Polymerization of coordinated monomers. II. Stereoregulation in the free‐radical polymerization of methacrylonitrile–zinc chloride or methacrylonitrile–stannic chloride complexes

The effect of complex formation on stereoregulation in free‐radical polymerization was studied. Complexes of methacrylonitrile with ZnCl 2 and SnCl 4 were prepared and their properties and structures examined. The complexes were polymerized by initiation of α,α′‐azobisisobutyronitrile or by irradiation with γ‐rays from a 60 Co source or ultraviolet rays either in solution or in bulk at various temperatures ranging from −78 to 100°C. The triad tacticities of the resulting polymethacrylonitrile were determined by converting it to poly(methyl methacrylate) for NMR spectroscopy. The radicals in complexed forms were studied by ESR spectroscopy with the polymerization system in toluene irradiated with ultraviolet rays at −120°C. The tacticities of the resulting polymers and their dependencies on the polymerization temperature were found to be characteristic of the complex species, i.e., the kind of metal chloride and the stoichiometry, being different from the tacticities and the dependencies, respectively, of the polymer obtained with pure methacrylonitrile. The 2:1 and the 1:1 complexes with SnCl 4 were found to give an eleven‐line and a nine‐line spectrum, respectively. On the basis of the results of both the tacticities and the ESR spectra, it was estimated that the proportion of the intracomplex reaction was 40%, and that the probabilities of isotactic diad addition of intra‐ and intercomplex reaction were 0.70 and 0.48, respectively.