【作者】 余雯雯；

【导师】 郑强； 杜淼；

【作者基本信息】 浙江大学 ， 高分子材料， 2013， 博士

【摘要】 由于具有可调控的软硬段,聚氨酯被广泛用于制备高性能阻尼材料。从分子动力学角度,深入研究聚氨酯的链结构、相形态与阻尼性能之间的关系,对于阻尼材料高性能化的实现,具有重要的理论价值和实际意义。本文在聚氨酯主链上引入悬挂链,对聚氨酯的结构与性能进行调控。考察了悬挂链长度、基团种类、硬段类型及含量、纳米粒子引入等因素对聚氨酯阻尼行为的影响,并通过动态力学分析(DMA)、宽频介电谱(BDRS)等手段,系统研究了体系在不同条件下的弛豫行为。论文得到了以下主要研究结果：1)通过扩链剂方法,成功合成了含不同悬挂链的TDI型聚氨酯,考察了悬挂链链长、极性及含量对微相分离、阻尼行为的影响。研究发现,随悬挂链链长增大,微相分离程度减小,氢键作用减弱,玻璃化转变温度(%)降低,Tg及Tg以上的内耗因子(tanδ)增大,阻尼温域(tanδ>0.5)变宽。借助BDRS,考察了悬挂链对分子松弛行为的影响。结果表明,引入悬挂链后,链段α松弛移向高频,材料脆性下降,与氢键相关的Ⅰ过程(高温低频区域)消失,Maxwell-Wagner-Sillars(MWS)界面极化过程加快。悬挂链链长一定时,增大悬挂链的极性(引入酯基),可使微相分离程度加剧,硬段间氢键作用增强,链段Tg升高,链段松弛、MWS界面极化过程变慢,脆性增加。2)基于MDI型聚氨酯比TDI型聚氨酯具有更规整的结构,合成了含悬挂链的MDI型聚氨酯。研究了其链长、极性对聚氨酯阻尼性能及介电弛豫的影响,并讨论了其与TDI型聚氨酯的分子松弛行为之间的差异。结果表明,与TDI型悬挂链聚氨酯相比较,MDI型具有较低的tanδ值。Ⅰ过程随长悬挂链的引入而消失,而当长悬挂链中引入酯基时,硬段间的氢键作用加强,Ⅰ过程重新出现,且其活化能随悬挂链的引入而降低。3)采用互穿网络共聚的方法,制备了聚氨酯／环氧互穿网络聚合物(PU/EPIPN),考察了悬挂链长度、含量及基团等因素对PU/EP IPN阻尼行为及力学性能的影响。结果表明,悬挂链的引入可显著提高PU/EP体系的最大损耗因子(tanδmax),但阻尼温域宽窄强烈依赖于微相分离程度。悬挂链含量同样显著影响PU/EP体系的阻尼性能,tanδ峰的峰宽和强度均随悬挂链含量增加而增大。与受悬挂链含量影响相比,PU/EP体系力学性能受悬挂链长度影响较小4)采用原位插层聚合法,制备了含悬挂链和不含悬挂链的PU/PMMA/LDH纳米复合材料,考察了填料含量和悬挂链对纳米复合材料的阻尼及分子弛豫行为的影响。结果表明,当PU/PMMA/LDH中不含悬挂链时,低含量剥离态LDH使PU/PMMA/LDH体系tanδmax增大,而插层态的LDH (LDH含量>1wt%)则使复合体系的Tg升高、tanδmax降低。α介电松弛强度与LDH分散状态有关,随LDH含量的变化先增大后减小。此外,当PU/PMMA/LDH中含悬挂链时,随着LDH含量增加,高温橡胶态平台的内耗值升高。LDH与悬挂链显著拓宽了阻尼温域,且具协同效应；同时,Tg升高,链段松弛变慢,α介电松弛强度增大且分布变宽。LDH片层间的平均距离变短,MWS极化过程随LDH含量增加而加更多还原

