Change in the molecular weight distribution of poly(ethylene oxide) caused by the complexation with poly(acrylic acid)

The complexation between poly(ethylene oxide) (PEO) and poly(acrylic acid) (PAA) was made by using double the molar quantity of either polymer component at pH 2 where the resulting complex completely precipitates. After the removal of the precipitate, PEO or PAA remaining in the supernatant was subjected to gel permeation chromatography to investigate the change in the molecular weight distribution (MWD) caused by the complexation. No remarkable difference is observed in the MWD curves for PEO[1] (M_w=1.37 × 10⁴) before and after the complexation with PAA[1] (M_w=1.10 × 10³) and PAA[2] (M_w=4.16 × 10⁵). However, the MWD curves of PEO[2] (M_w=1.26 × 10⁵) and PAA[2] become shortened and shift to the low molecular weight side after the complexation with PAA[1] or [2] and PEO[2], respectively. This tendency is enhanced by increasing the complexation temperature. From these results, it is indicated that the complexation between PEO and PAA deals with an equilibrium reaction, and the equilibrium constant is dependent on the chain length of both polymer components and also on the complexation temperature.     

The intrinsic viscosity of poly(acrylic acid) and partially neutralized poly(acrylic acid) by isoionic dilution

The isoionic dilution method has been used to measure the intrinsic viscosity, [η], of a poly(acrylic acid) (PAA) sample as a function of neutralization degree, i, at low ionic strength, I = 1.0 × 10. The results obtained for the counterion activity are in close agreement with Manning's theory for counterion condensation. The influence of the ionic strength, I, on [η] and on the Huggins coefficient, k', was also examined and the exponents of the scaling laws relating these two parameters with I were found.     

Plasma‐induced graft polymerization of acrylic acid onto poly(ethylene terephthalate) films

The graft polymerization of acrylic acid was carried out onto poly(ethylene terephthalate) films that had been pretreated with argon plasma and subsequently exposed to oxygen to create peroxides. The influence of synthesis conditions, such as plasma treatment time, plasma power, monomer concentration, temperature, and the presence of Mohr's salt, on the degree of grafting was investigated. The observed initial increase in grafting with monomer concentration accelerated at about 20% monomer. The grafting reached a maximum at 40% monomer and subsequently decreased with further increases in monomer concentration. The reaction temperature had a pronounced effect on the degree of grafting. The initial rate of grafting increased with increasing temperature, but the degree of grafting showed a maximum at 50°C. The activation energy of the grafting obtained from an Arrhenius plot was 29.1 kJ/mol. The addition of Mohr's salt to the reaction medium not only led to a homopolymer‐free grafting reaction but also diminished the degree of grafting. The degree of grafting increased with increasing plasma power and plasma treatment time. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 2993–3001, 2001     

Characterization of acrylic acid grafted poly(ethylene terephthalate) fabric

The preirradiation grafting of acrylic acid (AA) onto poly(ethylene terephthalate) (PET) had been found to affect the thermal and physical characteristics of fabric. The grafted fabrics with various graft levels were characterized by thermal gravimetric analysis (TGA), ATR‐FTIR spectroscopy, contact angle, differential scanning calorimetry (DSC), X‐ray diffraction (XRD), atomic force microscopy (AFM), and scanning electron microscopy (SEM). The initial decomposition temperature and T₅₀ were increased with the increase in degree of grafting. The percentage crystallinity was decreased as the degree of grafting increases. The detailed elemental analysis was done by X‐ray photoelectron spectroscopy (XPS). The atomic ratio (O_1s/C_1s) was found to increase significantly with increasing the degree of grafting and reached 0.64 at 14.5% grafting from 0.38 for virgin PET. The surface topography and morphology was strongly influenced as the degree of grafting was increased. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Modification of polyester fibers by grafting with poly(acrylic acid)

The grafting of acrylic acid on PET using benzoyl peroxide has been investigated. The influence of the main parameters of grafting, the effect of additives on the degree of grafting, and the amount of homopolymer formed during the process have been determined. Futhermore, the values of apparent activation energy have been calculated. Also, the influence of the degree of grafting on the moisture sorption and swelling of modified fibers have been determined. By an additional treatment of the grafted fibers with antibiotics it is possible to provide the fibers with antibacterial properties. Liberation of antibiotics from fibers into solutions has been examined and mathematically described. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65:967–977, 1997     

