Terpolymerization of ethylene, norbornene and dicyclopentadiene catalyzed by modified cyclopentadienyl scandium complexes

Abstract

Cyclic olefin copolymers (COCs) with high glass-transition temperature (T_g) are of fundamental interest and practical importance. Herein we report the terpolymerization of ethylene (E), norbornene (NB) and dicyclopentadiene (DCPD) catalysed by fused-heterocyclic and pyridyl-modified cyclopentadienyl scandium complexes (1 and 2) in high activities (1.27 to 1.86 × 10⁶ g mol_Sc⁻¹ h⁻¹ bar⁻¹) to produce E/NB/DCPD terpolymers with adjustable structures. The terpolymerization proceeded in a controlled fashion, forming E/NB/DCPD terpolymers with moderate number average molecular weight (M_n = 4.9 × 10⁴–13.6 × 10⁴ Da) and relatively narrow polymer dispersity index (PDI = 1.7–2.3). By controlling the concentration of NB and DCPD in-feed, a series of terpolymers with NB + DCPD contents from 47.4 mol% to 59.8 mol% (NB 17.7 mol% to 42.2 mol%, and DCPD 8.8 mol% to 38.6 mol%) was obtained. The highest total cycloolefin incorporation was more than 50 mol%, indicating the existence of continuous cycloolefin –E(NB)(DCPD)E– units as proved by ¹H, ¹³C, ¹H–¹H COSY, ¹H–¹³C HSQC and ¹H–¹³C HMBC NMR spectroscopy. This phenomenon has not been observed in the binary copolymerization of E/NB and E/DCPD catalysed by rare earth catalyst systems in reported publications. The surprising finding may be ascribed to the use of two kinds of cycloolefins and novel efficient scandium catalysts. Hetero-cycloolefins promoted the cyclic olefin insertion of each other for rare earth catalysts. T_g values of the terpolymers range from 133.4 °C to 162.8 °C, which is in good agreement with NB and DCPD incorporation. The high DCPD content provides greater contribution to the high T_g value compared with NB in terpolymers. Further transformation of the CC double bond in E/NB/DCPD terpolymers to the hydroxyl group was achieved via sequential epoxidation and hydroxylation reactions, resulting in a huge increase of T_g from 162.8 °C to 202.3 °C and a large decrease in the water contact angle from 84.1° to 33.4°.