Graft polymerization of vinyl monomers onto cellulose in presence of soda lime glass. I

Sodium bisulfite–soda lime glass has proved to be a good initiator for polymerization and graft polymerization onto cellulose of some vinyl monomers. A scheme dealing with the mechanism of initiation has been proposed assuming trapping of the bisulfite radical inside the glass frame-work to form a so-called sulfur-impregnated solid. Such a solid has paramagnetic properties and acts on the vinyl monomers and cellulose as any free-radical-producing source thus leading to polymerization and graft polymerization onto cellulose. Other radicals containing sulfur, such as sulfite, sulfate, and persulfate failed to give such property with soda lime glass. With the sodium bisulfite–soda lime glass system the reactivity decreases in the order methyl methacrylate > ethyl acrylate > acrylonitrile which is inconsistent with the arrangement of acceptor monomers with decreasing electron-donating ability. This may reflect interference of the addition reaction which may take place between the monomer and bisulfite and the rate of which may depend on the activation energy of the monomer.     

On the reactivity of cellulose free radicals in graft copolymerization reactions

The formation and behavior of photo-and mechanoinduced free radicals in cellulose were studied by ESR spectroscopy and the capability of these free radicals to initiate graft copolymerization reactions was demonstrated. Although an 11-line ESR signal was detected from cellulose irradiated with ultraviolet (UV) light, a higher-intensity ESR signal with a five-line pattern was detected from a sample mechanically milled at 77 K. The decay of photoinduced free radicals when heated took place monotonously, whereas mechanoradicals exhibited an anomalous behavior with an increased signal intensity at 150 K before decaying at a higher temperature. Mechanoradicals have been found to react more efficiently and rapidly with oxygen and methyl methacrylate (MMA) than photoinduced free radicals. The peroxy mechanoradicals, however, were mobile and decayed more rapidly than the peroxy photoinduced radicals. Simultaneous graft copolymerizations of MMA to cellulose demonstrated that mechano-and photoinduced free radicals are capable of initiating grafting reactions, but a higher degree of grafting efficiency was obtained from cellulose treated mechanically.     

Kinetics of radiation-induced grafting reactions. II. Cellulose acetate–styrene systems

Kinetics of grafting reactions of styrene to preirradiated cellulose acetate have been studied by labeling the active sites with bromine atoms. The dilution of styrene monomer with methanol affected grafting reactions remarkedly: e.g., as the concentration of methanol in monomer solutions increased, the growth rates of individual graft radicals decreased while the average lifetimes increased. The integrated amounts of active sites which participated in grafting reactions were also affected by the constitution of monomer solutions and varied roughly in proportion to the extents of swelling of cellulose acetate. Grafting yields for styrene/methanol = 1/1 were higher than for 3/1 and 1/3 throughout the duration of grafting reactions, which is due not only to the high molecular weight of graft chains but also to the large number of graft chains for the 1/1 system compared to the other systems.     

Some aspects of graft polymerization of vinyl monomers onto cellulose by use of tetravalent cerium. IV

Intense agitation markedly decreased the homopolymer formation in homopolymerization reactions. Graft polymerization is similarly influenced, the main effect being on the propagation process. The results achieved in this work indicate that in grafting reactions, growing polymer radicals are produced mainly through the transfer of radicals formed at the cellulose backbone to the monomer where propagation takes place. The growing polymer radicals either recombine with active sites on the cellulose leading to grafting or react with each other through coupling and/or are oxidized with ceric ions to give homopolymer.     

