Postpolymerization <i>N</i> -Alkylamide Functionalization of Vinyl-Addition Polynorbornene Derivatives for Interchain Hydrogen-Bonding Interactions

A postpolymerization N-alkylamide functionalization strategy was employed to develop vinyl-addition polynorbornene (VA-PNB) derivatives capable of interchain hydrogen-bonding interactions. Vinyl-addition poly(5-methyl-2-norbornene-gradient-methyl 5-norbornene-2-carboxylate)s (VA-P(MeNB-grad-NBE)s) with varying methyl ester contents were synthesized using a catalyst system of Pd2(dba)3/PCy3/[Ph3C]+[B(C6F5)4]−. These copolymers reacted with various alkylamines under the catalysis of 1,5,7-triazabicyclo[4.4.0]dec-5-ene, affording vinyl-addition poly[5-methyl-2-norbornene-gradient-(methyl 5-norbornene-2-carboxylate-random-N-alkyl 5-norbornene-2-carboxamide)]s (VA-P[MeNB-grad-(NBE-r-NBRA)]s; R = H (hexyl), O (octyl), D (decyl), DD (dodecyl)). These terpolymers, along with a homopolymer (VA-PMeNB) and precursor copolymers, were subjected to a comparative analysis of their physical properties to elucidate the effects of N-alkylamide functionalization. Notably, introducing only 10 mol % N-dodecylamide side chains effectively improved both tensile strength and toughness, while resulting in only a minor decrease in the glass transition temperature. The successful formation of an adaptable network is achieved by low steric congestion and the dynamic hydrogen-bonding behavior of the N-alkylamide side chains, both of which are controlled by their content and length.