transient network formation of these linear building blocks is the possible clustering of the supramolecular linking motifs. Indeed, several works in literature mention that clustering and stacking of the reversible junctions in supramolecular polymer networks have been observed, leading to a high elastic energy storage, higher than the value expected by the supramolecular junctions only.1,83 In particular, in ref. [1], which investigated the network properties of unentangled, end-functionalized star-like building blocks in solution, mechanical reinforcement of the gels was attributed to the strong electrostatic interaction between the metal-ligand complexes. Another example is shown in refs. [84,85] for metallo-supramolecular polystyrene-[Ru2+]-poly(ethylene oxide) diblock copolymers. The charged complexes and the counter-ions associate into aggregates and therefore, create ‘association points’ between several terpyridines, acting as branching points.

18



secondary interactions between the PEO chains and the metal ions should be long enough to

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Since this association mechanism was not observed with sample Bi-PEO_0.5eq (see Section IV.3), neither in the rheological behavior nor in the SAXS data, clustering of the metal-ligand

The third process which could explain the creation of the observed transient network is the creation of few covalent bonds between PEO chains, due to the extra uncoordinated NiCl2 salts in the material, which can react locally and which can be consumed to generate chemical, i.e. covalent, branching or cross-linking. The fact that metal salts can act as crosslinking agents upon heating has already been reported in literature, for example with PVC.86 In such as case, only few cross-linking molecules are enough to build a transient network, combining covalent cross-linking points and supramolecular metal-ligand interactions. Furthermore, as illustrated in Figure 7b, the network is still breakable, through its reversible metal-ligand bonds.

In order to determine which of these possible mechanisms is at the origin of the gellike behavior observed with bi-functional PEO building blocks, we investigate in the next Section the viscoelastic properties of samples composed of mono- or non-functionalized building blocks in presence of nickel ions.

IV.5. Influence of the ions content on mono-functional PEO and non-functionalized building blocks

As shown in Figure 8, adding nickel ions in excess (compared to the stoichiometric value) to mono-functional building blocks also leads to the apparition of a clear lowfrequency plateau observed in the storage modulus of these samples. As mentioned in Section IV.4, this second plateau cannot be only due to the presence of metal ion-terpyridine associations since there is only one associative extremity per chain and it has been shown that the assemblies made of two building blocks behave like liquid-like samples (see Figure 4). Furthermore, this plateau cannot be explained by the possible clustering effect of the supramolecular linking motifs: this process would lead to the creation of star-like PEO structures containing several arms of molar mass of around 11 kg/mol and, as shown in Figure 8, such star-like architectures are relaxing too fast to lead to this very long low-frequency plateau. Also, if we consider that the second low-frequency plateau is due to the presence of large assemblies obtained via cross-linking reactions, this implies that, in order to reach 19



complexes should necessary involve the contribution of the metal ions in excess.

Soft Matter


DOI: 10.1039/C4SM02319F

terminal relaxation times larger than 1000 s, these assemblies, which are a small proportion, contain a large number of branching points in order to ensure the presence of very deep, slow relaxing, molecular segments, i.e. of generations corresponding to a very large seniority

explained based on a statistical rule of branching.

Therefore, based on these first results, the hypothesis of secondary interactions between the oxygen atoms and the extra metal ions (see Section IV.4) seems the most appropriate to explain the presence of a second plateau in the elastic modulus of monofunctional building blocks. However, it does not mean that this process alone is sufficient to justify the viscoelastic properties of sample Bi-PEO_1eq since there is an important difference between these systems. On Figure 8, one can observed that the level of the low frequency plateau of sample Mono-PEO-1eq is much lower, by nearly three orders of magnitude, than the value of the plateau modulus of the sample composed of bi-functional building blocks, which is comparable to the one of the PEO samples, equal to 1.45 MPa (see Section IV.2). By adding a larger amount of extra Ni2+, as in system Mono-PEO_2eq, the value of this second plateau slightly increases but still stays clearly below the plateau observed with bi-functional building blocks (which contains the same wt% if ions). Assuming that the plateau level scales with the square of the unrelaxed polymer fraction, one can estimate that the proportion of mono-functional building blocks which participates to the supramolecular network is around 3 wt% with 1 equivalent of ions, and 12 wt% with 2 equivalents of metal ions, to be compared to the almost 100 wt% of trapped building blocks for sample Bi-PEO-1eq.

