星形杂臂异戊二烯-丁二烯-苯乙烯橡胶的结构与性能

采用负离子溶液聚合法,以正丁基锂为引发剂、环己烷为溶剂、十二烷基苯磺酸钠/四甲基乙二胺为复合结构调节剂、二乙烯基苯为偶联剂制备了具有高抗湿滑性和低滚动阻力的星形杂臂异戊二烯-丁二烯-苯乙烯橡胶,考察了聚合温度及结构调节剂和偶联剂用量对聚合物微观结构、动态力学性能及力学性能的影响.结果表明,聚合物中非1,4-结构链节的含...     

Preparation and properties of poly(ethylene oxide) star polymers

Poly(ethylene oxide) (PEO) star polymers were prepared by anionic polymerization of methacryloyl chloride and glyceryl trimethacrylate with sec‐butyllithium in cyclohexane. The ensuing polymers were grafted with poly(ethylene glycol) of molecular weight 400. The final product was washed with methylene chloride and analyzed with infrared spectroscopy, differential scanning calorimetry, and thermogravimetry. Star polymers of PEO were also prepared by anionic polymerization of glycidol with sec‐butyllithium in cyclohexane. The initiator was chosen so as to yield a polymer of 10,000 molecular weight. The resulting polymers were analyzed by nuclear magnetic resonance, infrared spectroscopy, and thermogravimetry. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 322–327, 2003     

Preparation of pH-sensitive amphiphilic block star polymers,their self-assembling characteristics and release behavior on encapsulated molecules

Poly(ethylene glycol) (PEG), a polymer with excellent biocompatibility, was widely used to form nanoparticles for drug delivery applications. In this paper, based on PEG, a series of pH-sensitive amphiphilic block star polymers of poly(ethylene glycol)-block-poly(ethoxy ethyl glycidyl ether) (PEG-b-PEEGE) with different hydrophobic length were synthesized by living anionic ring-opening polymerization method. The products were characterized using ¹H NMR and gel permeation chromatography. These copolymers could self-assemble in aqueous solution to form micellar structure with controlled morphologies. Transmission electron microscopy showed that the nanoparticles are spherical or rodlike with different hydrophilic mass fractions. The pH response of polymeric aggregates from PEG-b-PEEGE was detected by fluorescence probe technique at different pH. A pH-dependent release behavior was observed and pH-responsiveness of PEG-b-PEEGE was affected by the hydrophobic block length. These results demonstrated that star-shaped polymers (PEG-b-PEEGE) are attractive candidates as anticancer drug delivery carriers.     

Polyisobutylene-based miktoarm star polymers via a combination of carbocationic and atom transfer radical polymerizations

Poly(isobutylene-b-styrene) (PIB-PS) copolymers and polyisobutylene (PIB) homopolymers were synthesized via quasiliving carbocationic polymerization from the initiator 3,3,5-trimethyl-5-chlorohexyl acetate, which contains a protected hydroxyl group. The PIB block was created at −70 °C in a methylcyclohexane/methyl chloride (60:40) cosolvent system, using TiCl₄ as co-initiator, followed optionally by sequential addition of styrene. Using a strong base, the acetate head group of the resulting block copolymer was cleaved to yield a hydroxyl group, which was subsequently esterified with the branching agent 2,2-bis((2-bromo-2-methyl)propionatomethyl)propionyl chloride (BPPC) to create dual initiating sites for atom transfer radical polymerization (ATRP). ATRP of tert-butyl acrylate was carried out using a Cu(I)Br/1,1,4,7,7-pentamethyldiethylenetriamine (PMDETA) catalyst system. In some cases, the ester side chains of the poly(tert-butyl acrylate) (PtBA) blocks were cleaved to create poly(acrylic acid) (PAA) blocks. The final miktoarm star polymers had compositions that were very close to theoretical.     

星形杂臂异戊二烯-丁二烯共聚橡胶的合成与表征

以环己烷为溶剂、正丁基锂(n-BuLi)为引发剂、四氢呋喃(THF)和五甲基二乙基三胺(PMDETA)为微观结构调节剂、二乙烯基苯(DVB)为偶联剂,采用"臂先"和"核先"相结合的方法合成了星形杂臂异戊二烯-丁二烯共聚橡胶[S-(PI)n-(PB)n],并对其结构进行了表征。结果表明,最佳聚合工艺条件为单体质量浓度0.1 g/mL、温度50~60℃、异戊二烯(Ip)聚合时间1 h;在偶联反应时间为1 h、[DVB]/[Li](摩尔比)为1.0、聚异戊二烯的单臂数均分子量为6×104~10×104的条件下,采用Ip与DVB(摩尔比5∶1)混合后的加入方式进行偶联反应,偶联效率可达70%,S-(PI)n-(PB)n的数均分子量为2.2×105~4.9×105,分子量分布可控制在1.80~2.10,PI和PB的平均臂数可达3~4,凝胶质量分数低于1.0%;当[THF]/[Li](摩尔比)为0.5、[PMDETA]/[Li](摩尔比)为1.0时,S-(PI)n-(PB)n中乙烯基质量分数可以达到63%。     

