Surface grafting of polyethylene by mutual irradiation in methyl acrylate vapor. IV. Kinetic analysis by quartz helix microbalances

A detailed kinetic study of the γ-ray-induced surface grafting of methyl acrylate (MA) onto polyethylene (PE) has been investigated by using quartz helix microbalances. Under typical graft conditions, the grafting rate increases, levels off, and then accelerates with irradiation time; i.e., the typical growth process of the surface grafting consists of an initial stage having an increasing rate of grafting, an intermediate stage having a constant rate, and an advanced stage having an accelerated rate. A homopolymer layer (consisting only of an MA component) begins to be formed on the inner graft copolymer layer (consisting both of MA and PE components) at the transition zone in grafting rate after a duration of a constant rate of grafting. Therefore, the increasing rate in increasing rate in the intial stage of grafting reflects the graft copolymerization in the graft copolymer layer (inside the PE sheet), and the increasing rate in the advanced stage reflects the growth of the homopolymer layer. Under grafting reflects the graft tage reflects the growth of the homopolymer layer. Under grafting conditions by which the homolymer layer is not formed throughout the whole grafting process, the surface grafting remains remains in the initial stage. On the order hand, under grafting conditions by which the homopolymer layer begins to be formed from an early stage of grafting, the surface grafting proceeds rapidly from the initial stage to the advanced stage and thus skips the intermediate stage.     

Surface grafting of polyethylene by mutual irradiation in methyl acrylate vapor. I. γ irradiation

Mutual irradiation of polyethylene (PE) in methyl acrylate vapor easily forms a poly(methyl acrylate) (PMA) homopolymer layer on the inner graft copolymer layer consisting of both PE and PMA components as a result of the rapidly increasing surface-graft composition. This growth process of surface grafting has been found to provide some specific kinetic features different from those in other surface-grafting systems. With formation of the surface homopolymer layer, low- and highdensity PE sheets give the same grafting rate, whereas both sheets give different rates in grafting stages or conditions in which the homopolymer layer is not formed. This result indicates that most monomers, penetrating across the surface, are entrapped or consumed in the surface homopolymer layer; accordingly the rate becomes independent of the type of PE sheets that have significantly different diffusion coefficients. The thickness of the inner graft copolymer layer, which is kept constant after homopolymer-layer formation, increases with decreasing dose rate and with increasing monomer vapor pressure and temperature. This behavior can be qualitatively explained according to an equation for the initial steady-state grafting depth.     

Surface grafting of polyethylene by mutual irradiation in methyl acrylate vapor. III. Quantitative surface analysis by x-ray photoelectron spectroscopy

X-ray photoelectron spectroscopy (ESCA) has been used for quantitative surface analysis of surface grafts prepared by mutual irradiation of polyethylene (PE) in methyl acrylate (MA) vapor with γ rays and high-energy electrons. The binding-energy shift between the C_1s electrons in the ester group of poly(methyl acrylate) (PMA) and in PE is large enough (ca. 3.6 eV) to distinguish the PMA and PE components. The C_1s peak-area ratio of ester carbon to other carbons is related quantitatively to graft composition by constructing a calibration curve for a given instrument and excitation source, with a series of homogeneous grafts of known composition used as the calibration standards. Using the calibration curve and the measured peak ratio, the surface composition of the surface grafts is determined. The relations between surface compositions according to ESCA and attenuated total reflection (ATR) infrared spectroscopy and between adhesive bond strength and ESCA composition are discussed. In the electron-induced grafts, the grafted surface reaches maximum adhesive bondability with attainment of 100 mole % MA in the surface detected by ESCA; i.e., with formation of a homopolymer layer. The ESCA composition can be used as an indicator of the presence of the homopolymer layer or as a criterion for predicting adhesive bond strength.     

13C NMR Study of the grafting of 13C labeled maleic anhydride onto PE,PP and EPM

The chemical structure of polyolefins grafted with maleic anhydride (MA) has been the subject of much speculation, but thorough experimental studies are rare. MA with 99% ¹³C in the double bond was synthesized and grafted onto PE, EPM and PP in the melt and solution. 1D INADEQUATE ¹³C NMR spectroscopy was used to characterize the products. Saturated, monomeric MA graft structures are formed. Only for grafted PE short MA oligomers are demonstrated. Grafting occurs on secondary and tertiary carbons depending on the composition of the polyolefin. For PP a new, unsaturated MA graft structure on the polymer chain terminus is identified. All graft structures are rationalized using a simple grafting mechanism.     

