Physico-Chemical Characterization of Poly(vinyl Chloride). IV. Branching

Degree of branching in PVC as a function of its temperature of polymerization has been determined by the catalytic hydrogenation (LiAlH4) of the polymer followed by IR measurements. The samples used were prepared at 55, 90, 130, and 160°C. A branching calibration curve (ACH3 /ACH2 vs CH3/CH2) was established for linear hydrocarbons, and was found to follow the relation, ACH3/ACH2 = 20(CH3 /CH2). This equation was used to characterize the branching indices of PVC samples studied. Branching values in units of 100(CH3 /CH2) were as follows: 55°C (1.92), 90°C (1.95), 130°C (2.61), and 160°C (2.96). These results are in agreement with the theoretical prediction that the degree of branching in PVC should decrease with the lowering of its temperature of polymerization because the energy of activation for the propagation step is smaller than that for chain the transfer step.