| Abstract: | Copolymers of vinyl chloride–vinyl acetate have been prepared with different vinyl acetate contents and molecular weights and under different polymerization conditions. A rheological study of these copolymers indicates that they behave in some ways like externally plasticized PVC. For instance, as the vinyl acetate content increases, the melt viscosity decreases, the flow activation energy decreases, and the copolymer becomes more Newtonian. However, the critical shear rate for melt fracture increases, resembling the addition of elastic polymers to PVC. An increase in copolymer molecular weight has a similar effect on the rheological behavior as in PVC, except that the flow activation energy is observed to increase rather than decrease. Decreasing the polymerization temperature affects the flow properties of the copolymer, probably due to changes in degree of branching and crystallinity. A copolymer made by the delayed addition of vinyl chloride, having a more random structure than one made by the conventional batch method, exhibited quite different flow behavior. It had a lower melt viscosity, higher critical shear rate, and lower flow activation energy. |
