Molecular weight distributions in radiation-induced polymerization. VI. γ-ray-induced polymerization of “dry” styrene in the solid state

The γ-ray-initiated polymerization of styrene in the solid state has been studied over the temperature range ?35°C to ?55°C for samples exhaustively purified and dried to remove residual water (“dry” samples). Comparison with kinetic results previously reported for dry samples in the liquid state indicates a sharp decrease in the rate of polymerization resulting from the liquid to solid state transition. The molecular weight distributions for in-source polymerization at ?35°C and ?40°C are bimodal in nature, and the appearance of a third peak is noticeable at ?47°C and ?55°C. In the case of postpolymerization at ?35°C the molecular weight distribution is bimodal as in the case of in-source samples. In the former case, however, the high molecular weight peak is predominant whereas the low molecular weight peak predominates in the latter. These results have been tentatively attributed to the postulated coexistence of two distinct propagating species which are radical and cationic in nature.     

Molecular weight distributions in radiation-induced polymerization. III. γ-Ray-induced polymerization of styrene at low temperatures

The kinetics of the γ-radiation-induced polymerization of styrene was studied at radiation intensities of 8 × 10⁴, 2.4 × 10⁵, 3.1 × 10⁵, and 8.3 × 10⁵ rad/hr over a temperature range of ?10°C to 30°C. The water content of the irradiated samples varied from 1.0 × 10^?3 to 7.5 × 10^?3 mole/l. The power dependence of the rate of polymerization on the dose rate at ?10°C varied from 0.53 to 0.71 as the water content of the sample varied from 7.5 × 10^?3 to 1.0 × 10^?3 mole/l. A value of 3.1 kcal/mole was determined for the overall activation energy. Molecular weight distribution studies by gel-permeation chromatography indicated the presence of two distinct peaks. The contribution of each peak was dependent on specific experimental parameters. Kinetic data and molecular weight distribution data indicate the coexistence of two propagating species. Analysis of the data strongly suggests that a free-radical mechanism and a cationic mechanism are involved.     

Molecular weight distribution studies. I. Radiation-induced polymerization of liquid α-methylstyrene

The concentration of water in purified and BaO-dried α-methylstyrene was found to be 1.1 × 10^?4M. The radiation-induced bulk polymerization of the α-methylstyrene thus prepared was studied in the temperature range of ?20°C to 35°C. The polymerization rate varied as the 0.55 power of the dose rate. The theoretical molecular weights and molecular weight distribution were calculated from a proposed kinetic scheme and these values were then compared with those found experimentally. The agreement between these two was reasonably close, and therefore it was concluded that, from the molecular weight distribution point of view, the proposed kinetic scheme for the cationic polymerization of α-methylstyrene is an acceptable one. The rate constant for chain transfer to monomer k_f changed with temperature and was found to be responsible for the decrease in the molecular weight of the polymer with increase in temperature. k_f and k_p at 20°C were found to be 0.95 × 10⁴ l./mole-sec and 0.99 × 10⁶ l./mole-sec, respectively.     

Molecular weight distributions in radiation-induced polymerization. V. A simultaneous kinetic and molecular weight distribution analysis of the liquid-state polymerization of styrene

The γ-ray initiated polymerization of styrene in the liquid state was investigated over the temperature range 0 to ?29°C at constant dose rate. The kinetics and molecular weight distributions were studied for samples prepared by standard techniques and samples subjected to exhaustive drying to remove residual water. In the former case, the rates of reaction were comparable to those for purely free radical polymerization, however, the resulting molecular weight distributions were distinctly bimodal, indicating an additional contribution from the cationic mechanism. On the other hand, the rates of polymerization for rigorously dried samples were 2 to 3 orders of magnitude greater than accepted free-radical values, and the molecular weight distributions were unimodal in nature. The experimental results were compared with theoretical kinetic data and molecular weight distribution data generated from a kinetic scheme taking into consideration polymerization via free-radical, cationic, and radical-cationic species, resulting in the evaluation of a number of quantities of interest. Substitution of determined values for the rate constants and G values results in good agreement between theoretically generated and experimentally determined kinetic data and molecular weight distribution data over the range of experimental conditions studied.     

