Complete NMR spectral assignments of siloxanol based copolycarbonate including the configurational copolymer structure and the determination of each monomer conversion

Abstract

Siloxanol based copolycarbonate(SicoPC) of which the constitutional monomers are diphenyl carbonate, bisphenol A, and polydimethylsiloxanol(PDMS), was prepared by melt transesterification polymerization. The objective was to investigate the monomer conversion ratio for each monomer and the configurational structure of the SicoPC. A laboratory scale 5L reactor was used in the siloxanol preparation where the reactor jacket oil temperature was kept constant at 230 °C throughout the first and second polymerization phases. The reaction pressure was varied. For the first phase, the pressure was dropped from the atmospheric pressure 1000–200 mbar during the target reaction time of 30 min to remove the byproduct phenol. The second phase, the full vacuum pressure of was maintained for the second 30-min polymerization phase. An hour of reaction under such a condition gave a product of a highly viscous melt, of which the number average molecular weight read approximately 3000 g/mol. Complete NMR spectral assignments of the obtained melt (expected to be SicoPC) were made using both 1H and 13C, followed by 2D NMR spectroscopy. The measurements confirmed that the obtained melt was indeed the expected SicoPC; the conversion ratio of each monomer, BPA, DPC and PDMS were 100%, 99.5% and 86%, respectively. Furthermore, the HMBC (heteronuclear multiple quantum coherence) experiment confirmed the most important fact in determining the configurational structure of a SicoPC – all the PDMS monomers were located at the end chain of SicoPC.