Interface development in polycarbonate/poly(methyl methacrylate) bilayer films

We report the effect of annealing over a range of temperatures and times on the mixing, stability, and interfacial width in thin bilayer films of bisp henol A-polycarbonate (PC) on deuterated poly(methyl methacrylate) (dPMMA). These bilayer films were highly stable when annealed at temperatures of up to 438 K, the temperature at which the degradation of the blends of these materials was first detectable by thermogravimetric analysis. At higher tem peratures, dewetting of the PC upper layer of the film occurred at an incre asing rate. Nuclear reaction analysis showed that the PC and dPMMA layers r emained segregated. Neutron reflectometry data showed that the interfacial width between the two polymer layers grew rapidly from 0.5 nm for an unanne aled sample to approximately 4.0 nm, the latter value being in good agreeme nt with the predicted value for the interfacial width in the absence of any reaction. Extended annealing at 438 K and lower temperatures had no effect on the interfacial width, whereas at higher temperatures, the interfacial width increased to approximately 5.5 nm before the films became unstable. T he broadening of the interface found at higher annealing temperatures was a ttributed to an increase in the miscibility of the polymers induced by the monomer from the unzipping of the dPMMA chains. There was no evidence of a thermally induced chemical reaction between the two polymers. (C) 2001 John Wiley & Sons, Inc.