Radiation-induced polymerization of glass-forming systems. V. Initial polymerization rate in binary glass-forming systems

The radiation-induced polymerization of binary systems consisting of glass-forming monomer and glass-forming solvent in supercooled phase was studied. The initial polymerization rates were markedly affected by T_g (glass transition temperature) and T_v of the system (30–50°C higher than T_g), which turned to be functions of the composition. The composition and temperature dependence of initial polymerization rate in binary glass-forming systems were much affected by homogeneity of the polymerization system and the T_g of the glass-forming solvent. The composition and temperature dependences in the glycidyl methacrylate–triacetin system as a typical homogeneous polymerization system were studied in detail, and the polymerizations of hydroxyethyl methacrylate–triacetin and hydroxyethyl methacrylate–isoamyl acetate systems were studied for the heterogeneous polymerization systems; the former illustrates the combination of lower T_g monomer and higher T_g solvent and the latter typifies a system consisting of higher T_g monomer and lower T_g solvent. All experimental results for the composition and temperature dependence of initial polymerization rate in binary glass-forming systems could be explained by considering the product of the effect of the physical effect relating to T_v and T_g of the system and the effect of composition in normal solution polymerization at higher temperature, which was also the product of a dilution effect and a chemical or physical acceleration effect.     

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.     

Radiation-induced polymerization of glass-forming systems. I. Effect of temperature on the initial polymerization rate

Radiation-induced polymerization of hydroxyethyl methacrylate (HEMA) and glycidyl methacrylate (GMA) was investigated. HEMA and GMA formed a stable supercooled or glassy phase by themselves at low temperatures. It was found that the initial polymerization rate was proportional to ca.0.5 power of the dose rate in the region of relatively high temperatures and the dose rate exponent changed sharply to 1.0 at a temperature T_r, at which the viscosity of monomeric systems reached ca. 10³ cP as the temperature decreased. Moreover, a maximum in the polymerization rate–temperature curve occurred at T_v. It was deduced that the polymerization mechanism changed from the stationary to the nonstationary at T_v. The temperature at which a minimum of the polymerization rate occurred could be calculated kinetically considering the viscosity dependency of termination rate, and it agreed well with that obtained experimentally. It was deduced that occurrence of the minimum polymerization rate above T_v was attributable mainly to the decrease in termination rate due to diffusion control.     

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.     

Cationic polymerization of 1,3-pentadiene in the presence of vanadium oxychloride

The cationic polymerization of 1,3-pentadiene in the presence of vanadium oxytrichloride is studied. 1,3-Pentadiene is shown to polymerize at a high rate to high monomer conversions in the absence of proton-donor compounds in the catalytic system. The initial rate of 1,3-pentadiene polymerization is proportional to the concentration of VOCl₃ in the system and demonstrates an extremal dependence on the initial concentration of 1,3-pentadiene. The polymerization process is distinguished by an induction period whose duration increases with a decrease in the reaction temperature. Regardless of polymerization conditions, with an increase in the monomer conversion, the molecular-mass distribution of the polymer widens owing to formation of a high-molecular-mass fraction, which, depending on reaction conditions, can be consumed in formation of the gel fraction. It is shown that the degree of unsaturation and the microstructure of poly(1,3-pentadiene) are almost independent of the polymerization conditions.     

Electroinitiated polymerization of butadiene sulfone

Electroinitiated polymerization of butadiene sulfone was achieved by direct electron transfer in acetonitrile—tetrabutylammonium fluoroborate system by controlled potential electrolysis technique. High conversions were obtained at reasonable temperatures and polymerization times. The polymer was found to be composed of linear segments along with some cyclic units. The effect of monomer concentration, temperature, and polymerization potential on the rate of polymerization was investigated. Temperature and polymerization potential have positive effects on the rate of polymerization. The effect of ultrasonic vibration was also investigated by conducting electrolyses at different monomer concentrations in the presence and absence of ultrasonic vibration. It was observed that the rate of polymerization increases significantly in the presence of ultrasonic vibration. The inverse relationship between the rate of polymerization and monomer concentration was observed in presence and absence of ultrasonic vibration.     

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.     

