Poly(N-isopropylacrylamide). I. Interactions with sodium dodecyl sulfate measured by conductivity

Conductometric titration of poly(N-isopropylacrylamide) (polyNIPAM) with sodium dodecyl sulfate (SDS) gave two apparent transitions labeled C1 and C2. The C1 transition was independent of polyNIPAM concentration in the 0.05–0.3 wt % range, whereas C2 was proportional to the polymer concentration. C1 corresponded to the onset of binding of surfactant with polymer. Arguments based on a simple mass action model for micellization are presented to show that C2, the second transition, is not due to any simple explanation such as being the point above which only free micelles are formed with surfactant addition. The cloud point of polyNIPAM increased with the amount of bound surfactant. This was attributed to electrostatic contribution of bound sulfate groups to the increased solubility of polyNIPAM. © 1993 John Wiley & Sons, Inc.     

交联聚(N-异丙基丙烯酰胺)/(海藻酸钠/聚(N-异丙基丙烯酰胺))半互穿网络水凝胶的制备及其溶胀性能

将线性聚(N-异丙基丙烯酰胺)(PNIPAAm)和海藻酸钠(SA)分子同时引入到PNIPAAm凝胶中,制备了交联聚(N-异丙基丙烯酰胺)/(海藻酸钠/聚(N-异丙基丙烯酰胺))半互穿网络(Cr-PNIPAAm/(SA/PNIPAAm)semi-IPN)水凝胶。在弱碱性条件下(pH=7.4),改变SA与线性PNIPAAm的质量比对Cr-PNIPAAm/(SA/PNIPAAm)semi-IPN水凝胶的溶胀度没有太大的影响。在酸性条件下(pH=1.0),其溶胀度随着SA与线性PNIPAAm质量比的减小而增大。由于亲水性SA与线性PNIPAAm的协同作用,Cr-PNIPAAm/(SA/PNIPAAm)semi-IPN水凝胶的消溶胀速率得到很大提高。     

Effects of Surfactants on Phase Transition of Poly(N-isopropylacrylamide) and Poly(N-isopropylacrylamide-co-dimethylaminoethylmethacrylate)

The effect of surfactants on the phase transition of poly(N-isopropylacrylamide) (PNIPAM) and poly(N-isopropylacrylamide-co-dimethylaminoethylmethacrylate) (P(NIPAM-co-DMAEMA)) was extensively investigated by a turbidometry. When the concentration of cetyltrimethyl ammoniumchloride (CTAC) increased from 0.01 to 0.32%, the cloud point of PNIPAM increased from 32 to 38.5°C. When the concentration of sodium dodecyl sulfate (SDS) increased from 0.01 to 0.08%, the cloud point increased from 32.5 to 38°C. The cloud points with SDS were higher than the values obtained with CTAC. In addition, SDS suppressed the temperature sensitivity much more effectively than CTAC did. The adsorption of the ionic surfactants (CTAC, SDS) on the polymer chains may account for the increase in the cloud point. On the other hand, Tween 20 had little effect on the cloud point and the temperature sensitivity of the homopolymer, possible because it is nonionic. The effect of surfactants on the phase transition of P(NIPAM-co-DMAEMA) exhibited a trend similar to the effect on the phase transition of PNIPAM.     

聚N-异丙基丙烯酰胺接枝聚苯乙烯高分子刷的构象

当长链高分子高密度接枝到一个表面上时,由于分子链间的相互作用使得接枝的高分子链扩张而形成伸直链的构象,这种形态被称为高分子刷.     

聚(N-异丙基丙烯酰胺)类材料的应用

聚(N-异丙基丙烯酰胺)(PNIPAAm)及其共聚物,在水溶液中表现出最低临界溶液温度(LCST),在LCST附近会发生可逆相转变。利用这种特性,可将热敏性高分子材料应用于生物医学工程、免疫分析、催化、分离提纯等领域。主要综述了热敏性PNIPAAm类高分子材料,在这些领域中的应用情况。     

Effect of Topology on the Properties of Poly(N-isopropylacrylamide) in Water and in Bulk

Three macrocyclic poly(N-isopropylacrylamide)s (PNIPAM) with molecular weight (MW) ranging from 6 to 19 kg/mol were synthesized by ‘click’ ring closure of the corresponding α-azido ω-propargyl telechelic linear PNIPAMs, themselves prepared by reversible addition fragmentation chain transfer (RAFT) polymerization of N-isopropylacrylamide. Differential scanning calorimetry (DSC) studies revealed that both the thermal phase separation in water and the glass transition in bulk of PNIPAM were affected by polymer topology. In aqueous solution, the cyclic polymers exhibit a higher phase separation temperature and broader phase transition range than the corresponding linear counterparts. In bulk, the cyclic polymers display a higher glass transition temperature of lesser molecular weight dependence, as compared to their linear precursors.     

