扫描探针显微技术研究聚苯乙烯单链颗粒的力学响应

首先通过极稀溶液滴膜的方法得到了聚苯乙烯的单链颗粒 .之后 ,采用稍浓溶液得到了既有单链聚苯乙烯颗粒又有多链 (上千根 )聚苯乙烯颗粒的样品 .力调制技术显示单链聚苯乙烯颗粒比多链聚苯乙烯颗粒软 ;另一方面 ,对多链聚苯乙烯颗粒和聚苯乙烯本体的纳米压印实验结果表明二者的模量是近似的 .因此 ,可以得出单链聚苯乙烯颗粒比本体聚苯乙烯软 ,这说明存在于聚苯乙烯单链颗粒中的分子链内的缠结点密度不如存在于本体中的分子链间的缠结点密度大     

Controlled Chain‐Scission of Polybutadiene by the Schwartz Hydrozirconation

Controlled chain‐scission of polybutadiene (PB), polyisoprene, and poly(styrene‐co‐butadiene), induced by bis(cyclopentadienyl) zirconium hydrochloride (Cp₂ZrHCl), was revealed at room temperature. The chain‐scission reaction of linear PB was studied by means of GPC, NMR spectroscopy, and MALDI‐TOF‐MS. It was confirmed that the molecular weights of degraded products were quasi‐quantitatively controlled by Cp₂ZrHCl loading, irrespective of the starting PB, whereas the microstructure of PB chains was crucial to the scission reaction. The hydrozirconation of model molecules indicated that the existence of an internal double bond in compounds with multiple double bonds was essential for chain cleavage. The chain‐cleavage mechanism was proposed to involve hydrozirconation of internal double bonds in PB chains and β‐alkyl elimination. Furthermore, metallocene‐catalyzed chain‐scission by a chain‐transfer reaction was developed. It is believed that the reported chain scission offers a promising pathway for end‐group functionalization by chain cleavage and presents a new application of Schwartz’s reagent.     

Analysis of reduced monoclonal antibodies using size exclusion chromatography coupled with mass spectrometry

Size-exclusion chromatography (SEC) has been widely used to detect antibody aggregates, monomer, and fragments. SEC coupled to mass spectrometry has been reported to measure the molecular weights of antibody; antibody conjugates, and antibody light chain and heavy chain. In this study, separation of antibody light chain and heavy chain by SEC and direct coupling to a mass spectrometer was further studied. It was determined that employing mobile phases containing acetonitrile, trifluoroacetic acid, and formic acid allowed the separation of antibody light chain and heavy chain after reduction by SEC. In addition, this mobile phase allowed the coupling of SEC to a mass spectrometer to obtain a direct molecular weight measurement. The application of the SEC-MS method was demonstrated by the separation of the light chain and the heavy chain of multiple recombinant monoclonal antibodies. In addition, separation of a thioether linked light chain and heavy chain from the free light chain and the free heavy chain of a recombinant monoclonal antibody after reduction was also achieved. This optimized method provided a separation of antibody light chain and heavy chain based on size and allowed a direct measurement of molecular weights by mass spectrometry. In addition, this method may help to identify peaks eluting from SEC column directly.     

A Monte Carlo simulation study of the effect of chain length on the hydrolysis of poly(lactic acid)

Abstract The intrinsic relationship between molecular chain length and the probability of chain reaction during poly(lactic acid)(PLA)hydrolysis was investigated by Monte Carlo simulation.The chain reaction rate was calculated by introducing a power function of different molecular chain lengths.The hydrolysis of both amorphous and extended-chain crystal PLA was selected as the model system.It is found that,the chain reaction probability was proportional to the chain length with a power of 0.4 for amorphous PLA and 0.7 1 for extended-chain crystal PLA,respectively.These results indicate that PLA with longer chain length usually exhibits larger reaction rate than that with shorter length.Comparing the hydrolysis of the two kinds of PLA,the competition between longer and shorter chains in the different condensed structures is different.     

卟啉铝催化下二氧化碳与氧化环己烯共聚反应研究

利用四苯基卟啉氯化铝(TPPAlCl)与双三苯基膦氯化铵(PPNCl)组成的二元催化剂催化二氧化碳与氧化环己烯共聚合,80℃下反应9h,二氧化碳-氧化环己烯共聚物(PCHC)的收率为97.2％,分子量分布窄(Mw/Mn=1.12),但数均分子量仅为6.8×103.研究发现溶剂的浓度和极性变化对聚合过程中的链转移反应影响...     

