TRACER DIFFUSION IN THE BLENDS OF POLYSTYRENE AND TETRAMETHYLBISPHENOL-A POLYCARBONATE

The tracer diffusion coefficients (D*) of deuterated tetramethylbisphenol A polycarbonate (d-TMPC) and deuterated polystyrene (d-PS) into protonated blends of TMPC/PS were measured in an effort to gain insight into the factors which determine the monomer friction coefficient of the individual components of a miscible polymer blend. Forward recoil spectrometry (FRES) was used to obtain the depth profile of deuterium after diffusion well above the glass transition temperature (T-g). The temperature dependence of the D*'s was measured for matrices with PS weight fraction w of 0, 0.5, and 1; in all cases the D* of TMPC was more strongly temperature dependent than that of PS, which is in contrast with the results in blends of PS/poly(xylenyl ether)(PXE) and in disagreement with the simple free volume model of the dynamics of polymer melts. At high molecular weights of the protonated matrix, diffusion of the deuterated tracer molecules was independent of the molecular weight of the matrix and scaled as M(-2), where M is the molecular weight of the tracer polymer, strongly suggesting that reptation is the diffusion mechanism in this regime. The reptation model was used to extract monomer friction coefficients for the PS (zeta(0,PS)) and TMPC (zeta(0,TMPC)) from their respective D*'s measured as a function of w at T = T-g + 45 degrees C. The monomer friction coefficient of TMPC was larger than that for PS by more than 100 times. The zeta(0) of each species depended strongly on composition at either constant T - T-g or constant fractional free volume. However, zeta(0),(PS)/zeta(0,TMPC) varied only moderately (by about a factor of 3) as a function of w, again in marked contrast with the results in blends of PS:PXE where it varied by about a factor of 10(3).