聚氨酯制备的多尺度模拟方案

针对聚氨酯材料特性设计了多尺度计算机模拟方案,并研究了不同原料及相同原料但不同官能度对所制备的聚氨酯材料力学性能和玻璃化转变温度的影响.基于原子级别的结构,建立了耦合聚合反应的粗粒化耗散粒子动力学模型来描述组分扩散及交联网络结构的形成过程.并反映射这个粗粒化结构到全原子级别来分析材料的力学性能和热力学性能.这个多尺度研究方案也可推广到研究多个竞争性因素同时主导的复杂体系中.     

骨架状聚氨酯海绵模板导向制备多级孔碳材料

多级孔结构碳材料具有结构多样、比表面积高、孔体积大和化学稳定性好等性质,不同尺度的孔道能协同发挥各自的传质优势,在吸附和分离、化学化工、靶向给药和能源储存等方面有独特表现并得到了广泛应用.近年来,国内外将聚氨酯海绵与其他尺度的模板剂相结合制备了许多不同结构的多级孔状碳质材料并应用到不同的领域.本文从多级孔碳材料的制备、结构和应用等角度综述了相关研究工作,并指出合成石墨化、各级孔道合理分配、孔壁薄和机械强度好的多级孔结构的碳材料仍面临诸多问题.     

高分子多尺度结构与动力学的固体NMR研究

高分子材料中的微观结构和动力学特征决定了材料的最终物理化学性能,并具有典型的时间和空间上的多尺度特性。在不同时空尺度上表征凝聚态下高分子中多尺度的结构、动力学及其动态演变等问题,进而阐明其结构-性能间的关系一直是高分子科学研究中的挑战性课题。目前,固体NMR技术已成为从原子至100nm的空间和10-9～10s的时间尺度上研究固态高聚物体系中多层次结构和复杂运动并阐明其结构与性能关系的有力工具。本文将综述我们近年来系统构建的多尺度固体NMR实验技术,及其在阐明高分子链结构、链间相容性和相互作用、界面相结构及相区尺寸、以及从高频到超慢链运动等问题中的应用。     

基于粗粒化模型对有机溶剂的分子动力学模拟

在基于Boltzmann分布对四种基本构象进行Monte Carlo取样后, 通过与全原子模型的范德华势比较得到了Gay-Berne (GB)参数. 又在对用量化计算得到的分子体系的电势进行电荷、偶极矩和四极矩的拟合后, 得到了电多极展开势(EMP)参数. 利用得到的粗粒化参数, 基于粗粒化模型, 对CHCl₃及四氢呋喃(THF)两种有机溶剂进行了分子动力学模拟(MDS), 并将结果同全原子模拟进行了比较. 计算结果表明用粗粒化模型从整体上能重复全原子模型的模拟结果, 但在某些细节的计算与全原子模型有偏差, 其原因可能是目前工作仅考虑了单位点情况, 为此今后在对具有复杂结构的分子进行粗粒化模拟时还应考虑合理放置及增加相互作用位点.     

超支化聚合反应的多尺度模拟

超支化聚合物具有与树枝状大分子相似的物理和化学性质,其具有合成简单、分子量分布宽等突出特点,超支化聚合物分子的结构形成取决于聚合反应过程,本文介绍了超支化聚合反应模拟研究的最新进展.首先介绍了八位置键涨落粗粒化格子模型在超支化聚合反应模拟中的应用,该方法考虑了聚合物分子空间位阻效应、分子内成环和反应点活性等影响因素,从而可以模拟不同类型的超支化聚合反应;为了定量描述单体和聚合物分子结构,研究者进一步发展了杂化多尺度超支化聚合反应模拟方法,该方法通过玻尔兹曼反演迭代方法获取单体和聚合物特异性粗粒化力场,然后通过粗粒化分子动力学方法结合反应性Monte Carlo方法对特异性超支化聚合反应进行定量模拟.多尺度聚合反应模拟不仅可以精确计算超支化聚合物分子量、多分散性指数和支化度等一般性聚合物参数,还可以获取分子成环率、超支化大分子构象等重要分子结构信息,在超支化聚合反应基础研究与预测方面具有重要应用价值.     

