疏水缔合聚合物溶液的性能

疏水缔合水溶性聚合物指在常规水溶性聚合物主链上引入极少量疏水基团所形成的一类新型聚合物。与部分水解聚丙烯酰胺(HPAM)相比,这类聚合物的分子量不高,但具有独特的溶液性能。本文综述了疏水缔合聚合物的增黏、耐温、抗盐、抗剪切的溶液性能。     

疏水性聚丙烯酰胺的合成实验研究

疏水性聚丙烯酰胺是一种重要的疏水缔合水溶性聚合物,它可以通过多种方法合成。本文结合均相共聚法和表面活性大单体法2种方法,以丙烯酸和Span80为原料首先合成了一种具有表面活性的疏水缔合型单体Span80-AA,然后将Span80一AA与丙烯酰胺聚合反应合成疏水性聚丙烯酰胺,并研究了时间、引发剂浓度、溶剂配比、大单体含量和温度对疏水聚合物粘度和分子量的影响,从而得到比较合适的实验条件。     

疏水缔合聚丙烯酰胺溶液的稳定性研究

用粘度法研究了用模拟胜利油田盐水配制的疏水缔合聚丙烯酰胺溶液在高温下的稳定性。实验发现聚合物溶液粘度下降很快,硫脲和小分子醇类能明显增强聚合物溶液的高温稳定性。其中硫脲能起到抗氧剂的作用,在短期内能使溶液保持较好的稳定性;小分子醇类能与聚合物交联,使疏水缔合聚合物溶液的网状结构得以维持。用硫脲和自制的多羟基化合物以1∶5比例复配后的稳定剂结合了这两类物质的优点,当加入量为100mg/L时,使聚合物溶液的高温长期稳定性有了很大的提高。     

疏水缔合聚合物的合成、表征及其溶液性能研究

采用自由基胶束聚合法,合成了一种疏水缔合型丙烯酰胺-烷基丙烯酸酯共聚物。用1HNMR谱和TEM对该共聚物进行了表征。用旋转黏度计测定了不同疏水基含量的聚合物的溶液性能,考察了温度对聚合物溶液性能的影响,同时研究了外加盐对聚合物溶液形貌的影响。     

超临界CO2下三元含氟疏水缔合聚合物的合成及溶液性能研究

设计聚合物的分子结构并在超临界CO2下以丙烯酰胺(AM)、2-甲基-2-丙烯酰胺基丙磺酸(AMPS)及甲基丙烯酸十二氟庚酯(G04)为单体合成三元含氟疏水缔合聚合物,并用FTIR和元素分析对结构进行表征。研究反应温度、压力及引发剂加入量对产物聚合反应转化率及相对分子量的影响,并对三元含氟疏水聚合物浓度对溶液表观粘度的影响进行研究。结果表明:在超临界CO2体系下可制备三元共聚含氟聚合物,且由于含氟疏水基团的存在,该聚合物水溶液具有明显的疏水缔合作用。     

pH响应乳液型聚丙烯酰胺的制备及其应用研究

为改善聚丙烯酰胺类乳液减阻剂的溶解性和稳定性，合成了pH刺激响应型表面活性剂的乳化剂，并合成具有pH响应能力的改性聚丙烯酰胺乳液。研究了油水比、乳化剂质量分数对乳液稳定性的影响，使用反相乳液聚合法得到改性聚丙烯酰胺乳液，最佳聚合条件为油水比为0.82、乳化剂质量分数为3%。利用FT-IR及¹HNMR对表面活性剂及聚合物的结构进行表征。结果表明，0.5%的改性聚丙烯酰胺乳液在pH小于6或大于8的水中可迅速破乳并溶解，在30 s内便能迅速起黏，并在1 min内达到最大黏度。用pH 10的水配制质量分数为0.5%的聚合物溶液，减阻率能达到63%;在盐水中减阻率达到60%。     

水解方法对疏水改性聚丙烯酰胺的性能影响

采用水溶液自由基胶束共聚法,通过氧化还原体系引发丙烯酰胺与自制功能单体聚合,以均聚后水解与均聚共水解方法分别制得疏水改性聚丙烯酰胺(HMPAM)。通过探针芘的荧光光谱、扫描电镜和表观粘度测定等手段,表征了HMPAM溶液中疏水缔合作用及分子聚集形态,研究了不同水解方法导致的浓度、温度、矿化度对HM-PAM溶液流变性能的影响。结果表明,均聚后水解产物分子量(1 000多万)大于均聚共水解产物的分子量,并且其在盐水溶液中存在明显的临界缔合浓度。但是均聚共水解产物产物在高温、高矿化度及97 d的老化实验条件下,其粘度保留率高于均聚后水解产物。     

