Liquid carbon dioxide as a solvent for the radiation polymerization of ethylene

The usefulness of liquid carbon dioxide as a solvent for polymerization of ethylene was studied. The effect of liquid carbon dioxide on the polymerization was investigated under conditions of the pressure of 400 kg./cm.² over the temperature range 20–45°C. by using γ-radiation and AIBN as initiators. The infrared spectrum of the polymers showed that carbon dioxide had little effect on the polymer structure. The polymers contained no combined carbon dioxide and only small amounts of vinylidene unsaturation. The methyl content of the polymers was 0.5–4.0 CH₃/1000C. The polymer yield and molecular weight were found to be decreased by the addition of carbon dioxide in both polymerization by γ-radiation and AIBN. The number of polymer molecules formed per unit time increased with the content of carbon dioxide in the γ-ray polymerization, and was constant in the case of AIBN. The advantages of the use of liquid carbon dioxide as a solvent in this polymerization were also considered from the viewpoints of the continuous process, the separation of polymer, the stability of carbon dioxide to radiation, and commercial applications.     

Synthesis,Thermal Properties,and Radiolysis of Poly(Cyclohexyl α-Chloroacrylate)

Cyclohexyl α-chloroacrylate (CCA) was polymerized by radical anionic and γ-radiation initiation. The anionic polymerization of cyclohexyl α-chloroacrylate gave moderately isotactic polymer in toluene and syndiotactic-rich polymer in THF. Poly(cyclohexyl α-chloroacrylate) (PCCA) was found to undergo two-stage weight loss in thermogravimetric analysis, and the first-stage weight loss was attributed to the lactonization reaction. PCCA degraded under γ-radiation, and the radiation yields of crosslinking and scission, G _x and G _s, were 0.6 and 3.8, respectively.     

Microwave‐improved polymerization of ϵ‐caprolactone initiated by carboxylic acids

The ring‐opening polymerization of ε‐caprolactone (ε‐CL), initiated by carboxylic acids such as benzoic acid and chlorinated acetic acids under microwave irradiation, was investigated; with this method, no metal catalyst was necessary. The product was characterized as poly(ε‐caprolactone) (PCL) by ¹H NMR spectroscopy, Fourier transform infrared spectroscopy, ultraviolet spectroscopy, and gel permeation chromatography. The polymerization was significantly improved under microwave irradiation. The weight‐average molecular weight (M_w) of PCL reached 44,800 g/mol, with a polydispersity index [weight‐average molecular weight/number‐average molecular weight (M_w/M_n)] of 1.6, when a mixture of ε‐CL and benzoic acid (25/1 molar ratio) was irradiated at 680 W for 240 min, whereas PCL with M_w = 12,100 and M_w/M_n = 4.2 was obtained from the same mixture by a conventional heating method at 210 °C for 240 min. A degradation of the resultant PCL was observed during microwave polymerization with chlorinated acetic acids as initiators, and this induced a decrease in M_w of PCL. However, the degradation was hindered by benzoic acid at low concentrations. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 13–21, 2003     

Features of Preparing the Butyl Acrylate–Acrylonitrile Copolymer by Radiation-Induced Emulsion Polymerization

Some specific features of the radiation-induced emulsion copolymerization of butyl acrylate and acrylonitrile and radiation-induced crosslinking of the resulting copolymer in the latex form were studied. The effect of polymerization conditions on the polymerization rate and the molecular mass of the polymer was determined. The copolymer was shown to undergo efficient crosslinking in the latex form by the action of -radiation. The radiation-chemical yield of crosslinking sites (G) and the average molecular mass (M _c) of chain segments between two adjacent network junctions were determined.     

