The graft copolymerization of styrene and lignin. II. Kraft softwood lignin

The radiation-induced graft copolymerization of styrene and various kraft softwood lignins was studied. Expression of the results as the usual “per cent graft” was impossible, because grafting caused the lignin to become extractable in solvents for the styrene homopolymer. However, evaluation of the effects of various solvents on the degree of reaction was made through an indirect, and possibly more characteristic, measure. Grafting was least pronounced under conditions of low lignin accessibility (e.g., when less than 10% methanol was present), but increased with the addition of better lignin solvents or with higher methanol concentrations. The precipitating nature of the latter conditions was also found to contribute to an accelerated rate of grafting. Surprisingly, the graft copolymer was found to degrade at higher doses. Proof of grafting is offered in a fractionation scheme. Measurement of the molecular weight of the polystyrene separated from the lignin backbone allows the estimation of approximately one polystyrene graft per lignin molecule in benzene-extractable copolymers. Two glass transition temperatures could be detected in several fractionated copolymers.     

The graft copolymerization of styrene and lignin. III. Chain transfer reactions of lignin and lignin model compounds

The effect of addition of lignin model compounds on the polymerization rate and molecular weight of polymer in the radiation-induced polymerization of styrene was studied. Guaiacol, a model for softwood lignin, reacted slowly with styrene radicals, while 2,6-dimethoxyphenol, a hardwood lignin model, was a much more efficient chain transfer agent. Studies with isoeugenol indicate that allylic or phenoxy radical stability in a conjugated system may terminate polymerization quite effectively. The results are discussed in the light of new and previous data with isolated lignins; they are consistent with the previously presented grafting scheme.     

Radiation-induced graft copolymerization of styrene to cellulose

The radiation-induced graft copolymerization of styrene to cellulose has been studied in vacuo at 30°C and at dose rates from (0.37 to 8.73) × 10^?2 W/kg. Dioxan was used as solvent for monomer and polystyrene homopolymer, and water (2% total volume) was incorporated as swelling agent for cellulose. The concentration of styrene in the bulk medium was varied from 0.432 to 3.46 moles/l., and the rates of both grafting and homopolymerization were shown to be proportional to [monomer] · [intensity]^1/2. The value of 3.3 × 10^?4 l. mole^?1 sec^?1 derived for k_p²/k_t in homopolymerization is similar to that for normal free-radical polymerization of styrene. However, reduced termination during grafting yielded a much higher value (58 l. moles^?1 sec^?1). Degradation of cellulose in the absence of monomer was followed viscometrically, and values of 13.5 and 24.6 were derived for G (scission) in vacuo and in air, respectively.     

Cation exchange membranes by radiation-induced graft copolymerization of styrene onto PFA copolymer films. I. Preparation and characterization of the graft copolymer

PFA-g-polystyrene graft copolymers were prepared by simultaneous radiation-induced graft copolymerization of styrene onto poly(tetrafluoroethylene-co-perfluorovinyl ether) (PFA) films. The effects of grafting conditions such as monomer concentration, dose, and dose rate were investigated. Three solvents, i.e., methanol, benzene, and dichloromethane, were used as diluents in this grafting system. Of the three solvents employed, dichloromethane was found to greatly enhance the grafting process, and the degree of grafting increased with the increase of monomer concentration until it reached its highest value at a styrene concentration of 60 (vol %). The dependence of the initial rate of grafting on the monomer concentration was found to be of the order of 1.2. The degree of grafting was found to increase with the increase in irradiation dose, while it considerably decreased with the increase in dose rate. The formation of graft copolymers was confirmed by FTIR analysis. The structural investigation by X-ray diffraction (XRD) shows that the degree of crystallinity content of such graft copolymers decreases with the increase in grafting, and consequently, the mechanical properties of the graft copolymers were influenced to some extent. Both tensile strength and elongation percent decreased with the increase in the degree of grafting. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 2095–2102, 1999     

Simulation and optimization of cellulose and styrene graft copolymerization process

Graft polymerization of styrene into cellulose was investigated using Ceric ions redox systems as initiator. A mathematical model with the D-optimal design combined with the least squares method was applied to the system. The variables considered in the model are the reactant variables i.e. monomer and initiator concentrations and the processing variables i.e. reaction time, temperature and agitation rate. The optimal composition and processing conditions were determined using a three dimensional space analysis.     