聚氨酯弹性体力学性能影响因素探讨

研究了合成方法、原料的种类与配比、硫化工艺条件等因素对聚氨酯弹性体力学性能的影响。结果表明,聚氨酯弹性体的结构与组成以及由此引起的微相分离程度的变化是影响弹性体性能的重要因素。对于同样的聚合多元醇、二异氰酸酯及扩链剂合成的弹性体,采用不同的硫化及熟化条件其力学性能不同,并找到达到最佳力学性能所需的工艺条件。     

超支化聚脲/聚氨酯-脲的合成及应用研究进展

超支化聚合物具有独特的分子结构,优越的热、力学性能,已成为高分子科学与新材料领域中的研究热点。超支化聚脲/聚氨酯-脲是在聚氨酯的研究基础上合成出的聚合物,二者在结构与性能上存在一些差异与共性。本文总结了超支化聚脲、聚氨酯-脲的常用合成方法,分析了各方法的优缺点,及其合成的材料的性能特点;论述了超支化聚脲和聚氨酯-脲在微胶囊、薄膜及涂层等方面的应用研究进展,并就目前超支化聚脲和聚氨酯-脲研究领域存在的不足及发展前景提出了自己的见解。     

POSS/聚氨酯复合材料结构与性能的研究进展

多面体低聚倍半硅氧烷(POSS)是新兴的有机/无机杂化材料,其特殊的笼状结构可以从纳米尺度上影响聚氨酯体系的结晶行为、微相分离程度、交联密度等结构特征。少量添加即可大幅提高聚氨酯的耐水性、热稳定性、力学性能,以及阻燃性能、黏结性能、韧性等。本文从POSS/聚氨酯复合材料的结构出发,介绍了化学合成POSS基聚氨酯及物理共混POSS/聚氨酯复合材料,总结分析了悬垂型、星型、串珠型以及物理混合POSS基聚氨酯复合材料的结构特点,以及POSS结构差异对其复合材料性能的影响与影响机理。     

一种X-射线不透性聚氨酯显影材料的制备及性能研究

利用对碘苯胺对含有过量异氰酸根的聚氨酯分子进行封端,合成了一种新型的X-射线不透性聚氨酯显影材料.利用X-射线映射对不同封端量聚氨酯的显影效果进行评定;利用DSC和TGA对其热性能进行表征,并评估封端反应对聚氨酯热稳定性的影响;利用噻唑蓝(MTT)比色法测试了材料的细胞毒性;并对具有不同碘含量聚氨酯材料的显影效果、相对分子量及其分布、力学性能进行了对比研究.研究结果表明,当碘含量达到3.5wt%左右时聚氨酯材料即可达到同等厚度铝板相同的显影效果,而且在此条件下,聚氨酯材料依然保持较好的力学性能和热稳定性.MTT法测试表明对碘苯胺封端的聚氨酯材料不具有细胞毒性.     

原子间相互作用对无序大分子结构和动力学影响的中子散射研究

不同单体在原子尺度的相互作用使得不同大分子体系在微观、介观的多尺度复杂结构及动力学行为有明显差异,从而进一步影响了体系的宏观性质.联用中子散射和计算机模拟,利用相同分子量和分子量分布的氘代大分子与氢化大分子具有相同分子结构、不同中子衬度,以及中子散射和计算机模拟宽广的时间、空间观察尺度,我们可以得到无序大分子体系最可几全原子结构,进而分析其从原子到纳米的多尺度空间结构,与从皮秒到微秒的多模式动力学行为的成因.近年来,我们使用该方法,从小分子到大分子的稀溶液、溶胀体系,从大分子熔体到玻璃态,成功分析了原子间相互作用对不同空间尺度结构和跨时间运动模式动力学行为的影响.本文介绍了这些典型的例子,希望将该方法推广到更广阔的研究领域,把大分子原子结构的多样性与多尺度的复杂结构和动力学有机地联系起来.     

