Study on the radical polymerization behavior of macromonomers

A study on the radical polymerization behaviors of styrene macromonomer (end group is methacrylate, M sub n = 12 400, M sub w /M sub n = 1.06, f = 0.86) and on the characterization of produced poly(macromonomer)s was performed to clarify the characteristic feature of macromonomer polymerization systems. Polymerizations were carried out with AIBN in benzene at 60 deg C. Degrees of polymerization (D sub p ) and the mean square radii of gyration ( < S exp 2 > sub b ) of produced poly(macromonomer)s and the polymerization rate (R sub p ) were determined by gel permeation chromatography combined with a laser light scattering detector. It was found that D sub p s of poly(macromonomer)s strongly depended upon the macromonomer concentration in feed ((M)) due to the gel effect; however, in contrast to the small monomer, D sub p is not dependent much upon the conversion. The ratio of < S exp 2 > sub b to that of the linear polystyrene of the same molecular weight, g, was also evaluated. It was found that g values at large D sub p were considerably small and that the dependence of g upon D sub p had almost the same tendency predicted for the star-shaped polymer in the molecular weight range of < 1 x 10 exp 6 . This indicates that the propagating poly(macromonomer) radicals are very compact, and consequently, the segment density around the propagating radical site is very large. The kinetic order of (M) in the polymerization equation of R sub p vs. (M) was found to be about two, and it tended to further increase at higher (M) due to the strong gel effect. The kinetic order of the initiator concentration ((I)) was found to be nearly 0.5 at low (M), whereas the order decreased at high (M) where poly(macromonomer)s of large D sub p were produced. This fact indicated that the bimolecular termination did become more difficult as a consequence of the high segment density around the propagating radical sites. Graphs. 45 ref.--AA