炭黑对丙烯酰胺单体自由基聚合的影响

凝胶注模成型是一种先进的胶态成型工艺，是制备大尺寸、复杂形状陶瓷制品最有效的一种方法。该方法在制备氧化铝等陶瓷制品时获得了巨大成功，但对含碳陶瓷料浆成型时却遇到了难题，由于碳对聚合体系具有较强的阻聚作用，往往造成含碳料浆不聚合或聚合程度较弱，影响成型坯体的质量，因此研究炭黑对丙烯酰胺单体自由基聚合的影响是解决以上难题的关键。为此通过测量聚合反应的热效应，研究了炭黑含量、反应温度、引发剂用量等因素对丙烯酰胺单体聚合的影响，计算了聚合反应的活化能。实验发现在聚合体系中添加极少量的乙酰丙酮可以显著提高丙烯酰胺的聚合转化率，通过对聚合体系聚合过程的分析，发现炭黑对聚合体系除了具有阻聚作用外，还会影响聚合体系的聚合诱导期。     

新水溶液均相法制备两性聚丙烯酰胺的研究

采用氧化还原引发体系与AIBA为复合分段引发剂,在绝热水溶液体系中进行丙烯酸钠／丙烯酰胺／丙烯酰氧基乙基三甲基氯化铵自由基共聚合。研究了聚合温度、氧化还原引发体系用量、AIBA用量、单体浓度、共聚单体中DAC、AM含量,复合分散剂用量及其HLB值等对聚合反应单体转化率和聚合物特性黏度的影响。聚合物特性黏度随引发剂用量和单体浓度的增大而增大的实验结果证实了该两性聚丙烯酰胺水溶液均相制备过程中凝胶效应的存在。     

氧化还原引发乳液聚合单体水溶性与动力学之间的关系

本文研究了以过硫酸钾／焦亚硫酸钠为氧化还原引发体系，在苯乙烯、醋酸乙烯酯为具体单体的乳液聚合中，单体水溶性与动力学之间的关系。通过实验考察了聚合温度、搅拌速率、电解质浓度对聚合反应转化率～时间关系的影响，并讨论了单体水溶性、自由基水相反应和聚合速率等之间的内在联系。同时得出该氧化还原引发下苯乙烯和醋酸乙烯酯体系的表观活化能分别为４７．０６ｋｊ／ｍｏｌ和约７０ｋＪ／ｍｏｌ。     

丙烯酰胺聚合物自由基聚合引发体系研究进展

丙烯酰胺类聚合物是应用较为广泛的水溶性高分子化合物,自由基聚合是大规模生产聚丙烯酰胺的有效方法。文章对自由基聚合偶氮类引发剂、氧化还原引发体系、复合引发体系的特点和研究应用进行了讨论,认为采用水溶性偶氮引发剂、含胺的氧化还原引发体系、含胺基功能性单体类引发剂等新型引发剂能制备高分子量的聚合物,合理设计新型复合引发体系可利于聚丙烯酰胺相对分子质量的进一步提高。     

采用ATRP反应合成嵌段共聚物P(n-BMA-b-NIPAM)的研究

采用原子转移自由基聚合(ATRP)反应合成了甲基丙烯酸正丁酯/N-异丙基丙烯酰胺嵌段共聚物(P(n-BMAb-NIPAM))。考察了引发剂、催化剂、反应温度等对聚合反应结果的影响,最终确定较为合适的反应条件,制备出分子量确定、分子量分布较窄的大分子引发剂,并成功引发第二单体继续通过ATRP反应,获得P(nBMA-b-NIPAM)。研究结果表明:所确定的ATRP反应体系能实现n-BMA的可控聚合,获得末端带溴原子的聚甲基丙烯酸正丁酯(P(n-BMA-Br))作为大分子引发剂继续通过ATRP反应引发N-异丙基丙烯酰胺(NIPAM),最后获得分子量确定、分子量分布较窄的嵌段共聚物P(n-BMA-b-NIPAM)。实验证明,利用高价态铜络合体系可以实现单体的可控聚合,而且可以保持聚合物末端较高的卤官能度。     

