The properties of cis-1

4-polybutadiene rubbers with different molecular weights which were obtained with titanium catalyst have been studied．The properties of raw cis-1，4-polybutadiene rubbers with different molecular weights are similar to each other with respect to (1) gel content，less than 1％，(2) cis-1，4-con-tent

93—97％，and (3) glass temperature，-110 to一114℃ (Table 1A)．However，the Mooney viscosity increases rapidly with [n] (Fig．1)．It is shown by stress-strain curves that a11 the cis-1，4-polybutadiene samples under examination do not crystallize during stretching (Fig．2)．The behaviour of cis-1，4-polybutadiene in milling is very sensitive to temperature．Carbon black compoundings have been carried out on an open laboratory mill at cylinder temperatures of 25，40，and 60。C，respectively． Smooth compounds from which vul-canizates with tensile strength over 200 kg／cm2 may be prepared can only be obtained at 25℃． When compounding is carried out at 40 or 60℃，cis-1，4-polybutadiene tends to crumble(Fig．4)，no smooth compound can be prepared，and the vulcanizate obtained loses tensile strength(Fig．3)．According to the following experimental results： (1)no gel formation，no signi ficant degradation，and no change in microstructure can be observed when cis-1，4一poly- butadiene is masticated either at 25℃ or at 40 or 60℃ (Fig．6 and Table 3)；(2)the effect of temperature on milling is reversible (Table 4)，it is presumed that the lOSS of tensile strength of the vulcanizate obtained from compound prepared at 40 or 60℃ is due to the difficulty of incorporation and dispersion of carbon black into the cis-1

4-polybutadiene rubber at a temperature above 40℃．This presumption is supported by the microscopic photographs of the CROSS-sections of the vulcanizates(Fig．5)．It is found that the tensile strength of the vulcanizate decreases rapidly as the mo-dulus(M300％) exceeds 60 kg／cm2 (Fig．8)．However，with a suitable amount of sulphur to control the degree of cross-14nking，vulcanizates of tensile strengths over 200 kg／cm2 can be obtained (Fig．8 and Table 1B)．The elastisity (Yerzley) and abrasive resistance of cis-1，4-polybutadiene vulcanizates are much better than those of natural rubber(Table 1B)．The effect of molecular weight of cis-1

4-polybutadiene on the mechanical proper-ties of the vulcanizate has been investigated． It is found that vulcanizates of tensile strength around 200 kg／cm2 can be obtained within wide range of molecular weights ([n] 2.5 to 3.6)，whereas elasticity increases with the M of the raw rubber(Fig．9)．