Study of energy transfer to solvent in radiation graft polymerization of styrene onto polyethylene

The radiation-initiated graft polymerization of styrene onto polyethylene was studied to determine whether energy transfer to diluent was responsible for the previously observed high orders of dependence of the grafting rate on monomer concentration. n-Octane was used as the diluent instead of benzene. If energy transfer from excited polyethylene to benzene were present, it should not be with n-octane. The percent swelling of polyethylene by various n-octane–styrene mixtures was determined. The compositions of various n-octane–styrene mixtures absorbed inside polyethylene were determined by ultraviolet and refractive index measurements and found to be richer in styrene than the corresponding mixtures in which the polyethylene had been placed. The graft polymerization rates were determined at 0.000761, 0.0371, and 0.213 Mrad/hr and plotted against the inside styrene concentrations on a log-log scale to yield the kinetic orders of dependence of rate on monomer as 2,3, and 3, respectively. It was concluded that energy transfer to diluent was not responsible for the high-order dependence observed.     

Kinetics of radiation-induced graft polymerization of styrene onto poly(ethylene oxide)

The graft polymerization of styrene onto preirradiated poly(ethylene oxide) was studied. From the measurement of swelling of the polymer in various solvents the solubility parameter of poly(ethylene oxide) was estimated as 9.3. The kinetic analysis of the reaction indicated that the graft polymerization was diffusion controlled. Kinetic parameters of the reaction such as \documentclass{article}\pagestyle{empty}\begin{document}$\int_0^t {R_i} dt,k_{p,} k_{tr}$\end{document}, and k_t were obtained in poly(ethylene oxide)-styrene system and compared with those in poly(isobutylene oxide)-styrene system.     

Radiation graft post-polymerization of sodium styrene sulfonate onto polyethylene

Post-irradiation grafting of sodium styrene sulfonate (SSS) in the presence of acrylic acid (AA) has been investigated on polyethylene (PE) pre-exposed to gamma radiation at room temperature in the air. Special attention was paid to the effect of low molecular weight salt additives on the kinetics of graft copolymerization of SSS and AA. The presence of SSS links in the grafted PE copolymers was detected by the methods of UV and FTIR spectroscopy. Based on the FITR spectroscopy and element analysis data, a mechanism was proposed for graft copolymerization of SSS and AA onto PE. The mechanical properties of the graft copolymers were studied. It was established that PE copolymers grafted with sulfonic acid and carboxyl groups have higher strength characteristics (16.3 MPa) compared to the samples containing only carboxyl groups (11 MPa).     

Pre-irradiation induced emulsion graft polymerization of acrylonitrile onto polyethylene nonwoven fabric

Acrylonitrile has been widely used in the modification of polymers by graft polymerization. In the present work, pre-irradiation induced emulsion graft polymerization method is used to introduce acrylonitrile onto PE nonwoven fabric instead of the traditional reaction in organic solvents system. The degree of grafting (DG) is measured by gravimetric method and the kinetics of the graft polymerization is studied. The existence of the graft chains is proven by Fourier transform infrared spectroscopy (FT-IR) analysis. Thermal stability of the grafted polymer is measured by Thermogravimetric analysis (TGA).     

Diffusion-controlled reaction. VI. Radiation graft polymerization of styrene to polyethylene

The radiation graft polymerization of styrene to polyethylene was studied under diffusion-controlled conditions of radiation intensity I, monomer concentration M₁, and polymer sample thickness L. The results of the present study together with previous work under diffusion-free conditions verify our theoretical model for the diffusion-controlled reaction. The grafting rate is inverse first order in L for diffusion-controlled reaction and independent of L for diffusion-free reaction. The order of dependence of grafting rate on radiation intensity for diffusion-controlled reaction is one-half that for diffusion-free reaction. Diffusion control leads to a decrease in the order of dependence of grafting rate on monomer concentration. The decrease is greater than theoretically predicted; possible reasons for this effect are described.     

