The changes of free rotation around the carbon‐carbon bonds in statistical chains of poly(styrene‐co‐dimethylitaconate) samples of different average composition were evaluated in terms of the σ‐parameter, the ratio of the end‐to‐end distance of the coil in the unperturbed state to the same distance in a freely rotating chain. Samples of copolymers were carefully fractionated and fractions of identical composition selected for viscosity and light scattering measurements were subjected to the KURATA‐STOCKMAYER extrapolation procedure, and KΘ and σ evaluated in terms of composition. Always between values of 2.17 and 2.02 for the parent homopolymers, σ goes through a slight minimum at about 33 mole‐% of styrene. The phenomenon seems to stress the significance of electrostatic forces between opposite and neighbouring substituents of the poly(dimethylitaconate) chain which are comparable to the mutual incompatibility of unlike monomer residues in the copolymer chain.
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Veličkoviča et al. (1969) studied this question.
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