RADICAL POLYMERIZATION BEHAVIOR OF MACROMONOMERS .2. COMPARISON OF STYRENE MACROMONOMERS HAVING A METHACRYLOYL END GROUP AND A VINYLBENZYL END GROUP

A study of the radical polymerization of styrene macromonomers having a methacryloyl end group (MA-PSt; Mn = 4400,12 400) and a vinylbenzyl end group (VB-PSt; M„ = 4980,13 200) was carried out by using gel permeation chromatography with a laser light scattering detector (LS-GPC) and electron spin resonance spectroscopy (ESR). It was shown that the degree of polymerization of poly(macromono-mer)s (Dp) measured by LS-GPC drastically varied with the macromonomer concentration in the feed ([M]); however, there was little difference in the Dpversus [M] curves between MA-PSt and VB-PSt of the same molecular weight. The Dpof poly(macromonomer)s was small (typically less than 10) at low [M] and increased rapidly with an increase in [M] followed by the sudden decrease to Dp= 1 at very high [M]. The Dpversus [M] relationship was strongly affected by the molecular weight (Mw) of the macromonomers. These Dp versus [M] relationships were quite similar to Dp(or Rp)versus the degree of conversion relationship of the polymerization system of conventional small monomers in the presence of the gel effect. This indicated that the diffusion-controlled effect in macromonomer systems could be clearly described by [M] and Mvof the macromonomer. It was also shown that time-conversion curves of these macromonomers were monotonie and exhibited no feature of the autoacceleration effect normally observed in the polymerization system of small monomers in the presence of the gel effect. In addition, the polymerization rate (Rp) of MA-PSt was considerably greater than that of VB-PSt of the same molecular weight. ESR spectra of the propagating radical of MA-PSt and VB-PSt were measured to evaluate the concentration of the propagating radicals. From the results of ESR and LS-GPC, the propagation rate constant kp, the termination rate constant kuand the radical lifetime τρ of the macromonomers are evaluated and discussed. © 1990, American Chemical Society. All rights reserved.