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.

Keywords:

• cationic polymerization
• polyindene
• indene-copolymer
• molecular weight
• thermal properties
• 5-ethylidene-2-norbornene
• random copolymerization

Acknowledgments

The financial support of the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES/PROCAD Project 200/2007) and Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq Projeto Universal 490845/2008-8) is gratefully acknowledged. The authors are grateful to Dr. Jairton Dupont of the Chemical Institute/UFRGS for his NMR analysis support and Dr. Ivo Vedana and Dr. Rosane Lighabue of the Chemical Faculty/PUC-RS for their GPC analysis support.