EPR investigation on radiation-induced graft copolymerization of styrene onto polyethylene: Energy transfer effects

In this paper, energy transfer phenomena concerning the in-source graft copolymerization of styrene onto LDPE were investigated through the EPR analysis of the radical intermediates. The model solution experiments have shown a substantial deviation of the experimental G (radicals) values with respect to the additivity law, which reflect the negative effect of the styrene monomer concentration on the initiation rate of the graft copolymerization.The EPR measurements performed on polyethylene-co-styrene graft copolymers of various composition following low-temperature vacuum gamma irradiation have confirmed the decrease of the total radical yields with increasing the styrene concentration. The effect was partly attributed to the heterogeneity of the graft copolymer matrix and to the lack of molecular mobility in the solid state at low temperature, which prevents the attainment of the favourable geometrical configurations in intermolecular energy and charge transfer events.     

Surface graft polymerization of glycidyl methacrylate onto polyethylene and the adhesion with epoxy resin

Surface graft polymerization of glycidyl methacrylate (GMA) was carried out onto a high- density polyethylene (PE) sheet pretreated with corona to introduce peroxides onto the PE surface. Graft polymerization of GMA was effected by UV irradiation of the coronatreated PE in the presence of monomer solution without the use of any photosensitizer. The graft layer was found by staining the PE cross section to localize in the surface region of PE. The physical change in the PE surface was characterized by scanning electron microscopy, while the chemical changes due to the GMA graft polymerization were assessed by the dynamic contact angle, FT-IR, and x-ray photoelectron spectroscopy (XPS) measurement. The peroxide formation by corona exposure was confirmed by the XPS measurement after derivatization with SO₂. The epoxy groups introduced onto the PE surface by the GMA graft polymerization were reactive with water (in the presence of HCI) and amines. The adhesion between the GMA-grafted PE and an epoxy resin was studied by means of a shear strength test method. The GMA-grafted PE exhibited strong interfacial adhesion with the epoxy resin, compared to the original and corona-treated PE. The adhesion strength of the GMA-grafted PE was nearly two times higher than that of the corona-treated PE. This strongly suggests that the enhanced adhesion between the surface-grafted PE and the epoxy resin is ascribed to covalent bonding of the epoxy groups on the GMA-grafted surface to the amines in the epoxy resin. © 1995 John Wiley & Sons, Inc.     

Solvent effects on the radiation-induced graft polymerization of styrene onto poly(isobutylene oxide)

The graft polymerization of styrene onto preirradiated poly(isobutylene oxide) (PIBO) with methanol and benzene was studied. The order of grafting yield and of the number-average molecular weight of graft chains decrease in the order; undiluted styrene > styrene–methanol (1:1) solution > styrene–benzene (1:1) solution. A kinetic treatment to calculate rate constants from the rate of grafting and the molecular weight of the graft chain was proposed. The propagation rate constant k_p was 0.2–0.3 l./mole-sec and the termination rate constant k_t was 1.0–16.0 l./mole-sec. The ratio k_p/k_t in this heterogeneous system was larger than that in homogeneous system by a factor of about 10⁴–10⁵.     

Kinetics of styrene polymerization at ultrahigh conversion

The radical-initiated bulk polymerization of styrene at low conversion can be adequately described by a simple kinetic scheme that involves initiation by the decomposition of a radical initiator, propagation, and termination by combination of polystyryl radicals. An integrated equation can be derived that will describe the relationship between monomer concentration and time. We have investigated the validity of applying equations of this kind in the 98–99.999% conversion range. From our experimental work we conclude that the initial rates at 130°C, when starting the polymerization at that temperature at more than 98% conversion, can be described by an integrated equation over at least two decades of monomer concentration. Deviations from the simple kinetics at ultrahigh conversion were observed after a certain time at 130°C. These are discussed and explained in terms of the kinetic assumptions made and an extended model is suggested to allow for depolymerization reactions that cannot be neglected at ultrahigh conversion.     

