聚异丁烯基热塑弹性体设计合成与性能

通过双端羟基聚异丁烯(HO-PIB-OH)与4,4'-二环己基甲烷二异氰酸酯(HMDI)及1,4-丁二醇(BDO)反应,设计合成一系列具有不同聚氨基甲酸丁二酯硬段长度的聚异丁烯基热塑弹性体(PIB-TPE),研究HMDI/PIB摩尔比值对PIB-TPE的聚集态结构、弹性回复、自修复性能、表面亲/疏水性、动态力学性能和拉伸性能的影响.结果表明:在PIB-TPE中,软段是完全饱和结构的PIB柔性链段,聚氨基甲酸丁二酯硬段通过氢键(无序氢键、有序氢键)形成结晶物理交联微区((3.6±0.5)nm),软段与硬段呈现明显的微相分离现象,常温下形成了三维超分子网络结构,高温下发生结晶熔融与氢键解离,超分子网络结构解散,形成黏流态,降低温度又可形成三维超分子网络结构;随着材料储存时间延长,无序氢键逐渐向有序氢键转变,有利于提高材料的拉伸强度和断裂伸长率.结晶熔融与氢键解离温度依赖于PIB-TPE中硬段长度,当HMDI/PIB摩尔比值小于19,硬段结晶熔融峰温度可达119℃以上,提高了PIB-TPE服役温度.PIB-TPE材料具有良好的弹性回复和自修复性能,且其膜表面的亲/疏水性可以通过HMDI/PIB摩尔比值或正己烷蒸汽常温下诱导表面自组装来调节,当HMDI/PIB摩尔比值从6增加至21,PIB-TPE膜表面的水接触角(WCA)由98.7°降低至77.8°,即由疏水性转变为亲水性.此外,PIB-TPE热塑弹性体中的完全饱和柔性PIB软段赋予其优良的减振阻尼性能,其损耗因子(tanδ)大于0.3的温域较宽(?55~25℃),且tanδ最大值(tanδ_max)达到1.05.上述多嵌段聚异丁烯基热塑弹性体在生物医用、减振阻尼、自修复等功能材料领域具有潜在的应用前景.     

含氮试剂对P-DCC／AICl3引发异丁烯正离子聚合的影响。

以对-二枯基氯（DCC），Alcl，体系引发异丁烯在二氯甲烷（CH2C12）正己烷（Hex）（40／60，V／V）混合溶剂中进行正离子聚合，探讨了DCC用量、含氮试剂2，6-二叔丁基吡啶（DtBP）和三苯胺（TPA）对异丁烯正离子聚合转化率、产物分子量及其分布的影响．结果表明，DCC和体系中微量水均可与A1C1，产生竞争络合，形成两种活性中心并引起相继的竞争引发，聚合产物的GPC谱图呈双峰分布，分子量分布宽；增加DCC用量有利于DCC与A1C1，的络合，致使链增长反应主要通过DCC与A1C1，络合形成的活性中心引发，但聚合产物分子量相对较低，分子量分布较宽；使用DtBP，可有效地抑制微量水引发及活性链向单体的转移反应，使分子量分布明显变窄，基本实现DCC的控制引发；采用DtBP与TPA共同调节聚合反应，可使聚合产物分子量分布变窄的同时，进一步提高分子量，从而得到相对较高分子量（Mw=103200）和单峰分子量分布（Mw／Mn=2．09）的聚异丁烯产物．     

Functionalization of living polyisobutylene: Preference for reduction over electrophilic addition

Polyisobutylene was synthesized using 2-chloro-2,4,4-trimethylpentane (TMPCl) as an initiator and TiCl₄ as a coinitiator. After taking a base sample, the living cation was reacted with 5 equivalents of (4-vinylphenyl)dimethylsilane (VPDMSi). It was observed that the cation preferred reduction by hydride elimination from VPDMSi compared to electrophilic addition of even a single vinyl group. It was postulated that the reduction of the cation in presence of strong Lewis acid such as TiCl₄ occurs readily before addition of cation to vinyl group. Thus saturated polyisobutylene was obtained with a terminal hydrogen group instead of chlorine group which is produced by conventional cationic polymerization.     

Molecular Modeling of Polyisobutylene. Application of the Modified Rotational Isomeric States Model for Polymers Comprising Four Rotational Isomeric States

Due to the presence of two alternating bond angles in the backbone of the polymeric chains, polyisobutylene (PIB) possesses four different rotational isomeric states. Accordingly, conformations of PIB could be represented by a four-state rotational isomeric scheme with only one adjustable statistical weight parameter. Rotational isomeric states (RIS) were determined at +25°, ?25°, +120°, ?120°. Conformations were divided into a “+class” and “?class,” with bond conformations tended to be followed by those from the same class and with changes from one class to the other rare. Since the configurational and thermodynamic properties of PIB depend to a great deal on the conformational characteristics of the polymer, a modified rotational isomeric state approximation was used to generate the initial configurations of the polymeric chains without allowing for any segment-segment overlap. Attempts were made to test the configurational properties of these systems against those determined experimentally to ensure that these configurations do represent realistically the polymeric system. Furthermore, these configurations were used to perform subsequent molecular dynamics runs to elucidate the effect of the molecular weight of the polymer and the temperature on some of its important thermodynamic properties, such as self-diffusion coefficient, thermal pressure coefficient, heat capacity, and dielectric constant.     

