Porous structure and rheological properties of hydrogels of highly water-absorptive cellulose graft copolymers

The porous structures of the highly swollen hydrogels of cellulose—acrylamide graft copolymers were studied by the solute exclusion technique. For these hydrogels, the cumulative volume of pores up to 560 Å in pore width was between 450 and 850 mL/g, and was between 20 and 30% of the total pore volume. With an increasing in the amount of crosslinker added in the grafting procedure, the cumulative pore volume up to 560 Å decreased. Furthermore, larger pores shrunk preferentially. In the range of concentration from 0.003 to 0.3%, the viscosity of the hydrogels increased remarkably with an increase in concentration. The concentration dependence of the viscosity showed a transition at about 0.03%, which corresponded to the reciprocal of the water retention values for each copolymer. At concentrations over 3%, fluidity of the hydrogels was lost and the water swollen copolymers became viscoelastic. This dynamic viscoelasticity remained essentially unchanged in the temperature range of 20 to 80°C. The dynamic viscoelasticity was dependent on the concentration, but the concentration dependence was smaller than that of the viscosity. The larger the amount of the crosslinker added, the larger the value of dynamic modulus became.     

Surface passivation of nylon‐6,6 films by graft copolymerization for reduction of moisture sorption

To improve the moisture sorption property of nylon‐6,6 film, ally pentafluorobenzene (APFB) was incorporated on the argon plasma‐pretreated nylon film by UV or thermally induced surface graft copolymerzation. The plasma pretreatment introduced peroxides that were degraded into radicals to initiate the graft copolymerization of APFB on the nylon surface. The modified surfaces were characterized by X‐ray photoelectron spectroscopy (XPS) and contact angle measurement. The moisture sorption was assessed by the coulometric test method. The efficiency of surface graft copolymerization was affected by plasma pretreatment time of the nylon substrate, as well as by the UV or thermal graft copolymerization time. The UV graft‐copolymerized nylon film exhibited a significantly lower extent of moisture sorption when compared to that of the pristine films, even at low graft concentration. However, the moisture sorption behavior for the thermally graft copolymerized films was similar to that of the pristine films. Contact angle and XPS measurements suggested that the reduction in moisture sorption for the UV graft‐copolymerized nylon‐6,6 film was attributable to the fact that the hydrophobic polymer layer was formed on the nylon surface, and the hydrophobic layer of an appropriate thickness could serve as an effective barrier to moisture. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 1366–1373, 2000     

Phase behavior and moisture sorption of deliquescent powders

Deliquescence lowering was investigated in powder blends of different particle sizes. Deliquescent compounds, widely used in edible products, were used to prepare two model blends: fructose–citric acid anhydrous (M1) and sucrose–sodium chloride (M2). The relationship between the water activity and the composition of each system was measured and used to build phase diagrams, from which information about the eutonic composition (EC) was extracted. Data were evaluated using five models (Raoult’s law, and the Ross, Ferro Fontán–Chirife–Benmergui, Zdanovskii–Stokes–Robinson, and extended Zdanovskii–Stokes–Robinson equations), and the extended Zdanovskii–Stokes–Robinson equation provided the best fit. The effects of formulation, compound ratio, particle size, degree of compaction, and storage RH on moisture sorption profiles were determined and varied for M1 and M2. The EC was 33:67 wt% citric acid:fructose for M1 and 16:84 wt% NaCl:sucrose for M2. Blending powders created sufficient particle intimacy to enable deliquescence lowering in both systems (the mutual deliquescence RH was 44.1% for M1 and 63.6% for M2), and the eutonic composition was the most susceptible to moisture-induced changes. The results of this study show that powder behavior in the presence of moisture can be largely predicted from equilibrium phase diagrams.     

Characterization of wool graft copolymers

In the present article, characterization of wool grafted with acrylate monomers such as methyl methacrylate (MMA), methylacrylate (MA), ethylacrylate (EA), and butylacrylate (BA) with respect to thermal behavior and viscosity average molecular weight (M_v ) is described. The modified wool shows improved thermal behavior.     

New syntheses of graft copolymers using the DPE-technique: ATRP graft copolymerization

Summary A new one-step synthesis of a set of macroinitiators for atom transfer radical polymerization (ATRP) via controlled radical polymerization is presented. The macroinitiators consist of methacrylate and p-chloromethylstyrene (CMS) and were synthesized by controlled radical polymerization in the presence of l,l-diphenylethylene (DPE) using azobisisobutyronitrile (AIBN) as initiator. The resulting macroinitiators were used for the ATRP of different methacrylates yielding graft copolymers which were characterized by SEC and NMR. Received: 25 July 2002/Revised version: 28 October 2002/ Accepted: 28 October 2002 Correspondence to Oskar Nuyken     

Synthesis and characterization of silicon-containing graft copolymers

Poly(4-t-butoxycarbonyloxystyrene)-g-poly(dimethylsiloxane) and poly(t-butylmethacrylate)-g-poly(dimethylsiloxane) with various chemical compositions were synthesized via free radical polymerization of 4-t-butoxycarbonyloxystyrene (TBCS) or t-butylmethacrylate (TBMA) with silicone macromers. These macromers were prepared by anionic ring-opening polymerization of hexamethylcyclotrisiloxane (D₃) and subsequent termination with a chlorosilane compound having a methacrylate functionality. The morphology of the graft copolymer systems was investigated by DSC and TEM.     

