聚合物基板表面状态对异相接枝的影响研究

研究了对于羟丙基纤维素（HPC）基板进行表面修饰时,基板表面状态的调控 对基板表面化学接枝的影响。用双官能团化合物2,4-甲苯二异氰酸酯（TDI）作为 接枝桥梁,其对位的异氰酸酯基先和基板上的羟基反应,保留的邻位异氰酸酯基进 一步再与丙烯酸的羟基反应,让接枝在基板上的活性丙烯酸分子继续和丙烯酸溶液 聚合,通过这种途径在基板表面修饰聚丙烯酸。基板制备时,由于不同介质对HPC 基板表面的不同诱导作用,导致表面组成各异,大大影响了接枝反应的效果。红外 光谱和二次离子飞行时间质谱均证明了可以用2,4-甲苯-二异氰酸酯（TDI）分子 做接枝桥梁在基板表面异相接枝上羟基并进一步接枝聚丙烯酸,从而达到修饰基板 的目的。     

Cellulose functionalization via high-energy irradiation-initiated grafting of glycidyl methacrylate and cyclodextrin immobilization

Cotton-cellulose was functionalized using gamma-irradiation-induced grafting of glycidyl methacrylate (GMA) to obtain a hydrophobic cellulose derivative with epoxy groups suitable for further chemical modification. Two grafting techniques were applied. In pre-irradiation grafting (PIG) cellulose was irradiated in air and then immersed in a GMA monomer solution, whereas in simultaneous grafting (SG) cellulose was irradiated in an inert atmosphere in the presence of the monomer. PIG led to a more homogeneous fiber surface, while SG resulted in higher grafting yield but showed clear indications of some GMA-homopolymerization. Effects of the reaction parameters (grafting method, absorbed dose, monomer concentration, solvent composition) were evaluated by SEM, gravimetry (grafting yield) and FTIR spectroscopy. Water uptake of the cellulose decreased while adsorption of a pesticide molecule increased upon grafting. The adsorption was further enhanced by β-cyclodextrin immobilization during SG. This method can be applied to produce adsorbents from cellulose based agricultural wastes.     

Comparison of pre-irradiation and mutual grafting of 2-chloroacrylonitrile on cellulose by gamma-irradiation

Radiation-induced graft polymerization is one of the best methods for obtaining materials with new properties. In this work, radiation grafting of 2-chloroacrylonitrile to cellulose by mutual and pre-irradiation grafting methods was investigated. The grafting yield was enhanced by applying the emulsion grafting method. The grafting yield determined in the above systems was observed as 27% at highest and 6% at lowest. The effects of concentration of monomer, reaction time and reaction temperature on grafting yield were studied. Evidence of grafting has been based on the comparative studies of cellulose and grafted cellulose by infrared spectroscopy, thermal analysis and contact angle measurement. Grafting enhances thermal stability of cellulose backbone.     

Pre-irradiation grafting of cellulose and slightly carboxymethylated cellulose (CMC) fibres

Acrylamide, hydroxypropyl acrylate, hydroxypropyl methacrylate and 2-ethylhexyl methacrylate vinyl monomers were grafted onto cellulose as well as onto cellulose of improved accessibility (slightly carboxymethylated cellulose (CMC)) by the pre-irradiation grafting technique. The effect of dose, monomer structure, crosslinking agent and carboxymethylation on the grafting yield was studied and the optimal conditions for the grafting were established. Grafting, with the exception of acrylamide (AAm), decreased the swelling of the samples, which is advantageous for some applications. In case of AAm decrease in swelling was observed only when crosslinking agent was applied. At low doses (<5 kGy) the high accessibility of carboxymethylated cellulose resulted in a higher grafting yield.     

Improved Graft Copolymerization of Some Modified Cellulose Polymers with Vinyl Monomers Using Dibenzoyl Peroxide (DBPO) as Initiator

An improved efficient method for grafting of mercerized cellulose with acrylonitrile, acylamide, 4-vinylpyridine and styrene monomers using dibenzoyl peroxide (DBPO) as an initiator was studied. The results show that the order of the reactivity of the monomers is styrene > 4- vinyl pyridine > acrylonitrile >acrylamide. Under optimal conditions, the extent of graft copolymerization of styrene onto cellulose has shown a substantial increasing trend. The percentages of grafting yield (G.Y.%), grafting efficiency (G.E.%), IR spectra, and X-ray diffraction were measured. The I t was shown that X-ray diffraction spectra of grafted cellulose increases one more peak than that of pure cellulose with a noticeable decrease in crystallinity.     

