Photografting of N‐isopropylacrylamide and glycidyl methacrylate binary monomers on polyethylene film: Effect of mixed solvent consisting of water and organic solvent

Photografting (λ > 300 nm) of N‐isopropylacrylamide (NIPAAm) and glycidyl methacrylate (GMA) binary monomers (NIPAAm/GMA) on low‐density polyethylene film (thickness = 30 μm) was investigated at 60°C using mixed solvent consisting of water and an organic solvent such as acetone. Xanthone was used as a photoinitiator by coating it on the film surfaces. A maximum percentage of grafting was observed at a certain concentration of acetone in the mixed solvent, which was commonly observed for both ratios of NIPAAm/GMA, 8/2 and 7/3. Based on the photografting of NIPAAm/GMA on xanthone‐coated film, monomer reactivity ratios of NIPAAm (r₁) and GMA (r₂) were calculated using the Fineman–Ross method. The values were 0.31 ± 0.1 and 4.8 ± 0.2 for the water solvent system, while they were 0.96 ± 0.1 and 4.9 ± 0.1 for the mixed solvent system. NIPAAm/GMA‐grafted films with a homogeneous distribution of grafted chains were formed by photografting using water and mixed solvents. The NIPAAm/GMA‐grafted films exhibited temperature‐responsive characters, whereas the grafted films showed a reversible change in the degree of swelling between 0 and 50°C, respectively. Epoxy groups in the grafted poly(NIPAAm/GMA) chains could be aminated with ethylenediamine in N,N′‐dimethylformamide at 70°C for 3 h. Complexes of the aminated NIPAAm/GMA‐grafted chains with cupric ion exhibited catalytic activity for the decomposition of hydrogen peroxide at 20 to 50°C. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 2469–2475, 2005     

Examination of the role of oxygen in the photografting of methacrylic acid on a polyethylene film with a mixed solvent consisting of water and organic solvents

The photografting of methacrylic acid (MAA) on a linear low‐density polyethylene film (thickness = 30 μm) under air and nitrogen atmospheres was investigated at 60°C in mixed solvents consisting of water and an organic solvent, with xanthone as a photoinitiator. The organic solvents used were acetone, methanol, tetrahydrofuran, and dioxane. A maximum percentage of grafting occurred at a certain concentration of the organic solvent in the mixed solvent. This was observed for the systems under both air and nitrogen. The grafting reaction under air exhibited an induction period, but the rate of grafting after the period was greater than that under nitrogen. The formation of poly(ethylene peroxide)s by photoirradiation seemed to be a factor for the accelerated photografting under air. On the basis of attenuated total reflection infrared spectroscopy and scanning electron microscopy of the grafted film, the MAA‐grafted chains of the sample prepared under air tended to penetrate more deeply inside the film than those of the sample prepared under nitrogen. The resulting grafted films exhibited a pH‐responsive character: the grafted films shrank in an acidic medium but swelled in alkaline medium. This was evaluated from measurements of dimensional changes in the grafted films. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 992–998, 2003     

Characteristics of acrylic acid and N-isopropylacrylamide binary monomers–grafted polyethylene film synthesized by photografting

Method for introducing grafted chains consisting of two types of monomer components, acrylic acid (AA) and N-isopropylacrylamide (NIPAAm), into low-density polyethylene (PE) film (thickness = 25 μm) was investigated by two photografting technique using xanthone photoinitiator at 60°C. In the first method (one-step method), AA and NIPAAm binary monomers were graftcopolymerized onto PE film. In the second method (two-step method), AA was first photografted onto PE film and then NIPAAm was further introduced into the AA-grafted PE film by a second-step photografting. Water absorbencies of the grafted films (one- and two-step samples) prepared by the one- and two-step methods, respectively, decreased in the order of AA-grafted film > one-step sample > two-step sample > NIPAAm-grafted film. The water absorbency steeply decreased at 20 to 40°C with increasing temperature when immersed in water at the temperatures (5–60°C) for 24 h. Thermosensitivity, which was defined as the ratio of water absorbencies of the grafted samples at 5 and 60°C, was higher for the one-step sample than the two-step one. The different extent of the water absorbency and the thermosensitivity between both samples is discussed in terms of location of grafted chains in the film substrate, which was determined by electron probe microanalysis and attenuated total reflection–infrared measurements, and monomer sequence distribution of the grafted chains. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67:2057–2064, 1998     

