Role of chain transfer in heterogeneous polymerization of ethylene

The role of chain transfer was studied for the radiation-induced polymerization of ethylene in precipitating media, namely n-butyl alcohol, tert-butyl alcohol and their mixtures. The affinities of those solvents for polyethylene are similar, but the chain-transfer coefficient of n-butyl alcohol is larger than that of tert-butyl alcohol. The polymerizations were carried out in a reactor of 100 ml under a pressure of 300 kg/cm², at 60°C, dose rate of 3.07 × 10⁴–1.75 × 10⁵ rad/hr in the presence of 50 ml of solvents. The polymerization in tert-butyl alcohol shows the kinetic behavior characteristic of a heterogeneous polymerization, such as rate acceleration, high dose rate dependence of polymerization rate, and low dose rate dependence of polymer molecular weight, whereas the polymerization in n-butyl alcohol does not exhibit such behavior and gives polymer having a molecular weight much lower than that of polymer obtained in tert-butyl alcohol. The polymer formed in tert-butyl alcohol exhibits a bimodal molecular weight distribution measured by gel permeation chromatography. In mixed tert-butyl alcohol and n-butyl alcohol solvent, with increasing fraction of n-butyl alcohol, the two peaks not only shift to lower molecular weight but the higher molecular weight peak becomes relatively small. Eventually, the polymer formed in n-butyl alcohol exhibits a unimodal distribution. Those results are well explained on the basis of the proposed scheme for heterogeneous polymerization.     

Radiation-induced heterogeneous polymerization of ethylene in the presence of ethyl alcohol

The radiation-induced heterogeneous polymerization of ethylene in ethyl alcohol was carried out in a reactor with a capacity of 100 ml under the following reaction conditions: temperature, 24 ± 3°C; pressure, 200–400 kg/cm²; amount of ethyl alcohol, 30–70 ml; dose rate, 3.7 × 10⁴?1.05 × 10⁵ rad hr. The effects of amount of ethyl alcohol, pressure, and dose rate on the rate of polymerization at the steady state, the amount of polymerized monomer, the molecular weight of polymer, and the number of polymer chains were studied compared with the results obtained in the polymerization in tert-butyl alcohol. It was found that there is an acceleration period in the early stage of reaction followed by a steady state. The rate of polymerization was maximum when about 50 ml of ethyl alcohol was used. The molecular weight of polymer increased with a decrease in the amount of ethyl alcohol. The dependences of pressure (p) and dose rate (I) on the rate of polymerization at steady state (R_s) and the molecular weight of polymer (M?_n) were expressed as follows; R_s ∝ p^0.74, M?_n ∝ p^0.3?0.4, R_s ∝ I^0.9 and M?_n ∝ I^{?0.1 ?0.0}. The results were analyzed by a kinetic treatment based on a reaction mechanism containing both first-and second-order terminations. The rate constant of first-order termination by radical occlusion was considerably larger than that in the polymerization in tert-butyl alcohol, because the affinity of ethyl alcohol for polyethylene is smaller than that of tert-butyl alcohol. It was found that chain transfer to ethyl alcohol takes place easily and the G value of ethyl alcohol for initiation is larger than 1.5.     

Effect of alcohols on the gamma-radiation-induced polymerization of ethylene

Gamma-radiation-induced polymerization of ethylene in alcohols such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, and n-pentyl alcohols was carried out under a pressure of 400 kg./cm.²at 30°C. at a dose rate of 1.4 × 10⁵ rad/hr. in a batch reactor of 100 ml. capacity. The yield and molecular weight of polymer formed in the alcohols (except tert-butyl alcohol) were much lower than those of the bulk polymerization under the same conditions, whereas the addition of tert-butyl alcohol increased the yield and reduced the molecular weight. From the infrared spectra of the polymers and those of the bromination products it was concluded that only primary OH exists in the polymer formed in methyl alcohol and that both primary and secondary OH are in the polymer formed in other primary alcohols. Both secondary and tertiary OH were observed in the polymer when the secondary alcohols were used, and only tertiary OH in the case of tert-butyl alcohol. These polymers were found to contain small amounts of vinylidene unsaturation and methyl group. On the basis of these results the roles of the alcohols in the polymerization are discussed.     

