Diffusion-controlled reaction. VI. Radiation graft polymerization of 4-vinylpyridine to polyethylene

The radiation-initiated graft polymerization of 4-vinylpyridine to high-density polyethylene was studied over a wide range of reaction conditions of radiation intensity I, monomer concentration M₁, and polymer film thickness L. The conditions included both diffusion-free and diffusion-controlled graft polymerizations. The results corroborate our previous theoretical predictions on the effect of I, M₁, and L on the experimental grafting rate. The grafting rate is inverse first order in L for diffusion-controlled reaction and independent of L for diffusion-free reaction. The dependence of grafting rate on radiation intensity decreases from 1/2 to 1/4 order for diffusion-controlled reaction. Diffusion control results in a decrease in the dependence of rate on monomer concentration. The observed decrease is somewhat greater than theoretically predicted.     

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.     

Some investigations on the post radiation grafting of acrylamide onto polyethylene films

A study has been made on the post radiation grafting of aqueous acrylamide onto low density polyethylene film. It was found that the addition of 0.05 wt % Mohr's salt reduced effectively the homopolymerization of acrylamide and the grafting process was successfully achieved. The dependence of the grafting rate on the preirradiation dose and monomer concentration was found to be of 1.43 and 1.4 order, respectively. The overall activation energy for the graft polymerization was found to be 13.5 and 1.95 Kcal/mol below and above 45°C, respectively. Some properties of the graft copolymer such as swelling behaviour, electrical conductivity, and reverse osmosis desalination of saline water (water flux and salt rejection), were also investigated and the possibility of its uses in the practical applications was discussed.     

Surface grafting of polyethylene by mutual irradiation in methyl acrylate vapor. II. High-energy electrons irradiation

Vapor-phase mutual grafting of methyl acrylate (MA) onto polyethylene (PE) at high dose rates from an electron accelerator yields the same surface graft structure as does the grafting at low dose rates from ⁶⁰Co sources; i.e., a homopolymer layer (consisting of only MA component) is easily formed on the inner graft copolymer layer (consisting of both MA and PE components) as a result of the continuously increasing surface graft composition. To produce the surface layer, 4-MeV electron irradiation with a linear electron accelerator requires only less than 3 min of irradiation time at dose rates of more than 2 Mrad/min, whereas γ irradiation with a ⁶⁰Co source requires at least 1 hr at dose rates of less than 2 × 10³ rad/min. The rate of monomer consumption (or polymerization) in the surface homopolymer layer shows no dependence of irradiation time and a positive dependence of dose rate. It has been suggested that this kinetic feature at the high dose rates shows some contribution of vapor-phase homopolymerization and subsequent deposition (onto the grafting surface) followed by recombination with the grafted side chain radicals, although secondary graft copolymerization from the grafted chain radicals is still the principal process for the growth of the surface homopolymer layer.     

Kinetic study of preirradiation grafting of acrylic acid onto poly(tetrafluoroethylene–perfluorovinyl ether) copolymer

A kinetic study has been made on the preirradiation grafting of acrylic acid (AAc) onto poly(tetrafluoroethylene–perfluorovinyl ether) (PFA) film. The effect of grafting conditions was investigated. The dependences of the grafting rate on preirradiation dose and monomer concentration was found to be of the order of 0.5 and 1.3, respectively. The final degree of grafting was found to increase with dose and monomer concentration. However, it decreases as the grafting temperature increase. The overall activation energy for the graft polymerization was calculated from Arrhenius plots to be 5.6 kcal/mol. The activation energy for this grafting system was found to be independent of preirradiation dose used in the range from 10 to 100 kGy. The relationship between the grafting rate and film thickness gave a negative first-order dependence. The results suggest that the grafting proceeds by radical mechanism with bimolecular termination of growing chain radicals. It was reasonable concluded that this grafting proceeds from the surface to the center of film with progressive monomer diffusion through the grafted layer which swells in the monomer solution.     

Diffusion control in radiation graft polymerization with varying dependence of rate on monomer concentration