矿化度对疏水缔合聚合物溶液溶解时间的影响研究

疏水缔合聚合物是在亲水的聚丙烯酰胺大分子主链上引入少量疏水基团合成的新型水溶型聚合物。其有耐温耐盐的良好特性。但是疏水基的引入降低了聚合物的水溶性,增加了溶解时间。本文以渤海某油田地层水的离子构成作为参考,通过配制不同矿化度溶液来溶解疏水缔合聚合物,探索矿化度对疏水缔合聚合物溶液粘度及溶解时间的影响,并从原理上解释了出现这些现象的原因。最终发现,随着矿化度升高,疏水缔合聚合物溶液粘度降低,溶解时间增大。这种现象是由于矿化度升高,溶液中电解质增多,溶液极性增强,影响了疏水缔合聚合物分子的展开和缔结。     

环糊精加速疏水缔合聚合物溶解机理研究

利用环糊精(CD)对疏水基团的包合作用,在疏水缔合聚合物溶解过程中向溶剂中加入环糊精,加快疏水缔合聚合物的溶解速度。当环糊精与疏水基团摩尔比(CD∶[H])≤1,随CD∶[H]增大,溶解时间大幅下降。当CD∶[H]=10时,缔合聚合物的溶解时间缩短至与聚丙烯酰胺相当。流变学结果证明,环糊精通过包合作用破坏疏水基团的缔合结构,大幅缩短缔合聚合物解缠结时间来加速疏水缔合聚合物的溶解速度。     

疏水单体含量对疏水缔合聚合物渗流特性的影响

利用串联平板夹砂渗流模型,研究了同粘度疏水缔合聚合物溶液在均质模型下的渗流特性。结果表明,在渗透率1.1~6.1μm2范围内,疏水缔合聚合物溶液在平板渗流模型中压力达到稳定的时间与疏水单体含量成正比;相同渗透率下,缔合聚合物在传播方向上的阻力系数和残余阻力系数呈增加趋势,且增加幅度与疏水单体含量成正比,而聚丙烯酰胺在介质中的渗流特性是不变的。采用微孔滤膜过滤方法,证明了疏水单体含量对渗流特性的影响在于其改变了溶液中聚集体尺寸。     

Thiolated chitosans: In vitro comparison of mucoadhesive properties

The aim of this study was to compare the mucoadhesive properties of thiolated chitosans with regard to their molecular mass and type of immobilized thiol ligand. Mediated by a carbodiimide, aromatic‐ and aliphatic‐thiol‐bearing compounds were covalently attached to low‐ and medium‐molecular‐mass chitosan. All synthesized conjugates displayed on average 320 ± 50 μmol of immobilized free thiol groups per gram of polymer. The rheological synergy was observed by the mixture of equal volumes of polymer with mucin solution. Because of the increase in viscosity of the conjugate/mucin mixture, the self‐crosslinking properties and the interaction of thiomers with the mucus layer could be confirmed. Further mucoadhesion of the chitosan conjugates was evaluated in vitro with the rotating cylinder method and tensile studies on excised porcine intestinal mucosa. The results show a significantly enhanced residence time (p < 0.05) on the mucosa of all thiolated chitosans compared to the unmodified polymer. Among all of the conjugates tested, the following rank order of mucoadhesion could be determined: Chitosan–thiobutylamidine > Chitosan–4‐mercaptobenzoic acid > Chitosan–glutathione > Chitosan–6‐mercaptonicotinic acid > Chitosan–N‐acetyl cysteine > Chitosan–thioglycolic acid > Unmodified chitosan. The charge, pK_a, and reactivity of the attached compounds were found to be important factors influencing the mucoadhesive potential of the polymer. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Preparation and viscosity behavior of hydrophobically modified poly(vinyl alcohol) (PVA)

In this study, a novel series of water-soluble hydrophobically modified poly(vinyl alcohol) (PVA) is prepared by chemical modification of PVA, with the objective of investigating the polymer's rheological behavior for enhanced oil recovery applications. The solution viscosity of the polymer obtained is studied with respect to the polymer concentration, temperature, salinity, polymer modification, aging, shear rate, and polymer molecular weight. The solution viscosity of the PVA is greatly enhanced by the modification. The modified PVA exhibits a relatively high salt tolerance, typical of nonionic polymers, in the range of 0–7.0 wt % NaCl concentrations, and the viscosity of the polymer solution is relatively invariant with NaCl above 3.0 wt % NaCl concentration. Below 3 wt %, the viscosity shows a maximum then a minimum, an unusual behavior. Generally, the polymer exhibits an almost constant viscosity at high shear rates and a typical shear thinning behavior at low shear rates. In addition, increasing polymer concentration and molecular weight leads to an increase in the polymer solution viscosity. Moreover, the polymer exhibits smaller solution viscosity at a high temperatre, and a slight decrease in viscosity is also exhibited by the modified polymer with aging. Comparison of the viscosities of 18 polymer modifications indicates that the larger the numbers of hydrophobic groups (side chains) in the polymer structure, the smaller the viscosity. Moreover, the longer the hydrophobic groups (side chains) in the polymer structure, the greater the viscosity, if their number is small. © 1995 John Wiley & Sons, Inc.     

