Department of Physics, Umeå University, 901 87 Umeå, Sweden.
Phys Chem Chem Phys. 2011 Sep 7;13(33):15047-54. doi: 10.1039/c1cp20785g. Epub 2011 Jul 21.
The thermal conductivity κ, heat capacity per unit volume ρc(p) and glass transition behaviour under pressure have been established for medium and high vinyl content polybutadiene PB with molecular weights 2600 and 100,000 and their highly cross-linked (ebonite) states obtained purely by high-pressure high-temperature treatments. Cross-linking eliminates the glass transitions and increases κ by as much as 50% at 295 K and 1 atm, and decreases ρc(p) to a limiting level close to that of the glassy state of PB, which is reached before the ultimate cross-link density is achieved. The pressure and temperature behaviours of κ are strongly changed by cross-links, which increases the effect of temperature but decreases the effect of pressure. We attribute these changes to a cross-linked induced permanent densification and consequential increase of phonon velocity simultaneously as conduction along polymer chains is disrupted. The glass transition temperatures for a time scale of 1 s are described to within 0.5 K by: T(g)(p) = 202.5 (1 + 2.94 p)(0.286) and T(g)(p) = 272.3 (1 + 2.57 p)(0.233) (p in GPa and T in K) up to 1 GPa, for PB2600 and PB100000, respectively, and can be estimated for medium and high vinyl content PBs with molecular weights in between by a constant, pressure independent, shift in temperature.
已经确定了具有 2600 和 100000 分子量的中高乙烯基含量聚丁二烯 PB 及其高度交联（硬橡胶）状态的热导率 κ、单位体积热容 ρc(p) 和压力下的玻璃化转变行为，这些状态纯粹通过高压高温处理获得。交联消除了玻璃化转变，并在 295 K 和 1 大气压下使 κ 增加高达 50%，并将 ρc(p) 降低到接近 PB 玻璃态的极限水平，在达到最终交联密度之前达到该水平。交联强烈改变了 κ 的压力和温度行为，增加了温度的影响，但降低了压力的影响。我们将这些变化归因于交联诱导的永久致密化，同时伴随着声子速度的增加，因为聚合物链的传导被中断。在 1 s 的时间尺度内，玻璃化转变温度可以描述为：T(g)(p) = 202.5 (1 + 2.94 p)(0.286) 和 T(g)(p) = 272.3 (1 + 2.57 p)(0.233) (p 在 GPa 范围内，T 在 K 范围内)，对于 PB2600 和 PB100000 分别高达 1 GPa，可以通过温度的恒定、与压力无关的偏移来估计分子量在中间的中高乙烯基含量 PB 的玻璃化转变温度。