20



value.87 This inhomogeneous repartition of the branched monomers cannot be consistently

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Bi-PEO-1eq

4

MonoPEO-2eq

G',G"(ω ) [Pa]


10

2

10

MonoPEO-0.5eq

MonoPEO-1eq

PEO-10k

0

10

-4

10

-2

10

0

10

ω [rad/s]

2

10

4

10

Figure 8: Storage (o) and loss () moduli of the metallo-supramolecular systems obtained by adding different equivalents of nickel ions to the mono-functional PEO building blocks. For comparison, the rheological data of sample Bi-PEO_1eq are also shown. The continuous curve (―) corresponds to the predicted moduli for star-like PEO chains with arms of 11 kg/mol.

In order to validate the proposition of secondary interactions between nickel ions and the oxygens of the PEO chains, which appear in systems containing an excess of Ni2+ ions, we then study the linear viscoelastic properties of pristine PEO chains, i.e. without terpyridine chain-ends, in which a small amount of ions is added. As shown in Figure 9, which compares the linear viscoelastic properties of the bi-, mono- or non-functionalized linear building blocks in the presence of an equal amount of nickel ions (corresponding to 1eq. for the bi-functional building block), one can observe a clear second plateau in the storage modulus for the nonfunctionalized PEO chains. The presence of this plateau, which is reversible, and thus cannot be due to covalent cross-linking, supports again the idea of supramolecular metal-ligand interactions between the metal ions and the oxygen atoms of the PEO building blocks,44,81,82 leading to the creation of PEO loops around the ions and with at least two different polymer chains surrounding a metal ion.

21


6

10

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6

Bi-PEO-1eq

4

10

Mono-PEO-2eq 2

PEO-10k-Ni2+

10

PEO-10k 0

10

-4

10

-2

10

0

10

ω [rad/s]

2

10

Figure 9: Storage (o) and loss () moduli of the metallo-supramolecular systems obtained by adding 1 equivalent of nickel ions to the mono-functional, bi-functional or non-functionalized PEO building blocks.

We also observe that, despite the larger proportion of free ions in the nonfunctionalized PEO samples, the level of its second plateau is even weaker than in the case of mono-functional building blocks. This difference in the plateau level could be attributed to the fact that, for a fixed proportion of ‘branching agents’, the polymer fraction which is immobilized between two of these branching points, depend on the length of the chains since the short chains contain a larger proportion of free dangling ends. Indeed, here, the linear assemblies of sample Bi-PEO-1eq obtained by metal-terpyridine associations are much longer than the linear assemblies of sample Mono-PEO-2eq, which are twice longer than the nonfunctionalized PEO chains. In order to determine if this difference in length is sufficient to explain the different plateau levels and thus, to determine if oxygen-metal interactions could explain the network-like response of sample Bi-PEO_1eq, we investigate the viscoelastic properties of a very long non-functionalized PEO sample, PEO-231k-Ni2+, in which a large proportion of Ni2+ ions has been added. With a molar mass of 231 kg/mol, the chains are longer than the supramolecular assemblies made of bi-functional building blocks in sample Bi-PEO_1eq. We therefore expect that, if oxygen-metal interaction is the only mechanism needed to obtain the full immobilization of the assemblies made of bi-functional building blocks, sample PEO-231k-Ni2+ should also show a gel-like behavior. 22


G',G"(ω ) [Pa]


10

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Results are shown in Figure 10. It is clear that again, part of the sample is trapped into a reversible network. However, similarly to the shorter non-functionalized sample and to the assemblies made of mono-functional building blocks, a large part of the polymer is still able

functional building blocks combined with metal ions in excess is not enough to explain the full immobilization of sample Bi-PEO-1eq. Obviously, the terpyridine groups play a role in

6

Bi-PEO-1eq

10

4

10

PEO-231k-Ni2+ PEO-231k

2

10

PEO-10k-Ni2+

-4

10

-2

10

0

10

ω [rad/s]

2

10

Figure 10: Storage (o) and loss () moduli of the metallo-supramolecular systems obtained by adding 1 equivalent of nickel ions to the blends of mono-functional, bi-functional or non-functional PEO building blocks.