Characteristics of methacrylic acid‐grafted polyethylene films prepared by photografting in the presence of polyfunctional monomers

Photografting of methacrylic acid (MAA) on low‐density polyethylene film (thickness = 30 μm), on which xanthone photoinitiator was coated earlier, in the presence of polyfunctional monomers such as N,N′‐methylenebisacrylamide, ethylene glycol dimethacrylate, and trimethylol propane triacrylate was examined at 60°C in water/acetone (3:1 v/v) mixture solvent. The photografting was retarded at the earlier stage of polymerization, and then accelerated when small amounts of the polyfunctional monomers (1–3 mol % of MAA monomer used) were added to the system. Addition of the polyfunctional monomers did not affect distribution of the grafted chains in the cross section of the resultant MAA‐grafted PE film, which was measured by electron probe microanalysis. The MAA‐grafted samples were subjected to adsorption of cupric ions at 25°C for 24 h in the system of pH = 5. The adsorption was considerably suppressed for the grafted samples prepared at the earlier stage of polymerization in the system with the polyfunctional monomers. The phenomenon was discussed in terms of the formation of crosslinked and branched structures in the MAA‐grafted chains depending on the polymerization stage in the system with polyfunctional monomers. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1262–1268, 2006     

Photografting of methacrylic acid on polyethylene film: Effect of mixed solvents consisting of water and organic solvent

Photografting of methacrylic acid (MAA) on linear low‐density polyethylene film (thickness = 30 μm) was investigated at 60°C in mixed solvents consisting of water and organic solvent with xanthone as the photoiniator. The organic solvents examined were acetone, methanol, tetrahydrofuran, and dioxane. A maximum percentage of grafting was observed at a certain concentration of organic solvent in the mixed solvent, depending on the nature of the organic solvent. Distribution of the grafted chains in the resultant MAA‐grafted film, which was examined by scanning electron microscopy and attenuated total‐reflection IR spectroscopy, was largely influenced by the use of the mixed solvent. The grafted samples swelled in the alkaline region and shrank in acidic medium, showing a pH‐responsive character. The extent of the pH‐responsive function was closely related to the location of grafted chains, which could be controlled by proper choice of the composition of organic solvent in the mixed solvent. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2454–2461, 2002     

Factors affecting photografting of methacrylic acid on polyethylene film in liquid phases system

Factors affecting photografting (λ > 300 nm) of methacrylic acid on low-density polyethylene film were investigated in liquid-phase system with water. Benzophenone was used as a sensitizer by coating it on the film surface. Factors examined were monomer concentration (1.3 wt% to 10.0 wt%), polymerization temperature (30°C to 70°C), and film thickness (30 μm and 80 μm). It was found that grafted polymer is formed preferentially as compared with homopolymer under conditions such as monomer concentration higher than 6.0 wt%, polymerization temperature higher than 50°C, and film thickness of 30 μm. The structure of the grafted samples obtained in the above systems was characterized by the grafted chains distributing over the film and the flat appearance of film surface. In the grafting systems using the monomer concentration lower than 6.0 wt%, the polymerization temperature lower than 50°C, and the film thickness of 80 μm, homopolymer was formed predominantly. The resultant grafted chains localized mainly on the film surface, which appeared to be grainy.     

