Crystalline Regio-/Stereoregular Glycine-Bearing Polymers from ROMP: Effect of Microstructures on Materials Performances

Abstract

Synthesis of amino acid or peptide-bearing polymers with controlled microstructures is still a long-going challenge in polymer chemistry in contrast to natural biopolymers with exactly controlled microstructures like proteins and DNA. Here, a series of new glycine-substituted cyclooctenes monomers were designed and synthesized. Ring-opening metathesis polymerizations (ROMP) of all 3-substituted monomers with Grubbs second-generation catalyst afford glycine-bearing polymers with high head-to-tail regioregularity and high <i>trans</i>-stereoregularity, whereas ROMP of 5-substituted monomers is neither regio- nor stereoselective. Theoretical study revealed that sterically cumbersome glycine substituent in the 3-position is crucial for the high regio- and stereochemistry in the polymerization. Of importance, differential scanning calorimetry and wide-angle X-ray scattering measurements show that unsaturated 3-substituted polymers are semicrystalline due to their high degrees of structure regularity and the strong hydrogen-bonding interactions between glycine side-chains. Such obvious crystallization behaviors before the saturation of the backbone will facilitate its future applications as biomimetic materials. Moreover, 3-substituted polymers with high <i>trans</i>-HT regularity exhibit much bigger water contact angle and higher cloud point than its random 5-substituted analogues, indicating that structure regularity of these glycine-bearing polymers can decide the surface hydrophilicity and thermoresponsive behaviors. These results demonstrate the dependence of glycine-bearing polymer properties on their microstructures. Finally, the less reactive internal <i>trans</i>-double bonds of the polymers undergo thiol–ene addition effectively, allowing the preparation of regiospecific glycine-bearing polymers with a range of features in a facile way