Temperature effects in γ-initiated polymerization of styrene. II

Experimental data are presented for the γ-initiated polymerization of commercial styrene at a series of temperatures above ambient. Examination of the early stages of polymerization (up to 10% conversion) has led to the following conclusions. For this system, there exists a critical temperature (109°C) above which the rate of polymerization is independent of dose rate, over a wide range of γ-intensities. This dose rate independence is ascribed to a “limiting rate of initiation,” characteristic of the intensity range. A consequence of this is that at a given temperature above the critical temperature the degree of polymerization is also dose rate-independent. The above phenomena can be expected in any vinyl monomer where the monomer is fairly active and produces relatively stable radicals. Experimental procedure is described, and kinetic analysis presented to substantiate the conclusions.