Effect of dose rate on the radiation-induced polymerization of ethylene in tert-butyl alcohol

The dependence of the dose rate on the rate of radiation-induced polymerization of ethylene in tert-butyl alcohol containing 5 vol-% water was studied. The reaction was carried out by use of a reactor with a capacity of 100 ml under the following conditions: pressure, 200 kg/cm²; temperature, 24 ± 3°C; dose rate, 3.7 × 10⁴?1.6 × 10⁵ rad/hr; amount of medium, 70 ml. The dose rate exponents for rate of the polymerization, the molecular weight, and the number of polymer chain were found to be about 0.8, ?0.1, and 0.9, respectively. These results were well explained with kinetic results (obtained by a novel analytical method) for the polymerization which contain both first-order and second-order terminations for the concentrations of propagating radical. The individual values of the rate constants in each elementary reaction were also obtained.     

A novel scheme of heterogeneous polymerization of ethylene

The heterogeneous polymerization of ethylene initiated by radiation in tert-butyl alcohol was studied. The polymerization was carried out in a 100-ml reactor at 25–100°C and pressures of 200–300 kg/cm² in the presence of 50 ml of tert-butyl alcohol containing 7 wt-% water. The amounts of polymerized monomer, the average molecular weight of polymer formed, and the molecular weight distribution of polymer were measured at various stages of reaction and at various temperatures. The molecular weight distribution was found to be very much dependent on the reaction time and temperature. For the polymer formed at 50–60°C in the very early stages of reaction, the molecular weight distribution is unimodal, and in the intermediate stage a shoulder appears at a molecular weight higher than the first peak which increases as the polymerization proceeds; eventually a bimodal curve is formed. The bimodal distribution curves were analyzed to determine the fractions and average molecular weights of the each peak. On the basis of these data for the molecular weight distribution and kinetic behavior, a new scheme for the heterogeneous polymerization is proposed which indicates that the polymerization proceeds via propagating radicals in two different physical states, namely, loose and rigid states.     

Effect of temperature on the radiation-induced polymerization of ethylene in various media

The effects of temperature on the radiation-induced polymerization of ethylene in bulk and in the presence of ethyl alcohol, n-butyl alcohol, tert-butyl alcohol, cyclohexane, 2,2,4-trimethylpentane, and 2,2,5-trimethylhexane were studied. The changes of the amounts of polymerized monomer with the reaction temperature were different from each other in these reaction systems, especially in the range lower than 60–80°C. At temperatures lower than 60–80°C, as the reaction temperature increases, the amount of polymerized monomer decreased in bulk and in the presence of tert-butyl alcohol. The amount was almost constant in the presence of ethyl alcohol and 2,2,4-trimethylpentane, and it increased in the presence of n-butyl alcohol, cyclohexane, and 2,2,5-trimethylhexane. However, in the temperature range higher than 60–80°C, the amount of polymerized monomer increased with increasing temperature in every reaction system except for bulk polymerization. The molecular weight of polymer decreased with increasing temperature in every reaction system except at temperatures lower than 25°C. The molecular weight of polymer formed in bulk, in tert-butyl alcohol, and also in 2,2,4-trimethylpentane were relatively higher than that in other reaction systems. A bimodal molecular weight distribution was observed for the polymer formed in bulk and in tert-butyl alcohol at 40–60°C. These results are discussed in connection with the heterogeneity of the reaction system. The differences due to temperature in each reaction system are explained as due to the difference in affinity of the reaction system for the propagating chain and in the facility of chain transfer to the medium.     

Effect of pressure on the radiation-induced polymerization of ethylene in tert-butyl alcohol

The effects of pressure of the radiation-induced polymerization of ethylene in tert-butyl alcohol were studied. The reaction was carried out by use of a reactor with a capacity of 100 ml under the following conditions; pressure, 60–400 kg/cm²; temperature, 24 ± 3°C; dose rate, 2.0 × 10⁴?1.6 × 10⁵ rad/hr; amount of medium (tert-butyl alcohol containing 5 vol-% water), 70 ml. The results of polymerization were analyzed by a kinetical treatment based on a reaction mechanism with both first- and second-order terminations for the concentration of propagating, radical. On the basis of the kinetical treatment the rate constants of each elementary reaction at several pressures were determined, and the activation volumes of elementary reactions were obtained and are discussed in connection with the reaction mechanism. Consequently, the rate constants of propagation, first-order termination, and second-order termination at pressure p and at 24°C were expressed by,      

Kinetic study of γ-radiation-induced polymerization of ethylene in the presence of acetylene

