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Pendant side-chain sterics against electrostatic forces: Influencing short-range ordering in random polyelectrolytes

Nwosu, Chinomso; Coughlin, E. Bryan

Journal of Polymer Science Part B: Polymer Physics, 2019, vol 57, 19, pp. 1325-1336

DOI:10.1002/polb.24876

Abstract

The length of pendant side chains in charged, random, comb-shaped polymers dictates the nature of their short-range ordering. Random copolymers, and terpolymer, of 4-vinylpyridine (4VP), styrene, and isoprene were synthesized and subsequently fully quaternized with 1-alkylbromides having varying number of carbons on the alkyl group ranging from 2 to 8. Evaluation by wide angle X-ray scattering revealed that dipole–dipole attraction facilitates the formation of ionomer cluster morphology in samples with two carbons on the pendant side chain, whereas for samples with four or more carbons on the pendant side chains, side-chain sterics was dominant resulting in periodic backbone spacing. Copolymers with isoprene, having flexible backbones, favor the formation of ionomer cluster morphology while styrene copolymers having rigid backbones disfavor the formation of ionomer clusters. An “in-line” dipole model was developed to predict the separation distance at which both ionomer cluster and backbone–backbone morphologies could coexist. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019, 57, 1325–1336

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