Synthesis of Polyelectrolyte and Studies of its Conductivity Changes with Respect to Molecular Weight

Aqueous solutions of acrylamide monomer were irradiated by γ-rays using a Co-60 source to synthesize polyacrylamide of different molecular weight (M_w). Solubility tests together with ultraviolet and infrared spectroscopic studies were performed for examining the irradiated samples to ensure that the prepared products were gradually converted from monomer to polymer (polyacrylamide), depending on the radiation dose. Various physico-chemical properties like polymer conversion, gel content, viscosity, and molecular weight of the products were determined. The conversion of polymer from monomer is initiated at a dose of 0.06 kGy and completed at about 0.14 kGy. The gel point, which indicates a dose for the onset of a network polymer structure, is identified to be 0.15 kGy providing valuable information about γ-ray synthesis of polyacrylamides. Viscosity and molecular weight are found to increase with radiation dose. Since polyacrylamides exhibit polyelectrolytic behavior in aqueous solutions, studies on conductivity changes of polyelectrolytes with respect to M_w, which is the main issue of this investigation, also were performed. The equivalent conductance of polyelectrolyte solutions was found to decrease with the molecular weight of the synthesized polymer. This change of conducting property of the prepared samples is explained based on the theory of polyelectrolyte solutions.     

Polymerization of vinyl chloride at reduced monomer accessibility. IV. The effect of diffusion control on polymerization rate,molecular weight,and thermal stability

The effect of diffusion control on the polymerization of vinyl chloride has been studied by observing the rate as well as the molecular weight and the thermal stability of the polymer formed. The polymerizations were performed at 97% of saturation pressure in a water-suspended system at 55°C, using emulsion PVC latex as seed and a water-soluble initiator. The monomer was charged as vapor from a storage vessel kept at a lower temperature. Characterization included determination of molecular weight distribution by GPC and viscometry, and thermal dehydrochlorination. The gas–liquid contact was varied by changing the speed of agitation and the design of the stirrer. With a propeller the polymerization rate increased with the agitation up to ca. 1000 rpm, where after it became almost constant. Simultaneously, the molecular weight and the thermal stability increased. This indicates diffusion control, and thus decreased monomer concentration, at low agitation speeds, while the polymerization becomes reaction controlled at higher speeds. By a comparison with earlier data, obtained at different pressures and under reaction control, the actual monomer concentration could be calculated, which allowed an evaluation of the mass transfer constant. The possibilities to encounter problems with diffusion control in commercial polymerization of vinyl chloride is discussed. It is demonstrated that diffusion control is utilized in continuous polymerization of vinyl chloride, which explains the lower thermal stability of such materials.     

超浓乳液聚合氧化还原引发体系的研究进展

介绍了超浓乳液的三个主要特点。从体系状态,单体含量,聚合速度,相对分子质量,聚合物形态和设备利用率方面比较了超浓乳液聚合与传统乳液聚合及本体聚合的区别。指出超浓乳液聚合中使用热分解引发剂所产生的问题及使用氧化还原引发剂的原因。还简单介绍了氧化还原引发体系的分类,回顾了前人在超浓乳液聚合工作中不同单体体系使用的氧化还原引发剂的情况,总结了不同单体体系中氧化剂还原剂的最佳配比,以及它们对动力学、相对分子质量的影响。最后展望了超浓乳液聚合新的发展方向。     

Synthesis and characterization of low‐molecular‐weight polyacrolein

Acrolein was polymerized in a polar solvent in the presence of terc‐ and sec‐butyl lithium as initiators. Using a low monomer to initiator molar ratio and 1‐h reaction time, cyclic structures were shown to be formed in the main chain of the resulting oligomers. The influence of different monomer to initiator molar ratios on molecular weight and on molecular weight distribution was investigated. Chain‐transfer reactions toward the monomer resulted in lower molecular weights and narrower polydispersions as [M]/[I] increased. The influence of initiator type on the polymer molecular weight was also evaluated. FTIR analysis of the degradation products at different heating temperatures indicated that the oligomers structure is composed of aldehyde, ether, and vinyl functional groups. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

反相微乳液聚合引发剂对聚丙烯酰胺分子质量影响的研究

分别以三种引发剂体系为引发剂,从引发机理出发,通过正交实验研究了丙烯酰胺反相微乳液聚合中引发剂种类、引发剂浓度、反应温度、单体浓度等对聚丙烯酰胺(PAM)相对分子质量的影响。结果表明,引发剂种类对水溶性PAM相对分子质量有显著的影响;过硫酸铵-亚硫酸氢钠和偶氮二异丁腈复合引发体系是合成高相对分子质量PAM的有效引发体系。该引发体系在反应温度为40℃,氧化还原引发剂与偶氮的质量比为1∶4,单体浓度为20%,引发剂浓度为0.3%,pH为9的最佳条件下合成的PAM相对分子量为1.44×107。     

