Pyrenyl fluorescence as a probe of polymer structure and diffusion in a polyethylene : poly(butyl methacrylate)-co-polystyrene interpenetrating network and related polymers

Dynamic and static photophysical and spectroscopic measurements have been u sed to analyze the microdomains of interpenetrating network (IPN) films con sisting of 1:1 polyethylene:(7:3)-poly(butyl methacrylate)-co-polystyrene. The primary probe, fluorescence from pyrenyl groups covalently attached sel ectively to the different elements of the IPN, has been monitored under a v ariety of conditions, including in the absence and presence of a fluorescen ce quencher, diethyl oxalate (DEO), which is not able to enter domains of p olyethylene. It has been possible to discern the parts of the IPN that are accessible to molecules of DEO and the rates at which DEO is able to enter them. Two diffusion coefficients, indicating parallel diffusion pathways, a re necessary to account for DEO entry into several of the films. The IPN co nsists of largely segregated domains, but there are extensive interactions between domains at their interfaces. Conclusions are derived from compariso ns of results from the IPN and films of their constituent polymeric element s when each is tagged with the lumophoric groups, as well as from films con taining noncovalently linked pyrenyl groups. These results help to clarify the picture of the network derived from structural studies by providing dyn amic insights into degrees of domain interpenetration and permeability.