The quantitative effect of diffusion control on the rate of radiation-initiated graft polymerization has been studied theoretically for systems in which the diffusion-free reaction may show various dependencies of rate on monomer concentration other than the usual first-order dependence. The study is also very general in that it can be applied to systems involving a variety of different modes of initiation and termination. Whether the grafting process is diffusion-free or diffusion-controlled has been analyzed in terms of the interaction of the initiation rate R_i, the propagation and termination rate constants k_p and k_t, the equilibrium solubility M of the monomer in the polymer, the polymer film thickness L, the diffusivity D of the monomer in the polymer, and the diffusion-free kinetic order of dependence v of the grafting rate on monomer concentration. The dependence of the grafting rate for both the diffusion-free and diffusion-controlled reactions on these parameters is expressed both by mathematical experssions and graphically. Diffusion control is shown to occur at a critical value of the parameter A which is proportional to L(k_pR_i^w/k_t^zD)^1/2M^(ε?1)/2 where w, z, and v have different values depending on the specific modes of initiation, propagation and termination in a particular grafting system. The grafting rate is shown to vary with the value of A according to specific mathematical expressions. In comparing diffusion-free to diffusion-controlled reaction, it is shown that the former is independent of L and D while the latter is directly dependent on L and inversely on D^1/2. Further, the change from diffusion-free to diffusion-controlled reaction involves a change in the dependence of rate on monomer from v-order to [(v ? 1)/2]-order. The nonsteady-state as well as the steady-state reaction rates have been analyzed.     

Radiation (60Co)-Induced Graft Copolymerization of Acrylamide on Jute Fiber

The radiation induced graft copolymerization of acrylamide onto jute fibers was studied following preirradiation of jute in air using a⁶⁰Co source of γ-radiation and subsequent polymerization of acrylamide in a limited aqueous system under nitrogen at 607°C. An increase of the time of preirradiation (at a fixed dose rate) increased the percent grafting measurably and the grafting efficiency marginall Grafting effects showed further improvement on addition of Fe²⁺ or Co²⁺ ions to the system prior to the polymerization step. Increasing the concentration of Fe²⁺ or Co²⁺ ion led to an increase in the grafting parameters with a leveling off effect in the higher concentration range, however. An increase in the polymer (jute) content for a fixed monomer content produced a significant increase in the efficiency of grafting, while % grafting followed a slowly decreasing trend.     

Radiation grafting kinetics of HEMADGDA onto silastic in different atmospheres

The radiation grafting kinetics of HEMA, as well as that of the mixture monomers of HEMA and DGDA have been researched. The effects of radiation dose, dose rate, and temperature on grafting are systematically researched in different atmospheres. It has been found that grafting is different in different atmospheres. The findings show that the depth distribution of HEMA/ DGDA monomer units in grafting layer is nonuniform. At first, HEMA grafting is superior, in the later stage of grafting, however, DGDA grafting is increased. The temperature effect on grafting is great at the beginning, it is less in the later stage of grafting.     

Effect of dose rate on radiation-induced polymerization of styrene adsorbed on silica gel

The effect of dose rate on the rate of polymerization and molecular weight distribution of radiation-induced polymerization of styrene adsorbed on silica gel was studied in a wide dose rate range of 4.4 × 10⁴ to 3 × 10⁸ rad/hr by γ rays of ⁶⁰Co and electron beams with a Cockcroft-Walton-type accelerator. Dose rate dependence on the initial rate of polymerization was about 1 below 3 × 10⁷ rad/hr, and it decreased gradually at high dose rates. Throughout the dose rate range, graft polymerizations and homopolymerizations by cationic and radical mechanisms proceeded simultaneously. Dose rate dependence of the cationic polymerization was 1 below 3 × 10⁷ rad/hr, while dose rate dependence of the radical polymerization was 0.65 below 3 × 10⁷ rad/hr. At high dose rates, molecular weight and fraction of graft polymer decreased, and fraction of cationic polymerization increased. A very high-molecular-weight graft polymer was formed above 4.4 × 10⁵ rad/hr at the initial stage of the polymerization. The dose rate dependence of this polymerization was larger than 1 and decreased with increase in dose rate. The polymerization seems to be related to an excitation of monomer or growing chain.     

Polypropylene Modification by the Radiation Graft Polymerization of N-Vinylcaprolactam

The radiation graft polymerization of N-vinylcaprolactam onto polypropylene films was studied. The radiation graft polymerization was performed with preirradiation in air (peroxide method) or using a direct method in aqueous solutions and organic solvents. The effects of radiation dose, reaction time, monomer concentration, and homopolymerization inhibitor on the radiation graft polymerization were studied. It was found that the radiation graft polymerization from a monomer emulsion in water occurred at the highest rate. The IR spectra of grafted polymers were obtained. With the use of differential scanning calorimetry and equilibrium swelling in water, it was found that the modified polymers of polypropylene with grafted poly(N-vinylcaprolactam) chains exhibited thermoresponsive properties.     