CMC/PNIPAAm半互穿网络水凝胶的溶胀动力学研究

以羧甲基纤维素钠(CMC)和N-异丙基丙烯酰胺(NIPAAm)为原料,制备了具有温度和pH敏感性的半互穿网络(CMC／PNIPAAmsemi-IPN)水凝胶,并研究了水凝胶在不同温度和pH值条件下的溶胀行为。结果表明：在弱碱性(pH-7．4)条件下,凝胶的溶胀速率和溶胀度都随着凝胶中CMC含量的增加而增大;而在酸性(pH-1．O)条件下则相反。在弱碱性条件下,水分子在凝胶中的扩散行为都可用non-Fickian扩散来描述,水分子在凝胶中的扩散系数D随着凝胶溶胀速率的增大而增大;在酸性条件下,20℃时凝胶的溶胀过程符合non-Fickian扩散规律,而37℃时凝胶的溶胀过程符合Fickian扩散规律,但水分子的扩散系数D相差不大。     

Effect of sodium dodecyl sulfate on the reactivity of copper(II) complexes with 2-dimethylaminomethylphenol

The effects of the anionic surfactant sodium dodecyl sulfate on complex formation of 2-dimethylaminomethylphenol (1) with copper(u) in aqueous solutions and on the kinetics of the reactions of copper(n) complexes of 1 with 4-nitrophenylbis(chloromethyl)phosphinate (2) were studied. The reactivities of the complexes in these reactions are higher than that of 1 at all concentrations of SDS studied (0.010–0.200 mol L^–1 with pH 7–9.Translated from Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 361–365, February, 1996.     

Application of poly(N-isopropylacrylamide) with pendent β-cyclodextrin to separation of a guest substance in an aqueous solution

Poly(N-isopropylacrylamide) with pendent β-cyclodextrin (PNI-PAAm-CD) was prepared by copolymerization of acryloyl-β-CD and NIPAAm. During the temperature-induced phase separation of an aqueous solution of PNIPAAm-CD, Toluidine Blue dye in the solution was separated into the precipitate of PNIPAAm-CD by way of inclusion complex formation.     

Mn~(2 )对聚N鄄异丙基丙烯酰胺的性能影响

合成了聚N鄄异丙基丙烯酰胺(PNIPAM)与Mn2 的配合物,并用荧光光谱、UV鄄Vis、FTIR、XPS进行了初步表征。说明Mn2 与PNIPAM侧链羰基氧或亚氨基氮原子发生了配位作用。由于Mn2 的发射光谱与PNIPAM激发光谱部分重叠以及Mn2 位于561nm的发射峰在Mn2 鄄PNIPAM体系发射光谱中消失,说明发生了较好的F觟rster能量传递。因此,在307nm紫外区荧光强度比PNIPAM增强了314%,使该配合物表现出较好的抑菌效果,而此时少量Mn2 对其低临界溶解温度(LCST)影响不大。     

Temperature-pH Sensitive IPN Hydrogels Composed of Silk Sericin and Poly （N-isopropylacrylamide）

In recent years IPN hydrogels have been attracted attentions as biomedical materials1-3. Among which poly(N-isopropylacrylamide) (PNIPAAm) was frequently used to impart temperature responsive function4, 5. Many of the second components were introduced for…     

Synthesis and Characterization of Poly(N-isopropylacrylamide) and Poly(vinyl acetate) Diblock Copolymers via MADIX Process

The synthesis of diblock copolymers of poly(N-isopropylacrylamide) (PNIPAM) and poly(vinyl acetate) (PVAc) was performed by macromolecular design via interchange of xanthates (MADIX) process. Following the preparation of methyl (isopropoxycarbonothioyl) sulfanyl acetate (MIPCTSA) as chain transfer agent, it was reacted with vinyl acetate to obtain PVAc macro-chain transfer agent. Then, block copolymerization was completed by successive addition of N-isopropylacrylamide (NIPAM). ¹H NMR spectroscopy confirmed the presence of both blocks in the copolymer structure, with the expected composition based on the feed ratio. Size Exclusion Chromatography (SEC) was used to investigate the relative values of molecular characteristics. Only 20% of PVAc was converted to block copolymer. The resultant block copolymer structures were further examined in terms of their morphologies as well as critical micelle concentration (CMC) by using ESEM and Fluorescence Excitation Spectroscopic techniques, respectively. Morphological characterization confirmed amphiphilic block copolymer formation with the existence of mainly ca. 100 nm well distributed micelles. The thermo responsive amphiphilic behavior of the block copolymer solutions were followed by Dynamic Light Scattering (DLS) technique.     

