Conformational inversion of polyethylene–polyvinyl acetate graft copolymer in selective solvents by viscometry

Viscometric measurements were performed for a low molecular weight polyethylene (LMWPE) and the LMWPE grafted vinyl acetate (E-g-VA) copolymer in a series of binary solvent mixtures, consisting of a polar and a non-polar solvents. The degree of grafting (DG) or VA content dependence of the intrinsic viscosity [η], Huggins constant kH, and the critical association concentration CA, of the polymers are investigated in the 1,2-dichloroethane (DCE)/cyclohexane (CYH) solvent mixtures, especially in Φc=0.3 and Φc=0.9 (Φc is the volume fraction of CYH in solvent mixtures). The opposite variations of [η], kH and CA with the increasing of DG of the polymers studied at 30°C were observed in different solvent mixtures of Φc=0.3 and Φc=0.9 respectively. Moreover, the inversion variation of [η] of E-g-VA graft copolymer and its parent polymer (LMWPE) occurred with the change of the composition of the solvent mixtures. A large difference of the viscous flow energy of the E-g-VA graft copolymers from two different kinds of solvent mixtures of Φc=0.3 and Φc=0.9 respectively was also found. These phenomena can be accounted for by the conformational inversion of the E-g-VA graft copolymer in the selective solvents.