混合气体在聚合物注射成型保压阶段中扩散的分子动力学模拟

构建了含有氧气、氮气分子和聚合物聚甲基丙烯酸甲酯（PMMA）高分子链的单元模型,并通过能量优化、退火等处理使其接近保压阶段状态,然后改变温度或压力进行分子动力学模拟,探讨微观尺度下混合气体（氧气和氮气）在聚合物PMMA中扩散的情况;并探讨了混合气体分子间相互作用的影响。模拟结果表明,随着温度或压力的增加,氧气和氮气在PMMA内的扩散系数增大;当温度或压力增大到一定程度时,扩散系数几乎不变,逐渐达到扩散平衡;模拟过程中发现气体分子在聚合物中的扩散过程中具有协同效应,混合气体的扩散系数大于纯气体的扩散系数。     

高分子聚合物中溶剂扩散系数的预测

溶剂分子在高分子聚合物中的扩散现象广泛存在于日常生活和工业生产中，对其研究具有普遍意义.Vrentas-Duda模型以自由体积理论为基础，所有参数不需扩散实验测量，由溶剂和高分子的分子性质独立确定，可用于预测高分子聚合物中低相对分子质量溶剂扩散系数.研究Vrentas-Duda模型对典型高分子/溶剂体系中溶剂扩散系数的预测准确性，通过将预测值与实验值比较，评价该模型在不同高分子体系中的适用情况.对处于橡胶态的各向同性高分子聚合物体系，Vrentas-Duda模型能够准确计算除存在氢键以外多数体系的溶剂扩散系数;相对于溶剂互扩散系数而言，溶剂自扩散系数的预测精度更高.     

超高压处理下BHT在不同分子量聚乙烯中扩散的分子动力学模拟

采用分子动力学模拟与实验结合的方法,对超高压处理条件下,抗氧化剂2,6-二叔丁基-4-甲基苯酚(BHT)在不同分子量聚乙烯(PE)中的扩散过程进行了模拟研究,通过分析超高压下PE的自由体积、PE分子链的活动性以及BHT的扩散轨迹,探讨了超高压下小分子物质在不同分子量聚乙烯中扩散的微观机理。结果表明,超高压下PE中BHT的扩散系数随压力、PE分子量的增加而减小,与迁移实验结果一致; PE的自由体积、PE分子链的运动能力随着压力、PE分子量的增加而减小,继而影响BHT的扩散,压力较低时,PE的聚合度越小,其自由体积、BHT的扩散系数和PE链的运动能力越容易受到高压的影响;超高压下BHT的运动轨迹表明,BHT在PE的基体中做缓慢蠕动式扩散,压力越高,PE分子量越大,其活动范围越小。     

聚丙烯／八苯基倍半硅氧烷的分子模拟和性质

利用分子动力学和COMPASS力场相结合的方法,求得八苯基倍半硅氧烷(OPS)粒子在聚丙烯(PP)体系中的扩散系数.通过对扩散系数的分析,发现OPS粒子和PP体系有很好的相互作用,加入少量(质量分数为1%)的OPS可以减小PP球晶的粒径.OPS在PP中扩散主要以孔穴运动为主,PP/OPS体系的压力势能波动较大,推断体系在压力变化环境下的性能较差.     

CO2和O2在聚乳酸/聚偏二氟乙烯共混物中扩散行为的分子动力学模拟研究

采用分子动力学模拟方法研究了CO₂和O₂分子在聚乳酸/聚偏二氟乙烯（PLA/PVDF）共混物中的扩散行为;通过菲克第一定律和Einstein关系式计算了共混物体系模型的自由体积分数以及CO₂和O₂分子在体系中的扩散系数,研究探讨了自由体积分数与探头半径的关系及自由体积分数与扩散系数的关系。结果表明,当PLA/PVDF共混物中PLA和PVDF的质量比为9∶1时,CO₂和O₂气体分子的扩散系数均为最小,共混物阻隔性能最好;共混体系中小分子的动力学半径越小,扩散系数越大;自由体积分数随硬球探头模型中探头半径的增大而减小;不同共混物体系中,自由体积分数的变化趋势与扩散系数一致,与Fox和Flory的自由体积理论相符。     