The effects of acetylene on the γ-radiation-induced polymerization of ethylene were studied from the viewpoint of kinetics. The experiments were carried out under a pressure of 150–400 kg/cm²; the temperature was 30°C; the dose rates were 2.7 × 10⁴ and 1.1 × 10⁵ rad/hr; the acetylene content was 0–2.21%. Both the polymer yield and the molecular weight increased acceleratively with the reaction pressure in the polymerization containing 0.18% acetylene. The yield increased almost proportionally with the dose rate, and the molecular weight was found to be almost independent of the dose rate in the polymerization containing 2.21% acetylene. The polymerization rate and the molecular weight increased with reaction time, but the increment decreased with increasing acetylene content. The degree of increase in the molecular weight also decreased with increasing time. These results were analyzed by using a graphical evaluation method for kinetics, and the effects of acetylene on each elementary step in the polymerization discussed.     

Radiation-induced homogeneous polymerization of ethylene in cyclohexane

The radiation-induced polymerization of ethylene in cyclohexane was carried out in a reactor of 100 ml capacity under a range of temperature of 25–150°C, dose rate of 4.1 × 10⁴–2.9 × 10⁵ rad/hr, pressure of 200 kg/cm², and amount of cyclohexane of 20–90 ml. The polymerization was found to proceed at a steady state from the beginning. The polymerization rate is maximum at ca. 50 ml of cyclohexane. The dose rate exponent of the polymerization rate was 0.6 at every temperature from 25 to 150°C. The polymer molecular weight is in the range of 10³–10⁴, independent of dose rate, and decreases with increasing amount of cyclohexane. The molecular weight distribution is unimodal and narrow. Kinetic analysis of these results indicates that the polymerization proceeds via a simple scheme of homogeneous polymerization and the polymer molecular weight was determined by the chain transfer reaction which takes place mostly with cyclohexane. The unimodal and narrow molecular weight distribution is also consistent with the homogeneous polymerization scheme.     

Effect of amount of medium on the radiation-induced polymerization of ethylene in tert-butyl alcohol

The kinetics of the radiation-induced polymerization of ethylene in the presence of various amounts of medium (tert-butyl alcohol containing 5 vol-% of water) was studied, and the effect of the amount of medium on the polymerization was investigated. The polymerization was carried out by use of a reactor of 100 ml capacity under the following conditions: temperature, 24 ± 3°C; pressure, 200 kg/cm²; dose rate, 2.0 × 10⁴?1.6 × 10⁵ rad/hr. The amount of polymerized monomer and the rate of polymerization were maximum when about 50 ml of the medium was used. Data obtained with the use of 30, 50, and 90 ml of the medium were analyzed kinetically and the rate constants of each elementary reaction were determined by the method based on a reaction mechanism which contains both first- and second-order terminations for the concentration of propagating radical. These results were compared with those obtained with the use of 70 ml of the medium already reported in the previous paper. The dose rate exponents of the rate of polymerization were about 0.7–0.8. It was found that G values for the initiation of ethylene and the medium were 1.5 and 3.8, respectively, and the rate of propagation was proportional to the fugacity of ethylene. It is supposed that the medium plays an important role in the first-order termination, because the apparent rate constant of the reaction was larger when a larger amount of medium was used.     

Emulsifier-free emulsion polymerization of tetrafluoroethylene by radiation. I. Effects of reaction conditions on the polymerization rate and polymer molecular weight

The radiation-induced emulsifier-free emulsion polymerization of tetrafluoroethylene was carried out at an initial pressure of 2–25 kg/cm², temperature of 30–110°C, and under a dose rate of 0.57 × 10⁴?3.0 × 10⁴ rad/hr. The rate of polymerization was shown to be proportional to 1.0 and 1.3 powers of the dose rate and initial pressure, respectively, and is maximal at about 70°C. The molecular weight of polytetrafluoroethylene (PTFE) lies in the range of 10⁵?10⁶, increases with reaction time in the early stage of polymerization, and is maximal at 70°C but is almost independent of the dose rate. An interesting discovery is that PTFE, a hydrophobic polymer, forms as a stable latex in the absence of emulsifier. When PTFE latex coagulates during polymerization under certain conditions, the polymerization rate decreases, probably because polymerization proceeds mainly on the polymer particle surface. The observed rate acceleration and successive increase in polymer molecular weight may be due to slow termination of propagating radicals in the rigid PTFE particles.     

