Dielectric Relaxation Spectroscopy of Gradient Copolymers and Block Copolymers: Comparison of Breadths in Relaxation Time for Systems with Increasing Interphase

Mok, Michelle M.; Masser, Kevin A.; Runt, James; Torkelson, John M.

doi:10.1021/ma100743s

Cited by 32 publications

(50 citation statements)

References 66 publications

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“…The sample exhibits two values of glass transition temperature, at −44.8 °C and at 134.8 °C, respectively. The first T g responses to PBuA domains, segregated in the copolymer; this value corresponds well to the literature data −48 °C 45. The second T g value can be attributed to CAB separate domains, T g of which is ∼130 °C,46 in dependence on the contents of acetyl and butyryl groups.…”

Section: Resultssupporting

confidence: 88%

Controlled grafting of cellulose esters using SET‐LRP process

Vlček

Raus

Janata

et al. 2010

J. Polym. Sci. A Polym. Chem.

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Here, we present the first example of application of single-electron transfer living radical polymerization (SET-LRP) process to a controlled grafting of cellulose esters, cellulose diacetate (CDA), and cellulose acetate butyrate (CAB). The cellulose ester macroinitiators with various functionality densities have been prepared by acylation of the backbones with 2-bromoisobutyryl (BrIB) and dichloroacetyl (DCA) groups, respectively. Methacrylate monomers were polymerized using DCA-functionalized macroinitiators in the presence of pentamethyldiethylene triamine as a ligand. At 30 C, the reaction is rather slow, reaching about 10% conversion after 3 to 6 h of polymerization, whereas the higher temperature (60 C) perceptibly speeds up the polymerization so that methyl methacrylate (MMA) conversion is $30% after 5 h. Graft copolymers with random-type and diblock-type grafts having amphiphilic character were also synthesized. For acrylate grafting (BuA and t-BuA), BrIB-functionalized macroinitiators are more convenient in a combination with a low concentration of Cu(0) and Me 6 TREN as a ligand and polymerization is detectably faster even at the lower temperature than that of MMA. Kinetic studies show ''living'' character of both the graftings. Important advantages of SET-LRP, compared with classic ATRP, are (i) higher polymerization rate, (ii) lower extent of recombination of the growing grafts and (iii) negligible coloration of the products with catalytic residua, so that the prepared polymers do not require additional careful purification.

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Section: Resultssupporting

confidence: 88%

Controlled grafting of cellulose esters using SET‐LRP process

Vlček

Raus

Janata

et al. 2010

J. Polym. Sci. A Polym. Chem.

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“…The relaxation scenario of the homopolymer is modified when it is linked to a block of very different mobility (very different T g ). A general observation in ordered phases of diblock copolymers is that the α-relaxation times of the blocks are close to those of the corresponding homopolymers, with shifts to shorter or longer times if the other block has respectively a higher or lower mobility [26,[29][30][31][32]. In spite of the similar values of the α-time scales, the dynamic response exhibits a strong broadening in the low-frequency side in comparison with the corresponding homopolymer [26,[29][30][31][32].…”

Section: Introductionmentioning

confidence: 94%

Dynamic Heterogeneity in Random and Gradient Copolymers: A Computational Investigation

et al. 2013

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By means of molecular dynamics simulations, we investigate the structural relaxation in disordered random copolymers and lamellar phases of gradient copolymers, containing chemical species of very different mobilities. Two models have been investigated: a generic bead–spring system and a MARTINI coarse-grained model of a polyester resin. The lamellar phase of the gradient copolymer is formed by domains rich in one species and poor in the other one, which are separated by broad interfaces. Unlike in strongly segregated block copolymers, there is a finite probability of finding monomers of a given species at any position within the domains rich in the other species. A direct consequence of this feature is that monomers can probe very different chemical environments, and because of the strong dynamic asymmetry between the two components, their relaxation are characterized by an extreme dynamic heterogeneity. This is confirmed by an analysis of dynamic correlators as a function of the distance to the interface. In the case of random copolymers long-range ordering is not possible, and local microsegregation results in a much weaker dynamic heterogeneity. The former features are consistent with the experimental observation of narrow glass transitions in random copolymers but extremely broad ones in lamellar gradient copolymers.

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“…A general observation is that the average α-relaxation times of each block are close to those of the corresponding homopolymer. However the dynamic response in the diblock ordered phase exhibits a strong broadening in the low-frequency side (long times) in comparison with that of the corresponding homopolymer [6,8,10,11].…”

Section: Introductionmentioning

confidence: 97%

“…The local segmental dynamics in ordered phases of diblock copolymers, i.e, the αstructural relaxation associated to the glass transition of each block, has been characterized in several works [5][6][7][8][9][10][11][12]. A general observation is that the average α-relaxation times of each block are close to those of the corresponding homopolymer.…”

Section: Introductionmentioning

confidence: 99%

Heterogeneity of the Segmental Dynamics in Cylindrical and Spherical Phases of Diblock Copolymers

2012

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We have performed simulations of a simple bead-spring model for cylindrical and spherical phases of diblock copolymers. We have analyzed in detail the dynamic heterogeneity of the structural α-relaxation of the component confined in the minority domains. In analogy with previous investigations on the lamellar phase of the same bead-spring model, the analysis reveals moderate gradients of mobility in the investigated temperature range, which qualitatively probes time scales up to 100 ns. Thus α-relaxation times measured at different distances from the domain center spread over less than one decade. The spatial extension of the gradients of mobility is apparently consistent with that previously observed in the lamellar phase of the same model. Gradients of mobility do not seem to be related to gradients of density within the domains, which are indeed absent. We have performed an analysis of selfand effective concentrations, a concept usually invoked to explain the α-relaxation in polymer mixtures and that has been recently adapted to the analysis of experimental data of diblock copolymers in ordered phases. The simulation results reveal a strong disagreement with the proposed empirical relation between self-and effective concentration, as well as with the Flory-Fox mixing rule for the dynamics. This suggests that the use of these relations may bias the analysis of experimental data.

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Dielectric Relaxation Spectroscopy of Gradient Copolymers and Block Copolymers: Comparison of Breadths in Relaxation Time for Systems with Increasing Interphase

Cited by 32 publications

References 66 publications

Controlled grafting of cellulose esters using SET‐LRP process

Controlled grafting of cellulose esters using SET‐LRP process

Dynamic Heterogeneity in Random and Gradient Copolymers: A Computational Investigation

Heterogeneity of the Segmental Dynamics in Cylindrical and Spherical Phases of Diblock Copolymers

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