二醋酸纤维素 -聚乙二醇接枝共聚物的核磁共振表征

用^1H NMR和^13C NMR核磁共振技术研究了二醋酸纤维素和聚乙二醇的接枝反应,并确定了^1H NMR和^13C NMR谱中各谱峰的归属,为证明二醋酸纤维素和聚乙二醇的接枝反应提供了依据。     

Effect of crystallinity on radiation-induced graft copolymerization on cellulose

With vinyl monomers, viz., styrene, butyl methacrylate, dimethylaminoethyl methacrylate, and ethyl acrylate, it was noted that higher per cent grafting was obtained with “recrystallized” cellulose than with “amorphous” cellulose. The possibility of the production of a porous structure in cellulose as a result of γ-irradiation followed by the dissolution of the reactive regions is suggested. DTA and DTG data of irradiated cellulose triacetate (CTA) reveal lowering of the melting point on irradiation, indicating a decrease in crystallinity. Decrease in density of cellulose on irradiation by γ-rays also indicates loosening of the structure of cellulose. It is postulated that grafting occurs in those regions of cellulose which were crystalline before irradiation, as well as in less crystallinie regions.     

Photo-induced graft copolymerization of methyl methacrylate on cellulose

Graft copolymerization initiated by ultraviolet light irradiation at 40°C in a hard glass vessel under nitrogen was examined. The graft copolymerization was observed to occur easily after some induction period without any use of photosensitizer, though it was found the per cent grafting and the grafting efficiency were markedly affected by the quantities of cellulose and monomer. In the system without cellulose, homopolymerization of methyl methacrylate hardly took place, but the use of cellulose caused the formation of homopolymer too, and a grafting efficiency in the range of 60–80% generally resulted. Ferric chloride or sodium anthraquinone-2,7-disulfonate (AQ) acted on the polymerization reaction as photosensitizers to reduce its induction period. Though ferric chloride acted to develop both the per cent grafting and the number of grafts, not the same effects were observed with AQ. Oxalic acid, which was employed with the object of eliminating very small amount of metals contained in cellulose, was found to act favorably in the formation of grafts, much like ferric chloride.     

Hydrophobic modification of cellulose nanocrystal via covalently grafting of castor oil

Hydrophobic cellulose nanocrystals (CNs) have been prepared by grafting isocyanate-terminated castor oil, a kind of natural vegetable oil, onto their surface. The existence of castor oil component in the modified cellulose nanocrystals was verified by Fourier transform infrared spectroscopy, solid-state ¹³C NMR spectra and X-ray photoelectron spectroscopy. At the same time, X-ray diffraction and transmission electron micrographs further proved that the crystalline structure and large aspect ratio of cellulose nanocrystals were essentially preserved after chemical grafting. Furthermore, the surface of modified cellulose nanocrystals appeared to be hydrophobic as indicated by contact angle measurements. The value of the polar component of surface energy decreased from 21.5 mJ/m² to almost zero via grafting castor oil. These novel hydrophobic castor oil-grafted cellulose nanocrystals appear as valuable alternatives to formulate bionanocomposites with non-polar polymers for optimized performances.     

二醋酸纤维素接枝聚己内酯的核磁共振表征

用^1H-NMR和^13C-NMR研究了二醋酸纤维素(CDA)和聚己内酯(PCL)的接枝共聚反应,确定了^1H-NMR和^13C-NMR谱中各谱峰的归属,为证明二醋酸纤维素和己内酯的接枝共聚反应提供了依据。     

Graft Copolymerization of 4-Vinylpyridine Onto Modified Cellulosic Fibers. the Ceric Ion Concentration Effect

The graft copolymerization of 4-vinylpyridine was carried out on mercerized cellulose and partially carboxymethylated cellulose (PCMC) using eerie ammonium nitrate (CAN) as the initiator. the grafting parameters (grafting efficiency (GE), graft yield (G), and total conversion (C¹)) were studied as a function of CAN concentration. It was shown that by increasing the CAN concentration, G and C, reached a maximum. the graft yields for PCMC were significantly higher than those for mercerized cellulose. the largest GE values appeared for PCMC and mercerized cellulose at low and high CAN concentrations, respectively. the Ce(IV) consumption during grafting increased with rising concentration of CAN, and it was greater in the case of PCMC than of mercerized cellulose. After acid hydrolysis of the polysaccharide backbone, the average molecular weight of grafts was determined viscometrically. Molecular weight decreased with initiator concentration. Graft frequency (GF), on the other hand, increased with CAN concentration. GF for PCMC was higher than that for mercerized cellulose. Ce(IV) consumption increased with CAN concentration and it was lower for mercerized cellulose than that consumed during grafting on PCMC. After that, the effect of CAN concentration on the graft copolymerization onto PCMC was examined while the total nitrate ion concentration was maintained constant at 1.59 M by addition of sodium nitrate. Maximum G, C¹ and Ce(IV) consumption were higher than in the previous case.     