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。     

Graft polymerization of vinyl monomers onto starch by use of tetravalent cerium

Grafting of acrylonitrile onto starch showed slightly higher yields when using soluble rather than insoluble starch, for reaction times < 1.5 hr. Beyond this time, the rate of grafting onto the soluble starch levels off, while that for grafting onto the insoluble starch proceeds leading to prograssive increase in the grafting yield. Momomer reactivity was in the following order: acrylonitrile > ethyl acrylate? methyl methacrylate. For the first two monomers, the order of reactivity is the reverse of that found for grafting onto cellulose; extremely low grafting yields resulted from grafting of ethyl acrylate rather than acrylonitrile onto starch. This result was attributed to the jelly nature of the polyethyl acrylate grafted starch, preventing diffusion of the monomer into the starch granules. This view was supported by the higher consumption of ceric ions at the start of the reaction, on grafting ethyl acrylate instead of acrylonitrile. As the reaction proceeds, the reverse takes place. Increase of ceric salt concentration, as well as the liquor to starch ratio, led to increased grafting yields.     

Electron spin resonance studies on radiation graft copolymerization. I. Grafting initiated by alkyl radicals trapped in irradiated polyethylene

The behavior of trapped radicals in polyethylene which is irradiated in air at room temperature, under grafting of methylmechacrylate or butadiene has been studied by electron spin resonance. Part of the alkyl radicals are converted to allyl radicals by reaction with double bonds and the others disappear by recombination under vacuum. The active species of grafting are alkyl radicals when the vapor pressure of monomers is relatively high, while at low pressure allyl radicals also play a role as well as alkyl radicals. In the grafting at 20°C, the grafting yields depend mainly on the decay rate of alkyl radicals which come out of the crystalline regions of polyethylene. The decay rate of alkyl radicals and the rate of grafting at the initial stage increase with decreasing crystallite size of polyethylene.     

Studies on New Hydrophobically Modified Water-soluble Cellulosic Graft Terpolymers

Hydrophobically modified water-soluble ion-containing cellulosic polymer possessing intra-or intermolecular modes of hydrophobic associations has been recently the object of our research^[1-4]. Based on the preparation of the surface-active monomer, dimethyloctyl (2-methacryloxyethyl)ammonium bromide (DMOA), new cellulosic graft terpolymers (NCGT) have been synthesized by grafting acrylamide (AM) and DMOA onto carboxymethyl cellulose (CMC) using potassium persulfate and dimethylaminoethyl methacrylate as the initiating system, and characterized by FTIR, elementary analysis, titration and GPC. To obtain the optimum reaction conditions, the influence of the feed ratio and addition order of raw materials, the concentration of initiators, temperature and pH on the grafting have been investigated.     

添加剂对高碱煤钠迁移和灰分烧结温度的影响

选取三种不同的添加剂（高岭土、SiO₂和Al₂O₃）,研究它们对高碱准东煤钠迁移和灰分烧结温度的影响,并且添加比例为1%-5%。结果表明,三种添加剂的钠捕集效率依次为：高岭土 > SiO₂ > Al₂O₃。钠捕集效率随着添加比例的增加而升高,但受温度影响比较复杂。高岭土的钠捕集效率在600-1000℃先增加后减小,并在900℃达到最大值,其余两种随温度的升高均减小。准东煤灰的烧结温度为803℃,添加高岭土后,烧结温度随添加比例的增加先降低后上升。当添加比例为3%时,因为钙长石和钙黄长石的低温共熔反应而达到最小值。SiO₂的添加比例为5%时,由于透辉石的生成和SiO₂本身的"骨架"作用,烧结温度迅速升高到879℃。Al₂O₃对烧结温度的影响最小。     

Surface grafting of polyethylene by mutual irradiation in methyl acrylate vapor. II. High-energy electrons irradiation

Vapor-phase mutual grafting of methyl acrylate (MA) onto polyethylene (PE) at high dose rates from an electron accelerator yields the same surface graft structure as does the grafting at low dose rates from ⁶⁰Co sources; i.e., a homopolymer layer (consisting of only MA component) is easily formed on the inner graft copolymer layer (consisting of both MA and PE components) as a result of the continuously increasing surface graft composition. To produce the surface layer, 4-MeV electron irradiation with a linear electron accelerator requires only less than 3 min of irradiation time at dose rates of more than 2 Mrad/min, whereas γ irradiation with a ⁶⁰Co source requires at least 1 hr at dose rates of less than 2 × 10³ rad/min. The rate of monomer consumption (or polymerization) in the surface homopolymer layer shows no dependence of irradiation time and a positive dependence of dose rate. It has been suggested that this kinetic feature at the high dose rates shows some contribution of vapor-phase homopolymerization and subsequent deposition (onto the grafting surface) followed by recombination with the grafted side chain radicals, although secondary graft copolymerization from the grafted chain radicals is still the principal process for the growth of the surface homopolymer layer.     

