Self-templated free-radical polymerization to form tactic chains in confined environment

Abstract

It is known that the free-radical propagation chain possesses no stereospecificity as the single electron in the p-orbital of radical is equally accessible to the reactants from the bilateral sides, leading to the formation of atactic polymer chains. This sterically uncontrolled radical chain propagation could be rectified through repressing the degrees of freedom of the reactive vinyl monomer molecules by compression as predicted by our molecular simulation. The simulation unveils that molecules undergo ordered alignment upon being compressed to a certain extent to counteract the increase in chemical potential. We validated this concept by polymerizing N-isopropylacrylamide, a solid monomer, in a highly confined environment, from which a block copolymers consisting of 68% isotactic blocks was achieved. The additional account was attained from polymerizing liquid styrene under compression, which led to 43.1% isotactic polystyrene blocks. It is thus conceived that an ordered array of vinyl monomers would regulate their steric orientation until they join the propagating polymer chains. In conclusion, specifically, molecular confinement results in self-templated effect and hence offers a unique pathway for stereoselective chain growth. © 2013 American Chemical Society.