Thermal behavior of poly(acrylic acid)–poly(vinyl pyrrolidone) and poly(acrylic acid)–metal–poly(vinyl pyrrolidone) complexes

Thermal analysis (TGA and DTA) of samples of PAA, PVP, PAA–PVP complexes, containing different weight fractions of PAA and ternary polymer–metal–polymer complexes, were studied. The activation energy parameters for the thermal degradation were also calculated. The study of the effect of FeCl₃, NiCl₂, and Ni(NO₃)₂ on the TGA and DTA curves of the complexes showed that the decompositions are dependent on the concentrations and the nature of the metal ions. The DTA traces of PAA–PVP complex containing FeCl₃, NiCl₂, and Ni(NO₃)₂ showed that the treatment of the complex with these metal ions causes considerable changes in the thermal decomposition of PAA–PVP complex. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 4049–4057, 2006     

Grafting of poly(acrylic acid) onto poly(amidoamine)-functionalized graphene oxide via surface-mediated reversible addition-fragmentation chain transfer polymerization

Graphene oxide was modified with third-generation poly(amidoamine) (PAMAM) to obtain dendrimer-grafted GO (DGO) with high content of functional groups. DGO's amine groups were conjugated with S-(thiobenzoyl)thioglycolic acid as proved by XPS and poly(acrylic acid) was grafted onto surface via RAFT polymerization (DGO@PAA). FT-IR results approved the synthesis of samples whereas TGA revealed 40.3% grafting of PAA. XRD patterns showed that with further modification, d-spacing increased. According to Raman spectra, modification resulted in more disordered structure whereas DGO@PAA showed a high value of I_D/I_G. Morphological studies were performed by SEM and TEM that showed a polymeric layer covered the surface of nanosheets.     

Thermal crosslinking of collagen immobilized on poly(acrylic acid) grafted poly(ethylene terephthalate) films

Graft polymerization of acrylic acid onto plasma‐treated poly(ethylene terephthalate) (PET) films was used to prepare surfaces suitable for collagen immobilization by dip‐coating. Such surfaces could be used as matrices for smooth muscle cell cultures in tissue engineering. Contact angle measurements showed that plasma‐treated and grafted PET films undergo considerable surface reorganization during storage under ambient conditions. However, after collagen immobilization the contact angle remained relatively stable. The amount of collagen initially attached to the film surface increased with increasing poly(acrylic acid) graft density, but subsequent washing in water led to significant collagen loss. This loss could nevertheless be substantially reduced by thermal crosslinking of the collagen in the range 110–130 °C. Atomic force microscopy (AFM) observations suggested that the washed crosslinked collagen has a very similar structure to that of the un‐crosslinked collagen. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1874–1880, 2002     

聚丙烯酸/丙烯酰胺高吸水性树脂吸附性能

用反相悬浮聚合法合成了聚丙烯酸/丙烯酰胺高吸水性树脂(PAAAM),讨论了其吸附CuCl₂、NiCl₂、CoCl₂溶液中金属离子的性能,考察了溶液pH值和初始浓度对金属离子吸附的影响。结果表明,PAAAM在不同pH值及浓度区间,对金属离子的吸附能力有较大差异,可被用于Cu(II)、Ni(II)、Co(II)的分离。同时还探讨了PAAAM在混合金属离子溶液中的吸附性能及反复利用的可能性,发现在混合溶液中PAAAM表现出对Cu（II）有较好的选择性吸附能力;4次循环后对Cu(II)、Ni(II)、Co(II) 离子的吸附量为最大吸附量的80%以上,重复使用效果理想。     

Ultra-fine polyelectrolyte fibers from electrospinning of poly(acrylic acid)

Ultra-fine polyelectrolyte fibers have been generated from electrospinning of poly(acrylic acid) in aqueous and DMF solutions. The fiber diameters ranged from 80 to 500 nm and increased with increasing solution concentrations and electrospinning voltages. The fibers generated from the aqueous solutions were more homogeneous in sizes, especially when NaCl or NaOH was added. Higher voltages in electrospinning of the aqueous solutions also resulted in fibers with larger heat capacity in the glass transition region, and higher dehydration temperatures. These polyelectrolyte fibers could be rendered water-insoluble by incorporating β-cyclodextrin (at 20 wt% of PAA) in the aqueous solution, then heat-induced crosslinking was performed at 140 °C for 20 min. The resulting hydrogel fibers showed strongly pH-responsive swelling behaviors.     