苯乙烯-异戊二烯-丁二烯橡胶接枝苯乙烯聚合动力学

以自制的4种苯乙烯-异戊二烯-丁二烯橡胶(SIBR)为增韧组分,采用本体聚合工艺,以过氧化苯甲酰为引发剂进行苯乙烯接枝聚合以制备高抗冲聚苯乙烯,考察了用量、相对分子质量及分子链结构不同的SIBR对苯乙烯聚合速率的影响,并比较了用不同橡胶改性聚苯乙烯时的聚合动力学行为。结果表明,SIBR的用量越大聚合速率越小,相对分子质量越大则聚合速率越大;按SIBR分子链序列结构的不同聚合速率还呈现出从大到小依次为线型嵌段SIBR、线型无规SIBR、星形嵌段SIBR及星形无规SIBR的规律。用不同橡胶增韧聚苯乙烯时的聚合速率从大到小依次为SIBR、丁苯橡胶及顺丁橡胶。苯乙烯的表观接枝率随着SIBR用量或其相对分子质量的增大而减小,且远大于使用顺丁橡胶。     

Ultraviolet-radiation-induced graft copolymerization of styrene and acrylonitrile onto cotton cellulose

Photoinitiated graft copolymerization of the vinyl monomers, styrene and acrylonitrile, onto cotton cellulose was studied using uranyl nitrate and ceric ammonium nitrate as photoinitiators. Uranyl nitrate photoinitiation showed a higher level of grafting for styrene, whereas in the case of acrylonitrile ceric ammonium nitrate was found to be the better photoinitiator. Optimized conditions of grafting, when employed to cotton swollen with sodium hydroxide and zinc chloride, enhanced the graft levels for both monomers. Grafted samples were subjected to thermal analysis, as well as estimation of moisture regain and tenacity. Thermal stability increased, whereas, the moisture regain and tenacity decreased, with the increase in graft add-on in the case of both monomers. Acrylonitrile-grafted cotton showed dyeability with cationic dye that improved with the level of graft add-on. Possible explanations have been given.     

Preparation and characterization of graft copolymer from dealkaline lignin and styrene

Graft copolymerization of styrene onto dealkaline lignin by ferrous chloride and hydrogen peroxide coinitiator has been achieved successfully. The influence of temperature and reaction time as well as the amount of the styrene monomer, initiator, and catalyst on the grafting copolymerization was investigated. The optimum reaction conditions were determined as follows: c (styrene) = 20.00 mmol, c (H₂O₂) = 5.00 mmol, c (FeCl₂) = 0.10 mmol, T = 30°C and t = 48 h. The optimum yield (Y), total conversion (TC), grafting efficiency (GE), and degree grafted (DG) values were 96.6, 96.3, 59.5, and 53.7%, respectively. The copolymer of lignin grafted PS was separated and characterized by elemental analysis, differential scanning calorimetry, Fourier transform infrared, thermogravimetry analysis, field emission‐scanning electron microscopy, gel permeation chromatography, and nuclear magnetic resonance. It was demonstrated that the solubility what the copolymer exhibited turned out to be the very reverse of the original lignin. The surface properties and structure of lignin were completely changed after grafting copolymerization. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41900.     

Solid phase graft copolymerization. I. Effect of initiator and catalyst

Polypropylene–maleic anhydride (PP–MA) graft copolymers were produced from isotactic homopolymer polypropylene (molecular weight > 150,000) utilizing the technique of solid phase graft copolymerization. A high degree of graft (about 8–10%) was achieved on 150 mesh (U.S. Standard Sieve) samples using this process. This free-radical-initiated, catalyst-aided grafting process was effective at low temperatures (100–120°C), atmospheric pressure, and low residence times (60 min). The powder was mixed in a low shear, fixed speed, continuous mixer where the ingredients were added in stages to effect the reaction. The interfacial agent was used to etch the polymer to provide sites for the reaction. The powder was removed from the reactor on completion of the reaction. This process can be further applied to graft other reactive monomers on polypropylene (PP).     

Radiation-Induced graft copolymerization,I. Graft copolymerization of methyl methacrylate onto nylon-6

The radiation-induced graft copolymerization of methyl methacrylate onto nylon fibers was investigated at room temperature. The homopolymer was separated by soxhlet extraction. The graft yield increases with increase of dose rate from 0.1768 to 0.7072 Mrad. The percentage of grafting increase with increasing monomer concentration. Addition of copper sulphate and a non-ionic surfactant, sodium lauryl sulphate, supresses the formation of homopolymer. The value of G_b, the number of branches per 100 eV of energy absorbed in the substrate polymer, and the value of α, the fraction of substrate polymer grafted, have been computed. A kinetic scheme has been suggested.     

