SYNTHESIS, CONFORMATION, AND FUNCTIONS OF HELICAL POLY(N-PROPARGYLAMIDES):

摘要

Poly(N-propargylamides) have proven to exist in the helical conformation which is stabilized by the intramolecular hydrogen bonds between the nth and n+2th pendant amide groups. The main chain is twisted from coplanarity that is surrounded by two helically arranged hydrogen-bond strands. The helical conformation is readily deformed into a randomly coiled state by external stimuli since the random coil-to-helix transition involves negatively very large entropy and enthalpy changes. In other words, the helical conformation of poly(N-propargylamides) is based on the well-balanced entropy and enthalpy contributions. This characteristic can be applied to various stimuli-responsive functional materials such as chromic materials and responsive organogels with volume change. The instability of polymers from monosubstituted acetylenes may render readers to conclude that poly(N-propargylamides) cannot be used in practical applications. However, our preliminary investigation has suggested that poly(N-propargylamides) are unexpectedly stable even in CHCl_3, in which polyacetylenes rapidly decompose. Especially, poly(N-propargylamides) having bulky pendant groups are quite stable. Therefore, we believe that poly( N-propargylamides) will serve as a new class of functional polymers for practical applications.