Effect of Linear and Ring-like Co-units on the Temperature Dependence of Nucleation and Growth in II-I Phase Transition of Butene-1 Copolymers

The phase transition from tetragonal form II to hexagonal form I was studied for the butene-1/ethylene and butene-1/1,5-hexadiene random copolymers, which have comparable molecular weight but distinct linear ethylene and ringlike methylene-1,3-cyclopentane (MCP) structural co-units, respectively. It is known that this solid phase transition follows the nucleation-growth mechanism, so the stepwise annealing protocol was utilized to investigate the influences of co-units on the optimal nucleation and growth temperatures. Compared with optimal nucleation and growth temperatures of -10 and 35 degrees C, respectively, in polybutene-1 homopolymer, two butene-1/ethylene copolymers with 1.5 mol% and 4.3 mol% co-units have the slightly lower optimal nucleation temperature of -15 degrees C but much higher optimal growth temperature of 50 degrees C. Clearly, the effect of ethylene co-unit is more significant on varying optimal temperature for growth than for nucleation. Furthermore, when the incorporated co-unit is ringlike MCP, the optimal nucleation temperature is -15 degrees C for 2.15 mol% co-units, the same with above BE copolymers, but -13 degrees C for a very low concentration of 0.65 mol%. Interestingly, the optimal growth temperature of butene-1/1,5-hexadiene copolymers with 0.65 mol%-2.15 mol% MCP counits increases to 55 degrees C, which is also independent on co-unit concentration. These obtained values of optimal temperatures provide crucial parameters for rapid II-I phase transition.

对丁烯 - 1/乙烯和丁烯 - 1/1,5 - 己二烯无规共聚物的从四方晶型II到六方晶型I的相变进行了研究，这两种共聚物具有相近的分子量，但分别具有不同的线性乙烯和环状亚甲基 - 1,3 - 环戊烷（MCP）结构共聚单元。已知这种固相转变遵循成核 - 生长机制，因此采用逐步退火方案来研究共聚单元对最佳成核温度和生长温度的影响。与聚丁烯 - 1均聚物中分别为 - 10℃和35℃的最佳成核温度和生长温度相比，含有1.5 mol%和4.3 mol%共聚单元的两种丁烯 - 1/乙烯共聚物的最佳成核温度略低，为 - 15℃，但最佳生长温度高得多，为50℃。显然，乙烯共聚单元对改变生长最佳温度的影响比对成核最佳温度的影响更为显著。此外，当引入的共聚单元为环状MCP时，对于2.15 mol%共聚单元，最佳成核温度为 - 15℃，与上述丁烯 - 1/乙烯共聚物相同，但对于0.65 mol%的极低浓度，最佳成核温度为 - 13℃。有趣的是，含有0.65 mol% - 2.15 mol% MCP共聚单元的丁烯 - 1/1,5 - 己二烯共聚物的最佳生长温度升高到55℃，这也与共聚单元浓度无关。这些获得的最佳温度值为快速的II - I相变提供了关键参数。