聚丙烯酰胺类水溶性聚合物制备中分子量的控制

聚丙烯酰胺类水溶性聚合物在油气开采过程中有着十分广泛的应用,其分子量的大小决定着产品的性能和用途。该类聚合物的合成一般采用自由基聚合,聚合反应中通过控制单体浓度、引发剂浓度、聚合反应温度可以调节聚合物的分子量。另外,通过选择引发体系、聚合工艺、适度交联以及添加链转移剂也可以达到控制聚丙烯酰胺类水溶性聚合物分子量的目的。     

农用高吸水性复合树脂制备方法

本发明属于农用高吸水性复合树脂的制备方法。采用自由基水溶液共聚合法，单体以水溶液形式使用。采用的水溶性不饱和单体为非离子型含亲水基团的丙烯酰胺，采用的阴离子单体为丙烯酸钾。聚合引发体系为氧化还原引发体系，氧化剂为过硫酸铵或过硫酸钾，还原剂为偏重亚硫酸氢钾或亚硫酸氢钠，交联剂为N，N′-亚甲基双丙烯酰胺，促进剂为三乙醇胺，复合添加剂为高岭土和膨润土。     

低相对分子质量阳离子聚丙烯酰胺的合成研究

以丙烯酰胺(AM)、二甲基二烯丙基氯化铵(DMDAAC)为原料采用水溶液聚合法制备了一种阳离子度为50%,相对分子质量100000～200000的低相对分子质量阳离子聚丙烯酰胺水溶液,研究了单体配比、投加浓度、聚合温度、引发体系等对反应的转化率和产物相对分子质量的影响.通过加入质量分数0.5%的抗交联剂CPL和螯合剂EDTA·2Na.采用三元复合引发体系可以将聚合反应不饱和单体的转化率提高到96%以上,并且通过控制分子质量调节剂SF的用量可以得到不同相对分子质量分布范围的阳离子聚合物.该产品对高含水原油采出液有独特的预脱水性能,可提高油田采出液油水分离设备的效率和油水分离效果,与反相破乳剂、净水剂等配合使用还可以提高其对含油污水的处理效果.     

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。     

苯乙烯／双（2,3—二溴丙基）反丁烯二酸酯共聚动力学

研究了苯乙烯／双（２，３－二溴丙基）反丁烯二酸酯共聚动力学，分别讨论了单体的配比，聚合温度，引发剂浓度对共聚合体系的转化率－时间曲线的影响，结果发现，聚合温度和引发剂浓度影响很大，单体的配比影响较小。所建立的反应速率模型可以对转化率小于２０％的聚合速率进行描述，而在高转化率下，由于凝胶效应的影响而难以准确描述。     

Amphiphilic particles with hydrophilic core/hydrophobic shell prepared via inverted emulsions

An aqueous solution of acrylamide, its crosslinker (N,N'-methylenebisacrylamide), and an oxidant (ammonium persulfate) was first used to prepare an inverted concentrated emulsion in hexane. Span 80, which is soluble in hexane, was employed as a dispersant. The polymerization of acrylamide in the concentrated emulsion was greatly accelerated by introducing an aqueous solution of a reductant (sodium metabisulfite); it started at room temperature and was completed in a few seconds, resulting in a pastelike product. The system thus obtained was subsequently diluted with hexane containing a hydrophobic monomer. When styrene was used as the hydrophobic monomer, cumene hydroperoxide (which, together with sodium metabisulfite present in the dispersed phase, constitutes the initiator for the polymerization of styrene) was dissolved in the continuous phase. When vinylidene chloride was employed as the hydrophobic monomer, no additional initiator besides sodium metabisulfite and ammonium persulfate already present in the hydrophilic phase had to be employed. The use of initiators which are present only in the hydrophilic phase, and hence also at the interface between this phase and hexane, ensured the polymerization of the hydrophobic monomer as shells that encapsulate the polyacrylamide latexes. Under the proper conditions, a porous outer shell can be generated, which makes the hydrophilic chains present inside accessible. Such hydrophilic core/hydrophobic porous shell particles can be dispersed in water, where they remain stable for a long time, and in hydrophobic liquids, where they remain stable for at least 24 h. For this reason, we call these kinds of particles amphiphilic particles. © 1996 John Wiley & Sons, Inc.     

