Statistical and block copolymers of n-hexyl isocyanate and 2–phenylethyl isocyanate via coordination polymerization. Synthesis, characterization and thermal properties

Abstract

The synthesis of statistical and block copolymers of n-hexyl isocyanate (HIC) and 2–phenylethyl isocyanate (PEIC), via coordination polymerization using a half-titanocene complex, was studied. The complex [CpTiCl2(O-(S)-2-Bu)] was employed as initiator of all the polymerization reactions. The homopolymerization of PEIC was initially attempted under various experimental conditions. The statistical copolymers were synthesized in different proportions of the two monomer units, and their reactivity ratios were estimated using the Fineman-Ross, inverted Fineman-Ross, Kelen-Tüdos and extended Kelen-Tüdos graphical methods, along with the computer program COPOINT. Structural parameters of the copolymers were obtained by calculating the dyad sequence fractions of the monomers and their mean sequence lengths. Furthermore, a systematic and detailed investigation was performed on the thermal degradation of the copolymers compared with the respective homopolymers, by Thermogravimetric Analysis, TGA, and Differential Thermogravimetry, DTG, within the framework of the Ozawa-Flynn-Wall and Kissinger-Akahira-Sunose methodologies. It was concluded that the thermal stability of the copolymers was affected by the ratio of the two monomers in their structure and was increased with the addition of PEIC monomers. Additionally, the mathematical model of the mechanism through which the thermal decomposition of the homopolymer PPEIC takes place, was further investigated. Block copolymers PHIC-b-PPEIC were also synthesized via the same coordination polymerization approach and sequential addition of monomers starting from the polymerization of HIC. The samples were characterized by Size Exclusion Chromatography, SEC, and NMR spectroscopy. Their thermal decomposition profiles were studied by TGA and DTG measurements and were compared with the corresponding statistical copolymers.