Water-absorbing characteristics of acrylic acid-grafted carboxymethyl cellulose synthesized by photografting

Cellulosic absorbents for water were synthesized by photografting (λ > 300 nm) acrylic acid (AA) onto fiberous carboxymethyl cellulose (CMC, degree of substitution [DS] = 0.1–0.4) at 30°C in the presence of N,N′-methylenebisacrylamide as a crosslinker. The CMC sample was pretreated with hydrogen peroxide in the presence of sulfuric acid to prepare CMC peroxides with a peracid type as a polymeric photoinitiator. The peroxides were active for the photografting and AA could be grafted onto CMC with percent graftings higher than 150% by photoirradiation of 10 min at 30°C. The amount of water absorbed increased with increasing percent grafting of AA and DS of CMC. The amount was reduced considerably when the absorbents were prepared by the photografting of AA onto crosslinked CMC in the absence of the crosslinker. Graft copolymers which display a decreasing water absorbency as a function of temperature were prepared by two methods: In the first synthesis method, AA and N-isopropylacrylamide (NIPAAm) binary monomers were graft-copoly-merized onto CMC samples using photoinitiation. In the second method, photografting of AA was followed by a second-step photografting of NIPAAm to produce a terpolymer with two types of side chains of differing repeat unit composition on the CMC substrate. Graft copolymers formed by both methods showed decreasing water absorbency as temperature increased with losses in water absorbency of up to about 60% as the temperature was increased above 30°C. Effects of NIPAAm composition and corsslinker content in the graft copolymers on the decreasing water absorbency as a function of temperature were also examined. © 1996 John Wiley & Sons, Inc.     

Effect of hydroquinone on location of methacrylic acid-grafted chains introduced into polyethylene film by photografting

Effect of hydroquinone (HQ) on photografting of methacrylic acid (MAA) on low-density polyethylene film (thickness = 30 μm) sensitized with xanthone was investigated at 60°C in water medium. Both the formation of grafted polymer and homopolymer were retarded by HQ. The contact angle of water on the MAA-grafted polyethylene films (sample with HQ) prepared in the system with HQ was larger than that of the grafted films (sample without HQ) prepared in the system without HQ. Based on electron probe microanalysis of the grafted films, it was found that distribution of grafted chains in the direction of film thickness is different between the both grafted films. Namely, the grafted chains of the sample with HQ distributed in the inside of the film compared with those of the sample without HQ. The difference in the distribution of grafted chains between the grafting systems with and without HQ was discussed in terms of effect of HQ on the photodecomposition of MAA-grafted chains and the subsequent initiation of polymerization by radicals due to the photodecomposition.     

Temperature-responsive characteristics of N-isopropylacrylamide-grafted polymer films prepared by photografting

Photografting of N-isopropylacrylamide (NIPAAm) on ethylene–vinyl alcohol copolymer films (thickness = 15,20, and 25 μm) and low-and high-density polyethylene films (thickness = 30 μm) was carried out at 60°C in a water medium. Xanthone was used as a photoinitiator by coating it on the film samples. The resultant NIPAAm-grafted films exhibited a temperature-responsive character, which was evaluated by measuring a dimensional change of the grafted films. The grafted films swelled and shrank in water at temperatures lower and higher than around 30°C, respectively. The character was found to be reversible between 0 and 50°C. It was observed that the extent of the character is largely influenced by film thickness, location of NIPAAm-grafted chains, and crystallinity of film substrate. © 1994 John Wiley & Sons, Inc.     

Thermoresponsive surface prepared by atom transfer radical polymerization directly from poly(vinylidene fluoride) for control of cell adhesion and detachment

Thermoresponsive surface was prepared from commercial poly(vinylidene fluoride) (PVDF) films via surface‐initiated atom transfer radical polymerization. The direct initiation of the secondary fluorinated site of PVDF facilitated grafting of the N‐isopropylacrylamide (NIPAAm) monomer. The PVDF surfaces grafted with poly(N‐isopropylacrylamide) [P(NIPAAm)] were characterized by X‐ray photoelectron spectroscopy. Kinetics study revealed that the P(NIPAAm) chain growth from the PVDF surface was consistent with a “controlled” process. The temperature‐dependent swelling behavior of the surfaces in aqueous solution was studied by atomic force microscope. At 37°C [above the lower critical solution temperature (LCST, about 32°C) of NIPAAm], the seeded cells adhered and spread on the NIPAAm grafted PVDF surface. Below the LCST, the cells detached from the P(NIPAAm)‐grafted PVDF surface spontaneously. The thermoresponsive surfaces are potentially useful as stimuli‐responsive adhesion modifiers in the biomedical fields.© 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Photografting of methyl methacrylate onto high‐density polyethylene initiated by aliphatic ketones