Gamma-radiation induced grafting of acrylonitrile onto guar gum: Influence of reaction conditions on the properties of the grafted and saponified products

In the gamma-radiation induced grafting of acrylonitrile onto guar gum, the influence of different concentration of the monomer acrylonitrile on the PAN add-on, the number average molecular weight of the PAN side chains, and the grafting frequency of the PAN side chains are reported. At 0.3 Mard dosage, the PAN add-on were 32.4, 48.5, and 66.2% and the number average molecular weight of the PAN side chains were 59,700, 132,200, and 238,900, respectively, at three different reaction conditions. The frequency of grafting also showed considerable variation at 0.2 Mrad dosage, for all three sets of samples. The viscosity of the aqueous dispersions of the saponified samples at different concentrations are also reported. The water absorbency of the saponified samples were evaluated and the values were around 250 g/g. The fall in viscosity of the aqueous dispersions on storage were also evaluated. The observed fall in viscosity was lower in the case of the product with higher PAN content. © 1993 John Wiley & Sons, Inc.     

Effects of residual monomer on the degradation of DL-lactide polymer

The effects of remaining monomer on hydrolysis of poly(DL -lactide) were examined by adding different amounts of monomer to purified polymer samples. The existence of monomer in the polymerization products was found to enhance hydrolytic degradation of the polymer. A porous texture was observed on the SEM photographs of degraded materials, which led to the conclusion that the remaining monomer enabled water molecules to gain better access to the polymer matrix through this porous structure. The effects of molecular weight and chemical composition of polylactides on the hydrolytic degradation were also studied. Poly(DL -lactic acid) with higher molecular weights showed longer retention of the initial properties such as molecular weight and tensile strength. Copolymerization of DL -lactide with glycolide enhanced the hydrolysis, probably because of increased hydrophilicity of the polymers. © 1998 SCI.     

苯乙烯热引发本体聚合的动力学研究 1 转化率与时间的关系

基于三段聚合模型 (TSPM) ,研究了 10 0— 2 0 0℃苯乙烯 (St)热引发本体聚合。结果表明 ,TSPM同样适用于描述 St热引发本体聚合。用文献中发表的大量实验数据进行 TSPM标绘表明 ,由低转化阶段向凝胶效应阶段转变时的临界转化率 x1与聚合温度无关 ,为一定值 ,大致等于 0 .5。同时 ,聚合各阶段的表观速率常数可用阿累尼乌斯 (Arrhenius)方程关联。用得到的表观速率常数计算方程和 x1,对转化率与时间关系进行了计算 ,并与文献中发表的大量实验数据作了比较。结果表明 ,二者较为吻合     

Microstructure of copoly(3-hydroxyalkanoates) produced in the anaerobic–aerobic activated sludge process

The sequence structures of bacterially synthesized copoly(3-hydroxyalkanoates), isolated from the sludge developed in the anaerobic–aerobic waste-water treatment process containing propionate as a carbon source, were analysed by ¹³C NMR spectroscopy. These copolyesters were composed of four different monomer units, 3-hydroxybutyrate, 3-hydroxyvalerate, 3-hydroxy-2-methylbutyrate and 3-hydroxy-2-methylvalerate. By using water/acetone mixed solvent, one of the copolyester samples was fractionated into fractions by differences in average molecular weights as well as in monomer compositions. The carbonyl carbon resonances, split due to differences in diad sequences, were analysed on the basis of Bernoullian statistics. It is suggested that these copolyesters were mixtures of random copolymers with different monomer compositions.     

Rheological properties and thermal transitions in millable polyurethane fluoroelastomers

A series of segmented polyurethane fluoroelastomers based on dimethylol‐terminated perfluoropolyethers (PFPEs), aliphatic diisocyanates and allyl functionality is presented. Depending on the type of diisocyanate monomer used, it was found that quite different prepolymer molecular weights were achieved. Thermal analysis by differential scanning calorimetry showed formation of polyphasic copolymers, either amorphous or semi‐crystalline depending on the monomer structure. Rheological measurements showed that much higher zero‐shear viscosity, a shorter Newtonian plateau and more marked shear thinning behaviour were achieved with polyurethanes based on hexamethylene diisocyanate (HDI) or H₁₂‐MDI monomers. Isothermal viscosity curves were fitted with either three‐ or two‐parameter empirical models, and relaxation times of the structures were estimated at the temperature of 120 °C. Copyright © 2004 Society of Chemical Industry     