Chemically induced graft copolymerization of acrylic acid onto polyester fabrics. I. Kinetic investigation of grafting

The kinetics of grafting of acrylic acid onto poly(ethylene terephthalate) fabrics initiated by benzoyl peroxide has been studied. Extent of grafting depended upon time, concentration of the initiator and the monomer, as well as the presence of the activator used. From the temperature dependence of the initial rate of grafting the overall activation energy for grafting was found to be 90 kJ/mol. The results of the monomer and temperature dependence found in this study are consistent with the rate expression derived from a normal kinetic scheme for grafting.     

Structure and properties of cellulose graft copolymers. I. Radiation-induced rayon–styrene graft copolymer

Rayon–styrene graft copolymers were prepared by the direct radiation method, with the use of the preswelling technique, by irradiation with γ-rays from ⁶⁰Co. The grafting was carried out in bulk styrene and in styrene–solvent mixtures, such as styrene–methanol and styrene–acetone, to study their effect on the graft copolymerization reaction and the structure of the resulting graft copolymer. The effects of carbon tetrachloride, a chain-transfer agent, was also investigated. Three different types of rayon yarn were used; Fortisan, a modifier-type high wet-modulus rayon, and a high-tenacity tire yarn, in order to study the effect of rayon microstructure on the grafting reaction. The molecular structure of the rayon–styrene graft copolymers was studied by hydrolyzing away the cellulose backbone and measuring the molecular weights of the grafted polystyrene branches. For grafting in bulk styrene, the molecular weights of the grafted polystyrene ranged from 400,000 to 1,000,000, while those of the polystyrene homopolymer formed in the outside solution were of the order of 30,000–50,000. The molecular weights of the grafted polystyrene branches tended to increase with per cent grafting in the graft copolymer. For grafting in styrene–methanol and styrene–acetone mixtures, the molecular weights of the polystyrene branches decreased with increasing solvent content. The addition of carbon tetrachloride to bulk styrene resulted in a sharp decrease in the molecular weights of the grafted branches. The grafting frequency or number of polystyrene branches per cellulose chain was calculated from the per cent grafting and the molecular weights of the polystyrene branches. The morphology of the rayon–styrene graft copolymers and some of their physical properties are discussed.     

New aspects of graft copolymerization of styrene onto cellulose induced by gamma rays

Graft products of styrene onto cellulose prepared by simultaneous gamma-ray irradiation under various conditions were acid-hydrolysed to recover polystyrene produced within the cellulose matrix. The polystyrene was subjected to gel permeation chromatography to determine the molecular weight (M) and further separated with a thin-layer chromatographic (t.l.c.) technique into two components, i.e. the true grafted side-chain polymer and attendant homopolymer. This t.l.c. experiment allowed an estimation of the true percentage grafting (Y). Influences of changing the reaction conditions upon the values of M and Y were thus investigated, and some newer aspects on vinyl polymerization occurring within the cellulose matrix are presented.     

Radiation-induced graft copolymerization of mixtures of styrene and acrylamide onto cellulose acetate. V. Studies on thermal behavior

The thermal behaviors of cellulose acetate, either grafted or ungrafted, were studied. A thermogram of cellulose acetate when grafted with acrylamide is characterized by an endothermic peak at 340°C. If, however, styrene is grafted, the thermogram shows two characteristic exothermic peaks at 330 and 420°C. A thermogram of the mixed graft comprising both acrylamide and styrene, on the other hand, is characterized by only one exothermic peak at 420°C. A consideration of various thermal data indicates that cellulose acetate when grafted is comparatively more stable than when not grafted. Again, styrene is found to be more effective than acrylamide in increasing the stability.     

