Pressure-volume-temperature behavior of several synthetic rubbers

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Abstract
The pressure-volume-temperature (P-V-T) relations were studied for cis-1,4-polybutadiene, cis-l,4-polyisoprene, and poly(styrene-butadiene) in the pressure range of 1 to 8000 kg/cm2 at 10 to 50°C. The specific volume of cis-1,4-polybutadiene and cis-1,4-polyisoprene decreased with increasing pressure and abruptly decreased at a certain pressure (low-pressure break). Above this pressure, the specific volume decreased smoothly with increasing pressure and then decreased abruptly again (high-pressure break). The compressibilities below and above the low-pressure break were of the order of 10−5 (kg/cm2)−1 up to the high-pressure break. Above the high-pressure break, the compressibilities reduced to the order of 10−6 (kg/cm2)−1. The P-V isotherms for poly(styrenebutadiene) showed only the high pressure break. An abrupt increase in specific volume occurred in the isobaric measurements for cis-l,4-polyisoprene at a pressure and temperature corresponding to the high-pressure break in the isotherms. From the temperature shift of the low-pressure break and the behavior of radiation-induced crosslinking with pressure, the low-pressure break was concluded to be due to partial crystallization. The high-pressure break was concluded to be due to the transition from liquid to densified glass, judging from the fact that the high-pressure break existed in poly(styrenebutadiene) and the result of isobaric measurements in cis-1,4-polyisoprene.