Surface graft polymerization of acrylamide onto poly(ethylene terephthalate) film by UV irradiation

To improve the low water wettability of poly(ethylene terephthalate) (PET), graft polymerization of acrylamide (AAm) by UV irradiation was performed onto the surface of a PET film with the simultaneous irradiation method without using a photo sensitizer. The PET film immersed in a 10 wt % deaerated aqueous solution of AAm was found to become highly hydrophilic upon UV irradiation. Optical microscopy on cross sections of grafted films showed that localization of the graft polymerization was restricted to a thin surface region of the film. Both the low concentration of polymer radicals formed by UV irradiation and the monomer penetration limited to the film surface would be responsible for localization of the grafted layer to the film surface region. Pretreatment of the PET film with benzyl alcohol was effective for enhancement of the graft polymerization. Retention of high hydrophilicity of the surface even after rigorous extraction of homopolymer and a comparative study of polymerization without UV irradiation strongly suggested that UV irradiation of the PET film under immersion in the deaerated AAm aqueous solution would lead to formation of the true graft copolymer.     

Radiation-induced graft polymerization of maleic acid and maleic anhydride onto ultra-fine powdered styrene–butadiene rubber (UFSBR)

The functionalization of ultra-fine powdered styrene–butadiene rubber (UFSBR) was carried out using gamma radiation-induced graft polymerization of maleic acid (MA) and maleic anhydride (MAH), respectively. It was found that the graft yield of MA onto UFSBR increased rapidly up to the peak and then decreased with increasing MA content. Moreover, the peak shifted to the direction of lower MA content with increasing absorbed dose. Similarly, there was the peak of graft yield with increasing MAH content for grafting of MAH onto UFSBR, whereas the peak of graft yield was achieved at 10 wt% MAH content at different absorbed doses. On the other hand, increasing absorbed dose and decreasing monomer contents are useful to improve the graft efficiency of MA and MAH. At high dose and low monomer content, the graft yield of MAH onto UFSBR is higher than that of MA. FTIR spectra confirmed that both MA and MAH can be grafted successfully onto the UFSBR under gamma irradiation, respectively. Comparing with maleation of rubber by melt grafting, the graft yield of MAH on UFSBR is higher, which can be attributed to the network structure and nanometer size of UFSBR as well as high energy provided by radiation.     

Reversible addition–fragmentation chain‐transfer graft polymerization of styrene: Solid phases for organic and peptide synthesis

The γ‐initiated reversible addition–fragmentation chain‐transfer (RAFT)‐agent‐mediated free‐radical graft polymerization of styrene onto a polypropylene solid phase has been performed with cumyl phenyldithioacetate (CPDA). The initial CPDA concentrations range between 1 × 10^?2 and 2 × 10^?3 mol L^?1 with dose rates of 0.18, 0.08, 0.07, 0.05, and 0.03 kGy h^?1. The RAFT graft polymerization is compared with the conventional free‐radical graft polymerization of styrene onto polypropylene. Both processes show two distinct regimes of grafting: (1) the grafting layer regime, in which the surface is not yet totally covered with polymer chains, and (2) a regime in which a second polymer layer is formed. Here, we hypothesize that the surface is totally covered with polymer chains and that new polymer chains are started by polystyrene radicals from already grafted chains. The grafting ratio of the RAFT‐agent‐mediated process is controlled via the initial CPDA concentration. The molecular weight of the polystyrene from the solution (PS_free) shows a linear behavior with conversion and has a low polydispersity index. Furthermore, the loading of the grafted solid phase shows a linear relationship with the molecular weight of PS_free for both regimes. Regime 2 has a higher loading capacity per molecular weight than regime 1. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 4180–4192, 2002     

Stimuli-responsive membranes through peroxidation radiation-induced grafting of 2-hydroxyethyl methacrylate (2-HEMA) onto isotactic polypropylene film (IPP)