The morphology of polyethylene prepared by γ-ray-induced polymerization in various solvents

Polyethylenes were prepared by γ-ray-induced polymerization in ethyl and n-butyl alcohols, tert-butyl alcohol containing 5 vol-% of water, 2,2,5-trimethylhexane, 2,2,4-trimethylpentane, and cyclohexane in the temperature range 25–90°C. The morphology of the polymers as-polymerized and studied by electron microscopy depends on three factors through the degree of undercooling: the affinity of the solvent, polymerization temperature, and the polymer molecular weight. Large lamellar crystals are formed even in the alcohols when at least two of them are chosen properly.     

Radiation-induced heterogeneous polymerization of methyl methacrylate in precipitants

The radiation-induced heterogeneous polymerization of methyl methacrylate in various precipitants, mainly methyl alcohol, was carried out, and the effects of reaction conditions on the polymerization behavior and the molecular weight distribution of polymer were studied. Bimodal molecular weight distributions were found for the polymer produced by the heterogeneous polymerizations in methyl alcohol and in tert-butyl alcohol. The apparent activation energy is 1.0 and 4.5 kcal/mole, respectively, for the polymerization at a monomer concentration of 10 vol-% in methyl alcohol above and below 35°C. The polymerization at a monomer concentration lower than 40 vol-% in methyl alcohol proceeded with the precipitation of polymer. The dose rate exponent of the mean rate of heterogeneous polymerization decreased from 0.5 to a smaller value as the polymerization progressed. The ratio of the two peaks in the bimodal molecular weight distributions of polymer produced in methyl alcohol was affected by the reaction conditions. These results show the coexistence in the polymerizations of two different physical states of propagating chain, a loose state and a rigid one. The reaction scheme is discussed in connection with the physical factors which affect the solubility or the mobility of propagating chains, and the rate of elementary reactions, which influences the degree of propagating chains.     

Monomer-isomerization radical polymerization of di-tert-butyl maleate and preparation of poly(fumaric acid) via pyrolysis

Di-tert-butyl maleate (DtBM) did not polymerize with 2,2′-azobis(isobutyronitrile) as a radical initiator, but DtBM easily homopolymerized via a monomer-isomerization radical polymerization mechanism to give a high molecular weight polymer when morpholine was added into the polymerization system as an isomerization catalyst. The feature of the monomer-isomerization polymerization of DtBM was investigated in detail. The polymer obtained was confirmed to consist of a poly(tert-butoxycarbonylmethylene) structure similar to that from di-tert-butyl fumarate. Subsequent pyrolysis of the resulting polymer at 180°C is a useful route to synthesis of a high molecular weight poly(fumaric acid). © 1993 John Wiley & Sons, Inc.     

Kinetics of the γ-radiation-induced polymerization of ethylene in liquid carbon dioxide

The γ-radiation-induced polymerization of ethylene with the use of liquid carbon dioxide as a solvent, was studied from the viewpoint of kinetics. The polymerization was carried out at conversions less than 10% under the pressure ranging from 100 to 400 kg./cm.², dose rates 1.3 × 10⁴?1.6 × 10⁵ rad/hr., and temperatures of 20–90°C. The concentration of carbon dioxide varied up to 84.1 mole-%. The polymerization rate and the polymer molecular weight were observed to increase with reaction time. This observation, however, becomes less pronounced with increasing concentration of carbon dioxide and with rising temperature. The exponents of the pressure and the dose rate were determined to be 2.3 and 0.85 for the rate, and 2.0 and ?0.20 for the molecular weight, respectively. From the kinetic considerations for these results, the effect of carbon dioxide on the initiation and termination reaction in the polymerization was evaluated.     

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.     

Photo-controlled/living radical polymerization of tert-butyl methacrylate in the presence of a photo-acid generator using a nitroxide mediator

The photo-controlled/living radical polymerization of tert-butyl methacrylate was performed using a (2RS,2′RS)-azobis(4-methoxy-2,4-dimethylvaleronitrile) initiator and a 4-methoxy-2,2,6,6-tetramethylpiperidine-1-oxyl (MTEMPO) mediator in the presence of a (4-tert-butylphenyl)diphenylsulfonium triflate photo-acid generator. The bulk polymerization was carried out at 25 °C by irradiation with a high-pressure mercury lamp. Whereas the polymerization in the absence of MTEMPO produced a broad molecular weight distribution, the MTEMPO-mediated polymerization provided a polymer with a comparatively narrow molecular weight distribution around 1.4 without elimination of the tert-butyl groups. The living nature of the polymerization was confirmed on the basis of the linear correlations for the first-order time–conversion plots and conversion–molecular weight plots in the range below 50% conversion. The block copolymerization with methyl methacrylate also supported the livingness of the polymerization based on no deactivation of the prepolymer.     

