NIPAM共聚物多孔水凝胶的光引发RAFT合成及其溶胀性能

采用光引发可逆加成-断裂链转移(RAFT)方法,在室温下先合成了链端含有三硫代碳酸酯基的大分子链转移剂聚(N,N'-二甲基丙烯酰胺)(PDMAM),然后与N-异丙基丙烯酰胺(NIPAM)、N,N'-二甲基双丙烯酰胺(BIS)交联共聚合,并通过聚乙二醇的制孔作用制得PNIPAM-g-PDMAM梳型/多孔水凝胶.采用FTI...     

Preparation de membranes mosaiques par greffage radiochimique dans des films de polytetrafluoroethylene

Mosaic membranes were prepared by two successive grafting steps of acrylic acid and 4-vinyl-pyridine into well localized domains of polytetrafluoroethylene films. The films were subjected to X-rays through a grid-shaped shield which activated linear zones of the film 0.5 mm wide, separated by 0.5 mm of unactivated film. The films were then grafted with acrylic acid, neutralized and subjected to a second irradiation through a shield which protected the grafted zones. 4-Vinylpyridine was then grafted into the stripes left unchanged after the first treatment. The following properties of the resulting mosaic membranes were examined: swelling in water, electric conductivity and ion-pair diffusion. The coefficients of ion-pair diffusion were found to be 100–1000 times higher for the mosaic membranes than for carboxylic membranes of the same grafting ratio.     

Preparation de membranes hydrophiles obtenues par le greffage de la n-vinylpyrrolidone dans le poly(chlorure de vinyle)

PVC films were radiation-grafted in NVP-methanol solutions. Unusual kinetics relations were observed: an increase in monomer concentration or in temperature decreased the reaction rate. These effects are attributed to a higher mobility of the growing chains leading to faster chain termination and resulting in a drop of the overall rate and shortening of grafted chains. The graft copolymers swell homogeneously in water and in methanol. The swelling rate and limiting swelling ratio increase linearly with the grafting ratio. The swelling ratio was found to depend on chain length, being higher for short chains. An irreversible increase of the swelling ratio was found by raising the temperature. These unusual swelling properties of the grafted films are attributed to strong interactions between pyrrolidone groups and the Cl atoms of the PVC.     

Relations entre la structure et les proprietes des membranes de polytetrafluoroethylene greffe—III. Membranes non-ionisables contenant de la poly-n-vinylpyrrolidone

Equilibrium properties (swelling) and transport phenomena (dialysis) of non-ionizable membranes, obtained by radiation grafting of N-vinylpyrrolidone onto thin PTFE films, were studied. Grafting was conducted by the direct method with monomer solutions in benzene. The overall activation energy of grafting determined between 20 and 50° is high (12.5 kcal mol^?1): the reaction is controlled by the monomer diffusion into PTFE film. The length of grafted chains increases with temperature.The molality of the membranes decreases when the temperature of grafting increases; for a given grafting ratio, the swelling is higher for membranes containing a small number of long grafts than for membranes with numerous short branches. The transfer of both ions and water is a function of the free volume in the films, it depends on the grafting ratio and is not influenced by the preparation conditions.     

Development of reinforced hydrogels — I. Radiation induced graft copolymerization of methylmethacrylate on non-woven polypropylene fabric

Polypropylene (PP) fibers were grafted with methylmethacrylate. Effects of direct and pre-irradiation method and monomer concentration on the degree of grafting were investigated. The grafted PP fibers were characterized by swelling measurements, IR spectroscopy and by its mechanical and thermal properties. It was found that the direct method was more efficient than the indirect or pre-irradiation method and the monomer concentration for highest degree of grafting was 40% of MMA. Mechanical properties (tensile strength) and thermal stability decrease with grafting yield. Those changes were related to degradation of tie molecules between crystals and formation of rigid branches of PMMA on PP amorphous phase.     

Caracterisation de la texture de films de PVA alcoyle. Par diffusion de la lumiere aux petits angles

Small-angle light scattering studies have been made on films prepared from polyvinylalcohol with octadecylic paraffinic chains grafted on the backbone in a sequential manner. The texture of these films is spherulitic and comparable to that observed in a semi-crystalline polymer. In the dry state, this very stable texture remains imperfect ever after various thermal treatments. The stability and imperfection are probably due to two causes: firstly, crystallizable units are grafted on to the backbone and consequently have a reduced mobility. Secondly, the presence of sequences of ungrafted PVA limits the spherulitic growth. In the presence of water, a tangential dilation of the spherulites is observed, without variation of the mean dimension. The presence of water facilitates the disorganization of the texture as soon as the temperature exceeds the melting point of the paraffins.     