Mechanical,thermal and morphological behavior of bismaleimide modified polyurethane‐epoxy IPN matrices

An intercrosslinked network of bismaleimide modified polyurethane‐epoxy systems were prepared from the bismaleimide having ester linkages, polyurethane modified epoxy and cured in the presence of 4,4′‐diaminodiphenylmethane. Infrared spectral analysis was used to confirm the grafting of polyurethane into the epoxy skeleton. The prepared matrices were characterized by mechanical, thermal and morphological studies. The results obtained from the mechanical and thermal studies reveal that the incorporation of polyurethane into the epoxy skeleton increases the mechanical strength and decreases the glass transition temperature, thermal stability and heat distortion temperature. Whereas, the incorporation of bismaleimide having ester linkages into polyurethane modified epoxy systems increases the thermal stability, tensile and flexural properties and decreases the impact strength, glass transition temperature and heat distortion temperature. Surface morphology of polyurethane modified epoxy and bismaleimide modified polyurethane‐epoxy systems were studied using scanning electron microscopy. Copyright © 2003 John Wiley & Sons, Ltd.     

Polyurethane anionomers. I. Structure properties of polyurethane anionomers

The influence of mono and divalent nontransition and transition metals on the glass transition and mechanical properties of polyurethane anionomers have been investigated. NCO-terminated prepolymer prepared from 4,4′-methylene-bis(phenyl isocyanate) (MDI) and poly(caprolactone) glycol (PCL) was chain extended with dimethylolpropionic acid (DMPA), and the anionomers obtained by neutralization of the prepolymer. The glass transition temperatures of polyurethane anionomers have been studied as a function of the counterion. From simple electrostatic considerations, it is shown that a linear relationship exists between the glass transition temperature and ionic potential (?) for these particular materials. The relation is; T_g = A? + B. The mechanical properties are greatly affected by the type of the counterion, and in some cases, such as monovalent and nontransition metals, the mechanical properties of the anionomers improved by increasing the ionic potential. On the other hand, transition metals containing anionomers exhibited good mechanical properties but no relationship was observed between the mechanical properties and the ionic potential. The extent of water absorption of PU anionomers follows the same relative trends as the tensile strengths of the transition metals with filled and partially filled d-orbitals.     

Polyurethanes for potential use in transparent armour investigated using DSC and DMA

A material combination that may be applied as transparent armour is glass-clad polyurethane. These are comprised of a relatively thin glass strike face and a relatively thick (transparent) polyurethane backing layer. Three transparent polyurethane samples were investigated using differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). The DSC results identified the glass transitions and in some cases the melting and crystallisation processes. The DMA experiments were only performed on heating around the glass transition region to further investigate this transition. The experiments were performed at three different frequencies (1, 10 and 100 Hz); the shift of the glass transition with the frequency was clearly observed. The method of time–temperature superposition was used to extrapolate the results to higher frequencies as the magnitude of the strain-rate occurring within ballistic applications is in the order of 1000 s⁻¹ or higher. Polyurethane with a rubbery behaviour at normal (low) strain rates can be stiff and brittle when used as an armour component (temperature below its dynamic T _g value).     

交联对聚己二酸乙二醇酯聚氨酯/甲基丙烯酸甲酯交联聚合物的力学阻尼、相容性及形态的影响

用紫外光聚合方法制备出一系列端乙烯基聚己二酸乙二醇酯聚氨酯(PEAPU)和甲基丙烯酸甲酯(MMA)AB交联聚合物(ABCP)。用粘弹谱仪、透射电子显微镜(TEM)和平衡溶胀法研究了AB交联聚合物的动态力学性能、玻璃化转变温度、形态和交联密度、观察到相应于聚氨酯和PMMA相两个玻璃化转变温度,TEM照片中的微相分离是更明显的,ABCP中的两个T_g内移表明,两种成分的化学交联增加了相互的可混性、与ABCP具有相同组成的IPN有比ABCP大得多的相区。氢键能够影响ABCP的相容性、形态和动态力学性能。     

Fabrication and characterization of functional graded polyurethane foam (FGPUF)

In this study, functionally graded polyurethane foams (FGPUFs) were produced using a layer‐by‐layer casting technique. Discontinuous FGPUFs were fabricated by this method. The scanning electron microscopy was used to study the morphology of all specimens. The mechanical properties of the polyurethane foams (PUFs) were evaluated by compression, indentation force deflection, drop weight tests, and dynamic mechanical thermal analysis. Scanning electron microscopy micrographs taken from different zones of functionally graded material showed the variation of the morphology of cells as well as the suitable interfaces between the layers of PUF. Investigation of mechanical properties suggested that FGPUF specimens have an optimum behavior between other specimens in compression and indentation force deflection tests. The results of drop weight test showed that FGPUF samples behaved like an energy absorber (14.31 KN) in comparison to other PUFs. The results of dynamic mechanical thermal analysis data showed an improvement in glass transition temperature (T_g) to −47.2°C and stability of modulus of FGPUFs as temperature increases.     