螺环二醇改性PET共聚酯的合成及性能

为了扩大聚对苯二甲酸乙二醇酯（PET）的应用范围,常通过引入第三单体来改变其性能。本研究以螺环二醇（SPG）为原料,采用酯交换法熔融缩聚合成了一系列不同单体含量的共聚酯。采用超高效聚合物色谱-多角度激光光散射仪（APC-MALLS）联用分析了共聚酯的分子量与分子量分布,利用核磁氢谱（¹H NMR）、傅里叶红外光谱（FTIR）研究了共聚酯的化学结构,同时采用差示扫描量热仪（DSC）、热重分析仪（TGA）和X射线衍射仪（XRD）研究了共聚酯的热性能以及结晶性能,测试了共聚酯的拉伸性能。结果表明,成功合成了符合纤维级聚酯数均分子量（M_n）和重均分子量（M_w）要求的共聚酯,分子量分布较窄,随着第三单体含量的增加,玻璃化转变温度从77℃提升至85℃,而熔融温度从255℃降低至222℃,热分解温度无明显变化,结晶性能下降。     

Preparation of plasma-polymerized membranes from fluoroalkyl acrylates and methacrylates and gas permeability through the membranes

Summary Plasma-polymerized membranes were prepared from fluoroalkyl acrylates and methacrylates by two different directions of monomer injection and the permeation rates of O₂ and n₂ through the membranes were investigated. The chemical structure and composition of the plasmapolymerized membranes varied significantly by the direction of monomer injection. The optimum plasma conditions to yield maximum gas separation characteristics was obtained by the remote plasma excitation at the W/FM value of 20 J/mg, where W is the discharge power, F is the monomer flow rate and M is the molecular weight of the monomer.     

Application of optimal temperature trajectory to batch PMMA polymerization reactor

A mathematical model is developed for the polymerization of methyl methacrylate (MMA) in a batch reactor. The model includes chain transfers to the monomer and solvent and termination by both combination and disproportionation and also takes into account the density change of the reactor contents and the gel effect. The usual pseudo-steady-state assumption is relaxed here. The validity of the proposed model is tested by an isothermal experiment of batch PMMA polymerization. Indeed, the experimental results show that the proposed model can describe the real polymerization system very well in view of both monomer conversion and average molecular weights. The optimal control theory is applied together with Pontryagin's minimum principle to calculate the optimal temperature trajectory for a batch polymerization reactor system which would lead to a polymer product having the desired properties set a priori. The performance index of the control system is composed of three factors—the desired monomer conversion and number- and weight-average molecular weights. The desired values of number- and weight-average molecular weights are obtained at a specified monomer conversion within acceptable error ranges. Control experiments are conducted to track the optimal temperature trajectory obtained from the model and the results are found to be in good agreement with the desired values. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 59–68, 1998     

Vapor phase polymerization of vinyl chloride

A study of the polymerization of vinyl chloride was made at conditions under which the monomer exists in the gas phase. In the presence of a bed of poly(vinyl chloride) particles, free-flowing product was obtained. By using free-radical initiators, such as dialkylperoxy dicarbonates or acetylcyclohexane sulfonyl peroxide, high initiator productivities were obtained in reaction periods of 1.5 to 3 hr. Although some modifiers, such as ethyl bromomalonate and bromoform, were demonstrated to lower molecular weight, satisfactory molecular weight modification was accomplished by adjusting polymerization temperature. Several peroxy compounds of different reactivity were studied. Hydrocarbon additives improve the polymerization rate. It is believed that the hydrocarbon and initiator are absorbed on the PVC particle surface and allow the monomer concentration to be increased at the polymerization locus. PVC particles of small size may be prepared in a liquid bulk polymerization for use as seed polymer for the vapor phase process. This provides a seed of high porosity which enables one to prepare a vapor phase product with suitable plasticizer absorption. The physical properties of products prepared by the vapor phase process were evaluated in a rigid formulation.     

聚苯乙烯纳米棒的界面法合成

首次采用界面聚合法成功地合成了聚苯乙烯(PS)纳米棒,利用透射电镜(TEM)、扫描电镜(SEM)、选区电子衍射(SAED)、红外光谱(FT-IR)及凝胶渗透色谱(GPC)等技术对其形貌和结构进行了表征.考察了单体浓度、反应时间与温度及有机溶剂等对聚苯乙烯形貌的影响.结果表明,以甲苯作为有机相溶剂、单体浓度为1.70 mol/L、60 ℃下反应10 h时能够得到平均直径为20 nm左右的纳米棒.样品的选区电子衍射(SAED)图与等规聚苯乙烯(i-PS)单链单晶的六方点阵衍射一致,GPC测试表明产物相对分子质量较低,且其分布范围较窄.     