残留溶剂在PMMA-CA聚合物膜中迁移及影响的多尺度分析

杂质对功能高分子聚合物理化性质的影响具有重要的学术价值与应用意义。今分别通过分子动力学(Molecular Dynamics,MD)及密度泛函(Density Functional Theory,DFT)等方法探索了聚合物玻璃态和橡胶态下溶剂扩散系数的不同以及残留溶剂对聚合物分子解离能的影响。根据自由体积理论,对聚甲基丙烯酸甲酯-丙烯酰胺杯芳烃(PMMA-CA)的玻璃化温度进行了分子动力学(MD)模拟,得到的自由体积与温度的关系曲线显示其玻璃化温度为395K。考察了玻璃态和橡胶态下溶剂扩散系数的不同,MD模拟得到的均方位移(Mean Square Displacement,MSD)曲线显示,聚合物在玻璃态下溶剂的自扩散系数远低于橡胶态下。通过密度泛函方法计算残留溶剂分子对杯芳烃解离能的影响,结果表明膜制备过程中残留的溶剂分子有利于杯芳烃的解离,但其影响比MMA分子共聚要弱得多。     

环氧树脂密度与二面角扭转能的仿真计算

基于COMPASS分子力场,利用分子动力学模拟方法和Materials Studio软件建立了低固化度交联耦合的双酚A型环氧树脂交联结构模型,并利用环氧树脂交联体系模型模拟计算了不同温度下交联环氧树脂的密度和二面角扭转能,以此预测了环氧树脂的玻璃化转变温度(Tg)。结果表明,计算得到的Tg与实验值具有良好的一致性,分子动力学模拟方法可以应用于复杂聚合物体系结构与性质的研究中。     

丁羟推进剂黏结体系中增塑剂迁移的分子模拟

为克服固体推进剂中增塑剂与黏结体系之间加速老化实验手段的不足,构建了增塑剂和黏结体系的分子模型.利用分子模拟方法在COMPASS力场下分析了增塑剂癸二酸二辛酯(DOS)在由端羟基聚丁二烯(HTPB)和异佛尔酮二异氰酸酯(IPDI)组成的黏接体系中的相容性和扩散性.用无定形动力学方法计算组分的溶度参数,判断DOS与HTPB、IPDI的相容性.结果表明,DOS与HTPB、IPDI相容性较好.这与由共混方法计算的结合能得到相容性好的结论一致;通过分子动力学方法模拟计算得到增塑剂DOS在黏结体系(HTPB-IPDI)中的扩散系数为1.2×10-7cm2/s.     

有机溶剂纳滤膜的润湿性对渗透和分离性能的影响

有机溶剂纳滤是一种绿色、高效、节能的新型膜分离技术，在回收和处理有机溶剂中具有广泛的应用前景。本文采用浸渍法分别将聚合物聚二甲基硅氧烷（PDMS）、嵌段聚醚酰胺（PEBAX2533）和聚乙烯醇（PVA）与聚砜（PS）超滤基膜复合，制备了3种不同润湿性的聚合物耐溶剂纳滤膜，研究了PDMS/PS、PEBAX/PS和PVA/PS复合膜对甲醇、乙醇、异丙醇、正己烷、正庚烷的渗透性能，考察了3种聚合物膜对伊文思蓝/甲醇溶液的有机溶剂纳滤性能。结果表明，有机溶剂在不同润湿性复合膜的渗透和传递性能与溶剂本身的溶度参数、分子量、黏度和极性等有很密切的相关性，溶剂的分子量、黏度、分子动力学直径越小，在同一极性复合膜中渗透通量越大；对伊文思蓝/甲醇溶液的有机溶剂纳滤分离表明，PDMS/PS和PEBAX/PS复合膜的截留率均可达90%以上，通量分别为 58.0L/(m²·h·MPa)和72.2L/(m²·h·MPa)；PVA/PS复合膜的截留率为85.1%左右，通量为57.5L/(m²·h·MPa)。     