Ozone-induced graft polymerization onto polymer surface

Ozone-induced graft polymerization was carried out to improve polymer surfaces. The polymers were exposed to ozone and the surface density of peroxides formed was determined by three methods; iodide, DPPH, and peroxidase method. The peroxide production could be readily controlled by the ozone concentration and the ozone exposure time. In addition, it was dependent on the kind of polymer. Further, it seemed probable that the ozone oxidation introduced peroxides not only on the outermost surface but also into a layer deeper from the outermost surface. Such polymeric peroxides were capable of initiating graft polymerization onto PU. All the physical and biological measurements on the grafted surface indicated that ozone-induced graft polymerization has effectively made the PU surface covered with the grafted water-soluble chains, their location being restricted to the film surface region. The interaction of the PU surface with blood components could be greatly reduced by the surface graft polymerization. © 1993 John Wiley & Sons, Inc.     

Cationic graft copolymerization of styrene onto natural rubber

The polymerization of styrene was carried out in a cyclohexane solution of natural rubber with stannic chloride. It was found that the grafting copolymerizations of styrene took place as well as the cyclization of rubber. The rate of polymerization of styrene was proportional to the second power of the concentration of styrene and to the concentrations of stannic chloride and natural rubber, respectively. The overall activation energy was about 6 kcal./mole. The percentage grafting increased with increasing concentration of rubber. On the other hand, the grafting efficiency showed the reverse tendency. The percentage grafting could be increased to 150% by the addition of nitrobenzene, a polar solvent.     

Cografting kinetics of styrene and ethyl acrylate onto polyethylene

Kinetic studies of cografting reactions of styrene (St) and ethyl acrylate (EA) onto preirradiated polyethylene (PE) have been investigated by means of bromine labeling and infrared spectroscopy. Kinetic data obtained from these methods, that is, the percent grafting, the number of graft chains, and growing rates, were obtained at temperatures of 0, 20, 40, and 50°C. The graft percent was virtually influenced by the degree of swelling. At 0°C, the mixing ratio of ethyl acrylate and styrene monomer before the beginning of the reaction was equal to the existence ratio in the graft chains after the reaction. Therefore, this reaction is considered to be diffusion-controlled. On the contrary, at 20 and 40°C, the existence ratio in graft chains after the reaction. Therefore, this reaction is considered to be diffusion-controlled. On the contrary, at 20 and 40°C, the existence ratio in graft chains agreed with the theoretical curve calculated from monomer reactivity ratio. The number of active graft chains for given times were 3～5 × 10^?7 mole/g PE and it decreased with temperature; 0 > 20 > 50°C. While the total number of graft chains is 5～15 × 10^?7 mole/g PE and it increased with temperature; 0 < 20 < 50°C. The growing rate were 1～5 monomer/site/sec for 0°C, 2～15 for 20°C.     

Photoinitiated grafting polymerization of acrylic acid onto the surface of polyethylene under pulsed laser radiation

Photoinduced grafting polymerization on the surface of PE films induced by nanosecond pulsed laser radiation is studied. The grafting is performed from the liquid phase composed of acrylic acid and a photoinitiator (benzophenone) dissolved in it. Pulsed laser radiation with a wavelength of 355 nm, a pulse duration of 11 ns, and a repetition rate of 10 Hz is used. Formation of the surface-graft polymer is followed by IR-ATR spectroscopy and contact-angle measurements. It is found that the time of laser treatment sufficient for the efficient modification of the PE surface with the grafted poly(acrylic acid) is in the range from 0.5 to 1.0 s at a laser-pulse energy density of 200–500 mJ/cm². At energy densities beyond this range, the efficiency of the reaction decreases rapidly. The results on laser grafting are compared with the results of grafting during UV irradiation with a lamp at a wavelength of 365 nm.     

Kinetics of styrene homogeneous polymerization to atactic polypropylene

The rate of polymerization of styrene initiated by hydroperoxidized atactic polypropylene in a homogeneous toluene solution has been measured at 60 and 70°C. The reaction is first-order with respect to styrene concentration and independent of the polymeric hydroperoxide concentration above 2 × 10^?5N hydroperoxide. The individual rate constants, length and frequency of the grafted polystyrene chains along the polypropylene backbone have been calculated and their significance discussed. The initiation rate constant compares closely with values reported for the analogous tert-butyl hydroperoxide-initiated polymerization. The rate constant for the chain transfer termination elementary step at 70°C., however, is 18 times the value reported for the tert-butyl hydroperoxide-initiated polymerization of styrene. This high constant accounts for the relatively low rates of polymerization observed and high termination rates. Chain deactivation is presumably accelerated by increased collisions between growing styrene chains and inactive propylene hydroperoxide and polystyrene molecules. Distribution of polystyrene grafts on polypropylene is estimated from knowledge of effects of styrene concentration, polymeric hydroperoxide concentration, and temperature upon the rate of polymerization.     