Preparation and characterization of uniform molecularly imprinted polymer beads for separation of triazine herbicides

Uniform molecularly imprinted polymer beads were synthesized by precipitation polymerization for separation of triazine herbicides. A series of imprinted polymers were prepared using ametryn as template and divinylbenzene as crosslinking monomer, in combination with three different functional monomers under different solvent conditions. Under optimized reaction conditions, we obtained uniform molecularly imprinted polymer microspheres that display favorable molecular binding selectivity for triazine herbicides. The imprinted polymer beads synthesized using methacrylic acid as functional monomer in a mixture of methyl ethyl ketone and heptane showed the best results in terms of particle size distribution and molecular selectivity. Compared with nonimprinted polymer microspheres, the imprinted microspheres displayed significantly higher binding for a group of triazine herbicides including atrazine, simazine, propazine, ametryn, prometryn, and terbutryn. For the first time, precipitation polymerization has been used to produce highly uniform imprinted microspheres suitable for affinity separation of triazine herbicides. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Synthesis, characterization and evaluation of amphiphilic diblock copolymer emulsifiers based on methoxy hexa(ethylene glycol) methacrylate and benzyl methacrylate

Linear, amphiphilic diblock copolymers based on the nonionic, hydrophilic monomer methoxy hexa(ethylene glycol) methacrylate (HEGMA) and the hydrophobic monomer benzyl methacrylate (BzMA) of different molecular weights and compositions were synthesized by group transfer polymerization. The molecular weights and comonomer compositions of these copolymers were characterized by gel permeation chromatography and proton nuclear magnetic resonance (¹H NMR) spectroscopy, respectively. Dynamic light scattering on aqueous solutions of the diblock copolymers indicated that all the copolymers formed aggregates whose size increased with the % w/w BzMA composition and with the overall molecular weight of the linear chains. Turbidimetry on 1% w/w aqueous copolymer solutions was used to determine the cloud points, which were found to increase with the composition in hydrophilic units and the linear chain molecular weight. After polymer characterization, xylene/water and diazinon (pesticide)/water emulsions were prepared using the above polymers as stabilizers at 1% w/w polymer concentration and at different overall organic phase/water ratios. At an organic phase/water mass ratio of 4/1, the lower molecular weight (2500 and 5000 g mol⁻¹) diblock copolymers provided stable single-phase o/w emulsions, matching the behavior of commercially available hydrophilic Pluronics.     

双溴封端三氟氯乙烯调聚物的研制

选择二溴四氟乙烷为调聚剂,以三氟氯乙烯为调聚单体,尝试了3种不同方法试图合成双溴封端的三氟氯乙烯均聚调聚物,通过实验比较了3种方法的优缺点,同时通过凝胶渗透色谱、元素分析以及核磁共振等手段对调聚物的分子量、端基类型及其结构形式进行了表征。结果表明本文的合成方法简单易行,可以合成不同分子量的双溴封端调聚物。     

Theoretical influence of polyester molecular weight distribution variation on melt viscosity during injection molding and extrusion as influenced by ester‐ester interchange

In this study Flory's initial molecular weight derivation involving polyester polymerization and ester‐ester interchange was expanded to address two types of blends relative to both the number average molecular weight and the weight average molecular weight. First, an add blend was considered where the numbers of molecules of the same length were simply added together to calculate new number and weight average molecular weights. Second, the complete transesterification blend was calculated using Flory's most probable distribution with the same number average as the add blend but with a very different weight average molecular weight. The ratio of the weight averages of the add blend to the transesterification blend were found to be significantly larger if the initial blending molecular weights were significantly different from one another. This ratio was also found to go through a maximum that occurred at approximately 50% by weight if the two different molecular weights had the same monomer molecular weight. If the monomer molecular weights were different, the location of this maximum could be quite different from 50% by weight. Since melt viscosity is proportional to the weight average molecular weight to a power ranging from 1 to 3.4, a very large ratio between weight average molecular weight of the add blend and the ester‐ester interchange blend was found to have a significant influence on the melt viscosity. A polyester blend mixture of micro‐domains of both a nearly pure add blend and a nearly complete ester‐ester interchange blend was used to explain how a short shot could be followed a few shots later with a part that flashed the mold in an injection molding application.     

萘钾及乙醇钾引发L-丙交酯开环聚合研究

分别以萘钾和乙醇钾为引发剂成功地引发了L-丙交酯的开环聚合,考查了不同的单体/引发剂(M/I,物质的量比)在不同的反应时间下对聚L-乳酸(PLLA)相对分子质量及其分布的影响。以FT-IR1、H-NMR、GPC和粘均相对分子质量测试等对所得PLLA进行了表征,结果表明,通过改变M/I,2种引发剂都能够有效地控制PLLA的相对分子质量;PLLA的相对分子质量分布随反应时间的增加而变宽,其中乙醇钾的引发活性比萘钾的高,得到PLLA的相对分子质量比萘钾引发时大,相对分子质量分布也较窄。