Two-dimensional nmr spectra of isotactic poly(methyl methacrylate) prepared with t-c49mgbr and detailed examination of tacticity

Abstract

Structures of the chain ends of the low molecular weight and highly isotactic PMMA prepared by t-C4H9MgBr in toluene were investigated extensively using 2D NMR technique. The 1H and 13C NMR signals of ॅ-CH3 and CH2 groups in the first two and the last two monomeric units of the chain were assigned unequivocally, and four types of end-structures, viz. mm and rm at ॅ-end and mm and mr at ३-end were identified. The configurations at the ॅ- and ३-ends were less isotactic than those of in-chain monomeric sequences, and the m/r ratios at the ॅ- and ३-ends were 10/1 and 6/4, respectively. Exact tacticity of PMMA was determined on the basis of the assignment, which revealed that isotacticities of the PMMAs prepared with t-C4H9MgBr in toluene at 蜢78ŶC were independent of molecular weight. Chemical shifts of configuration-sensitive peaks for fractionated dimers and trimers of MMA were found to be very similar to those of the corresponding structures in the polymer ends. © 1987 The Society of Polymer Science, Japan.