| Abstract: | Spectra of methyl methacrylate polymers in chlorofornm solution at 90° show three α-methyl proton peaks. Measurements of their areas in spectra of polymers prepared with free radical and anionic initiators indicate that these may be attributed to (1) iso- tactic sequences (ddd or lll), (2) syndiotactic sequences (ldl or dld), and (3) heterotactic sequences (ldd, dll, ddl, or lld). The conformation and stereochemical configuration of the chains may thus be examined with considerable discrimination; degrees of regularity. block sizes, etc. appear to be determinable. Free radical polymers of methyl methacrylate are found to be predominantly syndiotactic, whereas those produced with anionic initiators. such as n-butyllithium, are shown to be predominantly isotactic, in agreement with the findings of others. The backbone methylene resonance also shows striking changes with chain stereochemical configuration, such as to provide absolute, independent confirmation of the assigned structures. |
