Radiation-induced polymerization of glass-forming systems. IV. Effect of the homogeneity of polymerization phase and polymer concentration on temperature dependence of initial polymerization rate

The effect of homogeneity of polymerization phase and monomer concentration on the temperature dependence of initial polymerization rate was studied in the radiation-induced radical polymerization of binary systems consisting of glass-forming monomer and solvent. In the polymerization of a completely homogeneous system such as HEMA–propylene glycol, a maximum and a minimum in polymerization rates as a function of temperature, characteristic of the polymerization in glass-forming systems, were observed for all monomer concentrations. However, in the heterogeneous polymerization systems such as HEMA–triacetin and HEMA–isoamyl acetate, maximum and minimum rates were observed in monomer-rich compositions but not at low monomer concentrations. Furthermore, in the HEMA–dioctyl phthalate polymerization system, which is extremely heterogeneous, no maximum and minimum rates were observed at any monomer concentration. The effect of conversion on the temperature dependence of polymerization rate in homogeneous bulk polymerization of HEMA and GMA was investigated. Maximum and minimum rates were observed clearly in conversions less than 10% in the case of HEMA and less than 50% in the case of GMA, but the maximum and minimum changed to a mere inflection in the curve at higher conversions. A similar effect of polymer concentration on the temperature dependence of polymerization rate in the GMA–poly(methyl methacrylate) system were also observed. It is deduced that the change in temperature dependence of polymerization rate is attributed to the decrease in contribution of mutual termination reaction of growing chain radicals to the polymerization rate.     

Radiation-induced polymerization of glass-forming systems. II. Effect of temperature on the polymerization rate at higher conversion

The effect of temperature and conversion on the polymerization rate at higher conversion was investigated with regard to the γ-ray-induced polymerization of hydroxyethyl methacrylate (HEMA) and glycidyl methacrylate (GMA) in the supercooled phase. The polymerization rate changed from acceleration to depression at various conversions, depending on the polymerization temperature. It was found that T_v at which the viscosity of the system became ca. 10³ cpoise influenced the shape of the polymerization time–conversion curve. The experimentally obtained conversion reflection point in the polymerization time–conversion curve agreed with the conversion where the polymerization temperature is the same as the calculated T_v of the system. When the polymerization temperature was lower than T_v of the monomer, no acceleration of the polymerization occurred. When the polymerization temperature was higher than T_v of the polymer, no depression of the polymerization rate was observed. The effect of temperature on the saturated conversion (final conversion) was also examined in terms of T_g of the polymerization system. The experimentally obtained saturated conversion agreed with the conversion where the polymerization temperature is the same as the calculated T_g of the system.     

Radiation-induced polymerization of glass forming systems. VI. Polymerization rate at higher conversion in binary systems

The effect of temperature and composition on the inflection point in the time–conversion curve and the saturated conversion was investigated in the radiation-induced radical polymerization of binary systems consisting of a glass-forming monomer and a solvent. In the polymerization of completely homogeneous systems such as glycidyl methacrylate (GMA)–triacetin and hydroxyethyl methacrylate (HEMA)–propylene glycol systems, the time–conversion curve has an inflection point at polymerization temperatures between T_vm (T_v of monomer system) and T_vp (T_v of polymer system). Such conversions at the inflection point changed monotonically between 0 and 100% in this temperature range. T_v was found to be 30–50°C higher than T_g (glass transition temperature) and a monotonic function of composition (monomer–polymer–solvent). The acceleration effect continued to 100% conversion above T_vp, and no acceleration effect was observed below T_vm. The saturated conversion in homogeneous systems changed monotonically between 0 and 100% for polymerization temperatures between T_gm (T_g of monomer system) and T_gp (T_g of polymer system). T_g was also a monotonic function of composition. No saturation in conversion was observed above T_gp, and no polymerization occurred below T_gm. In the polymerization of completely heterogeneous systems such as HEMA–dioctyl phthalate, no acceleration effect was observed at any temperature and composition. The saturated conversion was 100% above T_g of pure HEMA, and no polymerization occurred below this temperature in this system.     