The preparation and characterization of some cellulose graft copolymers. V. ESR study of preirradiation grafting of styrene to cellulose acetate

Previous studies have shown a two-peak molecular weight distribution of the grafted polystyrene side chains from preirradiation-grafted cellulose acetate. ESR has been used to investigate this grafting system in further detail. It was found that the rate of decay of the trapped radicals on adding the monomer solution was quite slow and a substantial proportion remained after 3 days at 25°C. The G value for radicals lost was, however, in good agreement with the G (grafted side chains) produced during the same period. The ESR spectrum does not change on addition of the monomer solution. The explanation offered is that the side chains grow and terminate rapidly compared with the slow overall rate of decay. The grafting yield and the molecular weight of the grafted side chains continue to grow until the reaction is terminated, leading perhaps to the high molecular weight narrow distribution fraction.     

Some aspects of graft polymerization of vinyl monomers onto cellulose with the use of tetravalent cerium. V

The presence of occluded air lowers the ceric consumption between the beginning and end of the reaction time, decreases the grafting parameters, and increases the copper number. Grafting reactions carried out in presence of organic solvents show parameters that are lower than those obtained when the reactions are carried out in water. Solvents with high chain-transfer constants cause a marked decrease in the yield relative to the solvents of low chain-transfer constants. Conversion percentages are similarly influenced. However, the donor alcohols enhance polymer formation with the acceptor monomers; this is attributed to the ability of ceric salt solution to oxidize alcohol and hence initiate polymerization reaction. Scavenging of the free radicals by certain alcohols and competition between alcohol and cellulose for the ceric consumption are responsible for the low grafting yields achieved. The order of reactivity of monomers may change when solvents are used; it follows the relative differences in the chaintransfer constant of solvent with the different monomers. Pseudografting and complex formation, when they occur, interfere with the results achieved.     

Mechanism and selectivity of 2,3-dimethyl-2,3-diphenylbutane mediated addition of vinyltriethoxysilane to polyethylene

The thermolysis of 2,3-dimethyl-2,3-diphenylbutane (bicumene) at temperatures ranging from 220 to 310 °C is used to initiate the radical-mediated graft addition of vinyltriethoxysilane (VTEOS) to polyethylene. Model hydrocarbon studies indicate that the cumyl radicals generated by the slow decomposition of bicumene are capable of direct hydrogen atom abstraction at levels that are sufficient to sustain a graft propagation sequence of high kinetic chain length. The interaction of O₂ with cumyl radicals can lead to oxidation of the initiator and the hydrocarbon substrate, thereby enhancing the macroradical population and improving grafting rates and yields. In addition to providing remarkable kinetic chain lengths for VTEOS additions, high-temperature bicumene-based processes can induce HDPE and LDPE fragmentation such that the effects of radical combination on melt viscosity are counteracted. As a result, alkoxysilane-modified polymers that moisture-cure efficiently can be produced without incurring the undesirable increases in molecular weight that accompany conventional grafting processes.     

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.     

辐射交联制备改性CMC水凝胶的溶胀行为研究

利用丙烯酰胺 (AAm)接枝改性纤维素 ,然后进行羧甲基化反应得到高取代度的丙烯酰胺 羧甲基纤维素钠 (AAm CMC Na) .对该材料进行γ射线辐照制备出新型改性CMC水凝胶 .研究了这种水凝胶的溶胀动力学、交联动力学以及温度、pH值和无机盐浓度对水凝胶溶胀行为的影响 ,并与CMC Na水凝胶进行了比较 .结果表明 ,该水凝胶和CMC Na水凝胶相比 ,优点在于辐照交联所用的剂量下降 ,而且所需的CMC浓度减少 .AAm CMC Na水凝胶的溶胀度随温度升高而增大 ,在pH为 6～ 8范围内达到最大值 ,并随无机盐浓度与吸收剂量增加而下降 ,表现出较好的温度敏感性和pH敏感性 ,可望作为吸水材料和水保持剂     