Spatial inhomogeneity in poly(acrylic acid) hydrogels

The crosslink density distribution in gels known as the spatial gel inhomogeneity has been investigated in poly(acrylic acid) (PAAc) gels with the static light scattering measurements. PAAc gels were prepared at a fixed chemical crosslink density but at various initial monomer concentrations. The gels were characterized by swelling and elasticity tests as well as by light scattering measurements. PAAc gels exhibit a maximum degree of spatial inhomogeneity at a critical monomer concentration . shifts toward higher concentrations as the gel swells beyond its dilution degree after preparation. Depending on the polymer concentration in gels, swelling reduces or enhances the extent of the spatial inhomogeneities. It was shown that the apparent degree of the spatial gel inhomogeneity is determined by the combination of three effects, namely the effects of the effective crosslink density, charge density and segment density. The relative magnitudes of these effects vary depending on the polymer concentration and lead to the appearance of a maximum degree of spatial inhomogeneity at a critical concentration.     

Absorption and desorption of chromium ions by poly(acrylic acid) gels

The ability of crosslinked poly(acrylic acid) gels to retain chromium species was studied as a function of pH. Chromium retention was found to increase with pH according to two mechanisms. In the low pH range where chromium species are soluble, retention occurs via ion‐binding in the whole volume of the gel. At higher pH where insoluble chromium hydroxide particles are formed, retention comes from an adsorption process at the surface of the gel. The desorption of chromium species under acidic conditions was also investigated and found to be very dependent on retention mechanism and aging time of the polymer–chromium complex. When retention occurs by ion‐binding, only partial desorption was achieved at very short aging time. In contrast, a very fast desorption was observed when retention occurs via adsorption at the surface of the polymer gel. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 455–466, 1999     

Characterization of polyelectrolyte effect in poly(acrylic acid) solutions

The viscometric behavior of poly(acrylic acid) solutions, as well as their ion transport properties, were monitored as a function of polymer concentration and the addition of KOH in nonisoionic conditions. Polyelectrolyte effect was studied and characterized by conductivimetry as well as viscometric properties at the infinite dilution limit. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 191–196, 2003     

聚(N-异丙基丙烯酰胺)/聚丙烯酸半互穿网络微凝胶的合成及表征

利用IPN技术合成了一种具有温度和pH双重敏感性的聚（N-异丙基丙烯酰胺）/聚丙烯酸半互穿网络微凝胶（PNIPAM/PAAc semi-IPN）。这种微凝胶在酸性条件下发生典型的体积相转变;而在弱碱性条件下,当温度低于聚（N-异丙基丙烯酰胺）（PNIPAM）微凝胶的体积相转变温度（VPTT）时,微凝胶的粒径随着温度的上升而增大,当温度达到VPTT后,粒径突然急剧减小,并随着温度的逐渐上升而减小,最终趋向平衡。     

Cross-Linked Poly(acrylic acid) Microgels from Precipitation Polymerization

Cross-linked poly(acrylic acid) microgels were prepared via thermally initiated free-radical precipitation polymerization in a binary organic solvent. N,N′-Methylenebisacrylamide (MBA) and 2,2′-azobisisobutyronitrile were used as cross-linker and initiator, respectively. The effect of (MAB) concentration on different features of sample (i.e., spectral characteristics, glass transition temperature, equilibrium swelling, gel content and rheological properties) was investigated. The Flory-Rehner equation and rubber elasticity theory were used to discuss the network structure of polymer. Apparent and rotational viscosities were used to determine the optimal cross-linker concentration. The sample maximum with value of viscosity was obtained using 1.6 mmol/L of the cross-linker. In addition the m and n parameter of Ostwald equation were investigated as well.     

