Electron spin resonance studies on graft copolymerization of gaseous styrene onto preirradiated polypropylene. III. Preirradiation under vacuum followed by exposure to oxygen at −78°C

Grafting of styrene vapor was carried out onto polypropylene γ-irradiated under vacuum followed by exposure to oxygen at ?78°C. A comparison with the results on polypropylene irradiated in an oxygen atmosphere leads to an interesting result. Two samples were irradiated at room temperature under vacuum and in an oxygen atmosphere, respectively, the former being followed by exposure to oxygen. Although irradiation was carried out at room temperature for either sample and nearly the same amounts of the peroxy radicals are trapped, the former showed more grafting than the latter. The origin of this difference was investigated by means of electron spin resonance. Significant differences were observed in ESR spectra as well as in isothermal decays of the trapped peroxy radicals. In the former sample, the trapped peroxy radicals had a higher mobility, and consequently a significant hydrogen abstraction by the peroxy radicals was observed during storage at 40°C. This result supports the conclusion of the previous paper that the radicals effective in the grafting reaction of polypropylene preirradiated in an oxygen atmosphere are the carbon radicals which are produced by hydrogen abstraction by the peroxy radicals.     

Surface modification by continuous graft copolymerization. II. Photoinitiated graft copolymerization onto polypropylene film surface

A method for photochemically induced graft copolymerization of acrylamide (AM) onto polypropylene (PP) film surface by a continuous presoaking process under nitrogen atmosphere has been developed. After removal of homopolymer formed, ESCA, UV spectroscopy, contact angle, and adhesion measurements confirmed a photografted layer on the surface of the PP film. The results from spectral analysis and surface properties measurements were consistent. The best grafting yield was obtained for 7–10 s irradiation time. Stabilizing additives in the PP film had no evident effect on the photografting. Benzophenone was an efficient photoinitiator for photografting of PP film with AM. An AM concentration of 0.5–1.3M in the presoaking solution was appropriate in the present case. Acetone was the best solvent among the three alifatic ketones tested (acetone, methylethylketone, and methylpropylketone).     

Photoinduced graft polymerization of styrene onto polypropylene substrates

The photochemical grafting of styrene onto polypropylene (PP) using benzophenone (BP) and benzoin ethyl ether (BEE) as photosensitizers is described. The effects of various parameters (such as monomer and photosensitizer concentration, reaction time, and solvent) on percent grafting were studied. We found that BP is a very efficient photosensitizer for the grafting of styrene onto PP surfaces. Unlike BEE, BP does not initiate nongrafting homopolymerization reactions in solution which compete with grafting reactions. This is advantageous over other photosensitizers since homopolymer formed in solution can interfere with the grafting reaction as well complicate sample preparation and purification. The graft copolymers obtained using both BP and BEE were characterized by high resolution ¹H-NMR, optical microscopy and swelling studies. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 883–889, 1997     

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。     

聚丙烯纤维共辐射接枝苯乙烯的研究

以60Co γ射线为辐射源,在氮气保护下对聚丙烯(PP)纤维和苯乙烯-二乙烯苯在甲醇介质中进行共辐射接枝。结果表明,当接枝液中苯乙烯质量分数为20％-30％,辐射总剂量为25-50 kGy时,PP纤维的接枝率高。二乙烯苯相对苯乙烯的质量分数为2％时,纤维的接枝率和玻璃化转变温度最高,分别为701％和161.5℃。接枝反应离开辐射源后存在一定程度的后效应,放置一定时间和接枝液中加入适量无机酸均可有效提高PP纤维的接枝率。在相同条件下,用乙醇替代甲醇可以达到相近的接枝率。     

Gama radiation-induced graft copolymerization of N-p-hydroxyphenylmaleimide onto polypropylene films

Polypropylene (PP) films were grafted with N-p-hydroxyphenylmaleinide using γ-radiation. The effect of both monomer concentration and dose rate on the degree of grafting was measured. Characterization of the grafted PP films included IR spectroscopy, X-ray diffraction, mechanical properties, thermal stability and surface topology and the dyeing characteristics of the grafted films with different dyes were also investigated.     

