Carbon-based free radicals were generated by thermal cleavage of the tetraester Me2C(COOME)-CH2-CMe( COOMe )- CMe ( COOMe )-CH2-C( COOMe )Me2 which is a model for head-to-head units in a poly(methyl methacrylate ) chain. The resulting electron spin resonance spectrum had higher resolution than the 'nine-line' spectrum previously reported; this enabled identification of the component radicals. In the present case, the spectrum was well matched by a summation of spectra of the Me2C(COOME)-CH2-CMe( COOMe ) radical and the 1-methoxycarbonyl-1-methylethyl radical Me2-C-COOMe derived from it by loss of methyl methacrylate. Both of these radicals were generated in separate experiments. Radicals were also generated from starting materials containing a CD3 group in place of the single CH3.

Two isomeric pairs of 3-bromopropenoic acids were prepared and vicinal C-H couplings were measured in their 13C n.m.r. spectra. Complete C-H coupling schemes were also obtained for these and several other propenoic acids. It was seen that the ranges for 3Jtrans and 3Jcis did not overlap, and so a stereochemical assignment based upon n.m.r. data for a single isomer can be made with confidence.

Methyl (E)- and (Z)-2-methyl(3-D) propenoates were prepared from (E)-3-bromo-2-methylpro- penoic acid. Polymerization by free radical methods led to random incorporation, but anionic polymerization preserved labelling specificity, and the 1H n.m.r. spectra of the labelled polymers confirm earlier assignments. Dimethyl 2,3-dimethylbutanoate was prepared by two new methods from dimethylmaleic anhydride and converted by anionic polymerization into a methacrylate polymer with a head-to-head linkage approximately in the centre of the chain. Thermal degradation of this polymer could only be achieved at temperatures so high that labelled monomers were themselves isomerized. Methacrylate polymers produced by anionic polymerization in the presence of diisopropylamine do not exhibit the isotacticity found with this form of polymerization.