Specific heat capacity and melting/crystallization characteristics of polytridecanolactone

An investigation of the thermodynamical properties of polytridecanolactone (PTDL) was made with the aid of a differential scanning calorimeter (DSC). PTDL is a linear polyester and belongs to the polylactones, which have been poorly investigated. In this paper we contribute with specific heat capacity in the range 180-400 K, and melting and glass transition characteristics. Further, we present unique results corresponding to the effect of different cooling rates on crystallization temperatures and crystallization energies. PTDL has a melting temperature of 350 K, and a glass transition at about 237 K. The crystallization results show that PTDL crystallizes easily, with a crystallization degree of about 80%. In addition, the crystallization energy decreases with increasing cooling rate, and levels out at a constant value at higher cooling rates. The crystallization temperature, on the other hand, shows an increasing sensitivity of cooling rate, where the supercooling is increasing more rapidly at higher cooling rates. © 1994 John Wiley & Sons, Inc.     

Grafting of caprolacton to cellulose acetate by reactive processing

Cellulose acetate was successfully modified with caprolacton in an internal mixer at temperatures between 120 and 220 °C, and reaction times between 5 and 45 min in the presence of tin-octoate catalyst. The efficiency of modification and the structure of the product were analyzed by SEC, ¹H NMR, and FTIR spectroscopy. Significant modification of cellulose acetate did not occur at low temperatures, below 180 °C. Grafting efficiency increased with increasing temperature and time. The extent of grafting could be estimated from the amount of material extracted from the samples by toluene and by FTIR analysis, from the relative intensity of -CH₂- and -CH₃ vibrations. The amount of polycaprolacton homopolymer is relatively low at the end of the reaction; the efficiency of grafting is good. Although high temperature and long reaction time favor grafting, considerable degradation of the product occurs under these conditions. Quantitative analysis showed that the average length of grafted oligomeric caprolacton chains is around 3 monomer units. The chains attached to the CA backbone internally plasticize the polymer leading to a considerable decrease of its glass transition temperature.     

Radical and radiation-induced grafting of some synthetic high polymers within the temperature range of their glass transition

The temperature dependence of radiation-induced grafting onto poly(ethylene terephthalate), polyamides, polyacrylonitrile, and polypropylene has been investigated for several monomers. In all cases a maximum grafting yield is obtained when the reaction is performed in the temperature range of the glass transition T_g of the polymer used. This maximum yield does not only appear with radiation-induced simultaneous grafting. It also appears when the graft polymerization is induced by pre-irradiation or even by thermal decomposition of organic peroxides. It is assumed that the pronounced maximum of the reactivity at T_g is obtained because in the glassy state below T_g the radicals formed cannot react due to a reduced diffusion of the monomer, whereas above T_g the number of radicals available for polymerization will be reduced with increasing temperature.     

Dissipative crystallization of sodium salts of carboxymethyl cellulose

Drying dissipative patterns were observed at room temperature on a cover glass, a watch glass, and a Petri glass dish during the course of dryness of aqueous solution of sodium salts of carboxymethyl cellulose (NaCMC) having different molecular weights in the presence of sodium chloride and in their absence. Without salt, the polymers were slightly hygroscopic and did not dry up completely on the substrates. Single crystals of the NaCMC without salt were short rodlike and quite similar to those of the other polysaccharides studied hitherto, i.e., hydroxypropyl cellulose and sodium dextran sulfate. Morphology of the polymer crystals were short rods, long dendritic rods, and/or hedrite assemblies depending on location in the dried film and in the presence of sodium chloride. Spoke-like orientation of the long dendritic rods appeared on a cover glass and a watch glass especially for NaCMC of low molecular weights.