Effect of chain transfer agent on microstructure and thermal properties of cyclic olefin copolymer with low comonomer content.

Ethylene–norbornene copolymers were synthesized in a low-content norbornene window with rac-ethylene-bis(indenyl)zirconiumdichloride (EBI) catalyst to deeply investigate the microstructure of ethylene norbornene and thermal properties of copolymers with the addition of chain shuttling agent (CSA). Copolymers with norbornene content from 3 to 16% were obtained by changing the feed ratio in copolymerization. The melting temperatures (Tm) of the obtained copolymers were between 126.5 and 131 °C depending copolymer content. However, the copolymer with the highest norbornene in feed did not show any melting point and it was shown the glass-transition temperature (Tg) at 63.2 °C. The viscosity average molecular mass (Mv) of the produced copolymers without CSA was between 25,500 and 55,000 g mol−1; however, in the presence of CSA the Mv contents decreased between 6600 and 20,000 g mol−1 depending on CSA contents. The addition of CSA increased the catalyst activity in copolymerization, especially diethylzinc (DEZ) compared to tri isobutyl aluminum (TIBA). 13CNMR exhibited the presence of triads with a norbornene unit isolated between ethylene units or alternated meso-sequences of comonomer s. There were not detected any significant amount of two norbornene (NN) sequences. It was observed that with increasing chain shuttling agent in spite of decreasing norbornene content the heterogeneity of microstructure was increased. The results of thermal separation indicate more dispersion and heterogeneity in the presence of chain transfer agents (CTA). Dynamic mechanical thermal analysis (DMTA) results also indicate that the copolymerization with diethyl zinc, despite reducing the amount of norbornene, has led to the production of heterogeneous blocks in the polyethylene microstructure. [ABSTRACT FROM AUTHOR]