Thus, from Figures 8-10, we conclude that 1) In the presence of metal ions in excess, oxygenmetal interactions between these ions and PEO chains take place and lead to the immobilization of a fraction of the polymer melt. However, it does not allow the freezing of the motions of the whole sample, 2) Nearly 100 wt% of the assemblies made of bi-functional building blocks participate to the network, which cannot be only attributed to their long length compared to the assemblies made from the mono-functional building blocks, 3) Since crosslinking reactions are not observed with the PEO 231 kg/mol in which Ni2+ ions are added, one cannot explain the origin of the network formation by possible chemical cross-linking enhanced by the presence of uncomplexed ions.

23


the network formation of this last sample.

G',G"(ω ) [Pa]


to flow. This result suggests that the important length of the PEO assemblies based on bi-

Soft Matter


DOI: 10.1039/C4SM02319F

The only remaining process is a possible clustering of the terpyridine groups favored by the metal ions in excess. In the specific case of bi-functional building blocks, this could indeed lead to a freezing of the motion of the building blocks, which are fully trapped

the mono- and non-functionalized building blocks, which always keep a chain extremity which is free to move and relax.

IV.6. Control of the rheological properties by mixing mono- and bi- functional building blocks

As it has been observed in Section IV.3., the functionalized building blocks mixed with a stoichiometric amount of nickel ions are flowing, and their storage and loss moduli show a terminal regime. Their corresponding terminal relaxation time directly depends on the length of the supramolecular assemblies, which can vary from a weight averaged molar mass of 11 kg/mol for a single PEO chain to 86 kg/mol for the supramolecular chains based on the bi-functional building block (with 0.5 eq of metal ion). By blending bi- and mono- functional building blocks, one should be able to gradually vary this average length between these two extremes. On the other hand, it has been observed in the previous Sections that functionalized building blocks mixed with a larger amount of nickel ions do not flow anymore, mainly due to secondary interactions between the oxygen atoms of the PEO chains and the nickel ions. We have also observed that, for a given amount of metal ions, the level of the storage modulus plateau strongly varies with the functionality of the building blocks (see Section IV.5). Mixing bi- and mono- functional building blocks (while keeping the same equivalent amount of metal ions) should therefore allow us to control the level of this plateau.

This is tested in Figure 11, which presents the viscoelastic data of mixtures of bi- and monofunctional linear building blocks in different proportions. It is found that while for the blends containing less than 25 wt% of mono-functional building blocks, the viscoelastic behavior is similar to the sample containing 100 wt% of bi-functional building blocks, larger proportions of the mono-functional PEO block strongly influence this plateau level.

24



between terpyridine groups, while this process should not significantly affect the dynamics of

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Bi-PEO-1eq 6

25% Mono-PEO/75% Bi-PEO 10% Mono-PEO/90% Bi-PEO

75% Mono-PEO/25% Bi-PEO

4

10

Mono-PEO-1eq 2

10

-4

10

-2

10

0

ω [rad/s]

10

2

10

Figure 11: Storage (o) and loss () moduli of the metallo-supramolecular systems obtained by adding 1 equivalent of nickel ions to the blends of mono-functional and bi-functional PEO building blocks.

As mentioned in Section IV.5., the level of this low frequency plateau depends on the fraction of the samples which still contributes to the total stress once the dangling ends of the supramolecular assemblies as well as the unassociated chains have relaxed. It therefore corresponds to the chain fraction which is participating to the supramolecular network and cannot relax within the experimental frequency window. From the results shown in Figure 11, one can see that by adding mono-functional building block, the supramolecular network becomes softer. This can be first explained by the fact that, in average, the supramolecular assemblies obtained by using mono-functional building block have a lower molar mass than the one created from the association of 100 wt% of bi-functional building block. As a consequence, the proportion of dangling ends, which are able to relax at very high frequencies, increases. Furthermore, as described in Section IV.4, in presence of extra metal ions (compared to their stoichiometric ratio), clusters between the metal-ligand complexes act as extra branching points.

From these results, we conclude that the level of the low frequency plateau can be controlled by varying the association degree of these assemblies via the relative proportion of bi- and mono-functional building blocks.