Ultrasonically initiated emulsion polymerization of methyl methacrylate

The ultrasonically initiated emulsion polymerization of methyl methacrylate (MMA) was investigated. Experimental results show that sodium dodecyl sulfonate (SDS) surfactant plays a very important role in obtaining a high polymer yield, because in the absence of SDS, monomer conversion is near zero. Thus, the surfactant serves as an initiator and as interfacial modifier in this system (MMA/H₂O), and the monomer conversion increases significantly with increasing SDS concentration. An increase in the reactor temperature also leads to an increase in the monomer conversion. An appropriate increase in the N₂ purging rate also leads to higher conversion. The conversion of MMA decreases with increasing monomer concentration because of the higher viscosity of the system. With the experimental results, optimized reaction conditions were obtained. Accordingly, a high monomer conversion of about 67% and a high molecular weight of several millions can be obtained in a period of about 30 min. Furthermore, transmission electron micrographs show that the latex particles prepared are nanosized, indicating a promising technique for preparing nanoscale latex particles with a small amount of surfactant. In conclusion, a promising technique for ultrasonically initiated emulsion polymerization has been successfully performed. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3356–3364, 2001     

Free-radical polymerization of monomer-polymer solutions initiated by a peroxide-tertiary aromatic amine system

The free-radical polymerization of styrene and methyl methacrylate initiated by the peroxide-tertiary aromatic amine system in the presence of dissolved aromatic polyethers and fluoroelastomer has been studied with the use of quantitative chemical, thermometric, and gravimetric analyses. It has been shown that the rate of polymerization of monomer-polymer solutions is higher than that of pure monomers. The influence of the content of dissolved polymers on the conversion of monomers corresponding to the onset of the gel effect has been estimated. In the presence of the polymer being added, this phenomenon manifests itself at a lower fractional conversion of the monomer. The greater the content of the polymer and the higher the viscosity of the reaction system, the sooner the rise in the rate of polymerization. The experimental evidence of this study makes it possible to control the synthesis of composite materials from monomer-polymer systems.     

Kinetics of dispersion polymerization of soluble monomers. I. Methyl methacrylate

The kinetics of the free-radical-initiated polymerization of methyl methacrylate in n-dodecane to produce dispersions of polymer stabilized with a steric barrier of soluble polymer chains have been determined by thermal analysis. The mode of the polymerization can be described in terms of a bulk polymerization within the monomerswollen polymer particles. A theoretical expression has been derived on the basis of a reaction scheme in which all the radicals produced in the diluent phase are transferred immediately to the polymer particles, monomer swells the polymer particles in partition equilibrium with monomer in the diluent, and polymerization proceeds within the polymer particle according to the kinetics of bulk polymerization, taking into account Trommsdorff acceleration and plasticization effects.     

Controlled radical polymerization of methacrylates of various structures in the presence of the AIBN-FeCl3-N,N-dimethylformamide catalytic system

The controlled radical polymerization of methyl methacrylate, 2-ethoxyethyl methacrylate, and tert-butyl methacrylate conducted via atom-transfer radical polymerization in the presence of the AIBN-FeCl₃· 6H₂O-N,N-dimethylformamide catalytic system is studied. For all the systems under study, the rate of reaction is first order with respect to the monomer concentration. The number-average molecular mass of the polymers linearly increases with conversion, and their polydispersity indexes are below 1.6. The rate of polymerization decreases in the following sequence: 2-ethoxyethyl methacrylate > methyl methacrylate > tert-butyl methacrylate. The presence of ω-terminal chlorine atoms in polymer macromolecules is confirmed by ¹H NMR spectroscopy and through the block copolymerization of methyl methacrylate with a poly(ethoxyethyl methacrylate)-based macroinitiator.     

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     

Free-radical polymerization of methyl methacrylate and p-fluorostyrene in the presence of the Mn(acac)3–AlEt3 catalyst system

Methyl methacrylate and p-fluorostyrene were polymerized with manganese (III) acetylacetonate–aluminum triethyl catalyst at 60°C in a benzene medium. Maximum activity was found at Al/Mn ratio of 4. Maximum percent conversion of polymer was obtained when the aging time of the catalyst was 10 min. The rate of polymerization was first order with respect to monomer. The rate of polymerization with respect to catalyst and cocatalyst were found to be 0.5 and 1.5, respectively. The overall energy of activation for the polymerization of methyl methacrylate and p-fluorostyrene were found to be 52.6 and 57.0 kJ/mole, respectively. A free-radical mechanism is postulated.     

High-conversion polymerization. I. Theory and application to methyl methacrylate

The concept of polymer entanglements has been applied in conjunction with classical free-radical kinetics to describe vinyl polymerizations carried to high conversion. A kinetic model has been developed on the assumption that two populations of radicals exist in a high-conversion polymerization system: those radicals whose chain lengths are long enough to become entangled with neighboring molecules and have, therefore, a restricted mobility; and those shorter radicals whose mobilities are not strongly affected by diffusional effects. It has also been assumed that the kinetic rate constant for the termination step between entangled radicals is inversely proportional to the mean entanglement density. The model contains only two parameters in addition to the kinetic rate constants required to describe low-conversion polymerizations. One of these parameters can be determined, at least in principle, from measurements of solution properties of the polymer-monomer mixtures. The model so developed has been tested against experimental data obtained from the literature on the bulk polymerization of methyl methacrylate. The agreement between predicted and experimental monomer conversions and molecular weight averages is found to be satisfactory.     

