Development of high-temperature separation techniques for the chemical composition analysis of ethylene - methyl methacrylate block copolymers

Abstract

AbstractEthylene - methyl methacrylate block copolymers are semicrystalline polymers that dissolve in organic solvents only at high temperatures. Accordingly, microstructure analysis by solution methods must be conducted at temperatures above 130°C. For the analysis of block copolymers of different compositions several analytical techniques were used, including high-temperature size-exclusion chromatography (SEC), hyphenated SEC-FTIR, and CRYSTAF (crystallisation analysis fractionation). While SEC with refractive index detection indicated a certain multimodality of the samples, SEC coupled with FTIR revealed that the samples were chemically inhomogeneous and may contain homo- and copolymer fractions. The presence of polyethylene and poly(methyl methacrylate) homopolymers in the copolymer samples was confirmed by CRYSTAF analysis, when the total concentration as well as the carbonyl group distribution were monitored separately. Chromatographic separation of the different sample components was achieved when liquid chromatography at critical conditions (LC-CC) was used. For the first time, true high-temperature LC-CC methods were developed operating at a column temperature of 140°C. As the stationary phase, silica gel was used. Suitable mobile phases were binary mixtures of 1,2,4-trichlorobenzene or 1,2- dichlorobenzene with cyclohexanone. Using LC-CC, the samples were separated into the copolymer and the homopolymer fractions.