Stimuli-responsive membranes were prepared by peroxidation radiation-induced grafting of 2-hydroxyethyl methacrylate (2-HEMA) onto IPP. The radioactive isotope ⁶⁰Co was used as the source of gamma radiation. A plausible mechanism of grafting has been proposed. Using this method, the degree of grafting and morphology could be controlled through the variation of reaction parameters such as total dose, inhibitor concentration, monomer concentration, reaction time, reaction temperature and solvents. Maximum percentage of grafting (210?%) was obtained at total radiation dose of 20?kGy. The graft copolymerization reaction was carried out for 3?h with 20?v/v% of the monomer (2-HEMA) in methanol at 85?°C using 0.06?wt% of FeCl₃ as inhibitor. The chemical structures of grafted membranes were characterized by Fourier transform infrared spectroscopy (FTIR) which indicates that HEMA has been grafted onto IPP. The atomic force microscopy (AFM), scanning electron microscopy (SEM) techniques were used to assess the morphological characterization of the membranes, revealing the roughness of the surface. These membranes were investigated for their swelling behavior. pH-sensitivity and the dyeability of the grafted and ungrafted membranes have also been studied.     

Radiation-induced grafting of diallyldimethylammonium chloride onto acrylic acid grafted polyethylene

Diallyldimethylammonium chloride (DADMAC) was grafted onto polyethylene (PE) films by a double grafting procedure. The PE film was initially modified by grafting acrylic acid (AA), through a mutual irradiation method. AA-g-PE film, thus obtained was subjected to subsequent radiation grafting reaction of DADMAC, to give a DADMAC-g-AA-g-PE film having a comb-type structure. The influence of different conditions, such as the extent of AA grafting, DADMAC concentration, absorbed dose and dose rate, on the grafting yield of DADMAC was investigated. A maximum DADMAC grafting of 30% was achieved. The equilibrium degree of swelling (EDS) of the grafted films were gravimetrically determined. TGA and FT-IR techniques were employed to characterize the grafted PE films.     

Radiation-induced grafting of vinyl benzyl trimethyl ammonium chloride onto nylon-6 fabric

Vinyl benzyl trimethyl ammonium chloride (VBTAC) was grafted onto nylon-6 fabric in the presence of 2- hydroxy ethyl methacrylate (HEMA) by the simultaneous irradiation method in the presence of air with ⁶⁰Co γ-radiations. An increase in grafting was observed with increasing dose. Fourier transform infrared (FTIR) and thermogravimetric analysis (TGA) confirmed the grafting of VBTAC. Morphological changes after grafting were confirmed by scanning electron microscopy (SEM). The X-ray diffraction (XRD) pattern showed changes in crystallinity on grafting. The initial studies carried out with grafted nylon fabric showed behavioural changes in the burning properties.     

Part I. On the synthesis and pyrolysis of a tetrafluoroethylene–acrylonitrile graft copolymer

Radiation-induced grafting of acrylonitrile onto films of polytetrafluoroethylene has been studied. Irradiation has been carried out in a ⁶⁰Co gamma source at ?78°C., and the graft polymerization was facilitated by being held at 100°C. for 150 hr. The amount of acrylonitrile grafted per unit surface area apparently increases with the thickness of the film. Grafting is also accompanied by slight swelling. This indicates that the reaction occurs in depth. The relative decrease of the amount of grafted acrylonitrile with thickness of the film, referred to the weight of the film, shows that grafting is controlled by the diffusion of the monomer. The rate of grafting was found to be lower in a material with a higher degree of crystallinity; i.e., grafting occurs faster in the amorphous areas of the polymer. The final yield of graft decreases with the temperature at which the reaction is carried out. This may be explained on the basis of kinetics or by assuming a simultaneous disappearance of free polymer radicals.     

Radiation-grafting of 4-vinylpyridine and N-isopropylacrylamide onto polypropylene to give novel pH and thermo-sensitive films

Here 4-vinylpyridine (4VP) was grafted onto polypropylene films (PP) by mutual irradiation method to give PP-g-4VP; N-isopropylacrylamide (NIPAAm) was then grafted onto the PP-g-4VP films to give (PP-g-4VP)-g-NIPAAm by pre-irradiation method, using a ⁶⁰Co γ-source. The dependence of grafting percentage on radiation dose, temperature, reaction time, and monomer concentration was studied. (PP-g-4VP)-g-NIPAAm films were characterized by infrared spectroscopy (FTIR-ATR), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). The critical pH point and lower critical solution temperature (LCST) were determined by swelling and water contact angle measurements. The LCST also was determined by DSC. The binary graft copolymer films are shown to be thermo-pH sensitive.     