SYNTHESIS OF POLYISOBUTYLENE WITH SEC-ARYLAMINO TERMINAL GROUP BY COMBINATION OF CATIONIC POLYMERIZATION WITH ALKYLATION

The highly reactive polyisobutylenes(PIBs) withα-double bonds(87.5 mol%) or tert-chloro(tert-Cl) groups(95 mol%) could be prepared via the cationic polymerization of isobutylene(IB) coinitiated by BF_3 or TiCl_4 respectively.The Friedel-Crafts alkylation of diphenylamine(DPA) with the highly reactive PIB withα-double bonds was further conducted under different conditions,such as at different alkylation temperature,in the mixed solvents of CH_2Cl_2/n-hexane with different solvent polarity and at DPA conce...     

Atomistic calculations of crystal structures of polyisobutylene

Semiempirical atomistic calculations are performed to investigate the crystalline structure of stretched poly(1,1-dimethylethylene), or polyisobutylene. The packing analysis was done without any lattice symmetry assumptions. The results are in good agreement with the x-ray analysis and favor Tanaka's model II. The calculations show several other crystalline structures with the chains in an all-gauche conformation. They have a somewhat higher density and may play a role in a hypothetical high-pressure phase of polyisobutylene.Dedicated to Prof. Dr. W. Pechhold on the occasion of his 60th birthday     

Synthesis of highly reactive polyisobutylenes with BF<Subscript>3</Subscript>·cyclohexanol initiating system

The selective cationic polymerization of isobutylene（IB）initiated by a BF₃·cyclohexanol（CL）complex was carried out from the mixed C₄ fraction feed containing the 4C saturated and unsaturated hydrocarbons at-20℃.The effects of CL concentration,BF₃ concentration,solvent for preparing BF₃·CL complex and polymerization time on the chemical structure of end groups,number-average molecular weight（M_n）and molecular weight distribution（MWD,M_w/M_n）of the resulting polymers were investigated.The experimental results indicate that the BF₃·CL complex initiating system exhibited an extremely high selectivity toward the cationic polymerization of IB in the mixed C₄ fraction feed and low molecular weight（M_n=900-3600）polyisobutylenes（PIBs）with large proportion of exo-double bond end groups were obtained.The exo-double bond content in PIB chain ends increased by increasing CL concentration or by decreasing solvent polarity in initiating system,BF₃ concentration and polymerization time.The M_n and MWD of the resulting PIBs were dependent on the concentrations of CL and BF₃.Highly reactive PIBs with around 90 mol%of exo-double bonds were successfully synthesized by the selective polymerization of IB from the mixed C₄ fraction feed,providing a potentially practical process for its simplicity and low costs.     

DCC/AlCl_3体系引发异丁烯正离子聚合

研究以对-二枯基氯(DCC)/AlCl3体系引发异丁烯在CH2Cl2/Hex(40/60,V/V)混合溶剂中进行正离子聚合,探讨了DCC用量、给电子试剂,如三苯胺(TPA)、2,6-二甲基吡啶(DMPy)对异丁烯正离子聚合转化率、产物分子量及其分布的影响.结果表明,在无给电子试剂存在时,DCC和体系中微量水均可与AlCl3产生络合竞争引起相继的引发竞争,聚合产物GPC谱图呈双峰分布,分子量分布宽,需要大量的引发剂DCC(DCC/H2O=5.3)来减少体系中微量水的不可控引发;在少量上述给电子试剂存在下,可提高DCC的引发效率,减少向单体链转移反应,提高聚合产物的分子量和使分子量分布呈较窄的单峰分布,即使在较低DCC用量下也可基本抑制体系中微量水的不可控引发,达到DCC定量引发,并得到分子量分布相对较窄(Mw/Mn≈2.3)的聚异丁烯产物.     

HES/TiCl4体系引发异丁烯可控正离子聚合

由六官能团引发剂环氧化角鲨烯(HES)与TiCl4组成引发体系,引发异丁烯(IB)在CH2Cl2/n-Hex(40/60,V/V)混合溶剂中进行正离子聚合,分别探讨了HES和2,6-二甲基吡啶(DMP)用量对IB正离子聚合转化率、产物分子量及其分布的影响.结果表明HES和微量水均可与TiCl4发生络合,并分别形成碳正离子和质子两种引发活性中心,导致聚合产物GPC谱图呈明显双峰分布.增加引发剂HES用量([HES]=2.64mmol/L),可以减少聚合体系中微量水的不可控引发,提高HES引发效率;在聚合体系中引入少量DMP时,可明显地减少微量水的不可控引发和提高HES的引发效率,使得即使在较低HES用量下([HES]=0.084mmol/L),也可达到主要由HES引发IB正离子聚合,制备出官能叔氯末端的六臂星形支化遥爪聚异丁烯,GPC谱图呈现单峰分子量分布,分布指数为1.5左右.