Radiation-induced graft copolymerization of mixtures of styrene and n-butyl acrylate onto cellulose and cellulose triacetate

Mixtures of styrene and n-butyl acrylate of various compositions were grafted onto cellulose and cellulose triacetate fibers preirradiated with γ-rays at 0°C in air. Monomer reactivity ratios of the grafted copolymers were found to be different from those of the nongrafted copolymers or those of AIBN-initiated copolymers. The active species initiating the graft copolymerization were trapped radicals for cellulose and peroxides for cellulose triacetate. Kinetic investigations of the graft copolymerization of styrene onto preirradiated cellulose triacetate fibers were also carried out, and it was found that the kinetic scheme for radical polymerization is also applicable to graft copolymerization in a heterogeneous system.     

Radiation-induced graft copolymerization of methacrylic acid onto polypropylene fibers. III. Characterization

Polypropylene-g-polymethacrylic acid graft copolymer, prepared by simultaneous-irradiation technique, was characterized to determine the structural changes, occurring in the copolymer. The presence of polymethacrylic acid graft in the copolymer was ascertained by infrared spectroscopy. Crystallinity of the grafted fibers, as deduced from X-ray diffraction pattern, showed a decrease with the increase in graft level in the fiber. Such a behavior has been attributed to the dilution of crystalline fraction of polypropylene by the incorporation of amorphous polymethacrylic acid chains in the fiber matrix, without disrupting the original crystallites of the backbone polymer. The density of the grafted samples showed a continuous increase with the increase in percent graft. However, the diameter did not change up to 16% graft content, beyond which an increase in the diameter was observed. This increase in diameter has been related with the sharp increase in disperse dye uptake of the grafted fiber at higher levels of grafting.     

Effect of lignin in graft copolymerization of methyl methacrylate on cellulose by ceric ion

The effect of lignin contained in cellulosic materials in graft copolymerization of methyl methacrylate on such materials using ceric ion as initiator was studied. It was found that the percent grafting and the average molecular weight of grafts became lower in samples having a larger lignin content but the number of grafts formed increased proportionally up to lignin content of about 2.5%. Ceric ion reacted at a faster rate with lignin than with cellulose in wood pulp, and the results indicating that the active sites formed on lignin by oxidation with ceric ion accelerate the formation of grafts and increase the number of grafts were obtained. But on the other hand, the active sites participated in the termination reaction of the growing graft polymer radicals to cause lowering of the average molecular weight of grafts.     

Effect of emulsifier type on the copolymerization of styrene and acrylic acid

In this work we report the emulsion copolymerization of styrene and acrylic acid using a cationic (cetyltrimethylammonium bromide or CTAB) or an anionic (sodium dodecylsulfate or SDS) emulsifier. Latexes were stable and monodisperse with spherical particles of ～100 nm for the CTAB latex and of ～70 nm for the SDS latex. However, a random copolymer was produced with CTAB whereas a “blocky” copolymer was obtained with SDS. Here we propose a mechanism to explain these structural differences in terms of the relative reactivities of styrene and acrylic acid and of their initial location and distribution in the SDS and CTAB emulsions.     

Polymerization and graft copolymerization of styrene initiated by ceric ion in acetonitrile/water solution

The polymerization of styrene initiated by a ceric ion/pinacol system and the graft copolymerization of styrene onto microcrystalline cellulose initiated by ceric ion were studied in the mixed solution composed of acetonitrile and water. Although the graft copolymer of polystyrene onto microcrystalline cellulose was not obtained in the acetonitrile solution, addition of water initiated the polymerization, and the grafting ratio was increased with increasing the water added. The rate of polymerization of styrene in the ceric ion/pinacol system increased similarly with increasing the water content in the solution. Acetonitrile is miscible with water, but the solution was separated to two phases by adding styrene into the solution containing above 20% of water; the monomer was dissolved in both acetonitrile and water phases. The polymer was undissolved in this mixed solution. The effects of water on the polymerization in the mixed solvent system are discussed from the standpoint of reaction mechanism.     

Graft copolymerization of lignosulfonate and styrene

A study was made of the graft copolymerization of calcium lignosulfonate with styrene. Heterogenous copolymerization were carried out with methanol as swelling medium, using ferrous ion as catalyst, and ozone and/or hydrogen peroxide as initiator. When using peroxide alone as initiator, monomer conversion was low; after ozonization of lignosulfonates, monomer conversion increased considerably and the grafting efficiency, as well as degree of lignosulfonate grafted, was improved. At 55°C, a 10-fold increase in conversion was observed for reactions with ozone-pretreated lignosulfonates. The investigated factors that affected the graft copolymerization were: the amount of peroxide and ozone charged, the reaction temperature and the ratio of styrene/methanol.