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.     

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.     

Ultraviolet radiation-induced graft copolymerization of 2-hydroxyethyl methacrylate onto polypropylene

Polypropylene staple fibers were grafted with 2-hydroxyethyl methacrylate (HEMA) using ultraviolet radiation in the presence of three different photoinitiators, uranyl nitrate (UN), ceric ammonium nitrate (CAN), and benzoin ethyl ether (BEE), separately. The parameters of grafting were optimized for obtaining maximum graft add-on. BEE appeared to be a better photoinitiator than the other two, giving maximum possible graft add-on. CAN, as a chemical initiator, did not show significant improvement in grafting. The moisture regain of the grafted polypropylene increased in proportion with the graft add-on. Dyeing with reactive dye could give only light color to the grafted fiber. Possible explanations have been given. © 1994 John Wiley & Sons, Inc.     

Radiation‐induced graft copolymerization of 2‐vinylpyridine and styrene onto isotactic polypropylene fiber

Isotactic polypropylene fiber (IPP) was graft‐copolymerized using 2‐vinyl pyridine (2‐VP) and styrene (sty) as the monomers by the mutual irradiation method in air. The percentage of grafting was determined as a function of various reaction parameters and it was found that the maximum grafting of 2‐VP (114%) and sty (76%) was obtained at an optimum dose of 1.08 × 10⁴ and 0.64 × 10⁴ Gy using 1.8 × 10⁻² mol of 2‐VP and 4.3 × 10⁻² mol of sty, respectively. The graft copolymers were characterized by differential scanning calorimetric analysis and isolation of the grafted chains from the grafted iPP samples. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 2959–2969, 1999     

Radiation-induced graft copolymerization of methacrylic acid onto polypropylene fibers VI. Dyeing behavior

The dyeing behavior of polypropylene-g-polymethacrylic acid fibers prepared by graft copolymerization of methacrylic acid onto polypropylene fibers by gamma-ray irradiation was evaluated for their dyeability characteristics using two basic dyes, rhodamine B and methylene blue. An increase in the dye uptake and moisture regain with the increase in graft content was observed. Such behavior has been attributed to the hydrophilicity imparted to polypropylene fiber by the presence of polar carboxyl groups in polymethacrylic acid grafts. The dependence of rate of dyeing on the percentage graft was evaluated. The diffusion coefficient of the fiber showed an increase with the increase in graft content and has been related to the structural changes occurring during grafting.     

Radiation-Induced graft copolymerization of methacrylic acid onto polypropylene fibers. V. Mechanical properties

Mechanical properties of polypropylene-g-poly(methacrylic acid) fibers, prepared by graft copolymerization of methacrylic acid onto polypropylene fiber using simultaneous gamma ray irradiation technique, were evaluated. In general, an improvement in the mechanical behavior of the polypropylene fiber by grafting was observed. Denier and initial modulus of the fiber showed a linear increase with the percent graft, and elongation showed an opposite trend. The results have been explained in terms of reinforcing effect of poly(methacrylic acid) grafts and reduction in the segmental mobility of the polymeric chains. Tenacity also increases up to certain graft level, beyond which a sharp decrease occurs, probably due to the influence on the compactness of the macromolecular chains with the further grafting.     

Radiation-Induced graft copolymerization of methacrylic acid onto polypropylene fibers. IV. Thermal behavior

Thermal behavior of polypropylene-g-poly(methacrylic acid) fibers prepared by graft copolymerization of methacrylic acid onto polypropylene fibers, using simultaneous-irradiation technique, was evaluated by thermogravimetric analysis, differential scanning calorimetry, and limiting oxygen index measurements. In general, the thermal properties of polypropylene fiber were markedly improved by the grafting of methacrylic acid. The inherent crystallinity of polypropylene, as deduced from DSC, did not show any change in the grafted fibers, suggesting that the grafting occurs in the amorphous region, without disrupting the crystalline part of the polymer. The LOI of grafted fibers showed an increase over the original fiber.     