New epoxy thermosets modified with amphiphilic multiarm star polymers as toughness enhancer

The synthesis and characterization of two novel amphiphilic multiarm star polymers with linear polyethylene glycol (PEG) and poly(ε-caprolactone) (PCL) arms and their use as toughening modifiers of epoxy anhydride thermosets are reported. The new star polymers were obtained by partial pegylation of a hyperbranched polyester and subsequent growth of PCL arms. The curing process was studied by calorimetry and thermomechanical analysis, demonstrating the accelerating effect and the influence on gelation of the hydroxyl terminal groups. The curing kinetics was analyzed by model-free and model-fitting methods. The final properties of the resulting materials were determined by thermal and mechanical tests. The addition of the star-like modifiers led only to notable improvement on impact strength in the material containing a 10% of the star with PCL and PEG arms, without compromising glass transition temperature and thermal stability. The morphology of the resulting materials depended on the structure of the toughness modifier used, as demonstrated by electron microscopy, but all modified thermosets obtained showed phase-separated morphologies with nanosized particles.     

Structural studies of poly(butyl acrylate) - poly(ethylene oxide) miktoarm star polymers

Structural behavior of miktoarm star polymers comprising poly(butyl acrylate) (PBA) and poly(ethylene oxide) (PEO) arms was studied by means of Differential Scanning Calorimetry (DSC), Wide Angle X-Ray Scattering (WAXS), Polarized Optical Microscopy (POM) and Fourier Transform Infrared Spectroscopy (FTIR) methods. The aim of this study was to correlate changes in the composition of the arms of the PBA/PEO miktoarm star polymers with their structures. As a consequence of increasing PBA content, the decrease in crystallinity of the studied PBA/PEO heteroarm star copolymers was observed. Regardless of the copolymer composition, fraction of oxyethylene units in the crystalline PEO phase was similar in all investigated systems. The POM images showed spherulitic morphology of the materials having low PBA content, while an increase in PBA arms fraction leads to the formation of less ordered structures. The analysis of FTIR vibrational spectrum indicates helical conformation of PEO chains in the crystalline phase. Isothermal crystallization studies carried out using the FTIR technique suggest the existence of isolated domains in the nanoscopic scale of investigated materials.     

双亲聚合物的合成及其溶液性质的研究进展

综述了双亲聚合物的合成方法,包括经典自由基聚合法、活性离子聚合法、"活性"/可控自由基聚合法及其他方法,着重介绍了近年来才兴起的"活性"/可控自由基聚合法;简要介绍了有关其溶液性质的研究,包括双亲聚合物在选择性溶剂中的胶束化行为,其胶束的增溶作用,并介绍了双亲聚合物在固/液、气/液界面的吸附行为.最后,对双亲聚合物今后的发展方向进行了展望.     

新型对称性两亲含硅聚合物的合成与界面性能

基于原子转移自由基聚合(ATRP)机理,以二甲基一氯硅烷封端的烯丙基-聚乙二醇为起始剂,甲基丙烯酸乙酯(EMA)为单体,通过控制反应温度,合成了一系列聚合度(DP_(NMR))分别为0. 74,1. 67和3. 07的新型对称性两亲含硅共聚物(PEMA-b-Si-PEG-Si-b-PEMA),并评价了该共聚物在氯仿/水界面的界面活性和吸附行为。结果表明:该类聚合物可以有效降低氯仿/水界面张力,具有最短PEMA链的聚合物可将氯仿/水界面张力从32 m N/m降低至约23 m N/m。动态界面张力分析表明:低浓度的共聚物在吸附的初始阶段符合扩散控制,且较短的PEMA链段有利于产生较快的扩散速率。平衡界面张力分析表明:随着界面浓度的增加,共聚物将表现出多种吸附状态,其吸附状态的数量以及聚合物在界面的偏摩尔面积将随着PEMA链长度的增加而增加。     

用大分子多官能团引发剂合成杂臂星形苯乙烯-异戊二烯-丁二烯共聚物(英文)

采用负离子聚合技术,将合成的二烯烃活性链与SnCl4偶联,再与双锂短链偶联,制备出含碳锡键的大分子多官能团引发剂,并用其制备了2种杂臂星形苯乙烯-异戊二烯-丁二烯共聚物.结果表明,杂臂星形共聚物的偶联度可达80%.在聚异戊二烯(PI)-Sn-[丁苯橡胶(SBR)]3的PI臂中,1,4-结构摩尔分数为93.3%;在无规共聚SBR臂中,聚苯乙烯摩尔分数为28.8%,PI和SBR臂的玻璃化转变温度(Tg)分别为-91.3 ℃和-31.4 ℃.在聚丁二烯(PB)-Sn-(SBR)3的PB臂中,1,4-结构摩尔分数为90.1%;在无规共聚SBR臂中,聚苯乙烯摩尔分数为25.6%,PB和SBR臂的Tg分别为-87.9 ℃和-48.0 ℃.     

