BLENDS OF BISPHENOL-A POLYCARBONATE AND ACRYLIC POLYMERS .3. EFFECT OF IMIDE CONCENTRATION ON COMPATIBILITY

Imide units copolymerized with MMA units have been selected in order t o improve compatibility between PC and acrylics through specific inter action or internal repulsion. Good dispersion of acrylic inside a PC m atrix has been observed upon melt mixing, which can be partially expla ined by the good rheological agreement between these two polymers. Tra nsmission electron microscopy has shown that the system remains phase separated from 5 to 95 wt % of PC. Phase diagrams for three different imide concentrations have been drawn. Results obtained by DSC (convent ional and with enthalpy relaxation) are similar to those obtained by o ptical cloud point detection. The phase diagrams show the raise of the PC/PMMA demixtion curve (LCST type) when percentage of imide increase s in the acrylic phase. Theoretical calculations on binary interaction energy density show a slight improvement of the interaction between a crylic and PC when imide percentage increases. Cloud point measurement s on 50/50 PC/acrylic blends varying the imide concentration show that the improvement of compatibility deduced from the raise of the demixt ion curve ( LCST type) is more related to a kinetic effect (the high T -g of imidized samples is reducing macromolecule mobility) than specif ic interactions. The calculated favorable interactions are probably to o weak to be detected with cloud point measurements. The microstructur es obtained after crystallization of the PC phase under solvent vapors is phase separated PC/acrylics blends can also be explained by T-g ef fects. Moreover, solvent vapor exposure could be a powerful tool to de termine the real thermodynamic behavior of the blends at room temperat ure. (C) 1997 John Wiley & Sons, Inc.