低分子质量PDMDAAC粘土稳定剂的合成

在低温、低浓度的条件下,以甲酸钠为链转移剂,在氧化还原引发体系中采用水溶液聚合方法合成了分子质量在1000～6000的PDMDAAC。通过单因素研究方法,考察了单体质量浓度、聚合温度、引发剂用量、还原剂用量、链转移剂用量对聚合物特性粘数和单体转化率的影响。评价了不同质量分数下PDMDAAC的防膨率,并将PDMDAAC与无机粘土防膨剂KCl复配后进行评价比较,防膨率高达到96％。     

低粘度聚丙烯酰胺的合成研究

采用链转移法合成了低粘度聚丙烯酰胺。探讨了反应温度、单体浓度、链转移剂、引发剂等对聚合物体系粘度的影响。确定了在单体浓度为30.0%,反应温度为80～90℃,链转移剂浓度为(2～6)×10-2mol/L,引发剂浓度为(3.5～18)×10-3mol/L的实验条件下,获得了粘度为1×102～1×104mPa.s的低粘度聚丙烯酰胺产品。并对该类低粘度聚丙烯酰胺在Si3N4结合SiC耐火材料方面的应用进行了初步研究。     

超低分子量聚丙烯酰胺的水溶液聚合

本文从丙烯酰胺单体出发,以过硫酸铵为引发剂,甲酸钠为链转移剂,采用水溶液聚合法合成了分子量在(2.6～10)×104范围内的聚丙烯酰胺,探讨了反应温度、单体浓度、分子量调节剂、引发剂等因素对聚合物分子量的影响.     

聚丙烯酰胺的合成及性能

以丙烯酰胺(AM)为单体,(NH_4)_2S_2O_8,NaHSO_3为氧化还原引发体系,采用水溶液聚合法制备聚丙烯酰胺(PAM)。研究了PAM的结构、性能和相对分子质量,同时考察了反应温度及单体、引发剂和链转移剂的质量分数对聚合反应转化率及PAM相对分子质量的影响。傅里叶变换红外光谱谱图中998 cm~(-1)处C=C双键的伸缩振动吸收峰消失以及在X射线衍射谱图中衍射角为20°～23°出现PAM特征弥散衍射峰,表明AM聚合生成了PAM。PAM热分解分3个阶段进行,其玻璃化转变温度随相对分子质量增大而升高。提高反应温度、增大引发剂和单体质量分数都可以提高单体转化率。升高反应温度、降低单体质量分数、增加引发剂和链转移剂质量分数均可以降低PAM的相对分子质量。     

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。     

反馈过程神经网络法测定聚丙烯酰胺分子质量

利用反馈过程神经网络学习记忆和训练,建立了丙烯酰胺聚合反应的升温曲线(温度随时间变化曲线)与平均分子质量的关系,预测聚丙烯酰胺平均相对分子质量的误差在4％以内,表明该方法简单有效,可以节省大量的实验工作量。     

链转移剂对聚丙烯酰胺产品分子量和不溶物的影响

以丙烯酰胺(AM)、丙烯酸(AA)为原料,采用低温复合引发剂体系(叔丁基过氧化氢-硫酸亚铁与偶氮引发剂)制备了高分子量阴离子聚丙烯酰胺产品.探讨了不同链转移剂及其使用量对聚丙烯酰胺产品分子量和不溶物的影响.实验结果表明,次亚磷酸钠的链转移效果较好,在使用量为20×10-6时,所得聚丙烯酰胺产品分子量接近1900万,不溶物小于0.3％.     

