【作者】 高秋爽；

【导师】 武德珍；

【作者基本信息】 北京化工大学 ， 材料科学与工程， 2012， 博士

【摘要】 在高性能聚合物领域中，聚酰亚胺以其优异的性能指标受到科学家们的广泛关注，改性后的聚酰亚胺则显示出了许多更加出色的性能。将硅元素引入到聚酰亚胺基体中可以有效使杂化材料的粘结性增强、介电常数和吸水率下降，因此成为改性聚酰亚胺的主要研究方向之一。梯形聚倍半硅氧烷（ladder-like polysilsesquioxane, LPSQ）具有独特的双链结构，拥有优异的化学、物理性能。另外，其分子链长度、官能团以及官能度都可以根据需要进行调控。因此，本课题首次提出将LPSQ引入到聚酰亚胺基体中制备出高性能聚酰亚胺杂化薄膜。并且通过研究杂化薄膜的结构与性能的关系，实现聚酰亚胺性能可调控这一目标。主要的研究工作如下。本文通过平衡缩聚法和溶胶-凝胶法分别合成了高、低两种不同分子量的苯基梯形聚倍半硅氧烷（LPPSQ），利用凝胶渗透色谱法（GPC）对其分子量进行表征，利用傅立叶红外光谱（FTIR）、核磁共振（NMR）、X射线衍射（XRD）及分子模拟对LPPSQ的梯形结构进行表征，结果表明，该梯形聚合物的规整度会随着分子量的提高稍有下降。通过调节含有巯基和苯基官能团的两种单体的投料比，合成了巯基含量可控的巯基苯基梯形聚倍半硅氧烷（LPMPSQ），利用FTIR、29Si-NMR和XRD对投料比不同的两种LPMPSQ的结构进行表征，结果表明，含巯基单体的用量对产物中巯基的含量有着直接的影响。利用发烟硝酸将LPPSQ的侧基硝化，得到了硝苯基梯形聚倍半硅氧烷（LPNPSQ）；利用水合肼将LPNPSQ的侧基还原，即可得到氨苯基梯形聚倍半硅氧烷（LPAPSQ）。利用FTIR、NMR、XRD和分子模拟分别对LPNPSQ和LPAPSQ进行结构表征，结果表明，经过化学改性后，LPSQ的梯形结构骨架得到了较好的保持，但由于取代反应随机发生在间位或对位，其规整度稍有下降。并且，通过调节硝化作用的时间或还原催化剂的用量，可以实现LPSQ官能度可控。将制备好的一系列不同分子量、含有不同官能团以及具有不同官能度的LPSQ分别引入到聚酰亚胺基体中，制得了一系列聚酰亚胺/梯形聚倍半硅氧烷（PI/LPSQ）杂化薄膜。由于LPSQ的掺杂量、分子量、官能团、官能度的不同，相应制得的杂化薄膜的性质也各不相同。利用XRD、扫面电子显微镜（SEM）和X射线光电子能谱仪（XPS）对PI/LPSQ杂化薄膜的结构进行表征；利用动态热分析仪（DMA）、热失重仪（TGA）、万能材料试验机、水接触角和吸水率对杂化薄膜的性能进行表征。研究表明：（1）随着掺杂量的提高，LPMPSQ粒子的数量和尺寸都明显增大，表面硅元素含量随之提高，吸水率随之下降；掺杂量对热稳定性没有明显的影响；在掺杂量低于10wt%的时候，可以得到表面硅含量较高且力学性能较好的杂化薄膜。（2）LPMPSQ的分子量对杂化薄膜的热性能没有明显影响。在掺杂量低于10wt%的时候，两相的相互作用力占主导作用，长链LPMPSQ杂化薄膜的力学性能较好；随着掺杂量进一步提高，两相的相分离开始逐渐占主导作用，长链的LPMPSQ比短链的更容易发生团聚，从而影响其力学性能。（3）LPPSQ、LPNPSQ、LPAPSQ与聚酰亚胺基体间分别存在弱氢键、物理缠结、化学交联三种类型的相互作用，作用力依次由弱到强。较强的界面相互作用可以明显提高LPSQ在聚酰亚胺基体中的分散性，从而提高杂化薄膜的热性能、力学性能，但较强的相互作用力同时也限制了LPSQ向杂化薄膜表面的迁移和富集，使其表面改性效果不明显。（4）利用不同氨苯基含量的LPSQ研究其官能度对杂化薄膜的影响。随着LPSQ中氨苯基含量的提高，杂化体系的交联密度也随之上升，这种变化使杂化薄膜的表面性能、热性能以及力学性能都随之发生改变。过高的氨基含量不但会使杂化体系的交联密度过高导致材料变脆，而且过多的氨基与聚酰胺酸分子链上的羧基进行反应导致聚酰亚胺的亚胺化不完全。（5）通过跟踪PI/LPPSQ和PI/LPMPSQ两种杂化薄膜在不同处理条件下的表面硅元素含量，研究热亚胺化过程对杂化薄膜的影响。杂化薄膜表面硅元素的变化规律说明，LPSQ向杂化薄膜表面迁移和富集主要发生在溶剂挥发的过程中，即晾膜的过程；而在热亚胺化过程中，只有少量的LPSQ随着温度的升高继续向杂化薄膜表面迁移。研究发现，在PI/LPMPSQ杂化薄膜中，聚酰亚胺基体会随着亚胺化温度的升高逐渐向LPMPSQ粒子表面包覆，与PI/LPPSQ体系相比，证明了巯基与聚酰亚胺基体间存在较强的相互作用。更多还原