纤维素纳米纤维接枝聚(N-异丙基丙烯酰胺)水凝胶的制备与表征

将具有温度响应的聚N-异丙基丙烯酰胺(PNIPAm)接枝到电纺纤维素纳米纤维膜上,制备温度响应型纤维素接枝聚N-异丙基丙烯酰胺(PNIPAm-g-Cell)纳米纤维水凝胶。 研究接枝单体(N)与纤维素(c)的质量比、反应温度、反应时间和引发剂浓度对产物接枝率、溶胀性和形貌的影响。 结果表明,最佳聚合反应条件为m(N):m(c)=15:1、反应温度40 ℃、反应时间3 h、引发剂浓度为10 mmol/L,得到PNIPAm-g-Cell接枝率和溶胀率分别为35%和31%。 与PNIPAm相比,PNIPAm-g-Cell水凝胶的低临界相转变温度(LCST)显著升高,说明亲水性纤维素的引入改变了体系的亲疏水平衡。 去溶胀动力学测试表明,0.5 min内接枝率为25%和35%的水凝胶保水率分别降低至93%和61%。 说明接枝率越高PNIPAm-g-Cell水凝胶对温度的响应速度越快,对温度越敏感。     

Preparation and Antibacterial Function of Quaternary Ammonium Salts Grafted Cellulose Fiber Initiated by Fe2 +-H2O2 Redox

The surface contact disinfecting technique is a newly developed method for water sterilization. In this paper, the grafted quaternary ammonium salts (QAS) antibacterial fibers were prepared and designed to apply for the surface contact disinfecting process in water treatment. The antibacterial fibers were directly prepared by grafting methacryloxylethyl benzyl dimethyl ammonium chloride (DMAE-BC) onto cellulose fiber using thiocarbonate-H₂O₂ redox system. All kinds of factors in the grafting reactions, such as reaction time, reaction temperature, monomer concentration, initiator concentration, which influence the percentage of grafting, were studied and optimized. The modified cellulose fibers were characterized by Fourier transform infrared spectroscopy (FTIR) and scanning electron microscope(SEM). The effects of the percentage of grafting of the grafted cellulose fibers on bactericidal activity were also studied. The spread plate method was used to characterize the bactericidal activity. The disinfection process was further investigated by directly observing the morphology of the bacterial cells adsorbed on the antibacterial fibers with SEM and measuring extracelluar total protein concentration in suspension. The poly(DMAE-BC)-grafted cellulose ?ber was found to exhibit particularly high activity against E.coli.     

原子转移自由基聚合方法在纤维素及其衍生物改性方面的应用Ⅱ

原子转移自由基聚合反应(atom transfer radical polymerization,ATRP)是纤维素及其衍生物进行修饰改性的一种有效途径。通过ATRP对纤维素及其衍生物进行改性,可以得到不包含相应均聚物的纯接枝产物,且接枝链的长度及分子量分布均可控。通过ATRP不仅可对纤维素进行本体改性,还可对其进行表面改性。原子转移自由基聚合方法在纤维素及其衍生物改性方面的应用Ⅰ″一文介绍了通过ATRP对纤维素及其衍生物进行本体改性的研究进展。本文概述了通过ATRP对纤维素及其衍生物进行表面改性的研究进展。     

Enzyme-catalyzed transesterification of vinyl esters on cellulose solids

Enzyme-catalyzed transesterification of several cellulose solids in organic media have been investigated. Several protease enzymes were made soluble in organic media through ion-paired enzyme–surfactant complexes. Subtilisin Carsberg was found to be catalytically active in the transesterification of cellulose with vinyl propionate and vinyl acrylate in anhydrous pyridine. The ester carbonyl groups in acylated cellulose derivatives were confirmed by Fourier transform infrared spectroscopy. The surfaces of these cellulose derivatives became hydrophobic as demonstrated by increased water-contact angles. The enzyme-catalyzed transesterification was confirmed to regioselectively target the primary hydroxyl group of cellulose by reactions on specifically substituted cellulose. The cellulose esters from enzyme-catalyzed transesterification could be hydrolyzed partially by the same enzyme in aqueous media, and were thus biodegradable. Surface grafting of cellulose acrylate was demonstrated using azobisisobutyronitrile-initiated polymerization of acrylonitrile in dimethylformamide. Polyacrylonitrile (PAN)-g-cellulose shows a different thermal behavior from cellulose, homopolymer PAN, and PAN/cellulose blends. The grafted PAN on PAN-g-cellulose at a 16% grafting add-on is incapable of cyclization. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1931–1939, 2001     