Radiation polymerization of methacrylates controlled by a chain transfer catalyst

The effect of γ-radiation dose and chain transfer catalyst on polymerization of methyl methacrylate (MMA) and copolymerization of MMA with hydroxyethyl methacrylate or triethylene glycol dimethacrylate has been investigated. The addition of 5 × 10^?4?10^?3 mol/L of bis[(difluoroboryl) isopropylpyridine dimethylglyoximato]cobalt(II) (Co(II)) makes it possible to produce macromonomers MM _n ⁼⁼ bearing terminal double bonds and having a degree polymerization of n = 2?40 and a polydispersity index of 1.05?1.15. It has been found that the degree polymerization of the macromonomers increases with the increasing γ-radiation dose and monomer conversion through the mechanism of the reversible β-cleavage of the terminal unit: R _k ^? + MM _n ⁼ ? MM _k+1 ⁼ + R _n-1 ^? followed by the living polymerization of both radicals. This reaction may compete with the catalytic chain transfer reaction and have a significant effect on the evolution of the molecular weight characteristics of the macromonomers during the course of MMA (co)polymerization.     

Alternating copolymerization of ethylene with maleic anhydride

The copolymerization of ethylene with maleic anhydride was carried out with γ-radiation and a radical initiator, i.e., 2,2′-azobisisobutyronitrile and diisopropyl peroxydicarbonate under pressure at various reaction conditions. The homopolymerization of neither monomer was observed in this system. In the γ-ray-initiated copolymerization the G value (polymerized monomer molecules per 100 e.v.) was shown to be between 10³ and 10⁴. It was found that the dose rate exponent of the rate is approximately unity, and the rate is proportional to the amount of ethylene monomer. Apparent activation energies of 1.8 and 27.5 kcal./mole were obtained for γ-ray-initiated and AIBN-initiated copolymerization, respectively. Since the composition of copolymer is independent of monomer molar ratio and the molar ratio of ethylene to maleic anhydride in the polymer is approximately unity, the monomer reactivity ratios were obtained as r_E ? 0 and r_M ? 0 for γ-ray-initiated polymerization at 40°C. Alternating copolymerization was, therefore, concluded to occur. Infrared analysis of the copolymer is almost consistent with this. The copolymer in the solid state is amorphous. It is soluble in water, cyclohexane, and dimethylformamide and insoluble in lower alcohols, ether, and aromatic hydrocarbons. The aqueous solution of polymer gave a strong acid.     

Molecular weight and antioxidant effects on the structure of irradiated linear low density polyethylene

Linear copolymers of ethylene and butene-1 with uniform chemical microstructure and very narrow molecular weight distribution are used to study the effects of ionizing radiation. The well characterized copolymers are irradiated at room temperature with γ-rays from a ⁶⁰Co source. To follow the evolution of the molecular structure with the radiation doses, changes in molecular weight averages M_n and M_w are measured by membrane osmometry, light scattering and GPC.The influence of the original linear polymer molecular weight is examined in the range of 50,000–100,000. The effects of antioxidant are explored irradiating samples with and without additive.     

Effect of γ-radiation on radionuclide retention in compacted bentonite

Compacted bentonite is proposed as an engineered barrier in many concepts for disposal of high level nuclear waste. After the initial deposition however, the bentonite barrier will inevitably be exposed to ionizing radiation (mainly γ) under anoxic conditions. Because of this, the effects of γ-radiation on the apparent diffusivity values and sorption coefficients in bentonite for Cs⁺ and Co²⁺ were tested under different experimental conditions. Radiation induced effects on sorption were in general more noticeable for Co²⁺ than for Cs⁺, which generally showed no significant differences between irradiated and unirradiated clay samples. For Co²⁺ however, the sorption to irradiated MX80 was significantly lower than to the unirradiated clay samples regardless of the experimental conditions. This implies that γ-radiation may alter the surface characteristics contributing to surface complexation of Co²⁺. With the experimental conditions used, however, the effect of decreasing sorption was not large enough to be reflected on the obtained D_a values.     

