An unexpected stereochemical bias in the RAFT syntheses of styrene/p-bromostyrene copolymers uncovered by the Kerr effect

Gurarslan, Rana; Tonelli, Alan E.

doi:10.1016/j.polymer.2016.02.032

Cited by 6 publications

(2 citation statements)

References 21 publications

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“…This means that the calculated ΔSconfs are close to zero, indicating little deviation from their Fox behavior as observed in Figure 1(a). We characterized the structures and behaviors of S/pBrS copolymers made by brominating atactic polystyrene and by controlled ATRP and RAFT co-polymerization [14][15][16][17][18]. In Figure 2 we present the glass-transition temperatures measured for random and random-blocky comonomer sequences as a function of comonomer composition [11].…”

Section: Vc/ma and Vdc/ma Copolymersmentioning

confidence: 99%

Conformational Source of Comonomer Sequence-Dependent Copolymer Glass-Transition Temperatures

Tonelli,

Shen

2023

Preprint

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This brief review addresses the source of the dependence of copolymer glass transition temperatures (Tgps) on their comonomer sequences. Here we show that a comparison of the conformational entropies obtained from the Rotational Isomeric State (RIS) conformational models of the poly-A and poly-B homopolymers and their resultant poly-A/B co-polymers, i.e., ΔSconf = (XASA + XBSB) - SA/B (X = comonomer fraction), can be used to predict/understand the Tgps of copolymers. For copolymers with ΔSconf ~ 0, we expect their Tgps to follow Fox behavior and to depend only on copolymer composition, because of the similar conformational flexibilities of the A and B homo- and A/B-copolymers. When the conformational entropy ΔSconf is negative the A/B copolymer is assumed more flexible than the weighted sum of polymer-A and polymer-B conformational entropies, resulting in Tgps that are lower than expected from the Fox equation. Conversely, a positive ΔSconf suggests the copolymer’s lower flexibility, resulting in higher Tgps than expected from the Fox relation. We use the successful comparison of the observed dependence of numerous copolymer Tgps to demonstrate the validity of using their calculated RIS conformational entropies to predict their comonomer sequence dependencies.

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Section: Vc/ma and Vdc/ma Copolymersmentioning

confidence: 99%

Conformational Source of Comonomer Sequence-Dependent Copolymer Glass-Transition Temperatures

Tonelli,

Shen

2023

Preprint

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“…To develop a deeper understanding of the relationship between the homopolymer/solvent gel morphology and the resulting copolymer microstructure of the gel-state functionalized copolymers, a high-resolution, quantitative measure of the copolymer sequence, as offered by 13 C NMR spectroscopy, is required. For pure polystyrene, the NMR signal of the phenyl ring quaternary (C(1)) carbon in atactic polystyrene (aPS) and its phenyl ring-substituted derivatives exhibits high sensitivity to monomer configuration (i.e., tacticity), − composition, , and comonomer sequence distribution. ,,, Nevertheless, due to complexities in the C(1) resonances that arise from stereoirregularity and the chemical similarity of para-substituted styrene monomers, attempts by others to evaluate the comonomer sequence distribution of atactic polystyrene (aPS)-based copolymers by NMR have been generally unsuccessful. ,− Fortunately, for stereoregular syndiotactic polystyrene with high tactic purity, the spectral complexity of the brominated syndiotactic polystyrene (sPS- co -sPS-Br) copolymers used in this study is greatly reduced. Thus, the quaternary carbon resonances for styrene (C(1)) and brominated styrene (Br-Sty, C(1′)) monomers in this stereoregular model system are now recognized to be sensitive to neighboring monomers, which permits precise copolymer sequencing. ,, …”

Section: Introductionmentioning

confidence: 99%

High-Resolution Comonomer Sequencing of Blocky Brominated Syndiotactic Polystyrene Copolymers Using ¹³C NMR Spectroscopy and Computer Simulations

