Synthesis of hydrocarbon polymers by cationic polymerization and their thermal properties

Abstract

Cationic homo- and co-polymerization of indene (Ind), styrene (St), limonene (Lim), and 5-ethylidene-2-norbornene (ENB) was performed with AlCl3 in dichloroethane at −20 °C under inert N2. The aim of this work is to investigate the effect of the reaction conditions on the molecular weight of polyindene (PInd) obtained by cationic polymerization with AlCl3 without an electron donor, and also to determine the effect of the use of cyclic diolefin comonomers on the polymer properties. The polymers were synthesized at a monomer/catalyst molar ratio (MR) of 100; St and Lim showed the highest and lowest reactivity, respectively. The polymers were characterized by 13C and 1H NMR spectroscopy, Fourier transform infrared spectroscopy, ultraviolet–visible spectroscopy, size exclusion chromatography, differential scanning calorimetry, and thermogravimetric analysis. PInd with a number average molecular weight (M n) of 45 × 103 g/mol and a glass transition temperature (T g) of 207 °C was obtained, whereas only oligomeric polylimonenes were obtained. Cyclic diolefins depressed both the M n and T g values of the Ind-copolymers. There was a dramatic decrease in the M n of the polymers: those obtained at a MR of 1:1 in the feed presented M n values lower than 104 g/mol, with the exception of poly(Ind-co-ENB), which is cross-linked. Poly(Ind-co-Lim) with lateral double bonds, a comonomer content of 1 to 20 mol%, and T g values in the range of 140–200 °C were obtained.