通过RAFT聚合合成星型聚合物

采用先臂法合成(tBA/HDDA)星型聚合物。由丙烯酸正丁酯(tBA)的可逆加成-断裂链转移自由基聚合(RAFT),得到线型PtBA大分子链转移剂;PtBA与双官能团的偶联剂1,6-己二醇二丙烯酸酯(HDDA)反应得到星型聚合物。研究了偶联剂HDDA与线型PtBA大分子链转移剂的摩尔比对合成星型聚合物的影响。采用GPC法测定了线型大分子链转移剂PtBA及星型聚合物的分子量和分子量分布。结果表明,HDDA与PtBA的比例越高,星型聚合物的产率越大;超过一定值,则产生凝胶。GPC结果表示,所得星型聚合物的分子量大,分子量分布窄(PD I<1.19)。     

Swelling behavior of ordered miktoarm star block copolymer-homopolymer blends

We report the morphological characterization of asymmetric miktoarm star block copolymers of the (PS-b-PI)_nPS type where n=2,3 (denoted 2DB and 3DB miktoarm stars, respectively) and a symmetric super H-shaped block copolymer of the (PS-b-PI)₃PS(PI-b-PS)₃ type (denoted SH) which were synthesized by anionic polymerization. The initial volume fraction of PS (φ_PS) for each copolymer was 0.51-0.56, giving a lamellar morphology. Addition of homopolystyrene (hPS) with a molecular weight lower than the respective PS blocks in the neat materials lead to a transition from the lamellar structure to hexagonally packed cylinders. Addition of low molecular weight homopolyisoprene (hPI) on the other hand, only resulted in swollen lamellae even when the overall composition was highly asymmetric (80/20). Changes in the lamellar spacing as well as in the respective PS and PI layer thickness were measured by SAXS. The transition from lamellae to cylinders with increased PS content occurred without the observation of an intervening cubic morphology for the 2DB and 3DB miktoarm stars. However, blends with 30 and 35% hPS ((φ_PS)_total=0.68-0.70) with the super H-shaped block copolymer lead to the observation of lamellar-catenoid structures.     

Water-soluble and amphiphilic polymers

Summary Three PEO-PSt-PEO triblock polymers and their parent ho-nopolystyrene have been studied by means of light scattering technique in chloroform, toluene and ethyl acetate. It has been found that the weight average molecular weights calculated by using the equation Mapp- were unbelievable negative values; and the largest deviation appeared for the sample with PEO mole content of about 50%. Data of PSt-PEO-PSt triblock polymers in literature have been quoted and discussed.     

Photoresponsive submicron-sized hollow spheres obtained from amphiphilic azobenzene-containing random copolymer

This article reports the formation, morphology control, and photoresponsive properties of submicron-sized hollow spheres of an amphiphilic azobenzene-containing random copolymer (PEAPE). The hollow spheres were obtained by diluting the polymer disperse at 50 vol% water content with THF–water (v:v = 1:1) and slowly removing THF by evaporation. The size and shell thickness of the hollow spheres were determined by the polymer initial concentration in THF, water addition rate, and diluent volume. The ratio of the average shell thickness to the hollow sphere size was mainly affected by the diluent volume. By adjusting these factors, the size and shell thickness of the hollow spheres could be well controlled. The photoisomerization study indicated that hollow spheres possessed a compactly packed shell with density similar to that of their counterparts with solid interiors. Upon UV light irradiation, the hollow spheres in dispersions showed different photoresponsive properties depending on their size and shell thickness. For the “vesicle-like” spheres with a thin shell, photoinduced disaggregation was observed when irradiated with the 365 nm UV light.     

Water-soluble and amphiphilic polymers

SUMMARY The graft polymerization of acrylic acid (AA) on poly (vinyl alcohol) (PVAL) has been investigated by using either potassium persulfate (KPS) or ceric ammonium nitrate (CAN) as an initiator. In the case of KPS initiation, the formation of the graft polymer always lags behind the homopolymer formation. The graft polymer is separated by acetone, and the increase of reaction temperature favors the homopolymer formation at the early stage. In the case of CAN initiation, graft polymers with a high PAA content can hardly be obtained when the polymerization is performed under nitrogen and at < 0.06 mol/L HNO₃ concentration. It has been found that incorporation of a small amount of oxygen in a protective nitrogen gas accelerates markedly the graft polymerization, and that the resulting graft polymers can not be separated by acetone precipitation technique in most cases. The Dalian nitrogen (containing 0.7% oxygen) is a good protective gas for CAN—initiated PVAL—AA graft polymerization.     

