聚氨酯硬链段球晶生长与软硬链锻混容性的关系

线型可溶性聚氨酯的硬链段结晶难以长成球晶 ,然而本实验室已经证明即使从熔体结晶硬链段也是能够长成球晶的 .研究了聚酯与聚醚型聚氨酯硬链段长球晶的规律 ,并发现聚氨酯硬链段长球晶的难易与聚氨酯软硬链段混容性密切相关 .动态力学分析 (DMA)与示差扫描量热 (DSC)实验表明聚ε 已内酯 (PCL)、聚已二酸丁二醇酯 (PTMA)、聚四氢呋喃 (PTMO)及聚环氧丙烷 (PPO)型聚氨酯的软硬链段混容性从前至后递减 .从熔体退火结晶时 ,聚氨酯硬链段长成球晶的退火温度范围是有限的 ,软硬链段混容性越好 ,聚氨酯硬链段能长成球晶的温度范围越窄 ,所需长的时间越长 .聚氨酯硬链段长球晶的下限温度取决于软硬链段间所存在的氢键作用 ,聚氨酯硬链段长球晶的上限温度与软硬链段混容性直接相关 .

SPHERULITE FORMATION OF HARD SEGMENTS AND COMPATIBILITY BETWEEN SOFT AND HARD SEGMENTS IN POLYURETHANES

The spherulite growth of hard segments in polyurethanes and its relation to the compatibility between the soft and hard segments were studied.DMA and DSC measurements indicate that polyurethane with different soft segments(PCL,PTAM,PTMO and PPO) exhibit different compatibility between their soft and hard segments.The compatibility between hard and soft segmeats in polyurethanes decreases in a sequence of PCL,PTMA,PTMO and PPO.The temperature range for hard segments of polyurethane to grow spherulites in annealing from melt is limited.The better the compatibility between the soft and hard segments,the narrower the temperature range for spherulite formation and the longer the crystallization time.The low temperature limit of spherulite growth is 120℃ for polyurethane with MDI|BDO hard segments and does not change with soft segments.This limit is determined by the hydrogen bonds between the hard segments and soft segments.The high temperature limit of spherulite growth strongly depends on the compatibility between the soft and hard segments.The worse the compatibility,the higher the high temperature limit.Only when the temperature becomes high enough,the compatibility between the soft and hard segments can prevent the forming of spherulite.When the hard segments crystallize from melt,there exist a most appropriate temperature of forming spherulites,at which the amount of hydrogen bonds has a maximum as shown by FTIR.In such cases the crystallites and spherulites are more stable.