Metal-free click approach for facile production of main chain poly(bile acid)s

In this work, a metal-free click polymerization approach was developed to facilely produce versatile main chain poly(bile acid)s with high efficiency. No metal catalysts and organic solvents are required for the polymerization process, which exhibits multiple advantages, including less toxicity, being environmentally friendly and economically sound. Remarkably, the polymerization can finish within several minutes when the reactive monomers are in a crystalline state. Although the monomers are amorphous, no more than one hour is needed for completing the polymerization. The conversion efficiency can reach up to nearly 100% with the polymer molecular weight up to 93 500 Da, which still shows good solubility in most common solvents. The described approach is applicable for various bile acid monomers with different linkages, including long flexible alkyl chains, amide groups, phenyl groups and sterically hindered structures. Probably due to the strengthened hydrogen bonding interactions, π–π stacking and the hindrance effect introduced by the linkage used, the molecular weight and properties of the resulting polymers are strongly dependent on the monomer structures. Notably, by introducing a steric effect on azide groups (4e and 4f), the regioselectivity of the 1,4-triazole linkers is significantly improved from 60% to 85%. All the obtained polymers are thermally stable and display high resistance to thermal degradation.