THERMAL CROSS-LINKING OF CIS-1,4-POLYBUTADIENE AT ULTRAHIGH PRESSURES

cis-1,4-Polybutadiene (BR) samples, in the absence of crosslinking age nts, were simultaneously compressed by ultrahigh pressures (>4.0 GPa) and annealed between 25 and 180 degrees C. The BR samples were crossli nked when the annealing temperatures were above 100 degrees C. The Vic kers microhardness of the treated BR increased and the extent of swell ing decreased rapidly as the annealing temperature increased, indicati ng that the crosslinking density increased. Solid-state carbon-13 nucl ear magnetic resonance and Fourier transform infrared spectroscopy res ults showed that some C=C bonds in the BR were opened to form the cros slinking network structures with C-C Linkages and that a partial cis-t rans isomerization took place during the treatments. Differential scan ning calorimetry studies revealed that the glass transition temperatur e increased and the crystallinity decreased as the annealing temperatu re increased. When the annealing temperature exceeded 140 degrees C, t he treated BR samples lost their rubbery elastic characteristics compl etely and became brittle materials. (C) 1998 John Wiley & Sons, Inc.