Electron spin resonance studies on photodegradable polymers

Films of polyethylene (PE), polypropylene (PP), and polystyrene (PS) containing 1% of selected halogen compounds and films without additives were UV irradiated (253.7 nm) at 77°K and their electron spin resonance (ESR) spectra compared. In each case, the spectra were characteristic of the polymer, and the presence of the additive mainly enhanced the radical yield. No signal was observed for the additives alone after irradiation, suggesting that when incorporated into the polymer, they serve as photosensitizers rather than as primary sources of free radicals in promoting photo-chemical degradation.     

Graft copolymerization studies. III. Methyl methacrylate onto polypropylene and polyethylene terephthalate

The tert‐butoxy radical‐facilitated grafting of methyl methacrylate (MMA) onto commercial polypropylene (PP) pellets and fiber was investigated in heterogeneous conditions similar to practical systems. Free‐radical grafting of several other monomers onto PP fiber was also investigated. Also, preliminary data from the grafting of MMA onto poly(ethylene terephthalate) pellets is presented. The PP‐graft‐PMMA residues were detected by solid‐state ¹³C‐NMR and photoacoustic IR spectroscopy. There was a good correlation between the degree of grafting (DG) determined from these spectroscopic techniques and the results from gravimetric methods. A maximum grafting efficiency of over 50% was found, whereas DG (20%) remained constant at various PP pellet, initiator, and monomer concentrations. However, at relatively low PP fiber concentrations, the DG was 27%; the increase was most likely due to the greater surface area of the fiber. There was also a reduction in DG (14%) at relatively low initiator concentrations. The reaction conditions were altered to favor grafting by the addition of more polymer substrate. When the ratio of tert‐butoxy radicals to PP was decreased, more of the substrate remained unmodified, and empirical calculations showed the formation of grafts with up to 40 monomer units. At high initiator concentrations, calculations showed that the graft residues were 1–2 units long. Therefore, variation of the polymer, initiator, and monomer concentrations was shown to have a significant effect on grafting. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 898–915, 2002     

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.     

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.     

Effect of solvents on gamma radiation induced graft copolymerization of methyl methacrylate onto polypropylene

Methyl methacrylate was grafted onto polypropylene films using gamma radiation. Effects of different parameters, such as radiation dose, inhibitor concentration, monomer concentration, and type of solvents on the graft yield were investigated. It was established that the graft yield depends on the proper choice of solvent mixtures, and its maximum value can be obtained by using decalin/methanol mixture in the ratio 2 : 3 wt %. Thermal characteristics using differential scanning calorimetry shows that grafting has practically no effect on the crystallinity of PP. © 1997 John Wiley & Sons, Inc.     

Cation exchange membranes by radiation‐induced graft copolymerization of styrene onto PFA copolymer films. II. Characterization of sulfonated graft copolymer membranes

PFA‐g‐polystyrene sulfonic acid membranes were prepared by simultaneous radiation‐induced graft copolymerization of styrene onto poly(tetrafluoroethylene‐co‐perfluorovinyl ether) (PFA) film followed by sulfonation. The membrane physico‐chemical properties such as swelling behavior, ion exchange capacity, hydration number, and ionic conductivity were studied as a function of the degree of grafting. Thermal as well as chemical stability of the membranes was also investigated. The membrane properties were found to be mainly dependent upon the degree of grafting. The water uptake, ion exchange capacity, hydration number, and ionic conductivity of the membranes were increased, whereas the chemical stability decreased as the degree of grafting increased. The membranes showed reasonable physico‐chemical properties compared to Nafion 117 membranes. However, their chemical stability has to be further improved to make them acceptable for practical use in electrochemical applications. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1–11, 2000     

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.