Fabrication and properties of dense silicon carbide ceramic via gel-casting and gas silicon infiltration

The dense Silicon Carbide (SiC) ceramics are fabricated by means of gel-casting and gas silicon infiltration (GSI) using carbon black and α-SiC as raw materials. We have successfully introduced a new initiator AIBA which is very suitable to aqueous gel-casting system containing carbon black, overcoming the problems posed by the conventionally used initiator. We have investigated the influences of the monomer acrylamide (AM) content, the ratio of the monomer to crosslinking agent AM/MBAM content, the particle size distribution and the solid content on the mechanical and structural properties of samples. The result show that, the linear shrinkage of the green body can be reduced to 1.0% and its bending strength can reach 59.2 MPa at the optimized gel-casting process that has an AM content of 25 wt%, an AM to MBAM ratio of 12, a SiC particle distribution of 3/2 and a solid content of 60 vol%. After the GSI process, the bending strength and elastic modulus of the final products from such green bodies can reach 245 MPa and 220 GPa respectively. The study highlights that the combined application of the gel-casting and the GSI processes can produce high-quality silicon carbide ceramics that are suitable in the space optical applications.     

白炭黑原位复合聚丙烯酰胺水凝胶的流变行为与次级网络

采用水溶液聚合法以过硫酸钾为引发剂,丙烯酰胺为主要单体,聚乙二醇双丙烯酸酯为交联剂,与不同类型和不同添加量的白炭黑原位复合,合成制备出交联型和线型的两类复合聚丙烯酰胺凝胶,并获得了在50 000 mg/L的高矿化度盐水中吸水30倍后弹性模量达100 Pa以上的聚丙烯酰胺水凝胶.采用高级流变仪证实了白炭黑与聚丙烯酰胺形成的次级网络的存在,通过对比不同类型白炭黑和不同白炭黑填充量对聚丙烯酰胺水凝胶流变性能的影响,发现白炭黑填充形成的次级交联网络对聚丙烯酰胺水凝胶的模量和损耗角正切的影响规律,通过与合成的无化学交联的白炭黑原位复合聚丙烯酰胺模型化合物对比和FTIR分析,揭示了白炭黑次级网络对水凝胶的增强机理.     

高锰酸钾引发双水相中淀粉接枝丙烯酰胺共聚反应

在双水相中进行淀粉接枝丙烯酰胺共聚反应是一种新的聚合方法,对以聚乙二醇为分散介质、高锰酸钾为引发剂的双水相中淀粉接枝丙烯酰胺共聚反应进行了研究,考察了引发时间、引发剂浓度及配比对产品单体转化率、接枝率和接枝效率的影响。通过实验得到聚合反应的最佳工艺条件:引发时间为10 min,n(高锰酸钾)∶n(丙烯酰胺)=3.0×10-4∶1,n(高锰酸钾)∶n(H+)=1∶10,反应温度为50℃,反应时间7 h,此时得到的产品的单体转化率C为98.88%,接枝率G为144.53%,接枝效率GE为97.81%。最后通过红外光谱仪进行结构表征。     

Fiber-reinforced ceramic matrix composites processed by a hybrid technique based on chemical vapor infiltration,slurry impregnation and spark plasma sintering

Fabrication of multidirectional continuous carbon and silicon carbide fiber reinforced ceramic matrix composites (CMC) by a new short time hybrid process was studied. This process is based, first, on the deposition of fiber interphase and coating by chemical vapor infiltration, next, on the introduction of silicon nitride powders into the fibrous preform by slurry impregnation and, finally, on the densification of the composite by liquid phase spark plasma sintering (LP-SPS). The homogeneous introduction of the ceramic charges into the multidirectional fiber preforms was realized by slurry impregnation from highly concentrated and well-dispersed aqueous colloid suspensions. The chemical degradation of the carbon fibers during the fabrication was prevented by adapting the sintering pressure cycle. The composites manufactured are dense. Microstructural analyses were conducted to explain the mechanical properties achieved. One main important result of this study is that LP-SPS can be used in some hybrid processes to densify fiber reinforced CMC.     