聚丙烯酰胺类絮凝剂的分子设计与应用研究

介绍了近十多年来国内外聚丙烯酰胺类絮凝剂的应用研究成果和发展状况,从分子设计和絮凝机理角度对聚丙烯酰胺类絮凝剂在各种污水处理中处理特点与处理效果做了简单概述,重点探讨经合成或改性后其分子结构中功能单元的絮凝作用,并展望了聚丙烯酰胺类絮凝剂今后的发展特点。     

不同反应条件对星形聚(N-异丙基丙烯酰胺)制备的影响

采用可逆加成裂解链转移自由基聚合法(RAFT),以四羟基卟啉为核制备RAFT链转移剂,以N-异丙基丙烯酰胺为单体合成四臂星形聚(N-异丙基丙烯酰胺)。通过红外光谱仪、核磁共振氢谱仪对聚合物的结构进行表征,结果表明,已成功地合成出星形聚(N-异丙基丙烯酰胺)。同时,聚合物的相对分子质量随反应时间的延长和单体浓度的增大而不断增长,呈现出“活性-可控”聚合特征。     

低分子质量聚丙烯酸钠合成研究

以过硫酸铵为引发剂、亚硫酸氢钠为链转移剂,在水介质中合成了低分子质量聚丙烯酸钠.通过单因素实验和正交实验,考察了丙烯酸浓度、过硫酸铵用量、亚硫酸氢钠用量和反应温度等因素对聚丙烯酸钠分子量的影响,确定了各因素的影响主次顺序,获得了优化的合成工艺条件,即过硫酸铵最佳用量0.5 g、亚硫酸氢钠用量2.0 g、反应温度65℃、丙烯酸质量分数30%.     

Water‐soluble copolymers. V. Synthesis of low molecular weight amphoteric polyacrylamide by foamed copolymerization

Amphoteric polyacrylamide of acrylamide, acryloyloxyethyl trimethylammonium chloride, sodium acrylate, and acrylic acid was synthesized by foamed copolymerization. The effects of monomer concentration and composition, initiator concentration and composition, sodium bicarbonate and stabilizer content on the polymer intrinsic viscosity and monomer conversion were examined. The monomer conversion increased with increasing initiator concentration, sodium bicarbonate and stabilizer content. The polymer intrinsic viscosity decreased with increasing initiator concentration. The structure and low molecular weight of the amphoteric polymer were identified by fourier transform infrared spectroscopy (FTIR) and gel permeation chromatography (GPC), respectively. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

高分子量聚丙烯酰胺的合成与应用进展

对高分子量聚丙烯酰胺的应用现状、合成条件等进行了综合评述。概括了单体纯度、引发剂和引发方式、聚合工艺对分子量的影响,并对高分子量聚丙烯酰胺的发展方向进行了展望。     

驱油用水解聚丙烯酰胺分子量测定方法研究进展

聚合物分子量及分子量分布是水解聚丙烯酰胺评价和合成研究的重要指标之一,在研究其黏度、水力学半径、降解规律和聚合物筛选评价等方面有着重要应用。本文简要回顾了黏度法、光散射法、凝胶色谱法、联用技术、场流技术的基本原理及在测定水解聚丙烯酰胺分子量中的应用及发展情况。黏度法设备简单,对操作人员要求较低,易于掌握,是目前主要评价手段;光散射法对样品除尘等要求较高,主要用于机理研究与分析,在大庆油田已有应用;驱油用的水解聚丙烯酰胺由于分子量大、非体积效应显著,应用凝胶色谱技术测其分子量还需要做大量的研究工作;场流技术能有效解决聚合物分子的剪切断裂问题,具有比较广阔的发展前景。     

Calculating molecular weight distributions in emulsion polymerization under conditions of diffusion limited chain transfer

When highly reactive chain transfer agents with low water solubilities (e.g., long chain thiols) are used in emulsion polymerizations, transport of the chain transfer agent (CTA) from the monomer droplets to the polymer particles can become diffusion limited. Consequently, the concentration of CTA in the particles is lower than expected, resulting in apparent transfer constants that can be much lower than the actual transfer constants obtained from studies with homogeneous systems such as bulk or solution. Furthermore, molecular weights will be greater than those obtained in homogeneous systems with the same overall concentration of CTA. There are currently no techniques or methodologies available for predicting molecular weight distributions when the transport of CTA is diffusion limited. Apparent transfer constants may be used but they are typically restricted to a given system and operating conditions. In this work, we describe how the actual CTA concentration in the polymer particles can be estimated through analysis of instantaneous molecular weight distributions. This information is then used to calculate the cumulative molecular weight distribution during the polymerization. Comparisons with experimental molecular weight distributions validate the essential correctness of the approach, but also highlight potential problems. The extension of the approach to online applications is discussed. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 217–227, 2000     