25


G',G"(ω ) [Pa]


10

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DOI: 10.1039/C4SM02319F

V. Conclusion

We have studied the linear viscoelastic properties of supramolecular assemblies

which have been end-functionalized by terpyridine groups. We have shown that by adjusting the amount of metal ions and the proportion of mono- versus bi-functional building blocks, one could control the terminal relaxation time as well as the level of the low-frequency plateau of these supramolecular assemblies.

In particular, it was shown that by adding metal ions in an amount larger than the stoichiometric amount, secondary interactions are taking place, which lead to the creation of a reversible polymeric network. We attributed these reversible interactions to metal-oxygen interactions between these extra metal ions and the PEO chains themselves. However, while this extra association leads to the partial gelation of the system, it stays relatively weak and did not allow explaining the nearly full gelation of the assemblies made of bi-functional PEO building blocks. By confronting the viscoelastic properties of a long, non-functionalized PEO polymer to the behavior of the assemblies created from bi-functional building blocks, both systems containing an excess of free nickel ions, we concluded that another association process is taking place in the sample containing bi-functional building blocks, in which both the metal-terpyridine complexes and the free metal ions play an active role. This could be due to possible clustering of the supramolecular motifs, as it has been observed in ref. [1,84,85].

This work gives us a solid starting point to explore more complex architectures of building blocks, based on both supramolecular and covalent cross-linking points. Furthermore, as perspective work, we would like to further investigate the immobilization effect of nickel ions on pure PEO chains, in relation with the architecture of the chains.

Acknowledgment

The authors are very grateful to Guido Heunen for his support with SAXS measurements, and to DESY (Hamburg, Germany) for allowing us to use their infrastructure and for their help. This work has been supported by the E.U. (Marie Sklodowska-Curie ITN ‘Supolen’, no

26



obtained by adding different amounts of nickel ions into linear entangled PEO building blocks

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607937). EVR and CAF are Research Associates of the FRS-FNRS. QV, JB and HG thank FRIA for financial support.

1. T. Rossow and S. Seiffert, Polym. Chemistry, 2014, 5, 3018.

2. T. Rossow, A. Habicht and S. Seiffert, Macromolecules, 2014, 47, 6473.

3. J. Brassinne, C. A. Fustin and J. F. Gohy, J. Inorg. Polym., 2013, 23, 24.

4. J. B. Beck and S. J. Rowan, J. Am. Chem. Soc., 2003, 125, 13922.

5. S. Rowan and J. Beck, Faraday Discuss., 2005, 128, 43.

6. J. R. Kumpfer, J. J. Wie, J. P. Swanson, F. L. Beyer, M. E. Mackay and S. J. Rowan, Macromolecules, 2012, 45, 473.

7. R. Yerushalmi, A. Scherz, M. E. van der Boom and H. B. Kraatz, J. Mater. Chem., 2005, 15, 4480.

8. N. Nath and A. Chilkoti, Adv. Mater., 2002, 14, 1243.

9. G. Decher and J. B. Schlenoff, Multilayer Thin Films, Eds. Wiley-VCH Verlag GmbH: Weinheim, 2003.

10. M. A. C. Stuart, W. T. S. Huck, J. Genzer, M. Muller, C. Ober, M. Stamm, G. B. Sukhorukov, I. Szleifer, V. V. Tsukruk, M. Urban, F. Winnik, S. Zauscher, I. Luzinov and S. Minko, Nat. Mater., 2010, 9, 101.

11. K. Liu, Y. Kang, Z. Wang and X. Zhang, Adv. Mater., 2013, 25, 5530.

12. A. W. Bosman, R.P. Sijbesma and E.W. Meijer, Materials today, 2004. 7, 34.

27



References

Soft Matter


DOI: 10.1039/C4SM02319F

13. S. Seiffert and J. Sprakel, Chem. Soc. Rev., 2012, 41, 909.

15. W. Weng, J.B. Beck, A.M. Jamieson and S. J. Rowan, J. Am. Chem. Soc., 2006, 128, 1166663.

16. T. F. A. De Greef, M. J. Smulders, M. Wolffs, A. P. H. J. Schenning, R. P. Sijbesma and E. W. Meijer, Chem. Rev., 2009, 109, 5687.

