【作者】 李红英；

【导师】 余鼎声； 张军营；

【作者基本信息】 北京化工大学 ， 材料学， 2006， 博士

【摘要】 本论文首次通过阴离子开环共聚，成功地将POSS大分子作为多官能团单体，与环硅氧烷在KOH硅醇盐或Me₄NOH硅醇盐等碱性催化剂的作用下，直接合成交联聚硅氧烷：通过调节POSS大分子和环硅氧烷单体的种类以及化学计量比，可合成出一系列不同种类和不同交联密度的交联聚硅氧烷；并对其阴离子开环共聚机理以及极性调节剂DMAc对凝胶时间的影响进行了详细讨论；同时借以凝胶含量和溶胀比、GPC、FT-IR、固体¹³C和²⁹Si NMR、WAXD、DSC以及TG等手段对所得聚合物的微观结构以及热性能进行了详细考察。通过对单体、催化剂以及温度的分析，本实验选用了D₄、Ph₈D₄等环硅氧烷以及Octaisobutyl-POSS、Dodecaphenyl-POSS、Octaphenyl-POSS等POSS作为共聚单体，在KOH硅醇盐（聚合温度为100～120℃）或（CH₃）₄NOH硅醇盐（聚合温度为80-100℃）的催化作用下进行阴离子开环共聚。具体对以下四个阴离子开环共聚体系进行了详细讨论：Octaisobutyl-POSS/D₄阴离子开环共聚体系（A）：Dodecaphenyl-POSS/D₄/Ph₈D₄阴离子开环共聚体系（B）：Octaisobutyl-POSS/D₄/Ph₈D₄阴离子开环共聚体系（C）：Octaphenyl-POSS/D₄/Ph₈D₄阴离子开环共聚体系（D）。实验表明：无论是溶解度较好的Octaisobutyl-POSS，还是溶解度较差的Dodecaphenyl-POSS或Octaphenyl-POSS，在碱性催化剂的作用下甚至超过24 hrs都不能均聚，然而在相同情况下，却能很快与环硅氧烷共聚。由此可推出POSS与环硅氧烷倾向于形成无规共聚物，而不是嵌段共聚物。无规共聚机理一般与单体均聚机理相同，因此得出POSS与环硅氧烷在碱性催化剂作用下的共聚机理和环硅氧烷均聚机理相同，均属阴离子开环聚合机理。现以聚合体系（A）为例加以说明POSS与环硅氧烷阴离子开环聚合机理，即KOH或Me₄NOH与D₄反应生成相应的硅醇盐催化剂，并引发D₄产生阴离子活性中心。我们认为链增长首先是阴离子活性中心在D₄、Octaisobutyl-POSS或所形成的中间体的硅-氧键上的硅原子上进行亲核进攻，从而导致其电子云密度重新分布，以至在加热的情况下硅-氧键断裂形成新的阴离子活性种。然后新的活性种继续参与反应，并逐步增长。最后由于Octaisobutyl-POSS结构中含T链节-O_{[C（CH3）3]（O-）SiO}-结构单元而形成交联聚硅氧烷。本实验主要考察了极性调节剂DMAc对凝胶时间的影响。结果表明：在POSS与环硅氧烷的四个共聚合体系中，不添加任何极性调节剂，反应24 hrs，体系都未曾出现凝胶，但极性调节剂DMAc的少量加入，却能明显地影响其阴离子开环共聚反应，不但能使POSS与环硅氧烷的共聚得到可能，而且其凝胶时间随极性调节剂用量的增加大大缩短，聚合速度大大增加。在聚合体系（A）中，当Octaisobutyl-POSS单体加入量为0时，所得聚合物可基本被抽提干净，溶胀比无穷大，为线型聚合物；而只要添加极少量的Octaisobutyl-POSS单体，所得聚合物就不能被抽提干净，大约有80％的残余物，溶胀比也大大降低，则为交联聚合物，而且，随Octaisobutyl-POSS单体用量增加，溶胀比降低；而凝胶含量基本不变。在其它的聚合体系中也可得出同样的结论。将聚合体系（B）中所得的聚合物经索氏提取器提取12hrs后的提取液作GPC分析，可得出在该提取液中基本上没有分子量很高（数万以上）的高聚物，而主要由上百至数千的齐聚物组成，由此得出高分子量的聚硅氧烷基本被交联。借助于凝胶含量和溶胀比、GPC、FT-IR、固体¹³C和²⁰Si NMR、WAXD等表征手段再次证实了POSS参与阴离子开环聚合反应以及所得产物属结晶度很低的交联聚硅氧烷。但在前三个聚合体系中，POSS大分子单体反应程度较大，而在聚合体系（D）中，Octaphenyl-POSS反应很不完全，这主要是由于其溶解度不好的缘故。借助于DSC、TG等热性能测试手段表明了所得交联聚硅氧烷具有明显的玻璃化转变温度以及良好的热稳定性。与用KOH硅醇盐所合成的交联聚硅氧烷相比，用Me₄NOH硅醇盐所合成的交联聚硅氧烷具有更好的热稳定性。更多还原