The temperature dependence of nematic liquid crystalline polymer melt diffusion

Polymer chain diffusion in the nematic mesophase was studied using a model main chain liquid crystalline (LC) polyether based on 2,2'-dimethyl-4,4'-dihydroxyazoxybenzene and mixed alkane spacers. A side chain LC polymethacrylate containing an azobenzene mesogenic group was also investigated. Tracer diffusion coefficients were determined as a function of temperature by an ion-beam depth profiling technique, forward recoil spectrometry. The results confirm that main chain LC polymer chain dynamics are dramatically affected by phase transitions and sample geometry. This behaviour is in marked contrast to the side chain LC polymer which exhibited no phase dependence on the part of the tracer diffusion coefficient.     

The temperature dependence of nematic liquid crystalline polymer melt diffusion

Abstract

Polymer chain diffusion in the nematic mesophase was studied using a model main chain liquid crystalline (LC) polyether based on 2,2′-dimethyl-4,4′-dihydroxyazoxybenzene and mixed alkane spacers. A side chain LC polymethacrylate containing an azobenzene mesogenic group was also investigated. Tracer diffusion coefficients were determined as a function of temperature by an ion-beam depth profiling technique, forward recoil spectrometry. The results confirm that main chain LC polymer chain dynamics are dramatically affected by phase transitions and sample geometry. This behaviour is in marked contrast to the side chain LC polymer which exhibited no phase dependence on the part of the tracer diffusion coefficient.     

Natural catalytic immunity is not restricted to autoantigenic substrates: identification of a human immunodeficiency virus gp 120-cleaving antibody light chain

The autoimmune repertoire is well known from previous studies to be capable of producing catalytic antibodies directed to self-antigens. In the present study, we explored the ability of 26 monoclonal light chains (L chains) from multiple myeloma patients to cleave radiolabeled gp120, a foreign protein. One L chain with this activity was identified. 125I-gp120 and unlabeled gp120 were cleaved at several sites by the L chain, as shown by SDS-polyacrylamide gel electrophoresis, autoradiography, and immunoblotting, respectively. The apparent dissociation constant of the L chain was 130-145 nM, indicating high-affinity gp120 recognition. 125I-albumin was not cleaved by the L chain, and various proteins and peptides did not inhibit gp120 cleavage by the L chain, suggesting that the activity is not a nonspecific phenomenon. The substrate recognition determinants may be conserved in different HIV-1 strains, because gp120 isolated from strains SF2, MN, and IIIB was found to be cleaved by the L chain. Micromolar concentrations of a synthetic peptide corresponding to residues 23-30 of gp120 inhibited the cleavage of 125I-gp120, suggesting that these residues are components of the epitope recognized by the L chain. The toxic effect of gp120 in neuronal cultures was reduced by about 100-fold by pretreatment of the protein with the L chain. These observations open the possibility of utilizing gp120-cleaving antibodies in the treatment of AIDS.     

端基附壁高分子模型链的塌缩转变

借MonteCarlo和模拟退火方法研究了端基附壁高分子尾形链在不同温度下的形态变化 ,链的模型采用有最近邻相互吸引作用的自避行走 .计算机实验结果表明 ,对于端基附壁的高分子尾形链 ,与自由链一样 ,当温度逐渐降低时高分子链会发生从松散的无规线团到紧密球体的塌缩转变 .计算机模拟得到了端基附壁链的均方末端距及其分量 ,均方回转半径及分布随温度的变化 .由于刚性壁的影响 ,使得有限链长的高分子尾形链与自由链相比 ,其表示链尺寸 温度关系的曲线要稍低 .模拟还发现 ,在高温时壁对链形状的影响比较大 ,壁垂直方向上尺寸明显大于平行方向的尺寸 ,后者接近于自由链的尺寸分量 .然而 ,低于θ温度时 ,尤其是完全塌缩之后 ,壁对链形状的影响已经很小 .     

Calculation of hydrophile-lipophile balance for polyethoxylated surfactants by group contribution method

Based on Davies' group contribution method, hydrophile-lipophile balance (HLB) values were calculated by effective chain length (ECL) instead of actual chain length of straight alkyl chain, polyoxyethylene (EO) chain, and polyoxypropylene (PO) chain. Linear equations were adopted for the effective chain length of straight alkyl chain and PO chain; a Gamma probability density function (PDF) was used to describe the contribution of each EO group to HLB and the effective chain length of EO chain could be obtained by integrating Gamma PDF. The HLB values of 224 nonionic surfactants were calculated and the average absolute error is less than 1.5, which is much better than the results obtained by Davies.     