Polymerization of diallyl phthalate in solution by γ-radiation

The polymerization of diallyl phthalate has been studied in two solvents, benzene (G_Radical = 0.7) and chloroform (G_R = 11.2), γ-radiation being used to investigate the effect of the solvent on the rates of polymerization and also chain transfer to the solvent. Kinetic analysis shows that in benzene solution the initiating species come almost exclusively from the monomer, but in chloroform they arise only from the solvent. The latter was further confirmed from the chlorine analysis of the polymer wherein chloroform appears to have telomerized with diallyl phthalate. In neither of the solvents was high molecular weight polymer obtained. The k_p/k_t^1/2 for the polymerization of DAP was found to be 3.3 × 10^?4 and 1.17 × 10^?3 in benzene and chloroform solutions, respectively. The chain-transfer constant C_S was 11.25 × 10^?3 and 9.75 × 10^?3 for benzene and chloroform, respectively.     

Synthesis and Characterization of Novel Methacrylic Copolymers: Determination of Monomer Reactivity Ratios

A new methacrylic monomer, 4‐nitro‐3‐methylphenyl methacrylate (NMPM) was prepared by reacting 4‐nitro‐3‐methyl phenol dissolved in methyl ethyl ketone (MEK) in the presence of triethylamine as a catalyst. Copolymerization of NMPM with methyl methacrylate (MMA) has been carried out in methyl ethyl ketone (MEK) by free radical solution polymerization at 70±1°C utilizing benzoyl peroxide (BPO) as initiator. Poly (NMPM‐co‐MMA) copolymers were characterized by FT‐IR, ¹H‐NMR and ¹³C‐NMR spectroscopy. The molecular weights (M_w and M_n) and polydispersity indices (M_w/M_n) of the polymers were determined using a gel permeation chromatograph. The glass transition temperatures (T_g) of the copolymers were determined by a differential scanning calorimeter, showing that T_g increases with MMA content in the copolymer. Thermogravimetric analysis of the polymers, performed under nitrogen, shows that the stability of the copolymer increases with an increase in NMPM content. The solubility of the polymers was tested in various polar and non‐polar solvents. Copolymer compositions were determined by ¹H‐NMR spectroscopy by comparing the integral peak heights of well separated aromatic and aliphatic proton peaks. The monomer reactivity ratios were determined by the Fineman‐Ross (r₁ =7.090:r₂=0.854), Kelen‐Tudos (r₁=7.693: r₂=0.852) and extended Kelen‐Tudos methods (r₁=7.550: r₂= 0.856).     

Polymer degradation during radiation-induced emulsion polymerization of styrene

Styrene was polymerized in emulsion with initiation by γ-rays at a dose rate of 0.6 Mrad/hr. Polymerization rates were as expected from previous reports by others. No branching or crosslinking was detectable, and the M _w/M _n ratio of the polystyrene did not change significantly during the course of the polymerization reaction. The molecular weight of the product polymer decreased with increasing conversion, in contrast to the behavior of chemically initiated emulsion polymerizations. Monomer-free polystyrene does not degrade under the same radiation conditions, and the progressive decrease of polymer molecular weight with conversion is shown to result from the presence of monomer.     

Thermal behavior of carbon fiber precursor polymers with different stereoregularities

The effect of stereoregularity, in terms of isotactic triad content on the thermal behavior of carbon fiber precursor polymers synthesized through different polymerization routes such as solid state and radical solution polymerization techniques, was investigated by the thermogravimetric analysis and differential scanning calorimetric measurements. The isotactic contents of I-PAN and A-PAN were estimated with ¹³C NMR. The thermal cyclization reactions of atactic polyacrylonitrile (A-PAN) with low isotactic content (26.4–29.7 %) occurred at a lower temperature than that of isotactic polyacrylonitrile (I-PAN) with higher content (48.7–51.6 %). The percentage of mass loss observed in I-PAN was less as compared to A-PAN. The molecular mass characteristics of PAN obtained through solid state and radical solution polymerization were [M _n (10.2–14.3 × 10⁴), M _v (2.44–3.26 × 10⁵)] and [M _n (10.2–14.3 × 10⁴), M _v (2.29–2.74 × 10⁵)] Daltons (Da).     