Water-soluble and amphiphilic polymers

Summary Thin filns of PSt/PMAA and PEO-PSt-PEO block polyners were deposited on a polystyrene substrate by solution adsorption (with or without solvent treatnent), and the filn surfaces were characterized by neans of XPS. Direct solvent-casting of PEO-PSt-PEO from benzene solutions resulted in PSt-rich surfaces, whereas PMAA richer surfaces were obtained for PSt/PMAA filns cast from DMF solutions. Moreover, solvent treatment after casting had profound effect on the filn surface conposition. Treatment with water markedly increased the surface concentration of polar PEO segments. In the case of PSt-PMAA block polymers, the PSt content on the surface increased in the order of water< ethanol < cyclohexane < petroleum ether, the last-named giving films with almost pure PSt surface. It is well worth noticing that the bulk conposition had little to do with the surface conposition for both PSt/PMAA and PEO-PSt-PEO block polyners within the conposition range investigated when subsequent solvent treatnent was applied.     

Banded texture of photo-aligned azobenzene-containing side-chain liquid crystalline polymers

Poly(6-[4-(4-cyanophenylazo)phenoxy]x-methylene methacrylate) (P_x, x is 2 or 6) were synthesized and used to study the texture of side-chain liquid crystalline polymers (SCLCPs) after photoinduced orientation. With increasing temperature of irradiated P₂ film up to 125 °C, just above its T_g, 123 °C, a banded texture was observed for SCLCPs under polarized optical microscope (POM). There is no banded texture of irradiated P₆ (T_g, 72 °C) film when heating to 75 °C. The formation of the banded texture is considered to be due to co-existing of in-plane and out-of-plane orientation mesogens in P₂ film, which is explained in terms of a molecular model. Based on our experimental results, factors of irradiation light intensity, film thickness, and heating rate on the formation of the banded texture were studied in this work.     

Synthesis of deuterobutadiene-butadiene AB2 and AB3 miktoarm star copolymers

The synthesis of well-defined, monodisperse AB₂ and AB₃ miktoarm star copolymers, in which A is polydeuterobutadiene and B is polybutadiene, is described. The synthetic procedure involved reacting living polydeuterobutadiene with a large excess of either methyltrichlorosilane or tetrachlorosilane to yield a ‘one-arm star’. SEC traces of this ‘one-arm star’ are indistinguishable from that of the uncoupled polydeuterobutadiene indicating no further coupling to form multi-arm stars occurs. Unreacted chlorosilane was removed by distillation and the introduction of an excess of living polybutadiene generates the star. The star polymer was isolated from the precursor polybutadiene by fractionation. Received: 27 April 1998/Revised version: 15 June 1998/Accepted: 16 June 1998     

Phase separation phenomena in aqueous solutions of amphiphilic poly(ethylene oxide) star polymers

Three- and four-armed star polymers with poly(ethylene oxide) arms capped with hydrophobic end-groups were synthesized from nonylphenoxypoly(ethylene glycol)s and well defined tri- and tetraisocyanates. The latter were hydrosilylation products of m-isopropenyl-,-dimethylbenzyl isocyanate (m-TMI). In aqueous solution the arm ends associate, and above a critical star concentration the mixture phase separates into a dilute phase and a condensed gel phase. Their respective polymer concentrations remain constant as long as the two phases coexist, their volume fractions being proportional to the total polymer concentration. Brookfield viscosity measurements confirm the formation of the gel phase which resembles an amphiphilic hydrogel. It exhibits a high affinity for hydrophobic compounds.     

Synthesis of azobenzene-containing polymers and investigation of their substituent-dependent isomerisation behaviour

A variety of 4,4′-substituted azobenzenes has been synthesised and the kinetics of the thermal cis–trans-relaxation of the substances was studied in detail in solution and embedded in a poly(methyl methacrylate) (PMMA) matrix by UV–Vis spectroscopy. Considerable differences in relaxation times were found for the various azobenzenes which interestingly could not be fully explained by simply comparing the substituents with regard to their electron-donating or -withdrawing nature. Any substituents, especially very polar ones, increase the thermal cis–trans-reaction rate. Some of the chromophores were covalently attached to a PMMA-copolymer and we found that this significantly slowed down the isomerisation kinetics compared to the embedding of low molar mass azobenzenes in a polymer matrix. But our study showed also that, even at room temperature, the thermal cis–trans-relaxation of 4,4′-substituted azobenzene chromophores can never be fully suppressed, but only slowed down.