Abstract
Large fractions of polyisobutylene chains may be obtained from precipitation induced by acetone added to solutions of polymer in a binary mixture (chloroform and dichloromethane). Fractions were characterized by weight average molecular weights, M ̄ w , and average radii of gyration, R ̄ 2 G , obtained from light-scattering measurements performed on a good solvent (cyclohexane); the product M ̄ w × R ̄ 2 G was found to vary according to the formula: M w × R 2 G = 1.33 × M m w with m = 2.22; while the intrinsic viscosity of fractions was found to vary as: [keta;] = 1.11x10 -4 × M m w with n = 0.76. Considering that m = 2 v + 1 and n = 3 v − 1, where v is the critical exponent associated with the description of properties of polymer chain solutions; values of v derived from m and n were found to be 0·61 or 0·58, respectively; the theoretical value is known to be 0·588. Polydispersity indices, l, were obtained from g.p.c. measurements: 1.1 < l < 1.3.
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