Molecular weight distribution in radiation-induced polymerization. I. γ-radiation-induced free-radical polymerization of liquid styrene

The kinetics of γ-radiation-induced free-radical polymerization of styrene were studied over the temperature range 0–50°C at radiation intensities of 9.5 × 10⁴, 3.1 × 10⁵, 4.0 × 10⁵, and 1.0 × 10⁶ rad/hr. The overall rate of polymerization was found to be proportional to the 0.44–0.49 power of radiation intensity, and the overall activation energy for the radiation-induced free-radical polymerization of styrene was 6.0–6.3 kcal/mole. Values of the kinetic constants, k_p²/k_t and k_trm/k_p, were calculated from the overall polymerization rates and the number-average molecular weights. Gelpermeation chromatography was used to determine the number-average molecular weight M?_n, the weight-average molecular weight M?_w, and the polydispersity ratio M?_w/M?_n, of the product polystyrene. The polydispersity ratios of the radiation-polymerized polystyrene were found to lie between 1.80 and 2.00. Significant differences were observed in the polydispersity ratios of chemically initiated and radiation-induced polystyrenes. The radiation chemical yield, G(styrene), was calculated to be 0.5–0.8.     

Grafting of polymers onto and/or from silica surface during the polymerization of vinyl monomers in the presence of γ‐ray‐irradiated silica

The effects of radicals on silica surface, which were formed by γ‐ray irradiation, on the polymerization of vinyl monomers were investigated. It was found that the polymerization of styrene was remarkably retarded in the presence of γ‐ray‐irradiated silica above 60 °C, at which thermal polymerization of styrene is readily initiated. During the polymerization, a part of polystyrene formed was grafted onto the silica surface but percentage of grafting was very small. On the other hand, no retardation of the polymerization of styrene was observed in the presence of γ‐ray‐irradiated silica below 50 °C; the polymerization tends to accelerate and polystyrene was grafted onto the silica surface. Poly(vinyl acetate) and poly(methyl methacrylate) (MMA) were also grafted onto the surface during the polymerization in the presence of γ‐ray‐irradiated silica. The grafting of polymers onto the silica surface was confirmed by thermal decomposition GC‐MS. It was considered that at lower temperature, the grafting based on the propagation of polystyrene from surface radical (“grafting from” mechanism) preferentially proceeded. On the contrary, at higher temperature, the coupling reaction of propagating polymer radicals with surface radicals (“grafting onto” mechanism) proceeded to give relatively higher molecular weight polymer‐grafted silica. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2972–2979, 2006     

Kinetic evidence of a “matrix effect” in the bulk polymerization of acrylonitrile

The kinetics of the γ-ray-initiated polymerization of acrylonitrile in bulk are reexamined in broad ranges of temperatures and radiation dose rates. The discussion of the results coupled with an analysis of earlier data indicate that the polymerization of acrylonitrile proceeds by different mechanisms depending on the reaction temperature. Above 60°C the precipitated growing chains recombine readily; therefore, the autoaccelerated conversion curves cannot be accounted for by an “occlusion effect.” It is suggested that autoacceleration is caused by a fast propagation taking place in oriented monomer aggregates which result from dipole-dipole association of the monomer with the polymer chains formed in the early stages of the reaction (“matrix effect”). Below 10°C the precipitated growing chains are buried in the dead polymer and monomer diffusion toward the occluded chain ends is very limited (“occlusion effect”). Between 10 and 60°C the system gradually changes from one dominated by “occlusion” to one where the “matrix effect” determines the kinetic behavior. The conclusion based on kinetic data is in agreement with results obtained from studies of the postpolymerization in these various systems.     

Anionic polymerization of N-ethyl-2-vinylcarbazole and N-ethyl-3-vinylcarbazole

The polymerization of N-ethyl-2-vinylcarbazole and N-ethyl-3-vinylcarbazole by an anionic mechanism has been demonstrated. Polymerization reactions were monitored by ultraviolet/visible spectroscopy and λ_max and ε values for the propagating carbanions determined. The 2-vinyl monomer exhibits all the features of a standard “living” polymer; the carbanion is stable at ambient temperatures and high molecular weight, M?_n ? 10⁶, narrow distribution polymers and block copolymers with styrene have been prepared. The carbanion from the 3-vinyl monomer is much less stable and a clean polymerization can only be conducted at temperatures below -60°C. A comparison of the anionic polymerization characteristics of the N-, 2-, and 3-vinyl carbazole monomer series is presented.     

