Supramolecular polymer gels formed from carboxy-terminated telechelic polybutadiene and polyamidine through amidinium-carboxylate salt bridge

In this article, we report the preparation and properties of the bulk supramolecular polymer gels prepared from a polybutadiene based on the amidinium-carboxylate salt bridge, highlighting the difference from a well-established network system based on carboxylic acid and amine. We have prepared the amidinium-carboxylate salt bridge-based supramolecular polymer gels from a carboxy-terminated telechelic polybutadiene and a linear polyamidine having N,N′-di-substituted acetamidine group in the main chain. FTIR analysis along with Small angle X-ray scattering measurements indicated that the salt bridge was attributed to the gelation through three-dimensional network formation. Virtually no fluidity was observed for the supramolecular gel containing equimolar amounts of the carboxyl group and the amidine group, which showed a high G′ value of about 1 MPa at room temperature and a Tgel of 37 °C. For comparison, the supramolecular polymer gels crosslinked by ammonium-carboxylate salt were prepared using a linear polyethyleneimine instead of the polyamidine. The gel with equimolar amounts of the carboxyl group and the secondary amino group showed liquid-like fluidity with a G′ value of about 0.01 MPa at room temperature, which was attributed to the fact that a certain amount of the carboxyl group remained as its free form without salt formation, as evidenced by FTIR analysis.