The photografting of a water‐insoluble monomer methyl methacrylate (MMA) onto high‐density polyethylene (HDPE) initiated by an aliphatic ketone/water/alcohol initiating system has been reported. The aliphatic ketones, such as acetone, butanone, and cyclohexanone, could effectively initiate the grafting reaction when they were mixed with water and ethanol to form homogeneous aliphatic ketone/water/ethanol mixed solvents that could dissolve the water‐insoluble monomer. The nature of aliphatic ketone affected the grafting; at the same aliphatic ketone/water/ethanol volume ratio, the grafting system containing acetone or butanone always led to a higher extent of grafting than that containing cyclohexanone. Water also played a very important role in the grafting reaction; in the tested range, the rate of formation of grafted PMMA on HDPE increased with the increase of water : volume ratio. The grafting of MMA carried out in 5 acetone/40 water/55 ethanol mixed solvent led to the highest extent of grafting. ATR‐FTIR characterizations of the grafted samples proved the successful grafting of MMA onto HDPE. SEM investigations of the HDPE surfaces grafted in different aliphatic ketone/water/ethanol mixed solvents indicate the morphologies of grafted surfaces varied with the mixed solvents used. This study broadened the application fields of the aliphatic ketone/water/alcohol initiating system for photografting. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Photografting of acrylamide on ethylene–vinyl alcohol copolymer film

Photografting (λ > 300nm) of acrylamide on ethylene-vinyl alcohol copolymer film (vinyl alcohol unit = 56 mol%, film thickness = 20μm) was investigated at 60°C in water medium, where photoinitiators were coated on the film earlier. The percent grafting decreased in the order of xanthone ≈ benzophenone > anthraquinone > benzoyl peroxide. The graft efficiencies in each sensitized system were less than 30%, showing a predominant formation of homopolymer. Grafting of acrylamide on the film was also initiated in systems with and without photoirradiation when ceric salt was used as an initiator. Based on electron probe microanalysis of the grafted films, the grafted chains of the sample prepared by photografting were distributed inside the film, while those of the sample prepared by ceric salt-initiated grafting without photoirradiation were located mainly on the film surface. The grafted films prepared by the former system exhibited a higher moisture permeability than those prepared by the latter system.     

Glow-discharge-induced graft polymerization of acrylic acid onto poly[1-(trimethylsilyl)-1-propyne] film

Graft polymerization of acrylic acid onto poly[1-(trimethylsilyl)-1-propyne] [poly(TMSP)] film was examined. The water contact angle of poly(TMSP) film decreased remarkably from 90 to 15° by plasma treatment, which gradually increased up to 40° after several days. When the film exposed to a glow discharge was heated in an aqueous solution of acrylic acid at 80°C for 24 h, graft polymerization proceeded on the film surface, which was confirmed by ATR-IR and ESCA spectra. Graft polymerization effectively occurred above a threshold temperature (80°C). The water contact angle of the grafted film was about 30°, and did not change with time. In contrast, when a poly(TMSP) film exposed to UV irradiation was heated in an aqueous solution of acrylic acid, graft polymerization took place not only on the film surface but also inside the film.     

Photografting of acrylonitrile and methacrylic acid on polyethylene film under air atmosphere

Photografting of acrylonitrile (AN) and methacrylic acid (MAA) on low-density polyethylene film (thickness 70 μm), on which benzophenone was coated earlier, was investigated at 60°C in water medium under air atmosphere. In the case of AN monomer, where grafted polymer was formed predominantly, oxygen in the system promoted the formation of both grafted polymer and homopolymer. With MAA monomer, in which homopolymer was formed preferentially compared to the formation of grafted polymer, the formation of homopolymer was accelerated by the presence of oxygen while suppressing that of grafted polymer. The formation of polyethylene peroxides by photoirradiation seemed to be a factor for the accelerated polymerization under air atmosphere. It was found that additives such as hydrazine and metallic ions (Fe²⁺, Cu²⁺, and Ni²⁺) are useful for enhancing the photografting under air atmosphere. © 1993 John Wiley & Sons, Inc.     

