Spatially intermittent polymerization

Abstract

Abstract A novel reactor has been designed which permits the precise determination of absolute rate constants in photoinitiated free‐radical vinyl polymerization. A solution of monomer and initiator flows through a dark tubular reactor past regularly spaced slots through which light shines. The alternating dark and light regions produce spatially intermittent polymerization (SIP) and make the system analogous to the well‐known rotating‐sector technique. However, the SIP reactor has the advantage of producing large volumes of reaction product, at low conversion, suitable for analysis of both conversion and molecular weight. This supplies the necessary data, from a single set of experiments, for the simultaneous determination of the rate constants for propagation and termination. Experimental data are reported at 25°C for methyl methacrylate which indicate that k p = 315 I./mole‐sec, independent of polymer molecular weight, and k t is dependent on molecular weight especially at low molecular weight, approaching a lower value of k t = 30 × 10 6 I./mole‐sec at a molecular weight of 10 6 . For styrene, measurements being made only at high molecular weight, k p = 74 ± 5 and k t = 37 ± 0.3 × 10 6 l./mole‐sec at 25°C.