【Abstract】 This dissertation successfully fabricated cross-linked polysiloxanes under base catalysts such as potassium hydroxide （KOH） siloxanolate or tetramethylammonium hydroxide （Me₄NOH） siloxanolate by anionic ring-opening copolymerization of cyclosiloxanes and Polyhedral Oligomeric Silsesquioxanes （POSS） as multifunctional monomers. A series of cross-linked polysiloxanes of kinds and different cross-linking density were synthesized by altering the kind and stoichiometry of POSS and cyclosiloxanes. And the mechanisms of anionic ring-opening copolymerization of POSS and cyclosiloxanes as well as the influences of the polar additive N, N-dimethylacetamide （DMAc） on gelation time were studied in detail. The characterization techniques including gel content and swelling ratio, GPC, FT-IR. solid-state ¹³ C and ²⁹ Si NMR、XRD、DSC and TG were used to discuss detailedly on the microstructure and thermal stability of the obtained cross-linked polysiloxanes.Studies on monomers, catalysts and polymerization temperature were our main focuses. One or Both of octamethylcyclotetrasiloxane （D₄） and octaphenylcyclotetrasiloxane （Ph₈D₄） , as well as one of three POSS including Octaisobutyl-POSS, Dodecaphenyl-POSS, Octaphenyl-POSS were used as comonomers to anionic ring-opening copolymerize under base catalysts such as KOH siloxanolate （at 100～120℃） or Me₄NOH （at 80～100℃） siloxanolate in this experiment. The following four anionic ring-opening copolymerization systems were studied: Octaisobutyl-POSS /D₄ anionic ring-opening copolymerization system （A）; Dodecaphenyl-POSS/D₄/Ph₈D₄ anionic ring-opening copolymerization system （B）; Octaisobutyl-POSS/D₄/Ph₈D₄ anionic ring-opening copolymerization system （C）; Octaphenyl-POSS /D₄/Ph₈D₄ anionic ring-opening copolymerization system （D）.No matter Octaisobutyl-POSS which has good solubility in D₄ or Dodecaphenyl-POSS and Octaphenyl-POSS which have poor solubility in D₄, they cannot homopolymerize even for more than 24 hrs under basic catalysts such as KOH, siloxanolate （at 100～120℃） or Me₄NOH （at 80～100℃） siloxanolate. However, they can quickly copolymerize with cyclosiloxanes at the same condition. Thereby, it can be concluded that POSS and cyclosiloxanes were inclined to form random copolymer, rather than block copolymer. The mechanism of random copolymerization commonly accords with the homopolymerization mechanism of monomers; therefore, the copolymerization mechanism of POSS and cyclosiloxanes under basic catalysts is the same as the homopolymerization of cyclosiloxanes. so they all belong to anionic ring-opening polymerization.The anionic ring-opening copolymerization mechanism was illuminated with the example of copolymerization system （A）. The base such as KOH or Me₄NOH reacts with D₄ to generate the corresponding siloxanolate catalyst. which initiates D₄ to yield the base catalyzed （or anionic） active species. The chain propagation is believed to proceed first with the nucleophilic attach of the anionic active species on the silicon atom of siloxane linkage and then with the subsequent redistribution of electron cloud density. Then the siloxane linkage is dissociated by heating to yield new anionic active centers, which continue to react and then propagate gradually. Finally the random cross-linked polysiloxane is formed because the octaisobutyl-POSS contains the O{[C（CH₃） ₃] （O-）SiO}-units （i.e. T bonding）.The effect of the polar additive DMAc on gelation time was discussed. The results indicated that they were difficult to react and didn’t even gel 24 hrs by anionic ring-opening copolymerization of POSS and cyclosiloxanes without any polar additives in the four copolymerization systems of POSS and cyclosiloxanes. But the polar additives DMAc, can dramatically affect the anionic ring-opening copolymerization. It not only made the copolymerization of POSS and cyclosiloxanes possible,but also decreased the gelation time distinctly. And the rate of polymerization increased greatly with the increase of DMAc.In copolymerization system （A）, when the content of Octaisobutyl-POSS monomer was O, the obtained polymer can be thoroughly removed through the extraction procedure. The gel content was infinitesimal and the swelling ratio was infinite, so it was linear polysiloxane. When a trace amount of Octaisobutyl-POSS was added, the obtained polymer can not be thoroughly removed through the extraction procedure, the remainder was about 80% and the swelling ratio also decreased dramatically. So it can be concluded that Octaisobutyl-POSS participated the anionic ring-opening copolymerization reaction and the obtained polymer was cross-linked polysiloxanes. In addition, as the octaisobutyl-POSS monomer increased, the swelling ratio decreased and the gel content was unchanged. The same conclusions can be drawn from the other copolymerization systems.The GPC analyses of the soluble part of the obtained polymers in copolymerization system （B） through the extraction procedure showed that the soluble polysiloxanes were mainly composed of the oligomers with low molecular weight of several hundreds to thousands, and few polymers with molecular weight higher more than ten thousands. Therefore, it can be believed that the polysiloxanes with higher molecular weight were almost cross-linked.The results of solid-state FT-IR. ¹³ C and ²⁹ Si NMR, XRD showed again that POSS was reacted with cyclosiloxanes via anionic ring-opening copolymerization and the obtained polymers were cross-linked polysiloxanes with very low crystalline degree. In the former three polymerization systems. POSS monomers were copolymerized nearly in accordance with the designed value and the reactions were more complete more than polymerization system （D）. which was much less than its designed value.The DSC and TG results indicated that the obtained cross-linked polysiloxancs exhibited distinct glass transition temperatures （T_g） and excellent thermal stability. Compared to that with KOH siloxanolate, the cross-linked polysiloxane synthesized with Me₄NOH siloxanolate had more preferable thermal stability.更多还原