Temperature effects in γ-initiated polymerization of styrene. II

Experimental data are presented for the γ-initiated polymerization of commercial styrene at a series of temperatures above ambient. Examination of the early stages of polymerization (up to 10% conversion) has led to the following conclusions. For this system, there exists a critical temperature (109°C) above which the rate of polymerization is independent of dose rate, over a wide range of γ-intensities. This dose rate independence is ascribed to a “limiting rate of initiation,” characteristic of the intensity range. A consequence of this is that at a given temperature above the critical temperature the degree of polymerization is also dose rate-independent. The above phenomena can be expected in any vinyl monomer where the monomer is fairly active and produces relatively stable radicals. Experimental procedure is described, and kinetic analysis presented to substantiate the conclusions.     

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.     

Vinyl polymerization. 416. Polymerization of vinyl monomer initiated by polyethyleneglycol

The polymerization of vinyl monomer initiated by polyethyleneglycol (PEG) in aqueous solution was carried out at 85°C with shaking. Acrylonitrile (AN), methyl methacrylate (MMA), and methacrylic acid were polymerized by PEG–300 (M?_n = 300), whereas styrene was not. The effects of the amounts of monomer and PEG, the molecular weight of PEG, and the hydrophobic group at the end of PEG molecule on the polymerization were studied. The selectivity of vinyl monomer and the effect of the hydrophobic group are discussed according to “the concept of hard and soft hydrophobic areas and monomers.” The kinetics of the polymerization was investigated. The overall activation energy in the polymerization of AN was estimated as 37.9 kJ mol^?1. The polymerization was effected by a radical mechanism.     

Gamma-ray induced polymerization of styrene in the presence of methanol

The kinetics and molecular weight distributions (MWD) of the gamma-ray induced polymerization of styrene in methanol were studied at 35°C, at low conversions and over a dose rate range of 2.76 × 10³ to 2.74 × 10⁴ rad/hr. The data obtained at low initial methanol content agreed with previously obtained results and the MWD of the polystyrene formed yielded a single unimodal peak with M?_n in the range of 35,000–480,000. However, at high initial methanol content and low dose rates, at least three peaks were clearly discernible over wide molecular weight distributions. The existence of these peaks is related to the kinetic data and the formation of three distinguishable regions in the polymerization system.     

Iron‐mediated atom transfer radical polymerization of styrene with tris(3,6‐dioxaheptyl) amine as a ligand

The atom transfer radical bulk polymerization of styrene with FeX₂ (X = Br or Cl)/tris(3,6‐dioxaheptyl) amine as the catalyst system was successfully implemented at 110 °C. The number‐average molecular weight of the polymers with a narrow molecular weight distribution (weight‐average molecular weight/number‐average molecular weight = 1.2–1.5) increased linearly with the monomer conversion and matched the predicted molecular weight. The polymerization rate, initiation efficiency, and molecular weight distribution were influenced by the selection of the initiator and iron halide. The high functionality of the halide end group in the obtained polymers was confirmed by both ¹H NMR and a chain‐extension reaction. Because of its water solubility, the iron complexes could be removed easily from the reaction mixture through the washing of the polymerization mixture with water. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 483–489, 2006     

Photoinduced ionic polymerization. VII. Cationic polymerization of cyclohexene oxide in solid state

Photopolymerization of cyclohexene oxide in the presence of electron acceptors was studied in a bulk system (in liquid as well as in solid states). The polymerization was proved to proceed by a cationic mechanism in both states by the effect of inhibitors. In a liquid phase the light intensity dependence of the rate of polymerization and the molecular weight distribution showed a contribution of a free ionic polymerization. Any discontinuous phenomenon in the rate as well as in the molecular weight was not discerned between liquid(above ?36°C) and plastic crystal (between ?36 and ?81°C) phases. A quantum yield of monomer consumption as high as 8 × 10³ was observed in the plastic crystal phase. Below ?81°C in the normal crystal phase the rate as well as the molecular weight was remarkably suppressed.     

“Living” radical polymerization of methyl methacrylate with diethyl 2,3-dicyano-2,3-diphenylsuccinate as a thermal iniferter

The bulk polymerization of methyl methacrylate (MMA) initiated with diethyl 2,3-dicyano-2,3-diphenylsuccinate (DCDPS) was studied. This polymerization showed some “living” characteristics; that is, both the yield and the molecular weight of the resulting polymers increased with reaction time, and the resultant polymer can be extended by adding MMA. The molecular weight distribution of PMMA obtained at high conversion is fairly narrow (M_w/M_n = 1.24≈1.34). It was confirmed that DCDPS can serve as a thermal iniferter for MMA polymerization by a “living” radical mechanism. Furthermore, the PMMA obtained can act as a macroinitiator for radical polymerization of styrene (St) to give a block copolymer. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 4610–4615, 1999     

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.     