Surface photografting polymerization of trimethylolpropane triacrylate onto LDPE substrate in tetrahydrofuran/water mixtures

A surface photografting polymerization (λ > 300 nm) of a multifunctional monomer which was trimethylolpropane triacrylate (TMPTA), was conducted with benzophenone (BP) as photoinitiator and LDPE as model substrate, in mixed solvents containing tetrahydrofuran (THF) and water. Proved by ATR‐IR, highly crosslinked grafted layer was generated rapidly under UV irradiation. Effects on percent conversion of grafting are detailed with, such as feed ratio of BP to TMPTA, mass percent of TMPTA in the reaction system, mass percent of water in the mixed solvents and addition of the second monomer, methyl methacrylate (MMA). As both verified by SEM and AFM, relatively planar grafted layer was produced when photografting was carried out merely in THF; adding water in the reaction system caused the formation of “craters” in the grafted layer. In addition, effects of mass percent of water in the mixed solvents, UV irradiation time, TMPTA concentration and addition of MMA on the size, shape and quantity of the “craters” were investigated by SEM. A plausible mechanism for the formation of “craters” is also proposed. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Surface photografting polymerization of vinyl acetate,maleic anhydride,and their charge‐transfer complex. IV. Maleic anhydride

In general, it has been accepted that maleic anhydride (MAH) cannot be homopolymerized under normal conditions. However, MAH can be grafted onto substrates under UV irradiation rather easily. In this study, the photografting polymerization of MAH was examined with low‐density polyethylene (LDPE) film as a substrate. The initiating performances of different photoinitiators, including benzophenone (BP), Irgacure 651, and benzoyl peroxide (BPO), were examined. The effects of some principal factors, such as the temperature, solvent, and UV intensity, on the grafting polymerization of MAH were also investigated. The results show that MAH can be smoothly grafted onto LDPE film by UV radiation. Enhancing the intensity of UV radiation and elevating the irradiation temperature facilitate the grafting polymerization of MAH. Among BP, Irgacure 651, and BPO, Irgacure 651 can initiate the polymerization of more MAH, but BP is more effective for the initiation of surface grafting polymerization. Solvents of MAH also have a great influence on the grafting polymerization; some of them even seem to take part in the reaction. The occurrence of photografting polymerization was verified with Fourier transform infrared and electron spectroscopy for chemical analysis spectra. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 87: 2318–2325, 2003     

Thermo‐ and pH‐responsive behaviors of graft copolymer and blend based on chitosan and N‐isopropylacrylamide

Thermo‐ and pH‐sensitive polymers were prepared by graft polymerization or blending of chitosan and poly(N‐isopropylacrylamide) (PNIPAAm). The graft copolymer and blend were characterized by Fourier transform‐infrared, thermogravimetric analysis, X‐ray diffraction measurements, and solubility test. The maximum grafting (%) of chitosan‐g‐(N‐isopropylacrylamide) (NIPAAm) was obtained at the 0.5 M NIPAAm monomer concentration, 2 × 10⁻³ M of ceric ammonium nitrate initiator and 2 h of reaction time at 25°C. The percentage of grafting (%) and the efficiency of grafting (%) gradually increased with the concentration of NIPAAm up to 0.5 M, and then decreased at above 0.5 M NIPAAm concentration due to the increase in the homopolymerization of NIPAAm. Both crosslinked chitosan‐g‐NIPAAm and chitosan/PNIPAAm blend reached an equilibrium state within 30 min. The equilibrium water content of all IPN samples dropped sharply at pH > 6 and temperature > 30°C. In the buffer solutions of various pH and temperature, the chitosan/PNIPAAm blend IPN has a somewhat higher swelling than that of the chitosan‐g‐NIPAAm IPN. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 1381–1391, 2000     