Flory溶液理论中待定参数的决定

用反相色谱法(IGLC)测定聚合物和溶剂的相互作用参数X,推算出Flory聚合物溶液理论中的交换能参数X_(12),结合本文估算的聚合物和溶剂的接触表面之比S_1/S_2,计算了聚二甲基硅氧烷(PDMS)、天然橡胶(NR)、聚苯乙烯(PS)和聚异丁烯(PIB)等溶液体系中,X和聚合物链节分率φ_2的关系,结果能与实验值很好符合,并且还计算了溶液的体积变化V~(?)/V~(?)和无限稀混合焓△H_(?)~∞.     

Swelling measurement of polymers in high pressure carbon dioxide using a spectroscopic reflectometer

We developed an in situ thickness monitor using a spectroscopic reflectometer to measure the swelling behaviors of polymer thin films in carbon dioxide up to 30 MPa. Because the change in thickness was measured under high-pressure CO₂, the measurement was performed through a sapphire window with a relatively high refractive index. We found that the window effect on the reflectivity can be successfully eliminated. To confirm the accuracy of the analysis, we measured the swelling behaviors of four polymers (poly(methyl methacrylate) (PMMA), polystyrene (PS), poly(n-butyl methacrylate) (PBMA), and poly(dimethylsiloxane) (PDMS)), and compared the swelling measurements with reported data. The swelling ratios of the polymers were in reasonable agreement with literature data. Notably, anomalous swelling was observed for PBMA and PDMS, although anomalous swelling has been observed in films much thinner than those of our samples, probably due to the low glass transition temperatures and high swelling ratios of PBMA and PDMS.     

注射保压过程中O2/N2分子在PMMA熔体内部的扩散行为

研究了注射成型保压过程中,不同工艺条件下O2/N2混合气体在聚甲基丙烯酸甲酯（PMMA）聚合物内部的扩散行为。针对注射成型工艺特点,将注射保压阶段的低分子扩散简化为不同温度条件下的准静态扩散行为;建立了包含O2/N2气体和10条聚合度为10的全同立构PMMA链团的扩散映射模型。经能量最小化及退火算法实现了扩散模型的能量初始化;基于COMPASS力场,实现了O2/N2混合气体在PMMA熔体内部扩散的分子动力学模拟实验。结果表明,O2和N2的扩散系数均随温度的升高而增大,且同一温度下,O2比N2更容易扩散;不同温度下O2和N2的均方位移函数（MSD）对数lg(MSD)与时间对数lg(t)关系曲线的斜率（n）都接近于1,符合Einstein扩散机制。     

异戊二烯在聚苯乙烯高分子膜中的扩散系数测定

为了探讨在反应挤出过程中异戊二烯在聚苯乙烯中的扩散传递机理,采用石英弹簧法测定了298.15K、308.15K和318.15K下异戊二烯在聚苯乙烯膜中的吸收动力学曲线。探讨了温度、压力、分子量对扩散吸收的影响,并对实验结果进行了关联。结果表明异戊二烯在聚苯乙烯膜中的扩散吸收呈S型吸收,由吸收曲线获得了平均扩散系数和平衡溶解度。     

Morphology of composite polymer emulsion particles consisting of two kinds of polymers between which ionic bonding intermolecular interaction operates

The morphology of particles (I) produced by seeded emulsion copolymerization of styrene (S) and sodium p-styrene sulfonate (NaSS) with butyl acrylate (BA)-methacryloyloxyethyl-trimethylammonium chloride (QDM) copolymer particles as seed was examined in comparison with poly(butyl acrylate) (PBA)-polystyrene (PS) composite polymer emulsion particles (II). In an electron microscopic observation, it was observed that II particles had an anomalous shape and the electron densities at different points in the particle were heterogeneous, whereas I particles had an almost spherical shape and the electron densities were homogeneous. The maximum tensile strength and toughnes were much larger in II than I. The dynamic mechanical studies indicate that II film had a macroheterogeneous structure consisting of PS-rich and PBA-rich phases, whereas I film had a microheterogeneous structure. These ressults suggest that there is an effect of intermolecular interaction between polymers of different kinds on the formation of heterogeneous structure in particles consisting of two kinds of polymers.     