Radical polymerization of isopropyl tert-butyl fumarate and maleate,and characterization of the resulting polymers

Radical polymerization of isopropyl tert-butyl fumarate (iPtBF) and monomer-isomerization radical polymerization of isopropyl tert-butyl maleate (iPtBM) were investigated with 2,2′-azobisisobutyronitrile as initiator in the presence and absence of morpholine (Mor) as isomerization catalyst. It was found that iPtBF gave high molecular weight polymers in high yield as previously observed for diisopropyl fumarate (DiPF) and di-tert-butyl fumarate (DtBF). It was confirmed that iPtBF produced by in situ monomer isomerization of iPtBM homopolymerized to give a polymer. Radical copolymerization of iPtBM with styrene in the presence and absence of Mor was also performed and monomer reactivity ratios obtained were compared. From the kinetic study of the isomerization of iPtBM, it was revealed that the isomerization rate showed first-order dependence on the concentration of iPtBM and Mor, and that the apparent activation energy was 29.4 kJ/mol. On pyrolysis of the poly(iPtBF) at 180°C, isobutene and isopropanol were eliminated rapidly to yield polymer containing carboxyl groups and anhydrides. The pyrolytic behavior was different from that of a copolymer of DiPF with DtBF.     

Preparation of functional polymers by living anionic polymerization: Polymerization of allyl methacrylate

The anionic polymerization of allyl methacrylate was carried out in tetrahydrofuran, both in the presence and in the absence of LiCl, with a variety of initiators, at various temperatures. It was found that (1,1-diphenylhexyl)lithium and the living oligomers of methyl methacrylate and tert-butyl methacrylate are suitable initiators for the anionic polymerization of this monomer. The temperature should be below −30°C, even in the presence of LiCl, for the living polymerization to occur. When the polymerization proceeded at −60°C, in the presence of LiCl, with (1,1-diphenylhexyl)-lithium as initiator, the number-average molecular weight of the polymer was directly proportional to the monomer conversion and monodisperse poly(allyl methacrylate)s with high molecular weights were obtained. ¹H-NMR and FT-IR indicated that the α CC double bond of the monomer was selectively polymerized and that the allyl group remained unreacted. The prepared poly(allyl methacrylate) is a functional polymer since it contains a reactive CC double bond on each repeating unit. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 2901–2906, 1997     

Controlled radical polymerization of a trialkylsilyl methacrylate by reversible addition–fragmentation chain transfer polymerization

The reversible addition–fragmentation chain transfer (RAFT) polymerization of a hydrolyzable monomer (tert‐butyldimethylsilyl methacrylate) with cumyl dithiobenzoate and 2‐cyanoprop‐2‐yl dithiobenzoate as chain‐transfer agents was studied in toluene solutions at 70 °C. The resulting homopolymers had low polydispersity (polydispersity index < 1.3) up to 96% monomer conversion with molecular weights at high conversions close to the theoretical prediction. The profiles of the number‐average molecular weight versus the conversion revealed controlled polymerization features with chain‐transfer constants expected between 1.0 and 10. A series of poly(tert‐butyldimethylsilyl methacrylate)s were synthesized over the molecular weight range of 1.0 × 10⁴ to 3.0 × 10⁴, as determined by size exclusion chromatography. As strong differences of hydrodynamic volumes in tetrahydrofuran between poly(methyl methacrylate), polystyrene standards, and poly(tert‐butyldimethylsilyl methacrylate) were observed, true molecular weights were obtained from a light scattering detector equipped in a triple‐detector size exclusion chromatograph. The Mark–Houwink–Sakurada parameters for poly(tert‐butyldimethylsilyl methacrylate) were assessed to obtain directly true molecular weight values from size exclusion chromatography with universal calibration. In addition, a RAFT agent efficiency above 94% was confirmed at high conversions by both light scattering detection and ¹H NMR spectroscopy. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5680–5689, 2005