Effects of γ-radiation on the thermal stability of cobalt oxides

Pure cobaltic oxide, prepared by thermal decomposition of pure basic cobalt carbonate in air at 500°C, was subjected to different doses of γ-radiation varying between 5 and 50 M rad. The influence of γ-radiation on the thermal decomposition of cobaltic oxide to cobaltous oxide and the re-oxidation of CoO to Co₃O₄ was studied using DTA, with a controlled rate of heating and cooling. The effects of γ-radiation on the specific surface area (S_BET) and oxidation character of Co₃O₄ were also investigated.The DTA investigation revealed that γ-radiation effectively decreased the thermal stability of cobaltic oxide to an extent proportional to the dose employed. The maximum decrease in the thermal stability of 60% was attained by exposing Co₃O₄ solid to 30 M rad. γ-Irradiation, however, exerted no detectable effect on the re-oxidation of CoO by O₂ to Co₃O₄.The S_BET measurements showed that the small dose (5 M rad) of γ-radiation effected a decrease of 15% in the surface area of Co₃O₄, the higher doses (10–50 M rad) caused a further slight decrease of 18% in its surface area.γ-Irradiation was found to decrease the oxidation character of Co₃O₄ to an extent proportional to the dose employed.The decrease in the thermal stability of Co₃O₄ due to radiation is explained in terms of the decrease in the oxidation character of cobaltic oxide observed after subjecting the solid to γ-radiation.     

有机/无机复合载体负载复合催化剂用于乙烯聚合时有机载体的作用

采用溶胶-凝胶法,将苯乙烯-丙烯酸(P(S-co-AA))共聚物包覆在以硅胶/MgCl2为载体的TiCl3催化剂(M-1催化剂)上,负载(n-BuCp)2ZrCl2后制得TiCl3/(n-BuCp)2ZrCl2复合催化剂,研究聚合物载体P(S-co-AA)在复合催化剂乙烯聚合中的作用.前期实验结果表明有机载体P(S-c...     

Miscibility behavior of di(ethyl-2 hexyl) phthalate in binary and ternary chlorinated polymer blends

The miscibility behavior of ternary blends made by the addition of di(ethyl-2 hexyl) phthalate (DOP) to a mixture of chlorinated polymers was investigated by differential scanning calorimetry. Two chlorinated polymer mixtures were selected: polyvinyl chloride (PVC) with a chlorinated polyethylene containing 48 wt% Cl (CPE48), and PVC with a chlorinated PVC containing 67 wt% Cl (CPVC67). Each binary DOP/chlorinated polymer pair is miscible whereas PVC/CPE48 and PVC/CPVC67 blends are immiscible. DOP/CPE48/PVC and DOP/PVC/CPVC67 ternary blends containing, respectively, more than 55 and 20% DOP exhibit a single glass transition temperature (T_g). The spinodal between the one-T_g zone and the two-T_g zone is symmetrical in the two cases. At high DOP concentrations, a quantitative analysis of the results leads to the conclusion of the presence of a true ternary phase. At low DOP concentrations where two T_gs are observed, the DOP is distributed equally between the two chlorinated polymers forming, in the DOP/CPE48/PVC case for instance, two binary DOP/CPE48 and DOP/PVC phases. The broad immiscibility zone observed in the DOP/CPE48/PVC ternary blend as compared to the DOP/PVC/CPVC67 blend appears to be mainly caused by the high molecular weight of CPE48, as compared with PVC and CPVC67. © 1994 John Wiley & Sons. Inc.     