Molecular docking,synthesis, and characterization of chitosan-graft-2-mercaptobenzoic acid derivative as potential drug carrier

Chitosan is a hydrophilic polymer with prominent mucoadhesive properties. However, it forms weak hydrogen bonds with mucin thus limiting its mucoadhesion and exhibit reduced bioavailability due to its short retention time in the body. The aim of the present study was to synthesize and characterize novel thiolated chitosan with improved functional property. A unique approach of using molecular docking to select ligand to chemically modify chitosan has been employed in the present research. A set of ligands were screened virtually using docking analysis and 2-mercapto benzoic acid showed the lowest glide score of −4.31 Kcal/Mol thus displayed better binding interaction with chitosan. Based on the docking results, the best-fit ligand was selected for wet lab synthesis. 2-Mercapto benzoic acid was covalently attached to chitosan via formation of an amide bond and the reaction was mediated by carbodiimide and N-hydroxysuccinimide. The synthesized polymer was in turn evaluated for zeta potential, Fourier transformed infrared, differential scanning calorimetry, molecular weight that confirmed conjugation of chitosan with the thiol ligand. The prepared thiomer was further subjected to mucoadhesion studies and displayed better mucoadhesion properties as compared to unmodified chitosan. Thus, the potential of the novel thiomer can be further explored as an excipient for drug delivery system with an emphasis on mucoadhesion.     

Rheological Behaviour of Poly (Acrylamide-G-Propylene Oxide) Solutions: Effect of Hydrophobic Content,Temperature and Salt Addition

Abstract

The viscosity of hydrophobically modified polyacrylamide was investigated as a function of polymer concentration in aqueous and in salt solutions, and also as a function of temperature. The graft copolymers were constituted of polyacrylamide backbone and different amount of hydrophobic polypropylene oxide) graft chains. Measurements of intrinsic viscosities have been performed by using a Contraves low-shear LS-40 rheometer. From these results, a dependence of the intrinsic viscosity of the polymer solution with the molecular weight was observed, where an increase of the latter resulted in higher intrinsic viscosity. In this case, the effect of the molecular weight was more emphasized than the effect caused by the slightly different degrees of hydrophobic incorporation. When enhancing the temperature, it was not verified a significant change on the reduced viscosities of the copolymer solutions and the graft chain length was also observed.     

Mechanical stability of high‐molecular‐weight polyacrylamides and an (acrylamido tert‐butyl sulfonic acid)–acrylamide copolymer used in enhanced oil recovery

High‐molecular‐weight partially hydrolyzed and sulfonated polyacrylamides are widely used in enhanced oil recovery (EOR). Nonionic polyacrylamide and polyacrylamide‐based microgels are also used in water shut‐off treatments for gas and oil wells. A comparative study of the mechanical degradation for three linear polyacrylamides and a microgel is presented. Mechanical degradation is quantified from the loss of the viscosity of the polymer solution as it passes through a stainless steel capillary with a length of 10 cm and an internal diameter of 125 µm. The critical shear rate above which degradation increases exponentially was found to depend on the chemical structure of the polymer, molecular weight, and electrolyte strength. The nonionic polyacrylamide shows higher degradation and lower critical shear rate compared with a sulfonated polyacrylamide with similar molecular weight. Moreover, the nonionic polyacrylamide with a higher molecular weight results in lower mechanical degradation. The higher mechanical stability of the sulfonated polymer is attributed to the higher rigidity of its molecules in solution. On the other hand, the ability of the high‐molecular‐weight polymers to form transient, flow‐induced microgels boost their mechanical stability. This ability increases with the increase in the molecular weight of the polymer. Indeed, the microgel solution used in this study demonstrates exceptional mechanical stability. In general, mechanical stability of linear polymers used in chemical enhanced oil recovery can be enhanced by tailoring a polymer that has large side groups similar to the sulfonated polyacrylamide. Also, polyacrylamide‐based microgels can be applied if high mechanical stability is required. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40921.     