Carbon nanofibers reinforced soy polyol-based polyurethane nanocomposites

Vapor-grown carbon nanofiber (CNF)-modified soy polyol-based polyurethane (PU) nanocomposites with different hydroxyl value of polyols (OH) were synthesized. The glass transition, thermal stability, mechanical properties, and morphology of the PU nanocomposites were characterized through differential scanning calorimetry, thermogravimetry, universal test machine, and scanning electron microscopy. The addition of CNFs increased the glass transition temperature as well as significantly improved tensile strength and Young’s modulus of PU nanocomposites. Meanwhile, thermal and mechanical properties of PU composites were influenced by the different hydroxyl value of polyols due to those different structures. In particular, in the case of 2 mass% CNF addition in PU derived from soy polyol with the OH number of 164 mg KOH g^?1, 20.8 °C improvement in the glass transition temperature, 115 % increment in tensile strength, and nearly eightfold increase in Young’s modulus were obtained.     

交联对聚己二酸乙二醇酯聚氨酯/甲基丙烯酸甲酯交联聚合物的力学阻尼、相容性及形态的影响

 用紫外光聚合方法制备出一系列端乙烯基聚己二酸乙二醇酯聚氨酯(PEAPU)和甲基丙烯酸甲酯(MMA)AB交联聚合物(ABCP)。用粘弹谱仪、透射电子显微镜(TEM)和平衡溶胀法研究了AB交联聚合物的动态力学性能、玻璃化转变温度、形态和交联密度、观察到相应于聚氨酯和PMMA相两个玻璃化转变温度,TEM照片中的微相分离是更明显的,ABCP中的两个T_g内移表明,两种成分的化学交联增加了相互的可混性、与ABCP具有相同组成的IPN有比ABCP大得多的相区。氢键能够影响ABCP的相容性、形态和动态力学性能。     

Atomistic investigation of segmental mobility in atactic poly(propylene)

An atomistic model previously developed for atactic poly(propylene) has been analyzed through molecular dynamics simulation to study the variation of static and dynamical properties across a temperature range centered around the experimental glass transition temperature. Although few effects are seen in structural measures such as chain conformation, shape, and packing, characteristic features associated with the onset of segmental motions are revealed in the simulation results on local dynamics. The mechanism by which the vinyl polymer chain undergoes thermally activated motion is found to involve a series of spatial displacement events (SDE) occurring topologically, spatially, and temporally in a discrete fashion. An attempt was made to correlate the motions of the active chain segments with structural and mechanical properties such as local volume and rotational stiffness. The results indicate that the ability of the segmental mobility to diffuse in space and time, in a dynamically percolative manner, is a significant feature of atomic motions in glassy polymers.     

Thermomechanical enhancement of DPP-4T through purposeful π-conjugation disruption

The design of polymer-based organic semiconductors that offer mechanical deformability while maintaining efficient semiconducting characteristics remains a significant challenge. Recent synthetic efforts have incorporated small alkyl segments directly into otherwise π-conjugated polymer backbones to enhance processability, mechanical deformability, and other properties. The resulting polymers can be used as stand-alone materials or as matrix polymers in complementary semiconducting polymer blends offering reasonable charge-carrier transport properties, thermal healing, and deformability. Here, a family of diketopyrrolopyrrole-tetrathiophene variants is explored via large-scale atomistic molecular dynamics simulations to examine the effect of alkyl segments incorporated into the polymer backbone on the polymer structure, dynamics, and thermal properties. Longer alkyl segments lead to polymer chains that are more flexible, compact, and mobile, with lower glass transition temperatures for the condensed phase.