Synthesis of ion-exchange membranes by radiation-induced multiple grafting of methyl α,β,β-trifluoroacrylate

Methyl α,β,β-trifluoroacrylate (MTFA) was grafted onto polymer films with the multiple grafting technique initiated by α-rays: the yields were similar to those of the single-step grafting procedure with any irradiation dose. Grafted polymer obtained in the single-step experiments were distributed mainly near the film surface, whereas graft polymer from the multiple grafting experiments were distributed uniformly in the film at graft yields greater than 20%. The electric resistance of the hydrolyzed multiple graft polymer film in a 2N NaOH solution was much lower than that of one-step graft film at the same graft yield.     

Controlled grafting of MMA onto cellulose and cellulose acetate

Homogeneous graft copolymerization of methyl methacrylate onto cellulose and cellulose acetate was carried out in various solvents and solvent systems taking ceric ammonium nitrate, tin (II) 2-ethyl hexanoate [Sn(Oct)₂] and benzoyl peroxide as initiators. The effect of solvents, initiators, initiator and monomer concentration, on graft yield, grafting efficiency and total conversion of monomer to polymer were studied. Formation of Ce³⁺ ion during grafting in presence of CAN enhances the grafting efficiency. Methylene blue was used as a homopolymer inhibitor and controlled the molecular weight of the grafted polymer and its effect on grafting was also studied. In presence of MB, amount of PMMA homopolymer formation reduced and consequently grafting efficiency increased. The number average molecular weights and polydispersity indices of the grafted PMMA were found out by gel permeation chromatography. The products were characterized by FTIR and ¹H-NMR analyses and possible reaction mechanisms were deduced. Finally, thermal degradation of the grafted products was also studied by thermo-gravimetric and differential thermo-gravimetric analyses.     

Raft mediated surface grafting of t‐butyl acrylate onto an ethylene–propylene copolymer initiated by gamma radiation

RAFT mediated grafting of poly(t‐butyl acrylate) onto the surface of a commercial poly(ethylene‐co‐propylene), Elpro, has been carried out using initiation by ⁶⁰Co γ‐radiation at 298 and 273 K. The polymerizations were in bulk monomer and using the RAFT agent 1‐phenylethyl phenyldithioacetate. The rates of homopolymerization and grafting were found to decrease with increasing RAFT agent concentration, indicating that both polymerization processes involve participation of the RAFT agent. There was good agreement between the predicted and experimental molecular weights of the homopolymer that had a narrow polydispersity. The poly(t‐butyl acrylate) grafts were hydrolyzed by trifluoroacetic acid to form poly(acrylic acid) grafts, which could either be further functionalized or used to control the surface polarity of the Elpro. ATR‐FTIR spectroscopy was used to characterize the grafts and Raman spectroscopy was used to assess the depth of the grafts. The water contact angle for the Elpro surface grafted with poly(acrylic acid) was found to be linearly dependent on the amount of the graft present. The living nature of the grafted chains was demonstrated by the addition of a second block of polystyrene. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1074–1083, 2007     

GRAFT COPOLYMERIZATION OF METHYL ACRYLATE ONTO CHITOSAN INITIATED BY POTASSIUM DIPERIODATONICKELATE (IV)

ABSTRACT

A novel redox system, potassium diperiodatonickelate [Ni (IV)]‐chitosan, was employed to initiate the graft copolymerization of methyl acrylate (MA) onto chitosan in alkali aqueous solution. The effects of reaction variables such as monomer concentration, initiator concentration, reaction time, pH and temperature were determined. By means of a series of copolymerization, the grafting conditions were optimized. The maximum grafting percentage obtained was 404.1% when 0.3 g chitosan was copolymerized with 1.8 mL monomer at 35°C for 5 hours with [Ni (IV)]=9.4×10^?4 M and the total volume was 20 mL. Ni (IV)-chitosan system is found to be an efficient redox initiator for this graft copolymerization. A single electron transfer mechanism is proposed to explain the formation of radicals and the initiation. The grafted copolymers were characterized by IR and X-ray diffraction diagrams. The thermal stability of chitosan and chitosan-g-PMA was studied by thermogravimetric analysis (TGA).     