Thermal degradation and combustion of polymeric blends

The thermal stability of polymer blends was investigated by means of gas chromatography–mass spectroscopy (GC/MS) and thermal analysis. Evaluated changes in thermal stability can be attributed to blending. On the other hand, we were interested in whether blending may provide a method to control thermal stability and combustibility of polymeric materials. A new scheme of thermal degradation for polystyrene‐polydimethylsiloxane (PDMS) blend was suggested. In the case of polystyrene (PS) as a part of the blend, the products of degradation of PS diffuse through the phase boundary, which cause interaction with PDMS polymers. Apparently, PDMS acts as an inert component, slowing down the termination reaction by dilution of macroradicals formed in random scission degradation process of the PS component. On the other hand, it stabilizes the PS by means of interpolymer recombination, which leads to cross products of thermal degradation. Two of the degradation products: 2‐phenyl‐4(1′,3′,3′,5′,5′‐pentamethylcyclotrisiloxane)‐butane and 2‐phenyl‐4(1′,3′,3′,5′,5′,7′,7′‐heptamethylcyclotrisiloxane)‐butane were assigned to the products of cross‐interpolymer recombination which can accelerate the process of PDMS depolymerization by means of radical initiation of PS* fragments. The connection between a polymer thermal oxidative degradation and its combustion under diffusion flames condition was shown by using composition of polypropylene‐polypropylene‐co‐polyethylene (PP/PP‐co‐PE). In general, the solid‐phase polymer reaction can play a very important role in the reduction of polymer combustibility. It was shown that the composition of PP/PP‐co‐PE (62 : 38) has the highest induction period of autooxidation, which correlates with its combustibility. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 3300–3311, 2002     

聚苯乙烯增强的室温硫化硅橡胶的制备及表征

以过氧化苯甲酰(BPO)为引发剂,使苯乙烯(St)在α,ω-羟基聚二甲基硅氧烷(PDMS)的甲苯溶液中进行自由基聚合制备PDMS/聚苯乙烯(PS)共混物,在甲基三乙氧基硅烷与PDMS的质量比为1∶1时,制得PS增强的室温硫化硅橡胶。研究了原料配比、BPO用量和甲苯用量对硅橡胶力学性能的影响,并对其微观结构进行了表征。结果表明,当PDMS/St(质量比)为60/40、BPO为PDMS质量的2.5%、甲苯/PDMS(质量比)为2时,所得硅橡胶的拉伸强度可达到3.8 MPa,PS的增强效果明显;该室温硫化硅橡胶具有微相分离结构,PS作为分散相分布于PDMS连续相中,且具有2个玻璃化转变温度。     

Preparation,morphology, and mechanical properties of elastomers based on polydimethylsiloxane/ polystyrene blends