Grafting onto cellulose. VIII. Graft copolymerization of poly(ethylacrylate) onto cellulose by use of redox initiators. Comparison of initiator reactivities

In an attempt to compare the relative reactivities of different redox systems in graft copolymerization of vinyl monomers onto cellulose, we studied grafting of ethylacrylate (EA) in aqueous medium by using the well-known redox intiator, ferrous ammonium sulfate–potassium persulfate (FAS–KPS) system, and its reactivity was compared with that of Fenton's reagent (Fe²⁺ ?H₂O₂) towards grafting of EA onto cellulose. Optimum conditions for affording maximum grafting were evaluated and percent grafting is expressed as functions of different reaction variables. Evidence of grafting was obtained from IR spectroscopic measurements, SEM, and TGA studies of the grafted and ungrafted cellulose. A plausible explanation for the observed reactivity pattern shown by (FAS–KPS) and (FAS–H₂O₂) redox systems is offered. Fenton's reagent (Fe²⁺ ?H₂O₂) was found to be several times more reactive than (FAS–KPS) redox system.     

Optimization of Preparation Process for Allylamine-bacterial Cellulose via Graft Copolymerization by Response Surface Methodology

In order to improve the efficiency of new adsorbent, grafting-allylamine bacterial cellulose（al-BC）, response surface methodology（RSM） was used for the optimization of preparation process. Three factors affecting the yield of grafting reaction are the amount of allylamine, the concentration of ceric ammonium nitrate（CAN） and the concentration of nitric acid. Based on the regression coefficient analysis in the Box-Behnken design, a relationship between the preparation variable and grafting yield was obtained. Square error analysis on main factors, and multi-variable interactions were employed for studying grafting yield. The results show that at the conditions of CAN of 23.00 mmol/L CAN, 0.17 mol/L nitric acid, adding an amount of grafting-allylamine bacterial cellulose of 26.49 mL/L made grafting rate reach maximum of 24.25% at 40℃ after the reaction for 4 h. The experimental results are in good agreement with the calculation values via proposed regression equation, indicating that the equation could be used to nredict and optimizate the preparation of grafting al-BC.     

Graft Copolymerization of Vinyl Monomers onto Cellulose and Cellulosic Materials

Abstract

Graft copolymerization is a novel method which has wide application in synthesizing new forms of polymeric materials and also in modifying the properties of natural polymers [1,2]. Much research has been done on grafting polymeric molecules on to cellulose to produce materials of new properties intermediate between those of cellulose and those of synthetics. A variety of property changes can be imparted to cellulose through grafting without destroying the crystallinity or crystallization potential of the substrate or reducing its melting point. Some of the most dramatic changes in properties which have been brought about by grafting to cellulose are viscoelasticity, stereoregularity, hygroscopicity, water repellency, improved adhesion to a variety of substances, settability, soil resistance, bacteriocidal properties, and thermal stability.     

Radiation effects on polymers—XI. Radiation grafting of acrylamide on to cellulose acetate reverse osmosis membranes

With the aim of improving properties of cellulose acetate membranes for reverse osmosis desalination, grafting was performed using high energy electrons. In this paper, the grafting parameters (radiation dose and method, monomer concentration, solvents, chain transfer agent and redox system) are considered; conclusions are drawn as to the grafting content and mode of grafting.     

Graft copolymerization of cellulose initiated by ceric salts: Effect of reaction conditions on the consumption of ceric ion

A soluble monomer [methyl acrylate (MA)] and an insoluble monomer [butyl methacrylate (BMA)] were grafted onto cellulose by three types of ceric salts under both oxygen-free conditions and in the presence of oxygen. For comparison, Ce(IV) consumption during cellulose oxidation was also determined under similar reaction conditions. Slightly more Ce(IV) was consumed during cellulose oxidation in the presence of oxygen. During graft copolymerization of MA under oxygen-free conditions, the consumption of Ce(IV) was much lower than during cellulose oxidation regardless of the type of ceric salt employed. The opposite was observed in the presence of oxygen: much more Ce(IV) was consumed during grafting than during cellulose oxidation. The consumption of Ce(IV) in the graft copolymerization of BMA by ceric sulfate was nearly independent of reaction conditions and it was approximately the same as in cellulose oxidation. In the reaction initiated by ceric ammonium nitrate under oxygen-free conditions, less Ce(IV) was once again used up during grafting than during cellulose oxidation. However, the difference was much smaller than in the case of MA.