Radiation-induced solid-state polymerization of derivatives of methacrylic acid. II. Postirradiation polymerization of octadecyl methacrylate

Octadecyl methacrylate (mpc ≈ 12°C.) polymerized readily in the solid state in the temperature range ?30 to +12°C. after gamma irradiation at ?196°C. The initial rate of polymerization and the “limiting” conversion increased with radiation dose and temperature. The temperature dependence of the rate corresponded to an “apparent” activation energy of 20 kcal./mole. Difficulties were experienced with polymerization during separation of the polymer from residual monomer, but these were minimized by using low radiation doses and a hot, selective solvent. The maximum conversion achieved was 70%. The polymer was crosslinked, even at low conversions.     

Emulsion atom transfer radical block copolymerization of 2‐ethylhexyl methacrylate and methyl methacrylate

The emulsion atom transfer radical block copolymerization of 2‐ethylhexyl methacrylate (EHMA) and methyl methacrylate (MMA) was carried out with the bifunctional initiator 1,4‐butylene glycol di(2‐bromoisobutyrate). The system was mediated by copper bromide/4,4′‐dinonyl‐2,2′‐bipyridyl and stabilized by polyoxyethylene sorbitan monooleate. The effects of the initiator concentration and temperature profile on the polymerization kinetics and latex stability were systematically examined. Both EHMA homopolymerization and successive copolymerization with MMA proceeded in a living manner and gave good control over the polymer molecular weights. The polymer molecular weights increased linearly with the monomer conversion with polydispersities lower than 1.2. A low‐temperature prepolymerization step was found to be helpful in stabilizing the latex systems, whereas further polymerization at an elevated temperature ensured high conversion rates. The EHMA polymers were effective as macroinitiators for initiating the block polymerization of MMA. Triblock poly(methyl methacrylate–2‐ethylhexyl methacrylate–methyl methacrylate) samples with various block lengths were synthesized. The MMA and EHMA reactivity ratios determined by a nonlinear least‐square method were ～0.903 and ～0.930, respectively, at 70 °C. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1914–1925, 2006     

Kinetics of dispersion polymerization: Effect of medium composition

The effect of the medium composition (monomer and solvent) on the kinetics of dispersion polymerization of methyl methacrylate (MMA) was studied via reaction calorimetry. It was found that increasing the monomer concentration increased the reaction rate; the exponent of the dependency of the initial reaction rate on the MMA concentration was found to be 0.93. Narrow particle size distributions were achieved at the lower monomer concentrations (0.24–0.81 mol/L) and a minimum size (2.45 μm) was found at an intermediate concentration (0.44 mol/L). The average molecular weight of the PMMA increased and the molecular weight distribution broadened with increasing monomer concentration. During a dispersion polymerization, the MMA concentration was found to decrease linearly with conversion in both phases, whereas the ratio of concentrations in the particles and continuous phase ([M]_p/[M]_c) remained constant (0.47) with partitioning favoring the continuous phase. The average number of free radicals per particle in MMA dispersion polymerization was estimated to be high from the nucleation stage onward (>5000). The increasing rate during the first ～ 40% conversion was primarily caused by the increasing volume of the polymer particle phase. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3638–3647, 2008     

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.     

Atom transfer radical polymerization of methyl methacrylate using copper-based homogeneous and heterogeneous catalysts

This study aimed at polymerization of methyl methacrylate with novel catalysts in the atom transfer radical polymerization (ATRP) condition at 90 °C. This was accomplished using CuBr/N-(2-aminoethyl)-3-aminopropyltrimethoxysilane (CuBr–AEAPTMS) as a homogeneous catalyst and one time with CuBr@AEAPTMS/SBA-15 as a heterogeneous catalyst. Catalysts were characterized using TGA, FT-IR, and UV–Vis spectroscopy. The structural analysis of the polymer was carried out by ¹³C NMR spectroscopy and GPC. Three characteristic parts of polymer produced by ATRP method including the initiator, monomer units, and end group was shown in ¹³C NMR spectra. In addition, the presence of C–Br unit showed that the polymerization process is alive. The ¹H NMR analysis was used for kinetic investigation of methyl methacrylate polymerization with homogeneous and heterogeneous catalysts that showed high monomer conversion (98 and 90% after 35 min, respectively) and good control of molecular weight with a dispersity (Р= 1.5–1.7). In addition, the plot of ln ([monomer]₀/[monomer] _t ) versus time gave linear relationships indicating a constant concentration of the propagating species throughout the polymerization. Finally, the results of the polymerization using heterogeneous catalyst compared with homogeneous catalyst revealed that it was according to ATRP method.     

