Radical Polymerization of Pendant (Meth)acrylates on a Rigid Helical Polyisocyanate Backbone Producing Poly(meth)acrylates with “Ideally” Atactic Main Chain Configuration

Abstract

This study includes a topic that poly(methyl methacrylate) (PMMA) with an “ideally” atactic main chain configuration, approximately triad tacticities of mm/mr/rr = 1/2/1, has been produced in solution by the “one-dimensionally regulated” radical polymerization using rigid helical polyisocyanate as a macromolecular template. Three types of isocyanate monomers with pendant (meth)acryloxy groups, such as 2-(methacryloxy)ethyl isocyanate (MOI), 2-[2-(methacryloxy)ethoxy]ethyl isocyanate (MOI-EO), and 2-(acryloxy)ethyl isocyanate (AOI), were polymerized using a titanium alkoxide complex to produce the corresponding polyisocyanates, MOI-n, MOI-EO-n, and AOI-n, respectively, in which n represents the number-averaged degree of polymerization. From the SAXS measurements of MOI-26 in hexafluoro-2-propanol and MOI-EO-38 in tetrahydrofuran at 25 °C, the polyisocyanates were found to be considered as rigid rod molecules. The radical polymerization of the pendant (meth)acryloxy groups was performed, and the polyisocyanate template was removed by alkali hydrolysis followed by methyl esterification, eventually producing the poly[methyl (meth)acrylate]s. The diad, triad, and pentad tacicities of the products were determined by the 1H and 13C NMR spectra, and these probabilities followed those calculated based on the Bernoulli statistics. The influences of the polymerization conditions, such as polymerization temperature and monomer concentration, on the tacticity of the final polymers were clarified. The effect of the flexible spacer between the polymerizable group and polyisocynate template was also evaluated. The radical polymerizations in which the polymerizable groups are molecularly regulated on a rod-like helical polyisocyanate backbone produced vinyl polymers with inimitable tacticities even in the solution state.