Preparation and Characterization of Temperature-responsive Porous Monoliths

A new temperature‐responsive porous monolith has been prepared by surface‐initiated activators generated by electron transfer atom transfer radical polymerization (AGET ATRP) grafting poly(N‐isopropylacrylamide) (PNIPAAm) within the pores of the porous polymer monolith. The grafting copolymerization was carried out by a method based on a continuous flow‐through technique without special deoxygenation procedure needed in the general ATRP. The addition of ascorbic acid could counteract the oxidation effect of oxygen diffusing into the reaction system. The resulting grafted monolith was characterized by a mercury intrusion method and the size of macropore was 3.65 µm, which was suitable for flow through the monolith for HPLC. The thermally responsive property of the grafted monolith was evaluated by HPLC using steroids with various hydrophobicities as probes. Through determination of retention factor of each steroid on the grafted monolith at different temperatures using water as mobile phase, it was found that the slope of the plot of retention factor of each steroid versus the temperature changed around the low critical solution temperature (LCST, 32°C) of PNIPAAm in water. It was relative to the grafted PNIPAAm temperature sensitivity that a hydrophobic and hydrophilic alternation would take place around its LCST. Based on this thermally responsive property, the grafted monolith was used as stationary phase for HPLC and to separate the steroids using water as mobile phase by changing the column temperature. As a mobile phase, water is much better than organic solvents concerning the environment.     

多孔β-磷酸三钙/壳聚糖/聚乙烯醇复合水凝胶的制备与性能

以NaCl为致孔剂,采用溶盐致孔法制备了多孔β-磷酸三钙/壳聚糖/聚乙烯醇（β-TCP/CS/PVA）复合水凝胶材料。 通过对比其含水率、溶胀比、拉伸强度、X射线衍射谱图、SEM和热重分析曲线,探讨了在相同环境下壳聚糖与β-磷酸三钙（β-TCP）的不同用量对聚乙烯醇(PVA)的结晶度以及对材料性能的影响。 此复合材料含水率为70%~76%。 当壳聚糖与β-TCP的质量比为2∶8时,复合材料的拉伸强度为0.56 MPa,断裂伸长率达到370%,其较好的力学性能,足以承受正常人眼压,可用作人工角膜周边支架材料。     

Membranes permselectives obtenues par greffage radiochimique des acides acrylique et methacrylique sur des films de poly(chlorure de vinyle)

Membranes were prepared by subjecting to gamma-rays PVC films swollen in a mixture of acrylic acid and methylene chloride. The kinetics of the reaction were investigated as a function of monomer concentration, temperature and dose-rate. The swelling properties of the resulting membranes were studied as well as those of PVC films grafted with methacrylic acid. It was found that PVC films grafted with methacrylic acid only swell slightly in water even for high grafting ratios and the swelling is very slow. At elevated temperatures the films swell more quickly and reach a higher limiting swelling, but the effect is small. PVC films grafted with acrylic acid swell much more quickly and reach much higher swelling ratios. The extent of swelling markedly increases with temperature but this effect is not reversible: once the membranes have reached a high swelling ratio at elevated temperatures, they keep the same ratio when dipped in water at 20°. The Arrhenius plot of the swelling ratio exhibits a break at 50–60° apparently corresponding to a glass transition temperature. In methanol the swelling is significantly higher for PVC films grafted with methacrylic than with acrylic acid. Swelling of the membranes was also investigated in mixtures of water with methanol and methanol with methylene chloride. The results are interpreted by assuming a strong dipole-dipole interaction between the grafted branches and the trunk polymer resulting in a quasimolecular dispersion of the carboxylic chains in the PVC matrix. The latter acts as a barrier against the penetration of water. Heat treatment favours a segregation of the two polymeric species into microphases and this non-reversible transformation is assumed to be responsible for the unexpected behaviour of PVC films grafted with acrylic acid. The significant differences between the properties of PVC films grafted with either acrylic or methacrylic acid are attributed to the much higher hydrophobic character of the methacrylic chains.     

Etude cristallographique de membranes obtenues a partir d'alcools polyvinyliques alcoyles

Low and wide angle X-ray diffraction was used to study the structure of paraffin grafted polyvinylalcohol membranes as a function of water content. The structure was found to be lamellar resulting in the pile-up of crystalline paraffin double layers, covered with polymer chains. Such an organization would be impossible if grafting of paraffin chains upon polyvinylalcohol were random. The membranes must be considered as two phase systems, consisting of amorphous and crystalline regions.     