New polymers with mesogens in the side chain and kinked aromatic structures in the main chain from the polyaddition of bis(epoxide)s and di(ester)s

Nine polymers with kinked aromatic structures in the main chain and biphenylene‐type mesogenic groups in the side chain were synthesized by the polyaddition of bis(epoxide)s and thio‐ and O‐esters. Tetrabutylphosphonium chloride and tetraphenylphosphonium chloride effectively catalyzed the polymerization. The thermal behavior of the polymers was measured by DSC and polarizing optical microscopy. The effect of annealing time on the degree of crystallization was investigated by DSC analysis. Polymers containing 100% of the kinked aromatic groups and 1,3‐propylene glycol in the main chain were amorphous. However, when half of the main‐chain aromatic moieties were composed of kinked groups and the other half of the aromatics were linear rodlike groups, the polymers were crystalline. The incorporation of kinked groups into the main chain of side‐chain liquid‐crystalline polymers suppressed the formation of liquid crystallinity. The polymer with mesogenic aromatic structures in both the main chain and the side chain was capable of forming a liquid‐crystalline phase. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 988–998, 2000     

Natural catalytic immunity is not restricted to autoantigenic substrates

The autoimmune repertoire is well known from previous studies to be capable of producing catalytic antibodies directed to self-antigens. In the present study, we explored the ability of 26 monoclonal light chains (Lchains) from multiple myeloma patients to cleave radiolabeled gp 120, a foreign protein. One L chain with this activity was identified. ¹²⁵I-gp120 and unlabeled gp 120 were cleaved at several sites by the L chain, as shown by SDS-polyacrylamide gel electrophoresis, autoradiography, and immunoblotting, respectively. The apparent dissociation constant of the L chain was 130–145 nM, indicating high-affinity gp 120 recognition. ¹²⁵I-albumin was not cleaved by the L chain, and various proteins and peptides did not inhibit gp 120 cleavage by the L chain, suggesting that the activity is not a nonspecific phenomenon. The substrate recognition determinants may be conserved in different HIV-1 strains, because gp 120 isolated from strains SF2, MN, and IIIB was found to be cleaved by the L chain. Micromolar concentrations of a synthetic peptide corresponding to residues 23–30 of gp 120 inhibited the cleavage of ¹²⁵I-gp 120, suggesting that these residues are components of the epitope recognized by the L chain. The toxic effect of gp120 in neuronal cultures was reduced by about 100-fold by pretreatment of the protein with the L chain. These observations open the possibility of utilizing gp120-cleaving antibodies in the treatment of AIDS.     

聚乙烯链在碳纳米管侧壁吸附的动力学模拟研究

利用经典的分子动力学模拟方法对聚乙烯(PE)分子在两种不同类型的碳纳米管(CNT)中的吸附进行了研究. 计算了两者之间的扩散系数和相互作用能; 利用PE链自身的扭转角分布和取向参数对PE链构象进行了分析. 结果表明, PE链可以在CNT上很好的吸附, 且PE的构象和吸附位置主要与温度和CNT的半径有关, 与管的类型关系不大.     

Effects of polymer chain length and stiffness on phase separation dynamics of semidilute polymer solution

Three-dimensional dissipative particle dynamics (DPD) simulations were performed to investigate the phase separation dynamics of semidilute polymer solutions with different polymer chain length and stiffness. For the polymer solution composed of shorter and more flexible chains, a crossover of the domain growth exponent from 1/3 to 2/3 was observed during the course of phase separation, indicating that the growth mechanism altered from diffusion to interfacial-tension driven flow. When the chain flexibility was kept the same but the chain was lengthened to allow for the chain entanglement to occur, the growth exponent changed to 1/4 in the diffusion-dominating coarsening regime while the growth exponent remained 2/3 in the flow-dominating regime. When the chain length was kept short but the stiffness was increased, the growth exponent became 1/6 in the diffusion-dominating regime and little effect was observed in the flow-dominating coarsening regime. The slow down of the phase separation dynamics in the diffusion-dominating coarsening could be explained by that the polymer chains could only perform wormlike movement when chain entanglements occurred or when the chain motion was limited by chain stiffness during phase separation. Moreover, when both the effects of chain length and stiffness were enhanced, polymer networks composed of longer and stiffer chains appeared and imposed an energy barrier for phase separation to occur. As a result, the polymer solution with stiffer and longer chains required a larger quench depth to initiate the phase separation and caused the delay in crossover of the coarsening mechanism from diffusion to flow.     

