Addition copolymerization of norbornene lactone catalyzed by Pd complexes

The addition copolymerization of norbornene (NB) with functionalized monomers can lead to the modification of physical properties of poly(NB). Herein, the synthesis of new copolymer of NB with exo-norbornene lactone (exo-NBL) is reported. The copolymerization proceeded by four Pd catalytic systems, and of these, Pd(allyl)IDippCl/AgSbF6 (IDipp = 1,3-bis[2,6-diisopropylphenyl]imidazolin-2-ylidene)) was the most effective for the incorporation of exo-NBL. Specifically, the copolymerization with exo-NBL/NB feed ratio of 50/50 at r.t. by 0.1 mol% of the Pd catalyst produced poly(NB-co-exo-NBL) with M-n of 87,000, and M-w/M-n of 1.2 in 40% yield, incorporating exo-NBL of 18 mol%. The time-conversion plots and H-1 diffusion ordered spectroscopy (DOSY) NMR analysis of the copolymer suggest that it has a random sequence. In contrast, no copolymer was formed from endo-NBL. This is because of steric hindrance of the endo-lactone moiety by considering the (co)polymerization of endo-5-norbornene-2-carboxylic acid methyl ester (endo-NBCO2Me). The incorporation of exo-NBL improves the solubility of poly(NB-co-exo-NBL) in several chlorinated solvents and gives high thermal stability with 10% weight loss at a temperature of more than 400 degrees C. Two amorphous halos corresponding to intra- and interchain distances were observed in the WAXD patterns, allowing to calculate d-spacing values, which are higher than that of poly(NB).

Automated summary

A new copolymer of NB with exo-NBL was successfully synthesized using Pd catalytic systems, leading to a polymer with improved solubility in chlorinated solvents and high thermal stability. This copolymer showed a random sequence and enhanced physical properties compared to poly(NB).