Effect of dicarboxy terminated polystyrene on strengthening immiscible polystyrene/poly(methyl methacrylate) interface

The fracture toughness between polystyrene (PS)/poly(methyl methacrylate) (PMMA) reinforced with reactive polymers, poly(glycidyl methacrylate) (PGMA) and dicarboxy or monocarboxy terminated PS (dcPS and mcPS), was measured by the asymmetric fracture test. Molecular weight effect of mcPS, although the molecular weight distribution is rather polydisperse, on the maximum achievable fracture toughness, G_max qualitatively agreed with the results of the monodisperse case^4,5). In the case of dcPS with M_w ≅ 142 K, G_max reached ca. 170 J/m² which is nearly 8 times higher than that of mcPS of molecular weight of about 150K. From the mechanical point of view, dcPS with a degree of polymerization (N) greater than the ratio of chain breaking force to monomeric friction force (f_b/f_mono) is more effective in enhancing the interfacial adhesion than mcPS since it provides two stitches to the interface. It was also shown by Monte Carlo simulation on reactive polymer system that the di‐endfunctional polymers are more effective than mono‐endfunctional polymers in reinforcing the week interface between immiscible polymers.     

ATRP of MMA under 60Co γ‐irradiation at room temperature

In this work, atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA) was successfully carried out at room temperature (25 °C) under ⁶⁰Co γ‐irradiation environment. The polymerization proceeded smoothly with high conversion (>90%) within 7 h. The polymerizations kept the features of controlled radical polymerization: first‐order kinetics, well‐predetermined number‐average molecular weights (M_n,GPC), and narrow molecular weight distributions (M_w/M_n < 1.25). ¹H NMR spectroscope and matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry confirmed that poly(methyl methacrylate) (PMMA) chain was end‐capped by the initiator moieties. The Cu(II) concentration could reduce to 20 ppm level while keeping good control over molecular weights. This is the first successful example for the ATRP of MMA under ⁶⁰Co γ‐irradiation at room temperature. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Emulsion polymerization of vinyl acetate using iodine‐transfer and RAFT radical polymerizations

This study deals with control of the molecular weight and molecular weight distribution of poly(vinyl acetate) by iodine‐transfer radical polymerization and reversible addition‐fragmentation transfer (RAFT) emulsion polymerizations as the first example. Emulsion polymerization using ethyl iodoacetate as the chain transfer agent more closely approximated the theoretical molecular weights than did the free radical polymerization. Although ¹H NMR spectra indicated that the peaks of α‐ and ω‐terminal groups were observed, the molecular weight distributions show a relatively broad range (M_w/M_n = 2.2–4.0). On the other hand, RAFT polymerizations revealed that the dithiocarbamate 7 is an excellent candidate to control the polymer molecular weight (M_n = 9.1 × 10³, M_w/M_n = 1.48), more so than xanthate 1 (M_n = 10.0 × 10³, M_w/M_n = 1.89) under same condition, with accompanied stable emulsions produced. In the M_n versus conversion plot, M_n increased linearly as a function of conversion. We also performed seed‐emulsion polymerization using poly(nonamethylene L ‐tartrate) as the chiral polyester seed to fabricate emulsions with core‐shell structures. The control of polymer molecular weight and emulsion stability, as well as stereoregularity, is also discussed. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

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.     

γ-辐照对PLLA分子量及结晶形态的影响

以左旋聚乳酸(PLLA)为研究对象,以多官能团单体三烯丙基异氰酸酯(TAIC)为交联剂,采用反应挤出技术制备了PLLA-TAIC体系,并利用60Co-γ射线源,在较低辐照剂量(Dose≤25kGy)范围内,对所制备的聚合物进行了γ-辐照。研究了γ-辐照剂量、交联剂含量对PLLA分子量和结晶形态的影响。结果表明,在0~25kGy辐照剂量范围内,PLLA-TAIC的粘均分子量(-Mη)随γ-辐照剂量的增加呈现出先升高后降低的变化趋势,辐照剂量为10kGy、TAIC含量为3份时,PLLA的-Mη提高的幅度最大;随着辐照剂量的增加,原料PLLA形成的球晶尺寸有所增大;对于γ-辐照的PLLA-TAIC体系,随着TAIC含量的增加,PLLA的结晶能力有所下降。