Polyborosiloxanes (PBSs), Synthetic Kinetics, and Characterization
Polyborosiloxanes (PBSs), Synthetic Kinetics, and Characterization
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DOI：
10.1021/ma500632f
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发表时间：
2014-07-22
期刊：
影响因子：
5.5
通讯作者：
Besseling, Nicolaas A. M.
中科院分区：
文献类型：
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作者：
Liu, Zhen;Picken, Stephen J.;Besseling, Nicolaas A. M.
我们通过将聚二甲基硅氧烷（PDMS）和硼酸（BA）的混合物加热到200 ℃来合成聚硼硅氧烷（PBS）。在反应过程中，PDMS链发生随机断裂，新的链端被-Si-O-（BO）（m）（OH）（n）部分修饰。这一见解是基于凝胶渗透色谱法（GPC）的结果在改性过程中的分子量分布的演变，结合傅里叶变换红外光谱（FTIR），以确定化学部分。我们发明了一种改进方法，其中通过硼氧烷键B-O-B的水解和随后除去释放的BA，可以将不明确的多分散极性端基转化为主要是硼基的-Si-O-B（OH）（2）。由于端基之间的氢键作用，所得PBS形成超分子弹性体。通过动态流变仪研究了超分子弹性体的粘弹行为，发现在改性后，即使平均聚合度降低，动态模量也显著增加。这可以通过修饰的链端之间的强相互作用来解释。此外，我们发现，通过严重脱水，硼醇基团转化为硼氧烷键。在暴露于环境湿度时，这些交联被水解，并且超分子弹性体被回收。
We synthesized polyborosiloxanes (PBSs) from poly(dimethylsiloxane) (PDMS) and boric acid (BA) by heating a mixture of these compounds to 200 degrees C. During the reaction the PDMS chains are subject to random scission, upon which the new chain ends get modified by -Si-O-(BO)(m)(OH)(n) moieties. This insight is based on gel permeation chromatography (GPC) results on the evolution of the molecular-weight distribution during the modification process, in combination with Fourier transform infrared (FTIR) spectroscopy to identify chemical moieties. We invented a refinement procedure in which the ill-defined polydisperse polar end groups can be converted into predominately borono, -Si-O-B(OH)(2), by hydrolysis of boroxane bonds, B-O-B, and subsequent removal of released BA. The resulting PBSs form supramolecular elastomers owing to hydrogen bonding among the end groups. The viscoelastic behavior of the supramolecular elastomers was investigated by dynamic rheometry, and we found that the dynamic moduli increases dramatically upon the modification, even though the mean degree of polymerization decrease. This is explained by the strong interactions between the modified chain ends. Furthermore, we found that by severe dehydration, the boranol groups are converted into boroxane bonds. Upon exposure to ambient humidity, these cross-links are hydrolyzed, and the supramolecular elastomer is recovered.