The interaction between poly(N-isopropylacrylamide) and salts in aqueous media: The “salting-out” phenomenon as studied by attenuated total reflection/fourier transform infrared spectroscopy

The effect of two strong salting-out salts (Na₂SO₄ and K₂SO₄) on the temperature-induced phase-separation process in aqueous solutions of poly(N-isopropylacrylamide) (PNIPA) was examined by attenuated total reflectance/Fourier transform infrared spectroscopy, differential scanning calorimetry, and viscosity measurements. On the basis of these measurements, a detailed scenario of the phase-separation process was deduced. The phase-separation scenario of solutions containing PNIPA and water was altered in the presence of sulfate ions. Here, the sulfate ions induced partial intrachain collapse, manifested by a relatively compact structure well below the lower critical solution temperature. This led to a more gradual, smooth phase transition, with temperature-resolved intrachain collapse and interchain aggregation and a lesser extent of hysteresis. Although at the macrolevel one may not be able to differentiate among various scenarios altering the solvent into a poor solvent, the aforementioned microlevel measurements provided a way to expose the difference between raising the temperature and adding cosolutes. Follow-up studies on the effect of salting-in salts will be presented. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 33–46, 2004     

聚丙烯酰胺/聚异丙基丙烯酰胺互穿网络水凝胶的制备与性能

采用分步法用电子加速器辐射合成了聚丙烯酰胺(PAAm)/聚异丙基丙烯酰胺(PNIPAAm)互穿网络水凝胶,并考察了温度、pH值、离子强度对其溶胀性能的影响.研究表明:互穿水凝胶具有温度敏感性,且其体积相变与互穿网络中PAAm和PNIPAAm含量有关,随着网络中PAAm含量的增加水凝胶的体积相变趋于平缓,可以通过改变PAAm和PNIPAAm的组成比来控制水凝胶的体积相变行为.此外,互穿水凝胶还具有pH敏感性和一定的抗盐性.     

海藻酸钠与N-异丙基丙烯酰胺接枝共聚及其温度、pH敏感特性研究

采用单铈盐引发体系制备海藻酸钠／聚N-异丙基丙烯酰胺接枝共聚物(SA-g-PNIPAAM),考察了引发剂浓度、反应温度、反应时间、单体浓度对接枝率的影响,并利用FTIR、DSC对SA-g—PNIPAAM进行了表征;结果表明,单铈盐引发体系可制备接枝率高的SA-g—PNIPAAM,具有温度、pH敏感特性的SA-g—PNIPAAM可望用于新型温敏／肠溶生物功能材料。     

The Effect of Number of Arms on the Aggregation Behavior of Thermoresponsive Poly(N-isopropylacrylamide) Star Polymers

The thermoresponsive nature of aqueous solutions of poly(N-isopropylacrylamide) (PNIPAAM) star polymers containing 2, 3, 4, and 6 arms has been investigated by turbidity, dynamic light scattering, rheology, and rheo-SALS. Simulations of the thermosensitive nature of the single star polymers have also been conducted. Some of the samples form aggregates even at temperatures significantly below the lower critical solution temperature (LCST) of PNIPAAM. Increasing concentration and number of arms promotes associations at low temperatures. When the temperature is raised, there is a competition between size increase due to enhanced aggregation and a size reduction caused by contraction. Monte Carlo simulations show that the single stars contract with increasing temperature, and that this contraction is more pronounced when the number of arms is increased. Some samples exhibit a minimum in the turbidity data after the initial increase at the cloud point. The combined rheology and rheo-SALS data suggest that this is due to a fragmentation of the aggregates followed by re-aggregation at even higher temperatures. Although the 6-arm star polymer aggregates more than the other stars at low temperatures, the more compact structure renders it less prone to aggregation at temperatures above the cloud point.     