Preparation of Cationic Membrane of Polyethylene Film by γ-Irradiation

Grafting of acrylic acid onto PE film by a pre-irradiation method was studied. In order to prevent formation of homopolymer, Mohr salt (NH₄)₂Fe(SO₄)₂ · 6H₂O was used, and the reaction was carried out in the presence of a swelling agent, such as methanol. The influence of different factors, such as dose, dose rate, and temperature, on the kinetics of the reaction was studied. The infrared spectrum of the grafted acrylic acid onto PE shows bands characteristic of carboxylic acids, which demonstrates that grafting has occurred. The grafting sites were shown to be of a semi-spongy shape and irregular structure which is thought to be due to the copolymerization of acrylic acid onto PE film.     

Plasma surface graft of N,N-dimethylacrylamide onto porous polypropylene membrane

Plasma graft onto microporous polypropylene (PP) membranes was studied. PP substrates had 0.45 μ of average pore size and 80 to 150 μ thickness and monomer for graft was N,N-dimethylacrylamide. Even by short exposure to argon and hydrogen plasmas less than 10 s, post graft polymerization was very fast. Grafting layer could be distinguished from relatively less-grafted portion by electron microscopy. However, graft was, more or less, noticed to form over cross-section of substrate. Plasmas were excited by 13.56 MHz radio frequency source and the wattage less than 10 W was usually enough to prevent PP from heat damage. Grafting rate was dependent on plasma-exposure time. For argon plasma at 10 W, 0.1 Torr (13.3 Pa), grafting rate decreased after maximum rate was observed at 10 s exposure. Analysis by electron spin resonance (ESR) revealed that relationship between spin concentration and irradiation time was somewhat different from reported data on polyethylene substrate. Alkyl radicals showing an eight-line-signal on ESR spectra were rapidly converted to peroxy radicals in air at almost 100%-yield. Both kinds of radicals could initiate graft, and alkyl radicals were found more active. Apparent activation energies were estimated to be 14.2 and 7.9 kcal/mol for graft polymerizations initiated by peroxy and alkyl radicals, respectively. Thermal analysis and X-ray diffraction revealed that graft may exist not only inner and outer surfaces but also in bulk region of substrate. For substrates more than 1000% grafted, even crystalline region was destroyed completely. Diffusion or absorption of monomer into bulk may be an important factor to support growth of graft polymer.     

Effective grafting of polymers onto ultrafine silica surface: Photopolymerization of vinyl monomers initiated by the system consisting of trichloroacetyl groups on the surface and Mn2(CO)10

The effective grafting of vinyl polymers onto an ultrafine silica surface was successfully achieved by the photopolymerization of vinyl monomers initiated by the system consisting of trichloroacetyl groups on the surface with Mn₂(CO)₁₀ under UV irradiation at 25 °C. The introduction of trichloroacetyl groups onto the surface of silica was achieved by the reaction of trichloroacetyl isocyanate with surface amino groups, which were introduced by the treatment of silica with 3‐aminopropyltriethoxysilane. During the polymerization, the corresponding polymers were effectively grafted onto the surface, based on the propagation of polymer from surface radicals formed by the interaction of trichloroacetyl groups and Mn₂(CO)₁₀. The percentage of poly(methyl methacrylate) grafting onto the silica reached 714.6% after 90 min. The grafting efficiency (proportion of grafted polymer to total polymer formed) in the polymerization of methyl methacrylate was very high, about 80%, indicating the depression of formation of ungrafted polymer. Polymer‐grafted silica gave a stable colloidal dispersion in good solvents for grafted polymer. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2157–2163, 2001     

Ultraviolet grafting of methacrylic acid and acrylic acid on high‐density polyethylene in different solvents and the wettability of grafted high‐density polyethylene. I. Grafting

Methacrylic acid (MAA) and acrylic acid (AA) were grafted onto high‐density polyethylene (PE) with UV initiation and a range of solvents. With acetone as the solvent, MAA was more easily grafted onto PE when the photoinitiator benzophenone was precoated on PE than when it was dissolved in the monomer solution. The grafting was faster in aliphatic solvents than in polar solvents or a UV‐adsorbing aromatic solvent (toluene). Acetone itself could initiate the photografting of both MAA and AA onto PE when it was mixed with water. The extent of grafting of MAA onto PE showed a maximum when there was about 40% acetone in the mixture. For AA, when the acetone/water concentration was 10%, the extent of grafting increased rapidly with the irradiation time. At higher acetone concentrations, the extent of grafting was low. Atomic force microscopy images showed that the surface topography of PE grafted with MAA in acetone/water was quite different from that obtained when the grafting was performed in other organic solvents. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 253–262, 2004