17. P. F. Cordier, F. Tournilhac, C. Soulie-Ziakovic and L. Leibler, Nature, 2008, 451, 7181, 977.

18. T. F. A. De Greef and E.W. Meijer, Nature, 2008, 453, 171.

19. D. Montarnal, F. Tournilhac, M. Hidalgo and L. Leibler, J. Polym. Science: Part A: Polym. Chemistry, 2010, 48, 1133.

20. L. Leibler, Progress on Polymer Science, 2005, 30, 898.

21. J. Yuan, X. Fang, L. Zhang, G. Hong, Y. Lin, Q. Zheng, Y. Xu, Y. Ruan, W. Weng, H. Xia and G. Chen, J. Mater. Chem., 2012, 22, 11515.

22. R.F.M. Lange, M. Van Gurp and E.W. Meijer, J. Polym. Science, Part A: Polym. Chemistry, 1999, 37, 3657.

23. J. Brassinne, A.M. Stevens, E. van Ruymbeke, J.F. Gohy, and C.A. Fustin, Macromolecules, 2014, 46, 9134.

24. S. Pensec, N. Nouvel, A. Guilleman, C. Creton, F. Boue and L. Bouteiller, Macromolecules, 2010, 43, 2529.

25. M. Bellot and L. Bouteiller, Langmuir, 2008, 24, 14176.

28



14. K. P. Nair, V. Breedveld and M. Weck, Macromolecules, 2011, 44, 3346.

Page 29 of 33


DOI: 10.1039/C4SM02319F

26. G. Porte, C. Ligoure, J. Appell and R. Aznar, J. Stat. Mech., 2006, P05005.

27. F. J. Stadler, W. Pyckhout-Hintzen, J.M. Schumers, C.A. Fustin, J.F. Gohy and C. Bailly,

28. K. E. Feldman, M. J. Kade, E.W. Meijer, C.J. Hawker, E. Kramer, Macromolecules, 2009, 42, 9072.

29. A. Goshe, J. Crowley, B. Bosnich, Helv. Chim. Acta, 2001, 84, 2971.

30. A. J. Goshe, I.M. Steele, C. Ceccarelli, A.L. Rheingold and B. Bosnich, Proc. Natl. Acad. Sci. USA, 2002, 99, 4823.

31. G. Lawrance, Introduction to Coordination Chemistry, Wiley, Chichester, 2009.

32. D. Xu and S. L. Craig, Macromolecules, 2011, 44, 5465.

33. D. M. Loveless, S. L. Jeon and S. L. Craig, Macromolecules, 2005, 38, 10171.

34. M. J. Serpe and S. L. Craig, Langmuir, 2006, 23, 1626.

35. W. C. Yount, D. M. Loveless and S. L. Craig, Angew. Chem., 2005, 44, 2746.

36. W. C. Yount, D. M. Loveless and S. L. Craig, J. Am. Chem. 70 Soc., 2005, 127, 14488.

37. W. C. Yount, H. Juwarker and S. L. Craig, J. Am. Chem. Soc., 2003, 125, 15302.

38. Y. Yan, A. de Keizer, M. Stuart and N. Besseling, Adv. Polym. Sci., 2011, 242, 91.

39. S. Schmatloch and U.S. Schubert, Macromol. Symp., 2003, 199, 483.

40. B.M. McKenzie and S.J. Rowan, Metallosupramolecular Polymers, Networks, and Gels, in Molecular Recognition and Polymers: Control of Polymer Structure and Self-Assembly, V.M. Rotello, S. Thayumanavan Eds., John Wiley & Sons, chap 7, p. 157–178, 2008. 29



Macromolecules, 2009, 42, 6181.

Soft Matter


DOI: 10.1039/C4SM02319F

41. W. Weng, Z. Li, A.M. Jamieson and S. J. Rowan, Macromolecules, 2009, 42, 236.

Pitsikalis and N. Hadjichristidis, Macromolecules, 2010, 43, 4401.

43.H. Kaczmarek, A. Kaminska, J. Kowalonek and A. Szalla, Journal of Photochemistry and Photobiology A: Chemistry, 1999, 128, 121.

44. H. Kaczmarek, A. Sionkowska, A. Kaminska, J. Kowalonek, M. Swiatek and A. Szalla, Polym. Degrad. Stab., 2001, 73, 437.