Synthesis and Characterization of Thermo-responsive Poly(N-vinyl-2-pyrrolidinone)-block-poly(N-isopropylacrylamide) Micelles

A novel thermo-responsive diblock copolymer of poly(N-vinyl-2-pyrrolidinone)-block-poly(N-isopropylacrylamide) (PNVP-b-PNIPAM) was synthesized. FT-IR, ¹H-NMR and SEC results confirmed the successful synthesis of PNVP-b-PNIPAM diblock copolymer via anionic polymerization. The polymeric micelles formed from PNVP-b-PNIPAM copolymer in aqueous solution were developed and characterized as a potential thermo-responsive and biocompatible drug delivery system. Micellization of the diblock copolymer in aqueous solution was characterized by dynamic laser scattering (DLS), turbidity measurement, tension measurement and transmission electron microscopy (TEM). The thermo-responsive polymeric micelles with the size ranges of 200 to 260 nm and thickness of 30 nm are localized, selected and targeted for drug release, having a great potential in response to external-stimulus such as temperatures from 35 to 39°C. The critical micellization concentration (cmc) of PNVP-b-PNIPAM in aqueous solution is 0.0026 wt% determined by turbidity measurement. The size of micelles determined by DLS increased from 163 to 329 nm with increasing concentration of PNVP-b-PNIPAM from 0.25 to 0.5 wt% in aqueous solution at 40°C, which is determined by DLS.     

Thermoreversible gelation on cooling and on heating of an aqueous gelatin–poly(N-isopropylacrylamide) conjugate

A polymer conjugate composed of 43 wt% gelatin and 57 wt% poly(N-isopropylacrylamide) (PNIPAAm) was prepared. The dynamic viscoelastic properties of an aqueous solution of the conjugate at the concentration of 5 wt% were examined. The solution was viscous fluid at 30°C and turned into an elastic homogeneous hydrogel upon heating above 34°C or upon cooling below 10°C. The resultant hydrogels turned back into a solution at the opposite temperature cycles of the gelation. It is considered that the driving force of the gelation is the intermolecular hydrophobic interaction of PNIPAAm blocks or the intermolecular helix association of gelatin blocks, respectively, on heating or on cooling. © 1998 John Wiley & Sons, Ltd.     

Thermo and pH Dual-Responsive Micelles of N-phthaloylchitosan-g-Poly(N-isopropylacrylamide) and Poly(acrylic acid-co-tert-butyl acrylate) for Drug Delivery

A novel amphiphilic copolymer N-phthaloylchitosan graft poly(N-isopropylacrylamide) and poly(acrylic acid-co-tert-butyl acrylate) (PHCS-g-PNIPAAm&P(AA-co-tBA)) was synthesized. The graft copolymer could form micelles in aqueous medium, and the critical micelle concentration (CMC) of the copolymer was 7.5 × 10^{? 3}mg/mL. The lower critical solution temperature (LCST) of the micelles was measured to be 30°C. Transmission electron microscopy (TEM) image showed that the micelles exhibited a regular spherical shape, and the mean diameter of the micelles was 94.1 ± 0.8 nm as determined by dynamic light scattering (DLS). The potential usefulness of the micelles as drug delivery systems was investigated using anti-inflammation drug prednisone acetate as the model. The drug loading capacity of the micelles was measured to be 22.86 wt%, and the DLS results showed that the mean diameter of the drug-loaded micelles was 133.3 ± 2.4 nm. In vitro drug release studies indicated that the micelles exhibited thermo and pH dual-responsive release profiles.     

Ultrasonic degradation of solutions of poly(vinyl acetate) in dioxan: The effects of the temperature and polymer concentration

The ultrasonic degradation of poly(vinyl acetate) (PVAc) solutions was carried out in dioxan at 25, 30, 35, 40, and 45 °C to investigate the effects of the temperature and solution concentration on the rate of degradation. The kinetics of degradation were studied by viscometry. The calculated rate constants indicated that the degradation rate of the PVAc solutions decreased as the temperature and solution concentration increased. The calculated rate constants were correlated in terms of the concentration, temperature, vapor pressure of dioxan, and relative viscosity of the PVAc solutions. This degradation behavior was interpreted in terms of the vapor pressure of dioxan, the viscosity, and the concentration of the polymer solutions. With increasing temperature, the vapor pressure of the solvent increased, and so the vapor entered the cavitation bubbles during their growth. This caused a reduction in collapsing shock because of a cushioning effect; therefore, the rate of degradation decreased. As the solution concentration increased, the viscosity increased and caused a reduction in the cavitation efficiency, and so the rate of degradation decreased. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 445–451, 2004