PREPARATION AND PROPERTIES OF POLY(VINYL ACETATE) SILICA-GEL MICROHYBRIDS

Poly(vinyl acetate) (PVAc) was incorporated into silica gel using the sol-gel process involving tetraethoxysilane (TEOS). In order to prepar e silica-gel microhybrids, two different processes were employed, and the physical properties of the resulting two sets of hybrids were comp ared. In the first method, PVAc was first mixed with TEOS in an aceton e solution and then cured using HCl and H2O. In the second method, an acetone solution of a copolymer composed of vinyl acetate (VAc) and vi nyl triethoxysilane (VTES) was first mixed with TEOS and then cured. T his copolymer contained 10 mol % of VTES component and was bound coval ently to silica-gel molecules. When comparing the properties of the hy brids, the dynamic modulus, E', increased with increasing amounts of T EOS over a wide temperature range: -20-120-degrees-C. E' of a hybrid f rom PAVc was lower than that of a hybrid from the VAc/VTES copolymer. A sharp peak in the loss modulus, E'', of a PVAc hybrid occurred at 40 -degrees-C, and its position did not change with TEOS content. In cont rast, the E'' peak of a copolymer hybrid was broad and its position al so shifted to a higher temperature as the TEOS content increased. The tensile strength of a PVAc hybrid increased as the amount of mixed TEO S increased, reaching a maximum of 30 MPa at 50 wt % of TEOS. However, the strength of a copolymer hybrid reached a maximum of 50 MPa at 50 wt % of TEOS. The differences in the physical properties between a PVA c hybrid and a copolymer hybrid arise from the difference in their str ucture. Organic polymer molecules in a copolymer hybrid combine covale ntly with silica-gel molecules through the VTES component, while a PVA c hybrid has no bonding between PVAc and silica-gel molecules. (C) 199 4 John Wiley & Sons, Inc.