Sustainable cycloolefin polymer from pine tree oil for optoelectronics material: living cationic polymerization of β-pinene and catalytic hydrogenation of high-molecular-weight hydrogenated poly(β-pinene)

Abstract

(−)-β-Pinene, a major constituent of pine tree oil, was cationically polymerized to generate a high-molecular-weight polymer and then subsequently hydrogenated via metal catalysts to give a high-performance, bio-based cycloolefin polymer with an alicyclic backbone. To obtain the high-molecular-weight polymer, the controlled/living cationic polymerization of (−)-β-pinene was investigated by an initiating system, consisting of a protonic acid, a Lewis acid, and an added base, along with an incremental monomer addition technique. Among the various systems, the RCl/EtAlCl₂/Et₂O system gave a high-molecular-weight poly(β-pinene) (M_w > 100 000). The catalytic hydrogenation of the obtained high-molecular-weight poly(β-pinene) was examined using various metal catalysts, among which Pd/Al₂O₃ enabled the quantitative hydrogenation (>99.9%) of the unsaturated CC group in the repeating unit under mild reaction conditions (1.0 MPa pressure of H₂). These reactions could be performed even at relatively large scales to produce several hundred grams of the polymer, which can be then processed through injection-molding. The synthesized bio-based cycloolefin polymers demonstrated promising potential properties as high performance optical plastics with good processability, low density, high optical transparency, low birefringence, non-hygroscopicity, high mechanical strength, and excellent thermal properties.