Polymer modified colloidal dispersions

The effect of added polyvinyl alcohol (PVA) and polyvinyl pyrrolidone (PVP) on a dispersion of polystyrene particles stabilised with grafted methoxy PEG chains is discussed. PVA adsorbed more strongly on the particles compared to PVP. Polymer addition led to stable mixtures in the case of PVA compared to depletion phase separation observed in the case of PVP. Rheological measurements showed thickening of the dispersion and absence of any structure in the case of PVA, in contrast to structure formation in the case of PVP due to depletion phase separation. A weak gel state was reached for ca. 7% w/w PVP. The observed behaviour is in accord with the relative propensity of PVA and PVP to interact with the particle surface, the grafted chains and their solubility in water. The solvency of the free polymer chains dominated the overall behaviour while the contribution from the incompatibility between free and grafted chains was conterbalanced by differences in the free polymer adsorption on the particles.     

Changes in row structure of extruded polyethylene film in grafting with styrene. II. Copolymer morphology

The morphology of extruded high-density polyethylene film grafted with styrene was studied by transmission electron microscopy of thin stained sections. Near the film surface grafted polystyrene was confined to amorphous layers between lamellar crystals of polyethylene. In the film interior separate polystyrene domains were also formed and became predominant in grafting in diluted styrene. The deciding factor for the location of grafted polystyrene is the chain length because only long chains can coalesce in large separate zones. The polystyrene zones expand by cracking the stacks of lamellae along the lamellar normals. Straightening of the twisted crystalline lamellae of polyethylene occurred in grafting. “Bubbles” of styrene homopolymer were formed under conditions of high monomer concentration. The effect of staining the graft by the Kanig method² was also discussed.     

Effect of swelling on radiation-induced grafting of styrene to polyethylene

The radiation-induced grafting of low-density polyethylene in contact with styrene solution was studied. The effect of the degree of swelling of the polymer on the rate of grafting was investigated by diluting the styrene with methanol and with n-octane. For styrene-methanol solution, the rate of grafting was found to increase with degree of swelling, passing through a maximum when the sorbed solvent reaches 6.2 wt-% (70 vol-% methanol in the outside solution) and decreasing therafter. The methanol fraction of the sorbed liquid is far too small to cause precipitation of the grafted chains and inhibition of their termination rate. The dilution of styrene by octane has no effect on the swelling of polyethylene, but it decreases the grafting rate over the entire concentration range. The results are explained in terms of the concentration of sorbed monomer and the viscosity of the amorphous region of the polyethylene swollen by nonpolar liquids. Supporting evidence for the mechanism is presented in the form of grafting kinetic data as a function of dose rate (2.8 × 10²?9.5 × 10⁴ rad/hr), and post-irradiation grafting measurements for polyethylene in methanol-styrene (70/30, v/v). The data indicate that at the maximum grafting rate an optimum is achieved between a high concentration of sorbed monomer and a low viscosity for the poorly swelled polymer matrix.     

Synthesis and Characterization of Chitosan‐graft‐Poly(3‐(trimethoxysilyl)propyl methacrylate) Initiated by Ceric (IV) Ion

The grafting of 3‐(trimethoxysilyl)propyl methacrylate (TMSPM) onto chitosan by ceric ion initiation was studied under homogeneous conditions in 2% acetic acid solution. The grafted polymer was characterized by FT‐IR, ¹H‐NMR, TGA and XRD and swelling studies. TGA results showed that the incorporation of TMSPM to the chitosan chains decreased the thermal stability of the grafted chitosan. Due to the grafting of TMSPM, the crystallinity of chitosan derivatives was found to be destroyed. The solubility of the grafted chitosan in water was improved. The effects of reaction conditions such as initiator concentration, monomer concentration, reaction temperature and reaction time were studied by determining the grafting parameters such as grafting and grafting efficiency. Under optimum conditions, the grafting parameters were achieved as 1440 and 97%, respectively.     

Peculiar swelling properties of PVC films grafted with acrylic and methacrylic acids

It was found that PVC films grafted with methacrylic acid do not swell in either water or methanol, two solvents of poly(methacrylic acid), even for high grafting ratios. The swelling of these films was examined in mixtures of methylene chloride with methanol and curves of different shapes were obtained depending on the grafting ratio. PVC films grafted with acrylic acid readily swell in both water and methanol but they remain hard in the swollen state. The equilibrium swelling increases with swelling temperature but this process is not reversible; films swollen at high temperature keep a high degree of swelling even when the system is cooled.     