Preparation of water‐soluble chitosan

An improved method of preparing water soluble chitosan was studied by N‐acetylation with acetic anhydride. Its merits were a simple processing technique, very short reaction time, little agent, high molecular weight of the product, and good water solubility. This article not only discusses the effect of several factors, such as the amount of reactants, concentration of hydrogen ions in the solution, and solvent system, on N‐acetylation but also some influential factors on the water solubility of N‐acetylated chitosan. Experiments showed that the amount of acetic anhydride was the most important factor affecting the N‐acetylation degree of the chitosan. The effect of the means of adding materials and the amount of solvent on the reaction could not be ignored. The solubility of half N‐acetylated chitosan was not changed with an increase in the molecular weight in water, and the water solubility decreased with increasing molecular weight in the alkaline region. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 3497–3503, 2004     

Grafting reaction of living polymer cations with amino groups on chitosan powder

The grafting of polymers having controlled molecular weight and narrow molecular weight distribution onto chitosan powder by the termination of living polymer cation with amino groups on chitosan powder was investigated in heterogeneous system. The amino groups of chitosan powder successfully reacted with living poly(isobutyl vinyl ether) [poly(IBVE)] and poly(2-methyl-2-oxazoline) [poly(MeOZO)] cation with controlled molecular weight and narrow molecular weight distribution to give the corresponding polymer-grafted chitosan powders. The percentage of poly(MeOZO) grafting gradually increased and reached 24.5% after 4 days. The solubility of poly(MeOZO)-grafted chitosan in water increased with an increase in the amount of grafted polymer. It was suggested that grafting reaction of living polymer cation with chitosan powder proceeds from surface amino groups to inner amino groups of the powder with progress of the reaction. The mole number of grafted polymer chain on chitosan powder decreased with an increase in the molecular weight of the living polymer cation because the steric hindrance of functional groups of chitosan powder increased with the increasing molecular weight of living polymer. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 1883–1889, 1998     

Effect of micro-aggregation behavior on the salt tolerance of polymer solutions

Polymer solution for oil displacement is mostly used in the middle and late stage of water flooding reservoir development, and reservoir groundwater conditions are often one of the main conditions restricting polymer application. Therefore, it is necessary to develop salt tolerance of polymer solutions with different aggregation behaviors, so as to facilitate the synthesis and optimization of suitable polymer systems. The differences in the micro-aggregation behavior of three polymers with different molecular structures were explored. On this basis, the effects of divalent metal cations on the properties of the polymer solutions were analyzed by assessing the micro-aggregation behavior, apparent viscosity, hydrodynamic size, and shear rheological characteristics. The results showed that the linear partially hydrolyzed polyacrylamide (HPAM) was seriously affected by divalent cations, and the viscosity decreased obviously. The aggregation behavior of the polymer changed by hydrophobic association can enhance the salt tolerance of the solution. The hydrophobically modified partially hydrolyzed polyacrylamide (HMPAM) with “chain beam” aggregation behavior has strong intermolecular connection, which enables it to withstand the content of calcium and magnesium ions of 1100 mg l⁻¹. When the content of calcium and magnesium ions exceeds 600 mg l⁻¹, dendritic hydrophobically associating polymer (DHAP) will destroy the interaction between molecular chains, resulting in the decrease of apparent viscosity and hydrodynamic size. For polymer flooding in high-salinity reservoir, salt tolerant polymer system can be constructed by optimizing molecular weight and hydrophobic group content.     

Preparation and performance study of functional polymer with self demulsifying

In polymer flooding, the residual polymer in the produced fluid can increase the stability of crude oil emulsion, thereby negatively affecting the demulsification process. Therefore, a polymer that has no effect on the stability of crude oil emulsion is required. Herein, a polymerizable monomer with a demulsification function (MD) was synthesized and then copolymerized with acrylamide, acrylic acid, and 2-acrylamide-2-methylpropane sulfonic acid to prepare a novel copolymer (self-demulsifying polymer, PDM). The dissolution time, solution viscosity, shear resistance, static adsorption on quartz sand, and the effect on the crude oil emulsion stability of PDM were compared with those of regular polyacrylamide (PAM). Experimental results showed that owing to the steric hindrance effect of MD, the molecular weight of PDM was lower than that of PAM. Both polymers exhibited satisfactory solubility, solution viscosity, shear resistance, and static adsorption, which can meet the requirements of polymer for use in oil displacement. However, in contrast to PAM, PDM had no negative effect on the crude oil emulsion stability. This study provides a new solution to the problem of increased crude oil emulsion stability in polymer flooding.     

Physico-Mechanical and Degradation Properties of Urea-Modified Chitosan Film Photocured with 1-Vinyl-2 Pyrrolidone

Chitosan and urea modified chitosan films were prepared by solution casting. To improve the physico-mechanical properties of the chitosan/urea films, four formulations were prepared using 1-vinyl-2-pyrrolidon (NVP) (varied from 10–80% by weight) in methanol along with photo-initiator. The films were soaked (1–4 minutes) in the prepared formulations and photo-cured under UV-light at different intensities (5–35 pass). The physico-mechanical properties, polymer loading, gel content, water uptake and simulating weathering test of the NVP grafted photocured chitosan/urea film were carried out. Degradation of the chitosan/urea film was also observed. The scanning electron micrographs of the photo-cured chitosan/urea film showed smooth surface, compact and homogeneous structure.