45. H. G. Elias, An introduction to polymer science, Weinheim: VCH, 1997.

46. R.H. Hoyler, C.D. Hubbard, S.F.A. Kettle and R.G. Wilkins, Inorg. Chem., 1966, 5, 622.

47. D. Montarnal, P. Cordier, C. Soulie-Ziakovic, F. Tournilhac, L. Leibler, J. Polym. Science: Part A: Polym. Chemistry, 2008, 46, 7925.

48. M. Doi and S. F. Edwards, The Theory of Polymer Dynamics; Oxford University Press: New York, 1986.

49. P. G. de Gennes, J. Chem. Phys., 1971, 55, 527.

50. M. Doi, W. W. Graessley, E. Helfand and D.S. Peason, Macromolecules, 1987, 20, 1900.

51. E. van Ruymbeke, R. Keunings and C. Bailly, J. Non- Newtonian Fluid Mech., 2005, 128, 7.

52. E. van Ruymbeke, D. Vlassopoulos, M. Kapnistos, C. Y. Liu and C Bailly, Macromolecules, 2009, 43, 525.

53. E. van Ruymbeke, R. Keunings and C. Bailly, J. Non-Newtonian Fluid Mech., 2002, 105, 153. 30



42. E. van Ruymbeke, D. Vlassopoulos, M. Mierzwa, T. Pakula, D. Charalabidis, M.

Page 31 of 33


DOI: 10.1039/C4SM02319F

54. J. M. Dealy and R. G. Larson, Structure and Rheology of Molten Polymers, Hanser

55. T. C. B. McLeish, Adv. Phys., 2002, 51, 1379.

56. H. Watanabe, Prog. Polym. Sci., 1999, 24, 1253.

57. W. W. Graessley, Polymeric Liquids & Networks: Dynamics and Rheology, Taylor & Francis, Inc. 2008.

58. F. Leonardi, A. Allal and G. Marin, Rheol. Acta, 1998, 3, 199.

59. C. Carrot and J. Guillet, J. Rheol., 1997, 41, 1203.

60. S. Piogé, C.A. Fustin and J.F. Gohy, Macromolecular Rapid Communications, 2012, 33, 534.

61. B. G. G. Lohmeijer and U. S. Schubert, Angew. Chem., Int. Ed., 2002, 41, 3825.

62. H. Hofmeier, R. Hoogenboom, M. E. L. Wouters, U. S. Schubert, JACS, 2005, 127, 2913.

63. E. van Ruymbeke, S. Coppola, L. Balacca, S. Righi and D. Vlassopoulos, J. Rheol., 2010, 54, 507.

64. E. van Ruymbeke, Y. Masubuchi and H. Watanabe, Macromolecules, 2012, 45, 2085.

65. E. van Ruymbeke, V. Shchetnikava, Y. Matsumiya and H. Watanabe, Macromolecules, 2014, http://dx.doi.org/10.1021/ma501566w.

66. E. van Ruymbeke, C. Bailly, R.Keunings, D. Vlassopoulos, Macromolecules, 2006, 39, 6248.

31



Verlag: Munich, 2006.