Chemorheological behavior of β‐SiAlON aqueous suspensions in gelcasting process

The chemorheological behavior of an aqueous suspension of monofunctional and difunctional monomers containing β‐SiAlON was investigated for gelcasting process. The effect of various parameters on gel and processing times was also studied. The time–temperature–transformation (TTT) diagram was used to correlate the pertinent processing parameters (time and temperature) with the gelation and processing times during in situ polymerization. The significant difference noticed between TTT diagrams of gel system containing β‐SiAlON and a pure gel system was a sharp shift of castable region to lower temperatures. This shift indicates that at the same monomers and initiator concentrations, the gelation can occur at lower temperature in the presence of SiAlON. These results clearly imply that the ingredient has accelerating effect on the polymerization reaction of acrylamide/methylene bisacrylamide. Reduction of polymerization activation energy from 72 kJ/mol for the monomer solution to 61 kJ/mol for a suspension containing SiAlON (35 vol%) confirmed this result. The impurities and surface groups of SiAlON are responsible for the accelerating effect of SiAlON. Furthermore, all suspensions showed shear thinning behavior, which were enhanced by β‐SiAlON rate of concentration increase. POLYM. ENG. SCI., 53:2123–2128, 2013. © 2013 Society of Plastics Engineers     

Gelcasting of silicon carbide ceramics using phenolic resin and furfuryl alcohol as the gel former

A new non-aqueous gelcasting system of phenolic resin and furfuryl alcohol combined with a curing catalyst was developed for casting of reaction bonded silicon carbide ceramics. This gelling system could be carried out in air, and the surface exfoliation phenomenon that seems inherent to the acrylamide gelcasting system could also be eliminated. Polymerization of the premix solutions and rheological properties of the non-aqueous silicon carbide suspensions were studied. After curing and subsequent pyrolysis of the concentrated silicon carbide suspension, homogenous silicon carbide/carbon green body with a relatively high strength of about 18 MPa could be formed. Dense complex-shaped SiC ceramic parts with flexure strength of 300±20 MPa and fracture toughness of 3.87±0.19 MPa m^1/2 can be successfully produced after reaction sintering at 1700 °C for 30 min under vacuum.     

The Influence of Polyethylene Imine on the Gelcasting of SiC With Two Different Initiators

In the present work, polyethylene imine (PEI) is used as dispersant to prepare SiC slurry for aqueous gelcasting. When ammonium persulfate (APS) is used as initiator, PEI accelerates the polymerization of monomers and the solidification of gelcasting slurry at 25°C. The reason is that tertiary amine in the structure of PEI and APS form a redox system as initiator. SiC gelcating slurry with PEI and APS solidifies in 2 min at 25°C, which makes the operation of casting impossible. However, when another initiator, 2, 2'-azobis [2-(2-imidazolin-2-yl) propane] dihydrochloride (AZIP·2HCl), is used, PEI does not accelerate but delays the polymerization of monomers because of the chain transfer. SiC gelcasting slurry in the presence of PEI and AZIP·2HCl has good fluidity and long idle time at 25°C. The slurry can be poured into the mold easily and solidifies in 5 min at 45°C. Therefore, PEI can be used as dispersant with the initiator of AZIP·2HCl in the gelcasting process, while PEI cannot act as dispersant when the initiator is APS.     

淀粉接枝丙烯酰胺的合成及其絮凝性能的研究

以玉米淀粉(St)和丙烯酰胺(AM)单体为原料,采用过硫酸钾引发剂合成了淀粉接枝丙烯酰胺共聚物(St-g-AM)。用红外光谱对接枝共聚物进行了结构表征,用粘度法测定了分子量。讨论了聚合反应的各个因素对接枝共聚反应的影响,考察了接枝共聚物的絮凝性能。结果表明,以接枝效率为考察目标,其最佳的合成工艺为:引发剂的浓度为0.07 g/100 mL,淀粉与丙烯酰胺的质量比为1∶2.2,反应温度为65℃,反应时间3 h。淀粉接枝丙烯酰胺共聚物比430万分子量的聚丙烯酰胺(PAM)对高岭土水样的絮凝性能更好,当接枝共聚物的投加量为6 mg/L时,对高岭土水样的浊度去除率达到81.77%。最佳条件所合成出的淀粉接枝丙烯酰胺的分子量为75万。