Role of molecular motions in polymer reactions. Part 2.—Low-temperature free-radical polymerization of vinyl bromide and of N-vinyl carbazole

Abstract

The individual rate constants for propagation and termination have been determined for the low-temperature solution free-radical polymerization of vinyl bromide and N-vinyl carbazole. The propagation rate constants can be expressed in the Arrhenius form: k_P,V.B.= 4.8 × 10⁷ exp (–7,100/RT), k_P,N.V.C.= 1.2 × 10⁶ exp (–6,900/RT). The termination rate constant for vinyl bromide can be written in the form, (2k_tc+2k_td)_V.B.= 2.8 × 10¹¹ exp (–3,900/RT). However, the termination rate constant for N-vinyl carbazole polymerization, like that of methyl methacrylate,³ does not satisfy the Arrhenius relationship, and becomes markedly reduced as the temperature is lowered from +10 to –30°C. These results are interpreted in terms of the cessation of backbone rotation in dissolved “stiff” macroradicals, which cessation markedly retards diffusion-controlled termination. The fact that the intrinsic viscosities of solutions of polymethyl methacrylate and poly N-vinyl carbazole are independent of temperature in these regions can be interpreted as confirmation of this phenomenon.