【Abstract】 In the field of high performance polymer, polyimide (PI) has receivedwide attention due to its outstanding properties. Furthermore, PI compositeshave shown very promising properties. Blending silicon element in PI matrixhas been one of the most important research trends, because the compositespossessed higher adhesive properties, lower dielectric constant and lowerwater absorption. Ladder-like polysilsesquioxane (LPSQ) has attractedconsiderable interest because of their excellent chemical, physical andelectrical properties derived from the unique double-chained skeleton.Moreover, the aspect ratio, functional groups and average functionality ofLPSQ are controllable according to diverse requirements. Thus, LPSQs werechosen to incorporate into PI matrix for the first time in order to fabricate highperformance PI. By studying the relationship between structure and propertiesof hybrid films, the performance of PI composite can be controlled ultimately.The main content of this dissertation are shown below.Two kinds of ladder-like polyphenylsilsesquioxane (LPPSQ) have beensynthesized by quilibrium polycondensation and sol-gel method, respectively.They were characterized by gel permeation chromatograph (GPC), Fouriertransform infrared (FTIR), nuclear magnetic resonance (NMR), X-raydiffraction (XRD) and molecular simulation. The results confirmed that the regularity of LPPSQ decreased slightly as the molecular weight increased.Mercapto functionalized ladder-like polysilsesquioxanes (LPMPSQs) havebeen synthesized with different feed ratio. They were characterized by FTIR,29Si-NMR and XRD. The results suggested that the dosage of mercaptomonomer had great effect on the final production. LPPSQ has been modifiedto ladder-like poly(nitrophenyl)silsesquioxane (LPNPSQ) andpoly(aminophenyl)silsesquioxane (LPAPSQ) by nitration and reductionreaction, respectively. They were also characterized by FTIR, NMR, XRD andmolecular simulation. The results confirm the ladder-like structures of LPSQand suggest the decrease of regularity after the chemical modification. Thefunctionality of LPSQ can be controlled by adjusting the time of nitrificationor the amount of reducing catalyzer agent.A series of LPSQs with different molecular weight, functional groups andaverage functionality was incorporated into PI matrix, respectively. ThesePI/LPSQ hybrid films showed different properties owning to the difference ofLPSQs. The structure of PI/LPSQ hybrid film was investigated with XRD,scanning electron microscopy (SEM) and X-ray photoelectron spectroscopic(XPS). The properties were studied using dynamic mechanical analysis(DMA), thermogravimetry (TGA), tensile tests, water contact angles analysisand water absorption test. The main conclusions are shown below.(a) With theincrease of LPMPSQ fraction, the concentration of silicon atom on the surfaceof the hybrid film keeps rising, and the water absorption capacity decreasesaccordingly. However, the doping content had no effect on the thermalstability of PI/LPMPSQ hybrid films. PI/LPMPSQ hybrid films stillmaintained excellent mechanical properties of PI when the doping content wasless than and equal to10wt%.(b) The molecular weight of LPMPSQ also hadno effect on the thermal properties of PI/LPMPSQ hybrid films. Themechanical properties depended on the interaction of the two phases when the doping content was less than and equal to10wt%. With the doping contentfurther increasing, the effect of phase separation became important.Long-chained LPMPSQ was more inclined to aggregation, so the mechanicalproperties of PI/long-chained LPMPSQ hybrid film were weaker thanshort-chained LPMPSQ’s.(c) There are hydrogen bonds, physicalentanglement, and chemical cross-link between LPPSQ, LPNPSQ, LPAPSQand PI matrix, respectively. The strong interfacial interactions can improvedispersion of LPSQ significantly, thereby improving the thermal andmechanical properties of hybrid films. However, these strong interactions canalso limit the migration and enrichment of LPSQ to the surface of the film.(d)With the increase of amino concentration in LPSQ, the cross-linking densityof hybrids raised and the interfacial interactions were enhanced, thereby themovement of PI and LPSQ was more restricted. As a result, the surface siliconconcentration decreased, Young’s modulus increased and the elongation atbreak dropped. Due to the incomplete imidization, both Tgand tensile strengthdecreased with the increase of amino content.(e) XPS results of PI/LPPSQand PI/LPMPSQ hybrid films showed that the migration and enrichment ofLPSQ to the surface of the film mainly occurred at solvent evaporation stagebefore heat treatment. It is worth mentioning that the polymer chains of PIseem to get absorbed on the surface of LPMPSQ particles after thermal curing.Compared with PI/LPPSQ, all the LPMPSQ particles were in close contactwith the PI matrix, which implied the existence of the relatively stronginteractions between mercapto groups and PI.更多还原