丙烯酰胺在聚乙二醇水溶液中可逆加成-断裂链转移聚合

结合双水相聚合和可逆加成-断裂链转移(RAFT)聚合,提出在聚乙二醇(PEG)水溶液中进行丙烯酰胺(AM)的RAFT双水相聚合,考察反应条件对聚合反应速率和产物分子量及分布的影响。结果表明:高引发剂浓度、单体浓度和聚合温度可以提高初始聚合速率和最终转化率,PEG和RAFT试剂浓度的增加会导致聚合速率减慢和最终转化率降低;峰值聚合速率随引发剂浓度、单体浓度和聚合温度的增加而增大,同时峰值聚合速率对应的时间提前;RAFT试剂浓度增加会推迟峰值聚合速率对应的时间,但可制得分子量分布较窄的产物;PEG浓度的增加会导致产物的分子量分布变宽。     

聚丙烯熔体流动指数与分子量及其分布的关系

研究了聚丙烯(PP)的熔体流动指数(MI)与聚合物不同分子量之间的关联性,对于分子量分布较窄的PP,数均分子量(Mn)、重均分子量(Mw)和粘均分子量(Mv)均能较好的关联;反之,MI与Mn关联性下降,而MI与Mn和Mv的关联性仍很好,尤其是MI与Mv的关联性受分子量分布的影响很小;MI与Z均分子量的关联性很差。同时．确定了MI与各种分子量之间的关联式,该式用于本体PP工艺反应器内氢气浓度的计算和MI的预测,与实验测量结果吻合良好。     

碳酸钠作为超高分子量聚丙烯酰胺水解剂的探索研究

研究了碳酸钠(Na2CO3)作为均聚后水解工艺生产超高分子量聚丙烯酰胺过程中的水解剂时,水解剂加入量、水解温度、水解时间等因素对产品质量的影响,并与氢氧化钠(NaOH)作为水解剂进行对比,探索了Na2CO3作为水解剂的可行性和优缺点。     

Effects of molecular weight and molecular weight distribution on creep properties of polypropylene homopolymer

The molecular weights of the industrial-grade isotactic polypropylene (i-PP) homopolymers samples were determined by the melt-state rheological method and effects of molecular weight and molecular weight distribution on solid and melt state creep properties were investigated in detail. The melt-state creep test results showed that the creep resistance of the samples increased by M_w due to the increased chain entanglements, while variations in the polydispersity index (PDI) values did not cause a considerable change in the creep strain values. Moreover, the solid-state creep test results showed that creep strain values increased by M_w and PDI due to the decreasing amount of crystalline structure in the polymer. The results also showed that the amount of crystalline segment was more effective than chain entanglements that were caused by long polymer chains on the creep resistance of the polymers. Modeling the solid-state viscoelastic structure of the samples by the Burger model revealed that the weight of the viscous strain in the total creep strain increased with M_w and PDI, which meant that the differences in the creep strain values of the samples would be more pronounced at extended periods of time.     

Efficient molecular weight control of bacterially synthesized polyesters by alcohol supplementation

The bacterial plastic poly(3‐hydroxybutyrate) (PHB) has many practical applications but its commercial potential is presently limited, partly due to the challenge of achieving appropriate mechanical performance characteristics. One method of tailoring the physical properties of the polymer is to control its molecular weight, which can be achieved by the addition of chain transfer agents such as poly(ethylene glycol) (PEG) to the culture medium during production. For the first time, PEG has been compared directly with alternative chain transfer agents, all of which contain at least one hydroxyl group. Methanol, ethanol and isopropanol all reduced the molecular weight of PHB produced by transgenic Escherichia coli by the same amount as PEG (～60%). PEG‐treated cultures grew to lower density and produced less PHB than control or alcohol‐treated cultures. Glycerol and sodium acetate were also tested, but only reduced the molecular weight by 15–24%. Naturally occurring short chain alcohols such as methanol and ethanol are a superior choice of chain transfer agent than the currently preferred PEG, as they achieve the same effect with reduced toxicity and are substantially less expensive. © 2013 Society of Chemical Industry