Influence of monomer activity coefficient upon polymerization rate

The monomer activity has been measured as a function of conversion in the methyl methacrylate polymerization up to 25% conversion. The influence of the monomer activity coefficient upon the polymerization rate is discussed; an equation is derived which allows an estimation of the change in termination rate constant. The values obtained for this change are compared with previous estimates that have neglected the influence of the activity coefficients.     

Continuous reaction system to investigate the dispersion polymerization of vinyl monomers in supercritical carbon dioxide

A laboratory‐scale continuous reaction system using a stirred tank reactor was assembled in our laboratory to study the dispersion polymerization of vinyl monomers in supercritical carbon dioxide (scCO₂). The apparatus was equipped with a suitable downstream separation section to collect solid particles entrained in the effluent stream from the reactor, whose monomer concentration could be measured online with a gas chromatograph. The dispersion polymerization of methyl methacrylate in scCO₂ was selected as a model process to be investigated in the apparatus. The experiments were performed at 65 °C and 25 MPa with 2,2′‐azobisisobutyronitrile as the initiator and a reactive polysiloxane macromonomer as a surfactant to investigate the effect of the mean residence time of the reaction mixture on the monomer conversion, polymerization rate, polymer molecular weight, and particle size distribution. The results were compared with those obtained in batch polymerizations carried out under similar operative conditions. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4122–4135, 2006     

In situ Fourier transform near infrared spectroscopy monitoring of copper mediated living radical polymerization

In situ Fourier transform near infrared (FTNIR) spectroscopy was successfully used to monitor monomer conversion during copper mediated living radical polymerization with N‐(n‐propyl)‐2‐pyridylmethanimine as a ligand. The conversion of vinyl protons in methacrylic monomers (methyl methacrylate, butyl methacrylate, and N‐hydroxysuccinimide methacrylate) to methylene protons in the polymer was monitored with an inert fiber‐optic probe. The monitoring of a poly(butyl methacrylate‐b‐methyl methacrylate‐b‐butyl methacrylate) triblock copolymer has also been reported with difunctional poly(methyl methacrylate) as a macroinitiator. In all cases FTNIR results correlated excellently with those obtained by ¹H NMR. On‐line near infrared (NIR) measurement was found to be more accurate because it provided many more data points and avoided sampling during the polymerization reaction. It also allowed the determination of kinetic parameters with, for example, the calculation of an apparent first‐order rate constant. All the results suggest that FTNIR spectroscopy is a valuable tool to assess kinetic data. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4933–4940, 2004     

The kinetics of the polymerization of methyl methacrylate initiated by t-butylmagnesium bromide in THF,toluene or mixed solvent

The kinetics of the solution polymerization of methyl methacrylate in THF, toluene and their mixtures were studied between 200 and 300 K using dilatometry (in the systems where it was valid), gravimetric determination and monitoring monomer and polymer concentrations by NMR spectrometry. The reaction followed zero order kinetics at 200 K, first order kinetics at 275 K and mixed order in between. At both the limits and intermediate range, the reaction followed an integrated rate equation consistent with terminationless propagation proceeding through a complex between monomer and the propagating species. Above 275 K, termination and side reactions were evident and the yields of high mol. wt polymer were small. Density-temperature calibrations for monomer in THF, toluene and mixtures were constructed for the range 190–283 K. However for polymerizations in toluene-rich mixtures, where very high mol. wt polymer forms, the contraction did not correlate linearly with conversion.     

Anionic graft polymerization of methyl methacrylate on starch and dextrin

The anionic graft polymerization of methyl methacrylate on the potassium alkoxide derivative of starch or dextrin in DMSO was studied. The effects of monomer and alkoxide concentrations as well as temperature were investigated. The yield of graft polymer increased with increasing alkoxide concentration. With increasing monomer concentration and with increasing temperature the extent of homopolymer formation increased. The composition of the graft polymers was found to depend on the reaction conditions. Graft polymers having about 10–40% poly(methyl methacrylate) were obtained. There were quantitative differences in yield of isolated graft polymer between starch and dextrin and these were ascribed to differences in the solubility properties of the carbohydrates. Evidence on the structure of the graft polymers and on the mechanism of the graft polymerization was obtained from acid hydrolysis of the graft polymers and determination of the molecular weights of the cleaved side chains.