et al. 2020

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This work demonstrates the first high-resolution comonomer sequencing of Blocky brominated syndiotactic polystyrene (sPS-co-sPS-Br) copolymers based on pentad assignments of the quaternary carbon region of the nuclear magnetic resonance spectrum. Copolymers containing p-bromostyrene (Br-Sty) units were prepared in matched sets using postpolymerization bromination methods carried out in the heterogeneous gel state (Blocky) and homogeneous solution state (Random). Quantitative information from the quaternary carbon spectra, heteronuclear multiple bond correlation spectroscopy, electronic structure calculations, and simulated statistically random copolymers was correlated to confirm the carbon resonance assignments for all 20 possible pentad comonomer sequences. Using the experimental pentad sequence prevalences, a computer code was developed to simulate chains with microstructures typical of each sample as a means to visually represent the copolymer blockiness with quantitative precision. Based on the microstructure and distribution of run lengths in these chains, the simulations revealed that the Blocky copolymers contain a high degree of blockiness. By comparing the run lengths in the simulated chains to the average number of styrene units in a crystalline segment of sPS (found by small-angle X-ray scattering), copolymer crystallizability was predicted. For the simulated Blocky B-21% (21 mol % Br-Sty) chain, the probability of randomly selecting a styrene unit in a crystallizable block was 25.8%, while that in the simulated Random R-18% was zero, in excellent agreement with the experimental crystallization behavior measured by differential scanning calorimetry. These predictions confirmed that the simulated chains accurately represent the ensemble of chains in their respective copolymer samples. Furthermore, each simulated Blocky chain contained one or more long sPS blocks that paralleled the measured 38–40 styrene units spanning a crystalline segment within the sPS/CCl4 gel. This finding affirmed that the long sPS segments originated from the precise lamellar structure within the heterogeneous gel morphology (i.e., block length is correlated with lamellar thickness). Overall, the ability to tailor the copolymer microstructure through control of the semicrystalline gel morphology opens the door to synthesizing ordered copolymers by postpolymerization functionalization processes with unprecedented levels of compositional control.

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Conformation and Configuration

Tonelli

2023

Encyclopedia of Polymer Science and Technology

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The unique feature of polymers is the flexibility of their long chains, achieved by rotation about their many backbone bonds, which enable them to assume an extremely large number of different Conformations. This is the source of their unique material behaviors, such as rubber‐like elasticity and their time and processing dependencies. Polymer conformations and material properties depend upon their Configurations, among which are the mode of enchainment of diene monomers, regiosequences (directions of monomer insertion), the stereosequences (stereochemical arrangements of atoms in the polymer chain), co‐monomer sequences of vinyl polymers, branches, and cross‐links. Polymer configurations cannot be altered without breaking and reforming their covalent bonds. In this article, we describe how the conformational characteristics of polymers can be rigorously treated, with account explicitly taken of their configurations, and how various conformationally averaged chain properties can be connected to the behaviors of their materials to allow improved structure–property relations. As examples, because 13 C NMR resonances depend on local polymer microstructures, the average bond conformation probabilities calculated for each microstructure can be used to assign their resonances. The applied to its dilute solution (the Kerr‐Effect) is very sensitive to the Configuration/Macrostructure of the overall polymer chain. When compared to the molar Kerr constants (mK) calculated for chains possessing the microstructures determined by 13 C NMR, the Macrostructures or complete molecular architectures of polymer chains may be revealed.

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An unexpected stereochemical bias in the RAFT syntheses of styrene/p-bromostyrene copolymers uncovered by the Kerr effect

Cited by 6 publications

References 21 publications

Conformational Source of Comonomer Sequence-Dependent Copolymer Glass-Transition Temperatures

Conformational Source of Comonomer Sequence-Dependent Copolymer Glass-Transition Temperatures

High-Resolution Comonomer Sequencing of Blocky Brominated Syndiotactic Polystyrene Copolymers Using ¹³C NMR Spectroscopy and Computer Simulations

Conformation and Configuration

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An unexpected stereochemical bias in the RAFT syntheses of styrene/p-bromostyrene copolymers uncovered by the Kerr effect

Cited by 6 publications

References 21 publications

Conformational Source of Comonomer Sequence-Dependent Copolymer Glass-Transition Temperatures

Conformational Source of Comonomer Sequence-Dependent Copolymer Glass-Transition Temperatures

High-Resolution Comonomer Sequencing of Blocky Brominated Syndiotactic Polystyrene Copolymers Using 13C NMR Spectroscopy and Computer Simulations

Conformation and Configuration

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Product

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High-Resolution Comonomer Sequencing of Blocky Brominated Syndiotactic Polystyrene Copolymers Using ¹³C NMR Spectroscopy and Computer Simulations