Graft polymerization of acrylic acid onto powdered polyethylene

Radiation-induced graft polymerization of acrylic acid onto powdered polyethylene samples of various granulometric compositions was studied. The resulting graft polymer can be used as a cation-exchange sorbent. The ion adsorption properties of the synthesized cation exchanger were characterized.     

Cationic graft copolymerization of styrene onto chlorinated butyl rubber

The graft copolymerization of styrene onto chlorinated butyl rubber (Cl-IIR) with stannic chloride as cationic catalyst was studied in cyclohexane, and the rate of polymerization, per cent grafting and grafting efficiency were obtained. Polymerization was carried out in a sealed tube. The product was precipitated in methanol and dried. The increase in weight of Cl-IIR used was regarded as styrene conversion, and the increase in weight after extraction by boiling acetone as the weight of grafted styrene. Grafting was confirmed by fractional dissolution and infrared spectra. The rate of polymerization of styrene was proportional to concentrations of styrene, Cl-IIR and SnCl₄. The per cent grafting increased with styrene and SnCl₄ concentration, but was constant with Cl-IIR concentration. It also increased with time and with halogen content in the polymer. The addition of a polar solvent such as nitrobenzene greatly promoted the grafting reaction and the per cent grafting was 200%.     

Invertase immobilization onto radiation-induced graft copolymerized polyethylene pellets

The graft copolymer poly(ethylene-g-acrylic acid) (LDPE-g-AA) was prepared by radiation-induced graft copolymerization of acrylic acid onto low density polyethylene (LDPE) pellets, and characterized by infrared photoacoustic spectroscopy and scanning electron microscopy (SEM). The presence of the grafted poly(acrylic acid) (PAA) was established. Invertase was immobilized onto the graft polymer and the thermodynamic parameters of the soluble and immobilized enzyme were determined. The Michaelis constant, K_m, and the maximum reaction velocity, V_max, were determined for the free and the immobilized invertase. The Michaelis constant, K_m was larger for the immobilized invertase than for the free enzyme, whereas V_max was smaller for the immobilized invertase. The thermal stability of the immobilized invertase was higher than that of the free enzyme.     

Surface modification of polyethylene fiber by graft polymerization

To improve the wettability and adhesion, graft polymerization of acrylamide (AAm) and glycidyl methacrylate (GMA) was performed onto the surface of ultra-high modulus polyethylene (UHMPE) fiber pretreated with Ar plasma. Following the plasma treatment and the subsequent exposure to air to introduce peroxides onto the fiber surface, graft polymerization onto the UHMPE fiber was allowed to proceed from the polymer peroxides either in deaerated monomer solution at an elevated temperature (degassing method), or in aerated monomer solution containing riboflavin at 30°C under UV irradiation (photoinduction method). The monomer solution was prepared from water and dioxane for AAm and GMA, respectively. After rigorous removal of homopolymers, surface analysis of the grafted fibers was performed with ATR-FTIR and XPS, which revealed that PAAm and PGMA chains were grafted in the surface region of fibers. The grafting rate of PAAm by the photoinduction method was much higher than that by the degassing method when compared at the same concentration of the AAm solution. The amount of PGMA grafted was greatly affected by UV irradiation time, but depended on plasma treatment time to an insignificant extent if the treatment was carried out for longer than 30 s. Reaction of propylamine with the PGMA-grafted surface resulted in the appearance of a nitrogen peak in the XPS spectrum, suggesting the presence of epoxy groups on the surface of PGMA grafted fiber. © 1994 John Wiley & Sons, Inc.