1H NMR spectroscopic differentiation of block copolymer, random copolymer and mixture of the corresponding homopolymers through end group and monomer sequence analyses

Abstract

Highly isotactic block and random copolymers of methyl methacrylate (MMA) and ethyl methacrylate (EMA) were prepared witht-C4H9MgBr in toluene at-60°C.1H NMR spectra of the copolymers were measured in nitrobenzene-d5 at 110°C and 500 MHz and analyzed in regard to monomer sequence and the end group. NMR signals due to the monomeric units provide clear indications for distinguishing the block copolymers from the random copolymers. The chemical shift of the initiator fragment signal is so sensitive to the adjacent monomeric unit that PMMA-block-poly(EMA) and poly(EMA)-block-PMMA can be differentiated spectroscopically. The main part of the spectrum for a mixture of PMMA and poly(EMA) prepared witht-C4H9MgBr is identical to those for the block copolymers but the mixture shows twot-C4H9-signals arising from both homopolymers and thus can be distinguished from the block copolymers.