Characterization of poly(vinyl alcohol) during the emulsion polymerization of vinyl acetate using poly(vinyl alcohol) as emulsifier

During the emulsion polymerization of vinyl acetate (VAc) using poly(vinyl alcohol) (PVA) as stabilizer and potassium persulfate as initiator, the VAc reacts with PVA forming PVA-graft-PVAc. When the grafted polymer reaches a critical size it becomes water-insoluble and precipitates from the aqueous phase contributing to the formation of polymer particles. Since particle formation and therefore the properties of the final latex will depend on the degree of grafting, it is important to quantify and to characterize the grafted PVA. In this work, the quantitative separation and characterization of the grafted water-insoluble PVA was carried out by a two-step selective solubilization of the PVAc latex, first with acetonitrile to separate PVAc homopolymer, followed by water to separate the water-soluble PVA from the remaining acetonitrile-insoluble material. After the separation, the water-soluble and water-insoluble PVA were characterized by Fourier Transform Infrared (FTIR) spectroscopy and ¹H and ¹³C nuclear magnetic resonance (NMR) analyses, from which the details of the PVA-graft-PVAc structure were obtained. © 1996 John Wiley & Sons, Inc.     

生物可降解高吸水性非织造布的研制

用聚丙烯酸接枝淀粉浆液，在ＰＶＡ非织造布上形成吸水树脂，从而得到高吸水性非织造布。对接枝单体的比例、交联条件、浸轧量及非织造布规格等因素对高吸水非织造布吸水性能的影响进行了讨论了并测定了其生物降解性能。     

Relations entre la structure et les proprietes des membranes de polytetrafluoroethylene greffe—I. Membranes monogreffees carboxyliques ou basiques

We have determined the equilibrium properties (neutralization and swelling and the transport properties: conductivity and dialysis) of hydrophilic membranes obtained by radiation grafting of acrylic acid or 4-vinylpyridine onto thin PTFE films. The presence of strong counter-ion-membrane interaction (PTFE-PAA-K⁺ and PTFE-P4VP-ClO^?₄) has been confirmed in the beginning of neutralization. The grafting ratios of the samples ranged between a few percent and several hundreds percent. The properties have been studied in connection with the average degrees of ionization and the average molalities of the reactive groups throughout the whole thickness of the membrane. The parameters of the synthesis which determine the structure of acid or basic grafted chains also have an influence on the properties of the resulting membranes. For a high dose-rate (> 100 rad min^?1), the properties of carboxylic membranes are related to the degree of cross-linking: for smaller dose rates, the properties are related to the length of the grafted branches and/or to the state of the skeleton of PTFE. For the basic membranes, the properties are controlled by the length of the grafted branches and the importance of the micro-phase-separation between PTFE and the grafted chains; for low dose rates, when the grafted branches are long, separation of hydrophobic and ionizable zones is noticed for grafting ratios higher than 5%. The carboxylic membranes with lower degrees of grafting, prepared with a high dose rate, exhibit very good permselectivity. The pyridinic membranes with a low degree of grafting could be of practical interest, viz. the manufacture of selective electrodes for perchlorate ions.     

Radiation-induced graft polymerization and sulfonation of glycidyl methacrylate on to porous hollow-fiber membranes with different pore sizes

An epoxy group containing monomer, glycidyl methacrylate, was grafted on to a porous hollow-fiber membrane, made of polyethylene, whose different pore sizes ranged from 0.2 to 0.5 μm. The resulting epoxy group was converted into a sulfonic acid group as a cation-exchange group to capture metal ions. The porous network was retained after grafting and subsequent sulfonation because the poly-GMA chains invaded the polymer matrix. An increase in the SO₃H group density of the graft chain decreased the permeability of pure water because the graft chains expanded toward the pore interior due to their mutual electrostatic repulsion. The ion-exchange adsorption of Pb ions during the permeation of a Pb(NO₃)₂ solution through the pores edged by the cation-exchange graft chains was observed with a negligible diffusional mass-transfer resistance.     

超临界二氧化碳体系中PVDF微孔膜的表面接枝改性

超临界二氧化碳（SCCO2）是一种T〉31．1℃,P〉7．38MPa的二氧化碳流体,不仅具有类似于气体的粘度和类似于液体的密度,而且可以通过改变温度或压力控制SCCO2的密度及溶解性．SCCO2对有机小分子具有优良的溶解、扩散和渗透性能,化学惰性,无污染,易于分离,作为一种聚合反应介质,受到学术界日益增多重视．SCCO2极低的粘度使其具有良好的流动性和扩散渗透性能,零表面张力使其对聚合物具有良好的润湿和增塑性,这将促进引发剂和聚合单体向微孔膜的外表面及内表面扩散．利用温度和压力改变SCCO2的溶解性能调整单体在聚合物相和SCCO2相之间的分布,进而控制微孔膜内外表面的接枝程度．所以SCCO2接枝聚合反应对于聚合物膜的表面改性具有极其重要的意义．