Photoreactive functionalization of poly(ethylene terephthalate) track-etched pore surfaces with "smart" polymer system's

Poly(ethylene terephthalate) (PET) track-etched membranes with a pore diameter of ca. 700 nm, optionally surface-functionalized to create a "carboxyl" or "amino" surface, were used for heterogeneous graft copolymerizations. Grafted poly(acrylic acid) acted as a pH responsive, "smart" polymer. To evaluate the surface-specific initiation of graft copolymerizations unmodified and primary functionalized membranes were systematically combine with three differently charged benzophenone derivatives as photoinitiators, which were adsorbed on the PET surface prior to the reaction. The functionalized membranes thus obtained were characterized for chemical structure and permeability as a function of pH. The pore structure with a narrow size distribution and the resulting high sensitivity of the membrane permeability tot he grafting functionalizations made the track-etched PET membranes a very useful tool for analyzing structure and function of responsive grafted-polymer layers. The primary functionalization of the base polymer witha molecular layer of a multifunctional alkylamine ("amino" surface) enhanced the efficiency of the subsequent graft copolymerization via photoinitiated hydrogen abstraction considerably because a high density of well accessible reactive groups had been introduced. The preadsorption of the photoinitiator on the base polymer surface was significantly improved by ionic interactions between the respective functional groups of the surface and the photoinitiator. Such a photoinitiator preadsorption, especially when combined with a reactive layer from the primary functionalization, enabled a very efficient and surface selective functionalization because a better control of grafting density and a reduction of photoinitiated side reactions along with a more efficient use of the photoinitiator were possible.