“Grafting-from” polymerization for uniformly bulk modification of pre-existing polymer materials via a supercritical-fluid route

A novel approach to uniformly bulk graft modification of pre-existing polymer materials without ungrafted homopolymers was achieved at relatively low temperature by means of gamma (γ)-rays pre-irradiation-induced “grafting-from” polymerization with supercritical carbon dioxide (scCO2) both as solvent and as swelling agent. The polymer substrates were first irradiated with γ-rays originated from cobalt-60 resource under nitrogen atmosphere at ambient temperature, and thereby leading to uniform formation of trapped radicals on polymer backbone. Then, the produced polymer-trapped radicals were utilized to initiate graft polymerization of vinyl monomers dissolved in scCO2 within polymer substrates. A combination of transmission electron microscopy, scanning electron microscopy and elemental analysis shows that side graft chains covalently bonded to polymer substrate backbone in nanometer scale are uniformly dispersed within polymer membranes with a thickness of 5 mm. Altering the experimental conditions can easily control the grafting yield with regard to side graft-chain length. This method can also be applied to various functional polymer chains covalently attached to different polymer substrates, even with high viscosity or limited solubility. The novel graft-polymer materials produced by this method are not formed in the absence of scCO2 and are impossible to prepare by conventional methodologies.