New ligands for atom‐transfer radical polymerization

A new type of ligands based on organic acids, such as acetic acid, iminodiacetic acid, succinic acid and isophthalic acid, has been successfully employed in the iron‐mediated atom‐transfer radical polymerization (ATRP) of vinyl monomers, such as styrene (St) and methyl methacrylate (MMA). The systems containing different organic acids can react at 250°C to 1300°C in “living”/controlled radical polymerizations giving polymers with relatively narrow molecular weight distributions (M_w/M_n = 1.2–1.5). ¹H NMR spectroscopy has been used to study the structure of the resulting polymers. Block copolymers were synthesized to confirm the ìlivingî nature of the system. The measured molecular weights are close to the calculated values for the polymerization of MMA and are somewhat lower than the theoretical ones for styrene.     

Olefin polymerization in liquid sulfur dioxide initiated by m-chloroperbenzoic acid. I. Homopolymerization of styrene and α-methylstyrene

Homopolymerizations of styrene (Sty) and α-methylstyrene (AMS) in liquid sulfur dioxide were carried out in the temperature range from ?10°C to ?78°C, using m-chloroperbenzoic acid as initiator. It is shown, through the effect of initiator concentration, temperature, and times of reaction on the conversion and molecular weight of the polymers, that AMS is more reactive than Sty because it requires a smaller amount of initiator for the same conversion to be reached, although the molecular weight of the resulting polymer is lower. A linear relationship has been observed for Sty between the degree of polymerization and the initiator concentration. Within the experimental conditions employed, the presence of polysulfones has been discarded by elemental analysis. The polymerization reactions are considered to be cationic in mechanism.     

Low‐temperature controlled free‐radical polymerization of vinyl monomers in the presence of a novel cyclic dixanthate under γ‐ray irradiation

The free‐radical polymerization of methyl acrylate (MA) has been studied in the presence of a novel cyclic dixanthate under γ‐ray irradiation (80 Gy min^?1) at room temperature (～28 °C), ?30 °C, and ?76 °C respectively. The resultant polymers have controlled molecular weights and relatively narrow molecular weight distributions, especially at low temperatures (i.e., ?30 and ?76 °C). The polymerization control may be associated with the temperature: the lower the temperature is, the more control there is. Matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry analysis of poly(methyl acrylate) (PMA) samples shows that there are at least three distributions: [3‐(MA)_n‐H]⁺ cyclic polymers, [3‐(MA)_n‐THF‐H]⁺, and [3‐(MA)_n‐(THF)₂‐H]⁺ linear PMAs. The relative content of the cyclic polymers markedly increases at a lower temperature, and this may be related to the reduced diffusion rate and the suppressed chain‐transfer reaction at the low temperature. It is evidenced that the good control of the polymerization at the low temperature may be associated with the suppressed chain‐transfer reaction, unlike reversible addition–fragmentation chain transfer polymerization. In addition, styrene bulk polymerizations have been performed, and gel permeation chromatography traces show that there is only one cyclic dixanthate moiety in the polymer chain. This article is the first to report the influence of a low temperature on controlled free‐radical polymerizations. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2847–2854, 2007     

Cationic polymerization of α-methylstyrene in dichloromethane initiated with system 2,5-dichloro-2,5-dimethylhexane-BCl3. I. Molecular weight distribution and stereoregularity of poly (α-methylstyrene)

In the polymerization of α-methylstyrene (α-MeSt) in dichloromethane in the temperature interval between ?60 and ?20°C the polymer yield decreased with increasing temperature depending on the initiating system used (I-IV) in the series II > I > IV > III, where I was a freshly prepared solution of 2,5-dichloro-2,5-dimethylhexane (DDH) with BCl₃ in dichloromethane, was the same solution as in the preceding case, but stored at room temperature one month and then used, III was a freshly prepared BCl₃ solution in dichloromethane, and IV was the initiation system “H₂O”/BCl₃. The polymer samples synthesized at ≤ ?30°C had a bimodal molecular weight distribution (MWD), which was attributed to the different participation of ionic pairs and free ions in the propagation reaction. The stereoregularity of the polymer observed (ca. 85% syndiotactic and ca. 15% heterotactic triads) determined from the ₁H-NMR spectra was not affected by the difference in the initiation system. MWD of the polymer samples was investigated by the GPC method