Reactivities of Conjugated Dienes Towards the 1-Methyl-1-(methoxycarbonyl)ethyl Radical

The relative reactivities of butadiene, isoprene, 2,3-dimethylbutadiene, 2,3-diphenylbutadiene and methyl methacrylate with the 1-methyl-1-( methoxycarbonyl )ethyl radical have been evaluated by using the 'polymer end-group method', and the data obtained compared with those for the same monomers in their reactions with the poly(methyl methacrylate ), 1-cyano-1-methylethyl and 1-phenylethyl radicals. The observed reactivity trends can be explained by variations in the Q and e values for the monomers, and show that the 1-methyl-1-(methoxycarbonyl)ethyl radical is a good model for the poly(methyl methacrylate ) radical. Further results indicate that a penultimate styrene unit does not affect the reactivity of a poly(methyl methacrylate ) radical, whereas a penultimate methacrylonitrile unit does.

Sequence Structure of Styrene-Butadiene Copolymer Determined by Ozonolysis-HPLC Method

The configurational sequence of styrene units and the arrangement of styrene and 1,2-butadiene units in styrene-butadiene copolymers were characterized by 1H- and 13C-NMR analysis of the ozonolysis products which were separated by a combination of GPC and HPLC. The ozonolysis products from diad and triad styrene sequences flanked by 1,4-butadiene units showed two and three peaks in HPLC, respectively, reflecting the diad and triad tacticity. The probability of racemic addition was found to be 0.56 and 0.58 for radical and anionic SBR, respectively. The ozonolysis products from styrene-1,2 sequences were separated into three fractions by HPLC. The first and second fractions were assigned to a 1,4-1,2 styrene-1,4 (VS) structure differed only in cotacticity. The third fraction was considered to be a mixture of the meso and racemic forms of the l,4-styrene-l,2-l,4 (SV) sequence. The GPC fraction corresponding to a sequence consisting of two styrenes and one 1,2 units was separated into four peaks by HPLC. Both large peaks contained SSV + VSS structures, where one peak consisted of meso configurations with respect to the two styrene units, and the second peak contained racemic styrene alignments. The two small peaks were SVS with the separation due to cotacticity. Based on the intensity of HPLC peaks, it was deduced that the addition of a 1,2 unit after the styrene terminal predominated the addition of a styrene unit after the 1,2 terminal.