Preirradiation grafting of N-vinyl-2-pyrrolidone onto poly(tetrafluoroethylene) and poly(tetrafluoroethylene-hexafluoropropylene) films

Preirradiation grafting of N-vinylpyrrolidone (NVP) onto poly(tetrafluoroethylene) (PTFE) and poly(tetrafluoroethylene-hexafluoropropylene) (FEP) films was investigated. The influence of grafting parameters such as preirradiation dose, monomer concentration, and grafting temperature on the rate and grafting yield was studied. Different solvents were used for diluting the monomer and it was found that the aqueous monomer solution at a concentration of 80 wt% was suitable for this grafting system. However, the graft polymerization of NVP in benzene terminated within a short time without significant grafting yield. The dependence of the grafting rate on preirradiation dose and monomer concentration was 1.2 and 1.07 order, respectively, for grafting onto PTFE films and 1.1 and 1.2 order, respectively, for grafting onto FEP films. Arrhenius plots for grafting onto PTFE films showed a breaking point at ca. 35°C and the overall activation energies were calculated as 23.6 and 9.0 Kcal/mol below and above 35°C, respectively. For grafting onto FEP films, however, no break was observed in the Arrhenius plots; the overall activation energy was 11.9 Kcal/mol. The swelling behavior and electric resistance of the grafted materials were investigated.     

蚕丝辐射接枝丙烯腈

以氯化锌水溶液为溶剂 ,用钴 60γ射线引发蚕丝均相溶液接枝丙烯腈 .研究了辐射吸收剂量、剂量率、铜离子浓度、蚕丝浓度和单体浓度及“后效应”对单体转化率、接枝率、接枝效率、接枝链分子量的影响 ;研究发现初始接枝效率主要取决于 [S]丝/ ( [S]丝 +[M]单) ,接枝效率随吸收剂量增加而增加 ;铜离子的存在使接枝链分子量下降 ,而对接枝率和接枝效率影响不大 ;用IR、TGA、DTA等多种方法对接枝物进行了表征 ,表明蚕丝接枝上聚丙烯腈后 ,其热学性能有较大提高 .     

Radiation-induced graft polymerization of acrylamide I. Preparation conditions and gel determination for polyethylene-grafted films

Radiation-induced graft polymerization of acrylamide (AAm) onto low-density polyethylene(LDPE) film has been investigated. The appropriate reaction conditions at which the graft polymerization was carried out successfully were selected. It was observed that the grafting process was enhanced remarkably by using distilled water as diluent. In this grafting system ammonium ferrous sulphate (Mohr's salt) was used as inhibitor to minimize the homopolymerization of AAm and the suitable concentration of such inhibitor was found to be 3 wt %. The dependence of the grafting rate on the monomer concentration was calculated to be 2.9 order, regardless of the irradiation atmosphere (N₂ gas or under vacuum). When the radiation grafting process was carried out under vacuum, higher degrees of grafting were obtained as compared to those in nitrogen gas or in air atmosphere. Network structure was formed in the graft copolymer and the gel formation was determined in the p-xylene-extracted grafted films. Results showed good evidence that the grafting process takes place by the front mechanism.     

辐射接枝医用水凝胶的研究Ⅰ.硅橡胶辐射接技N-乙烯基吡咯烷酮

采用填加SiO_2增强的甲基乙烯基硅橡胶混炼压片。通过~(60)Co-γ射线引发辐射硫化,利用共辐照方法,将N-乙烯基吡咯烷酮接枝到该硅橡胶上,制备了高纯度医用水凝胶。本文较系统地研究了接枝单体浓度、辐照剂量率、剂量、温度和接枝试片厚度等因素对接枝共聚反应的影响。建立了接枝速率与单体浓度、剂量率之间的动力学关系式:R_g=k[M]~(4/5)D~(1/2)。讨论了反应机制和接枝区域。     

Grafting of Acrylamide On 1, 1, 2, 2-Tetra-Chloroethane Preswelled Polyethylene Terephthalate) Films Using Azobisisobutyronitrile Initiator

Abstract

Graft polymerization of acrylamide (AAm) on 1, 1, 2, 2 tetrachloro-ethane (TCE) preswelled poly(ethylene terephthalate) (PET) films were performed with chemical initiation method using asobisiso-butyronitrile (AIBN) initiator. Temperature was found to have a greater effect on the swelling then the swelling time. Variation of the graft yield with polymerization temperature, time, AIBN concentration, AAm concentration, AIBN and AAm inclusion times were investigated. The optimum temperature for grafting was found to be 70°CC. The graft yield was observed to increase with polymerization time, AAm concentration, initiator and monomer diffusion time up to a saturation graft yield and then leveled off. An increase in AIBN concentration first enhanced the percent grafting then showed a decrease. The addition of some salts (Ni²⁺, Cr³⁺, Co²⁺, Cu²⁺) on the rate of grafting was also investigated. From the temperature dependence of the initial rate of grafting, the overall activation energy was found to be 4. 1 kcal/mol and relevant rate equation have been derived. The effect of grafting on film propities, such as water absorption capacity, intrinsic viscosity were determined. Grafted films were characterized by FTIR spectros-copy and scanning electron microscopy (SEM).     