高分子链形状与尺寸关联的Monte Carlo模拟

运用MonteCarlo方法对线型高分子链格点模型的构型进行了模拟,研究了构型的尺寸(采用平方末端距R²,平方回转半径S²来表征)和形状(由非球形因子A表征)之间的关联.对任何长度的高分子链,其关联系数CA,R²和CA,S²均为正值,表明高分子链的形状与尺寸之间存在正关联,即尺寸小的构型其非球形因子A一般也小,反之尺寸大的构型其非球形因子A一般也大.关联系数CA,R²和CA,S²均随链长的增大而减小,近似地与链长的倒数(n^-1)成正比.研究还表明,关联系数的极限值(链长n很大时)与格点的类型无关,与链样本产生的方式也无关,但与链是否考虑排斥体积有关,考虑了排斥体积后,关联系数增大.     

The dependence of the rules governing gas-phase combustion on the competition between chain propagation and chain termination reactions

The competition between chain propagation and chain termination reactions was shown to play an important role in gas-phase combustion. Conditions under which this competition to a substantial extent determined the critical ignition conditions and the rate of the process were analyzed. Examples that showed that ignoring the role played by chain propagation, chain termination, and chain branching reactions in branched-chain processes led to conclusions that contradicted experimental data were considered.     

Multiple topologies from glycopolypeptide-dendron conjugate self-assembly: nanorods, micelles, and organogels

Glycopolypeptides (GPs) were synthesized by ring-opening polymerization of glycosylated N-carboxyanhydride monomer and attached to hydrophobic dendrons at one chain end by "click" reaction to obtain amphiphilic anisotropic macromolecules. We show that by varying polypeptide chain length and dendron generation, an organogel was obtained in dimethylsulfoxide, while nanorods and micellar aggregates were observed in aqueous solutions. Assemblies in water were characterized by electron microscopy and dye encapsulation. Secondary structure of the GP chain was shown to affect the morphology, whereas the chain length of the poly(ethylene glycol) linker between the GP and dendron did not alter rod-like assemblies. Bioactive surface chemistry of these assemblies displaying carbohydrate groups was demonstrated by interaction of mannose-functionalized nanorods with ConA.     

Reaction kinetics in dilute solutions of chain molecules carrying randomly spaced reactive and catalytic chain substituents. II. Dependence of the ring closure probability on the solvent medium and the nature of the chain backbone

Ternary copolymers of acrylamide or methacrylamide with small proportions of comonomers carrying reactive p-nitrophenyl ester and catalytic pyridine groups in the side chains were prepared. The kinetics of the ester solvolysis was followed in highly dilute solutions, so that the rate was controlled by interaction of groups carried by the same chain backbone. Data were obtained in water and aqueous methanol and were interpreted by a computer simulation procedure in terms of the dependence of the probability of encounter between two chain substituents on their spacing along the chain backbone. This probability decreased more slowly with increasing separation of the interacting groups when the solvation of the polymer was reduced, but even in solvents approaching θ conditions the results deviated from theoretical predictions for chains without excluded volume. The formation of cyclic conformations is considerably more difficult in methacrylic than in acrylic chains, although the chain flexibility, as characterized by unperturbed chain dimensions, is very similar in the two systems.     

直线群及其在聚合物结构中的应用

对聚合物晶体中各种高分子链的构象进行了研究,找出了它们的三维对称性,并用直线群来表征。在此基础上,讨论了分子链在空间群中排布的规律性,即在空间群中高分子链的对称性与所在位置的对称性相呼应。并利用直线群讨论了有序-无序高分子链所在空间群转变的规律性。     

双噁唑啉对聚碳酸1,2-环己二酯的扩链研究

采用马来酸酐封端聚碳酸1,2-环己二酯(PCHC),使其末端羟基转变为端羧基(MA-PCHC),并以2,2'-双-(2-噁唑啉)(BOZ)为扩链剂进行扩链反应.研究发现,BOZ与MA-PCHC中的羧基等摩尔情况下,扩链效果最佳.扩链后的PCHC的数均分子量从扩链前的5.6×104增长到12.4×104.扩链后的PCHC...