Photopolymerization synthesis of poly(N-isopropylacrylamide) hydrogels

Poly(N-isopropylacrylamide) (NIPAAm) gels were formed by photopolymerization of NIPAAm in the absence of a crosslinker using a water solvent at 25°C. Factors affecting formation were the wavelength region of irradiated light, the type of photoinitiators, and the concentrations of the photoinitiator and monomer. A high-pressure mercury lamp (400 W) was used as a light source. An NIPAAm concentration of 10 wt % and irradiation time of 15 h was used for the photopolymerization. The gel (68% yield) was formed when the quartz glass system was used, but no gelation was observed for the Pyrex glass system that transmits light with π > 290 nm. The gel (100% yield) was easily formed, even in the latter system, when 30 mmol/L of hydrogen peroxide and potassium persulfate were used as the photoinitiator. Water soluble photoinitiators such as ferric chloride and sodium anthraquinone-2,7-disulfonate were not effective for the gel formation. Yield of the gel increased with increasing the potassium persulfate concentration (1–30 mmol/L), but it decreased when a high concentration of hydrogen peroxide (60 mmol/L) was used. The gel yield increased with the NIPAAm concentration (5–20 wt %). The degree of swelling of the resultant poly(NIPAAm) gels, which was measured by immersing the gels in water at various temperatures (0–50°C) for 24 h, steeply decreased at about 30°C with increasing temperature, exhibiting a temperature-responsive character. The gels swelled and shrank in water below and above the temperature, respectively. The extent of the character depended on the concentrations of hydrogen peroxide and monomer. The formation mechanism of the gel in the photopolymerization of NIPAAm using hydrogen peroxide photoinitiator was discussed. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65:1313–1318, 1997     

Improvement of gas barrier property of polyolefins by diamond‐like carbon deposition and photografting polymerization

The gas barrier properties of isotactic polypropylene (iPP) and high‐density polyethylene (HDPE) are both significantly improved by diamond‐like carbon (DLC) deposition and photografting polymerization using acrylic acid (AA) monomers. In fact, the gas barrier properties can be highly improved just by DLC or by AA‐photografting polymerization. The improvement observed by AA‐photografting polymerization is more pronounced than that by DLC deposition in our general experimental condition. In more detail, the oxygen barrier property of DLC‐deposited and AA‐grafted iPP is considerably improved by ～10 times when compared with that of neat iPP. As for HDPE, the oxygen barrier property is enhanced by nearly six times through DLC deposition and photografting polymerization. By observing the surfaces, 30 nm layer of DLC and 1.0 μm of AA‐grafted layer are firmly constructed on the polyolefins, which should contribute to the enhancement of the oxygen barrier property. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Preparation of alginate/poly(N‐isopropylacrylamide) semi‐interpenetrating and fully interpenetrating polymer network hydrogels with γ‐ray irradiation and their swelling behaviors

Semi‐interpenetrating polymer network (semi‐IPN) and fully interpenetrating polymer network (full‐IPN) hydrogels composed of alginate and poly(N‐isopropylacrylamide) were prepared with γ‐ray irradiation. The semi‐IPN hydrogels were prepared through the irradiation of a mixed solution composed of alginate and N‐isopropylacrylamide (NIPAAm) monomer to simultaneously achieve the polymerization and self‐crosslinking of NIPAAm. The full‐IPN hydrogels were formed through the immersion of the semi‐IPN film in a calcium‐ion solution. The results for the swelling and deswelling behaviors showed that the swelling ratio of semi‐IPN hydrogels was higher than that of full‐IPN hydrogels. A semi‐IPN hydrogel containing more alginate exhibited relatively rapid swelling and deswelling rates, whereas a full‐IPN hydrogel showed an adverse tendency. All the hydrogels with NIPAAm exhibited a change in the swelling ratio around 30–40°C, and full‐IPN hydrogels showed more sensitive and reversible behavior than semi‐IPN hydrogels under a stepwise stimulus. In addition, the swelling ratio of the hydrogels continuously increased with the pH values, and the swelling processes were proven to be repeatable with pH changes. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4439–4446, 2006