Preirradiation grafting of acrylonitrile onto polypropylene monofilament for biomedical applications: I. Influence of synthesis conditions

Graft polymerization of acrylonitrile onto polypropylene (PP) monofilament was carried out by a preirradiation method using a ⁶⁰Co gamma radiation source. The influence of synthesis conditions, such as preirradiation dose, reaction time, monomer concentration, reaction temperature and additives was determined. The grafting was considerably influenced by the instantaneous swelling of the monofilament in the reaction mixture during the course of the grafting process. The order of dependence of the rate of grafting on monomer concentration was found to be 1.04. The nature of the medium of the grafting and the additives had profound influence over the grafting reaction. The accelerative effects of solvent medium on the grafting were higher in methylethyl ketone (MEK) and dimethylformamide (DMF) as compared to methanol. At the same time, partial replacement of DMF with water led to acceleration in the grafting with peak maxima at 20% solvent composition. The addition of a small amount of sulfuric acid to the reaction mixture also resulted in a significant acceleration of the degree of grafting.     

Effect of amount of monomer on radiation-induced polymerization of styrene adsorbed on silica gel

The effect of amount of monomer on radiation-induced polymerization of styrene adsorbed on silica gel was investigated with the monomer amounting from less than monolayer adsorption to more than the equilibrium adsorption. The rate of graft polymerization and the molecular weight of the polymer changed with the amount of monomer adsorbed on silica gel. Maximum grafting efficiency was obtained at monolayer adsorption. The molecular weight of graft polymer was higher than that of homopolymer in both radical and cationic polymerizations, and the ratio in molecular weight of graft polymer to that of homopolymer tends to be unity with increasing amount of adsorbed monomer. These results can mainly be explained in terms of the number of initiating species (radical and cation) that change in relation to the amount of adsorbed monomer. Propagation and termination change with amount of adsorbed monomer in relation to the molecular mobility of adsorbed monomer. A very high-molecular-weight graft polymer is formed only with a small amount of adsorbed monomer in the initial stage. The grafting percent with a large amount of adsorbed monomer increased after most of the monomer has been polymerized. Secondary effect of radiation on the graft and homopolymers due to energy transfer from silica gel is suggested from the complicated phenomena in the later stage of the reaction.     

Preparation of cation-exchange membrane containing bi-functional groups by radiation induced grafting of acrylic acid and sodium styrene sulfonate onto HDPE: Influence of the synthesis conditions

Electron beam radiation induced grafting of acrylic acid (AA) and sodium styrene sulfonate (SSS) onto high-density polyethylene (HDPE) membranes was investigated by the pre-irradiation method, and a cation-exchange membrane containing bifunctional groups was synthesized. The effects of grafting conditions such as monomer concentration, radiation dose and temperature on grafting yield were studied. The dependence of grafting yield on pre-irradiation dose and monomer concentration was found to be 0.54 and 2.21, respectively. The activation energy for the grafting was calculated to be 22.2 kJ/mol. Infrared spectroscopy analysis of the grafted membrane confirmed the existence of sulfonate and carboxylic acid groups.     

Graft Polymerization of a Polymer Matrix: Grafting of Tetrafluoroethylene

Graft polymerization of tetrafluoroethylene on polyethylene preirradiated by γ-rays from a cobalt-60 source at ?196°C has been investigated in the region of PE devitrification. A calorimetric technique made it possible to establish that 1.5-2% of monomer dissolves in the amorphous regions of PE at low temperatures. Efficient grafting proceeds in the temperature range directly adjoining the PE devitrification region. The graft copolymer yield amounts to ca. 1200%. The intensification of grafting is apparently caused by the following: (1) because of previous solution of TFE in the PE amorphous regions and filling of the micropores, the reaction in the initial stage is not limited by diffusion; (2) and the initiation efficiency is increased by slow passage through the PE devitrification region. The breaking strength of the graft copolymer is higher than that for the PE copolymer irradiated by the same dose.     

无规聚丙烯接枝甲基丙烯酸的合成

采用溶液聚合的方法将无规聚丙烯 (APP)与甲基丙烯酸 (MAA)接枝共聚制得接枝共聚物APP -g -MAA。讨论了反应温度、反应时间、引发剂BPO浓度、单体MAA浓度对接枝率的影响。结果表明 :当聚合反应温度低于是 12 0℃时 ,接枝率随温度升高而降低。延长反应时间有利于提高接枝率。最适宜的引发剂浓度为 1% ,MAA/APP配比为 0 .2 5/1。利用红外光谱证实了接枝物APP-g -MAA的存在。