Polydimethylsiloxane/polystyrene (PDMS/PS) blends were prepared by radical copolymerization of styrene (St) and divinylbenzene (DVB) in the presence of α,ω‐dihydroxy‐polydimethylsiloxane (PDMS), using benzoyl peroxide as initiator. The PDMS/PS blends obtained by this method are a series of stable, white gums, when the feed ratio of PDMS to St is 60/40 and DVB to St is not more than 2.0 wt %. Elastomers based on PDMS/PS blends were formed by crosslinking PDMS with methyl‐triethoxysilicane (MTES). The MTES dosage was much larger than the amount necessary for end‐linking hydroxy‐terminated chains of PDMS, with the excess being hydrolyzed to crosslinked networks, which were similar to SiO₂ and acted as filler. Mechanical property measurements show that the elastomers thus formed exhibit superior mechanical properties with respect to pure PDMS elastomer and the elastomers based on PDMS/PS system we prepared before. Moreover, investigations were carried out on the elastomers by extraction measurement and scanning electron microscopy (SEM). The extraction data show that the sol‐fraction decreases with increasing the feed ratio of DVB to St. SEM observation demonstrates that the elastomer has a microphase‐separated structure consisting of dispersed PS domains within a continuous PDMS matrix, and the extracted material exhibits a porous structure. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Morphology of polystyrene/poly(dimethyl siloxane) blends compatibilized with star polymers containing a γ-cyclodextrin core and polystyrene arms

A star polymer with a γ-CD core and PS arms is used to compatibilize blends of the immiscible polymers PS and PDMS. The mechanism of compatibilization is threading of the CD core by PDMS and subsequent solubilization in the PS matrix facilitated by the star arms. Spun-cast films of this blend are examined with optical microscopy, scanning electron microscopy and atomic force microscopy. Blends without CD-star exhibit large-scale phase separation, whereas those containing CD-star exhibit very homogeneous morphologies in the optical microscope and nanometer-sized phase domains in the AFM. The effect of PDMS molecular weight on the blend morphology is insignificant. The morphology of the compatibilized films does not change significantly after annealing at 125 °C for 3 days, indicating that the CD-star polymer effectively stabilizes these blends at temperatures where both polymers are mobile and could otherwise undergo large-scale phase separation. The degree of compatibilization in these blends is correlated with the molar ratio of PDMS repeat units to CD-star molecules.     

固载离子液体聚合物的制备及其二氧化碳吸附性能

分别采用溶液聚合法和表面引发反向原子转移自由基聚合法(ATRP),在硅胶表面接枝离子液体聚合物,并对其进行了FTIR、TG和SEM表征。研究了固载离子液体聚合物样品的CO2吸附性能和CO2/N2的选择性能,探讨了CO2在固载离子液体聚合物上的吸附热力学和动力学行为。结果表明:由ATRP法制备的固载离子液体聚合物,其接枝量远大于溶液聚合法;而溶液聚合法制备的样品具有较发达的孔结构,在273 K、0.1 MPa时,样品的CO2吸附量达4.54%(1.03 mmol/g);固载离子液体聚合物较空白硅胶具有更优的CO2/N2选择性,且循环使用性良好;CO2在固载离子液体聚合物上的吸附为物理吸附;与离子液体聚合物相比,CO2在固载离子液体聚合物中的扩散效率更高。     

6FDA型聚酰亚胺中气体溶解行为的分子模拟

用分子模拟方法对6FDA-durene、6FDA-pPDA及其共聚物6FDA-durene/pPDA的链间距及自由体积进行了模拟计算,结果与文献实验值一致;采用巨正则Monte Carlo(GCMC)方法模拟了O₂、N₂、CH₄和CO₂在聚酰亚胺中的溶解,计算结果表明：COMPASS力场能较准确地描述O₂、N₂和CH₄在聚酰亚胺中的吸附溶解,O₂、N₂、CH₄的溶解系数模拟结果与实验数据吻合较好。CO₂的溶解系数计算值与实验值偏差较大(约50％),主要原因可能在于模拟过程中未考虑体积溶胀效应以及COMPASS力场不能精确描述CO₂与—CF₃基团的相互作用。同一聚合物中,计算所得气体溶解系数的大小顺序为CO₂>CH₄>O₂>N₂,与气体凝聚性趋势一致,同种气体在6FDA型聚酰亚胺中的溶解系数与其自由体积分数变化趋势一致。3种聚合物对CO₂/CH₄的溶解选择性高于O₂/N₂,共聚物与均聚物相比,气体溶解选择性没有明显提高。