【Abstract】 It is well-known that polyurethane with tuned soft and hard segments can be used as damping material. In order to obtain polyurethane damping materials with high-performance, it is necessary to investigate the relationship between the chain structure-morphology-damping properties for polyurethanes. In addition, the research of.molecular relaxation behavior is helpful for us to give a reasonable interpretation at the molecular level.In this work, the stucture of polyurethanes was controlled by introducing dangling chain into backbone network. The effect of dangling chains with different graded lengths, functional groups, types and contents of hard segment and the introduction of nanofillers on molecular dynamics of polyurethanes was probed by a combination of dynamic mechanical analysis (DMA) and broadband dielectric relaxation spectroscopy (BDRS). The main research contents and results are given as follows:1) The TDI-based polyurethanes with different dangling chain were successfully synthesized by using dangling chain extender, and the effect of dangling chains on phase-separated microstructure, damping property and molecular dynamics for polyurethanes was investigated. The value of loss factors (tan δ) near and above Tg increase with increasing dangling chain length, which results in a broader damping temperature range (tan δ>0.5). Tg shifts to a lower temperature and segmental dynamics becomes faster with increasing dangling chain length due to the weakened hydrogen bonds interactions and the decreased degree of micro-phase separation. Moreover, long dangling chains also cause the index of dynamic fragility (m) of polyurethanes to decrease.I process associated with hydrogen bonding is absent and MWS processes become faster after longer dangling chains are introduced into polyurethanes. The increased polarity of dangling chains through introducing ester groups slows down the segmental dynamics and MWS processes, while it increases the value of m and the degree of microphase-separation. 2) The dangling chain polyurethanes based MDI with regular structure were successfully synthesized. The effect of dangling chains length and polarity on damping property and molecular dynamics for polyurethanes was investigated, and the dynamics was discussed by comparison polyurethanes based MDI and TDI. It is found that MDI based-polyurethanes has lower value of tan δthan that of TDI based-polyurethanes. The long dangling chain makes I process absent. However,I process re-emerges owing to the strengthened hydrogen bonding, and its activation energy decreases with introducing ester group to dangling chain.3) A series of novel polyurethane (PU)/epoxy resin (EP) graft interpenetrating polymer network (IPN) composites with dangling chains were prepared. The effects of the dangling chain lengths, content, and groups on the damping properties and mechanical properties were investigated. The introduction of dangling chains significantly increase the tanδ peak value of PU/EP IPNs. However, the damping temperature range depends on the degree of microphase separation. The width and intensity of the tan δ peaks of PU/EP IPNs increase with the increased dangling chain content. The mechanical properties (tensile strength and elongation at break) are significantly affected not only by the dangling chain length but by the dangling chain content.4) A series of layered double hydroxides (LDH) filled polyurethane/poly(methyl methacrylate)(PU/PMMA) with/without dangling chain were synthesized by using methyl methacrylate in-situ intercalative polymerization. The effect of the contents of LDH and dangling chain on the damping and molecular dynamics of PU/PMMA was investigated. In the case of PU/PMMA without dangling chain, the value of tanδ eak for PU/PMMA/LDH nanocomposites increase with the increase of LDH content. However, when LDH content is higher than1.0wt%, intercalated LDH layers reduce molecular mobility of polymer matrix and result in lower value of tan δ peak and higher Tg than those of pure PU/PMMA. The dielectric strength of a-relaxation depending on the content and dispersed state of LDH increase firstly and then decrease with increasing LDH content. In the case of PU/PMMA with dangling chain, a plateau with a high tan δ value above Tg significantly broaden the damping temperature range, which is ascribed to the synergy between the dangling chain and LDH sheets. It is found that the dynamic a process slows down and Tg shifts to high temperature with increasing LDH content. In addition, The MWS processes become more faster with increasing the LDH contents due to the smaller mean distance d between the exfoliated LDH layers.更多还原