Soft Matter


DOI: 10.1039/C4SM02319F

67. M. Ahmadi, C. Bailly, R. Keunings, M. Nekoomanesh, H. Arabi, E. van Ruymbeke, Macromolecules, 2011, 43, 647.

69. A. Fradet and M. Tessier, Macromolecules, 2006, 39, 6238.

70. D. Durand and C. M. Bruneau, Macromolecules, 1979, 12, 1216.

71. L.J. Fetters, D.J. Lohse, D. Richter, T.A. Witten and A. Zirkel, Macromolecules, 1994, 27, 4639.

72. R. H. Holyer, C. D. Hubbard, S. F. A. Kettle and R. G. Wilkins, Inorg. Chem., 1966, 5, 622.

73. R. Hogg and R. Wilkins, J. Chem. Soc., 1962, 341.

74. M. E. Cates, Macromolecules, 1987, 20, 2289.

75. U. S. Schubert, H. Hofmeie and G. R. Newkome, Modern Terpyridine Chemistry, WileyVCH Verlag GmbH & Co. KGaA, 2006.

76. J. D. Fox and S. J. Rowan, Macromolecules, 2009, 42, 6823.

77. H. Kautz, D. J. M. van Beek, R. P. Sijbesma and E. W. Meijer, Macromolecules, 2006, 39, 4265.

78. L. Brunsveld, B. J. B. Folmer, E. W. Meijer and R. P. Sijbesma, Chemical Reviews, 2001, 101, 4071.

79. S. Schmatloch, A. M. J. van den Berg, A. S. Alexeev, H. Hofmeier and U. S. Schubert, Macromolecules, 2003, 36, 9943.

32



68. P. J. Flory, Chem. Rev., 1946, 39, 137.

Page 33 of 33


DOI: 10.1039/C4SM02319F

80. M. Burnworth, L. Tang, J. R. Kumpfer, A. J. Duncan, F. L. Beyer, G. L. Fiore, S. J. Rowan and C. Weder, Nature, 2011, 472, 334.

Poym. J., 1989, 25, 779. 82. P. G. Bruce, Dalton Trans., 2006, 1365.

83. F. Herbst, K. Schrofter, I. Gunkel, S. Grofger, T. Thurn-Albrecht, J. Balbach and W. H. Binder, Macromolecules, 2010, 43, 10006.

84. M. Al-Hussein, B.G.G. Lohmeijer, U.S. Schubert and W.H. de Jeu, Macromolecules, 2003, 36, 9281.

85. M. Al-Hussein, W.H. de Jeu, B.G.G. Lohmeijer and U.S. Schubert, Macromolecules, 2005, 38, 2832.

86. R.D. Pike, W.H. Starnes, J. P. Jeng, W.S. Bryant, P. Kourtesis, C.W. Adams, S.D. Bunge, Y.M. Kang, A.S. Kim, J.A. Macko and C.P. O’Brien, Macromolecules, 1997, 30, 6957.

87. R. J. Blackwell, O. G. Harlen, and T.C. B. McLeish, Macromolecules, 2001, 34, 2579.

33



81. G.G. Cameron, M.D. Ingram, M.Y. Qureshi, H.M. Gearing, L. Costa and G. Camino, Eur.

Correction: Nonlinear rheology of entangled polymers at turning point.

Mechanochemistry with metallosupramolecular polymers.

Mechanically triggered responses of metallosupramolecular polymers.

Simulating the flow of entangled polymers.

Nanoparticle Motion in Entangled Melts of Linear and Nonconcatenated Ring Polymers.

Nonlinear signatures of entangled polymer solutions in active microbead rheology.

Rheology of acrylic denture-base polymers.

Pulling-force-induced elongation and alignment effects on entanglement and knotting characteristics of linear polymers in a melt.

Photoinduced transformations of stiff-stilbene-based discrete metallacycles to metallosupramolecular polymers.

Rheology as a tool for evaluation of melt processability of innovative dosage forms.

Ductile thermoset polymers via controlling network flexibility.

Temperature dependent micro-rheology of a glass-forming polymer melt studied by molecular dynamics simulation.

Influence of Flame Retardants on the Melt Dripping Behaviour of Thermoplastic Polymers.

Effect of excluded volume on the rheology and transport dynamics of randomly hyperbranched polymers.

Investigation of Thermal and Viscoelastic Properties of Polymers Relevant to Hot Melt Extrusion, IV: Affinisol™ HPMC HME Polymers.

Self-Similar Conformations and Dynamics in Entangled Melts and Solutions of Nonconcatenated Ring Polymers.

A molecular dynamics investigation of the planar elongational rheology of chemically identical dendrimer-linear polymer blends.

Controlling spin transition in one-dimensional coordination polymers through polymorphism.

Fabrication of high-resolution 4,8(2) -type archimedean nanolattices composed of solution processable spin cross-over Fe(II) metallosupramolecular polymers.

Novel linear polymers able to inhibit bacterial quorum sensing.

Branched-linear and agglomerate protein polymers as vaccine platforms.

Shear rheology and structural properties of chemically identical dendrimer-linear polymer blends through molecular dynamics simulations.

Controlling the Structure and Length of Self-Synthesizing Supramolecular Polymers through Nucleated Growth and Disassembly.

Controlling the dimensionality of on-surface coordination polymers via endo- or exoligation.