聚乳酸的直接缩聚法研究

采用分子筛除水的方法进行了乳酸的直接缩聚,利用FT-IR研究了分子筛的除水效果。结果表明:分子筛具有良好的除水效果;催化剂的种类、用量及聚合条件对所得聚乳酸的分子量有较大影响;当以SnOct2+TSA为催化剂,聚合工艺为170℃/12 h,真空度为8 kPa时,所得聚乳酸的分子量可达7 600左右。     

Effect of poly(acrylic acid) end‐group functionality on inhibition of calcium oxalate crystal growth

A number of series of poly(acrylic acids) (PAA) of differing end‐groups and molecular weights prepared using atom transfer radical polymerization were used as inhibitors for the crystallization of calcium oxalate at 23 and 80°C. As measured by turbidimetry and conductivity and as expected from previous reports, all PAA series were most effective for inhibition of crystallization at molecular weights of 1500–4000. However, the extent of inhibition was in general strongly dependent on the hydrophobicity and molecular weight of the end‐group. These results may be explicable in terms of adsorption/desorption of PAA to growth sites on crystallites. The overall effectiveness of the series didn't follow a simple trend with end‐group hydrophobicity, suggesting self‐assembly behavior or a balance between adsorption and desorption rates to crystallite surfaces may be critical in the mechanism of inhibition of calcium oxalate crystallization. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Tailored hydrolytically stable polyacid gels based on curable poly(acrylic acid)s and bisacrylamides

Poly(acrylic acid)s (PAAs) with curable methacrylamide moieties as well as bisacrylamide crosslinkers are described as components for well‐defined hydrogels with increased hydrolytic resistance. PAAs with tethered curing moieties of different alkyl spacer lengths (?(CH₂)_n?, n = 2, 3, 6 or 8) were prepared via copolymerization of one‐sided methacrylated diamines with protected acrylic acid, followed by polymer‐analogous methacrylation and deprotection. Bisacrylamide crosslinkers were synthesized by acrylation of diamines with different cores and N‐substitutes like allyl, cyclopropyl or propyl groups. Both components were subsequently combined for the formation of novel amide based hydrogels. Network densities of the obtained gels were elucidated by rheokinetic investigations. © 2016 Society of Chemical Industry     

丙烯酸(酯)改性聚醋酸乙烯酯乳液的研制

采用半连续种子乳液聚合法,使用丙烯酸(AA)功能性单体和丙烯酸丁酯(BA)软单体对醋酸乙烯酯(VAc)进行了共聚改性,制备出高固含量(50.2%)的聚醋酸乙烯酯(PVAc)改性乳液。该乳液适合用于喷雾干燥法制备可再分散聚合物粉末,并且其耐水性和耐碱性等都得到了明显地改善。对影响共聚物的诸多因素进行了较为全面地考察,得出最佳的工艺条件为:AA用量为主单体质量的3%～4%,BA用量为主单体质量的5%～10%,保护胶体用量为混合单体质量的7.5%～15%,引发剂用量为混合单体质量的0.4%～0.5%,阴/非离子型复合乳化剂的质量比为1∶2～1∶3、用量为混合单体质量的2%～3%,分散剂、消泡剂和酸碱缓冲剂等助剂均为适量,加料时间为3～4h,反应温度为70～75℃。     

表面紫外光接枝聚丙烯酸的聚电解质刷型纳米纤维素晶须

为了研究快速地制备改性纳米纤维素的方法,将低相对分子质量(简称分子量,下同)聚丙烯酸(PAA)以紫外光引发聚合的方法接枝到纳米纤维素晶须上,制备出聚电解质刷型纳米纤维素晶须。采用红外光谱、固体核磁、透射电镜、X射线衍射、热重分析等对刷型纳米纤维素晶须进行了表征测试。考察了单体浓度、光引发剂用量、紫外光照射时间等对接枝聚合反应的影响。结果表明,PAA与纳米纤维素晶须的质量比大于1∶1,光引发剂用量为纳米纤维素晶须质量的0.8%~1.0%,反应时间为90 s时,所得接枝产物中羧基含量最高,达到0.012 75 mol/g。紫外光接枝减少了制备改性纳米纤维素的步骤和时间,将扩展纳米纤维素的表面改性方法和用途。