Crystallization and enthalpy relaxation of physically associating, end-linked polymer networks: Telechelic pyrene-labeled polydimethylsiloxane
Crystallization and enthalpy relaxation of physically associating, end-linked polymer networks: Telechelic pyrene-labeled polydimethylsiloxane
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DOI：
10.1007/s00289-004-0241-9
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发表时间：
2004-04-01
期刊：
影响因子：
3.2
通讯作者：
Torkelson, JM
中科院分区：
文献类型：
--
作者：
Jones, BA;Torkelson, JM
通过对远螺旋、芘端标记的聚二甲基硅氧烷及其前体、远螺旋、胺端标记的聚二甲基硅氧烷（PDMS）的热分析，确定了物理交联或凝胶化和分子量对聚二甲基硅氧烷结晶行为的影响。芘端标记的PDMS形成物理交联，而胺端标记的PDMS不形成物理交联。物理交联的存在导致在5度/分钟的淬火过程中PDMS结晶度的显著降低，这是分子量的显著函数。在从胺端标记的PDMS到芘端标记的PDMS过程中，25 kg/mol样品的PDMS结晶度从59%降低到30%，而4-7 kgimol样品的PDMS结晶度降低了一个数量级以上，从53%降低到2%到4%，后者的值取决于冷却周期开始时芘基单元实现的物理交联程度。PDMS的熔融温度是物理交联的强烈函数，而PDMS的玻璃化转变温度与分子量和末端单元类型无关。然而，在短暂淬火期间实现的PDMS的焓松弛或物理老化的程度在芘基端单元的存在下减少，因此物理交联。
The effects of physical crosslinking or gelation and molecular weight on the crystallization behavior of polydimethylsiloxane (PDMS) are determined by thermal analysis of telechelic, pyrene-end-labeled PDMS and its precursor, telechelic, amine-end-labeled PDMS. The pyrene-end-labeled PDMS forms physical crosslinks while the amine-end-labeled PDMS does not. The presence of physical crosslinks leads to a major reduction in PDMS crystallinity achieved during a 5 degreesC/min quench that is a striking function of molecular weight. In going from the amine-end-labeled PDMS to the pyrene-end-labeled PDMS, a 25 kg/mol sample exhibits a reduction in PDMS crystallinity from 59% to 30% while a 4-7 kgimol sample exhibits a reduction in PDMS crystallinity by more than an order of magnitude, from 53% to 2 to 4%, with the latter value depending on the extent of physical crosslinking achieved by the pyrenyl units at the start of the cooling cycle. The PDMS melting temperature is a strong function of physical crosslinking, while the PDMS glass transition temperature is invariant with molecular weight and type of end unit. However, the extent of enthalpy relaxation or physical aging of the PDMS achieved during a brief quench is reduced in the presence of pyrenyl end units and thus physical crosslinking.