An investigation of moisture sorption in microcrystalline cellulose using sorption isotherms and dielectric response

Measurements were made of the enthalpy changes, using sorption isotherms, and of the changes in dielectric response of microcrystalline cellulose discs when different amounts of water were added. The results are explained by means of a molecular model in which the water is sorbed in a step-wise process of hydrogen bonding.     

Modification of polysilanes: Preparation of comb-like graft copolymers

Poly(methylphenylsilylene) has been functionalized by protodearylation with trifluoromethanesulfonic acid. Comb-like graft copolymers have been prepared by polymerizing tetrahydrofuran. 2-methyl-2-oxazoline, and isobutylvinyl ether from a partially triflated poly(methylphenylsilylene) backbone. Model studies using trimethylsilyl trifluoromethanesulfonate to initiate the cationic polymerization of these organic monomers indicated that a promoter was required to achieve more efficient initiation.     

含聚氧乙烯支链的两亲性(丙烯酸丁酯-甲基丙烯酸甲酯)接枝共聚物的性能

由聚氧乙烯(PEO)大单体与丙烯酸丁酯(BA)、甲基丙烯酸甲酯(MMA)合成含PEO支链的两亲性(BA-MMA)三元接枝共聚物,对该共聚物的乳化性、吸水性和物理机械性能进行了研究.结果表明,合成的共聚物具有良好的乳化性及吸水性,并在一定组成下呈现热塑性弹性体的性质.     

Solution properties of dextran-polyacrylamide graft copolymers

Copolymers obtained by grafting polyacrylamide (PAA) onto polydextran (DEX) have been synthesised by ceric-ion-reduced redox initiation method. These copolymers have been characterized by light scattering, self-exclusion chromatography and viscometry in aqueous solutions. The short range molecular structure has been studied by small-angle X-ray scattering. From these results it is suggested that close to the anchoring point the grafted chains are extended while they take on a random conformation far from this point. A few investigations have been carried out in water/DMF (dimethyl formamide) mixtures. It is observed that the molecular weight depends strongly on the dimethyl formamide fraction. These results are discussed by contemplating the existence of PAA/DMF complexes.     

Flocculation properties of cellulose-acrylamide graft copolymers

The flocculation of aqueous suspension of microcrystalline cellulose powder grafted with polyacrylamide was studied. The correlation between the initial flocculation rate measured by means of turbidimetry and the length and number of the grafted polymer chain was discussed from the viewpoint of polymer bridging mechanism. The effect of the graft copolymer powder on the flocculation of kaolin suspension was also investigated.     

Synthesis and characterization of vegetable tannin-vinyl graft copolymers part I. Cutch-poly(methyl acrylate) graft copolymers

New graft copolymers were synthesized by grafting methyl acrylate onto cutch, a vegetable tanning agent, in acetic acid medium with hydrogen peroxide as the initiator. The graft copolymers were characterized by infrared spectroscopy and thermogravimetric analysis. The dependence of the percentage of grafting, monomer conversion, efficiency of grafting and rate of grafting on the concentrations of initiator, acetic acid, and cutch were investigated. The optimum experimental conditions for grafting were obtained. A probable mechanism of grafting was also proposed.     

The characterisation of polycarbonate-containing graft copolymers and the kinetics of graft polymerisation

This paper examines several procedures for selective degradation of the preformed polymer component (polycarbonate) of certain types of graft copolymers. A procedure based on a two-phase alkaline hydrolysis of the polycarbonate is identified as the preferred technique because it provides a clean system for the quantitative recovery and subsequent characterisation of the grafts. The application of the technique to a series of polycarbonate/polystyrene graft copolymers is reported. The kinetics of free-radical graft polymerisation of styrene and the molecular weight distributions of the polystyrene grafts are compared with those for styrene homopolymerisation performed at the same rates of initiation. This comparison allows several differences between the kinetics of graft and homopolymerisation to be identified, both prior to and after gelation. These factors are interpreted in terms of modifications to the rate coefficient for bimolecular termination of the propagating grafts. Two (possibly three) factors are identified which influence the polymerisation kinetics prior to gelation; their influences are contrary and their relative importances depend on the rate of initiation. After gelation an additional effect, termed the network effect, comes into force and dominates both the rates of graft polymerisation and the molecular weight distributions of the grafts.     

含聚氧乙烯链段的两亲性接枝共聚物的合成及应用

介绍了含聚氧乙烯链段的两亲性接枝共聚物的制备方法与应用近况。     

Preparation and water sorption properties of cellulose-polypropylene glycol block copolymers

A series of cellulose-polypropylene glycol block copolymers have been prepared by techniques described previously. The chain extension reactions used for their preparation were confirmed by i.r. and intrinsic viscosity data. The water sorption of films of the blocks was determined and the results, calculated on the cellulose content, compared with various forms of pure cellulose. It was found that lower crystallinity of the blocks was indicated by the higher water sorption values. As the size of the cellulose blocks was decreased the water sorption also decreased but the smallest block sample gave a higher value. It is believed that the polypropylene glycol blocks exert a restraining influence on the water sorption which is eventually overcome by the decrease in the crystallinity of the cellulose blocks as their size decreases.