Dispersion polymerization of styrene in ethanol: Monomer partitioning behavior and locus of polymerization

A thermodynamic model has been proposed for the simulation of monomer partitioning behavior in the dispersion polymerization of styrene in ethanol. The monomer concentration in the polymer particles is very low (20 vol% at 5% conversion) and decreases further as the polymerization proceeds. It is independent of stabilizer concentration but is strongly dependent on initial monomer concentration. The partitio n coefficient ([M_p]/[M_c]) of styrene increases from 0.8 to 1.1 with incresing conversion. There are two polymerization loci in dispersion polymerization, namely the continuous and polymer phases. Competition between solution and heterogeneous polymerization has been observed in this system. The rate of dispersion polymerization is dependent on initial monomer concentration but is independent of initiator concentration at higher conversions. The molecular weight of the polymers produced by this process increases with increasing conversion and decreases with increasing initiator concentration.     

Highly efficient and well‐controlled ambient temperature RAFT polymerization of glycidyl methacrylate under visible light radiation

A range of well‐defined poly(glycidyl methacrylate) (PGMA) polymers and their corresponding block copolymers were synthesized via 2‐cyanoprop‐2‐yl(4‐fluoro) dithiobenzoate or CPFDB‐mediated ambient temperature reversible addition fragmentation chain transfer radical polymerization or RAFT polymerization under environmentally friendly visible light radiation (λ = 405–577 nm), using a (2,4,6‐trimethylbenzoyl) diphenylphosphine oxide photoinitiator. As comparison, CPFDB‐mediated ambient temperature RAFT polymerizations of glycidyl methacrylate (GMA) under both full‐wave radiation (λ = 254–577 nm) and long‐wave radiation (λ = 365–577 nm) were also studied in this article. The results indicated that CPFDB moieties were significantly photolyzed under either full‐wave radiation or long‐wave radiation, thus undermining the controlled behavior of these RAFT processes. Whereas this photolysis was significantly suppressed under visible light radiation, thus CPFDB functionalities exerted well control over RAFT process, leading to a remarkably living behavior up to 90% GMA monomer conversions. This strategy facilitates the facile synthesis of well‐defined PGMA polymers. More importantly, under visible light radiation, a relatively high initial molar ratio of GMA to CPFDB and TPO led to shortening initialization period of RAFT process and accelerating overall polymerization rate. These effects are remarkably in favor of the facile synthesis of well‐defined PGMA polymers and PGMA‐based copolymers with high molecular weights. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5091–5102, 2007     

Free-radical polymerization of guanidine acrylate and methacrylate and the conformational behavior of growing chains in aqueous solutions

Monomer salts based on acrylic acids and guanidine—guanidine acrylate and methacrylate—have been synthesized, and the kinetic features of their free-radical polymerization in aqueous solutions have been studied. When polymerization is carried out in organic solvents (methanol, ethanol, or dioxane), the system is heterogeneous over the entire range of monomer concentrations. In aqueous solutions, the reaction systems are homogeneous only at small initial monomer concentrations (less than 1.30 and 0.40 mol/l for guanidine acrylate and methacrylate, respectively; the ammonium persulfate concentration is 5 × 10^?3 mol/l; pH ～ 6.5; 60°C). At higher concentrations, microheterogeneity appears from small conversions (～1%). This phenomenon is associated with the coiling of growing polymer chains owing to associative interactions between guanidine groups occurring in the monomer solution and carboxyl groups of (meth)acrylate polymer units. In aqueous solutions over the entire range of monomer concentrations (0.2–2.5 mol/l), the kinetic orders are the same as in the case of corresponding acrylic acids. The effects of composition of reaction solutions on changes in the initial rate of polymerization and the conformational behavior of the systems under study have been ascertained.     

Copolymerization of N‐vinylcaprolactam and glycidyl methacrylate: Reactivity ratio and composition control

Free‐radical copolymerizations of N‐vinylcaprolactam (VCL) and glycidyl methacrylate (GMA) were investigated to synthesize temperature‐responsive reactive copolymers with minimized compositional heterogeneity. The average copolymer composition was determined by Fourier transform infrared and nuclear magnetic resonance techniques. The reactivity ratios for VCL and GMA were found to be 0.0365 ± 0.0009 and 6.44 ± 0.36 by the Fineman–Ross method and 0.039 ± 0.006 and 6.75 ± 0.29 by the Kelen–Tudos method, respectively. When prepared by batch polymerization, VCL–GMA copolymers had a highly heterogeneous composition and fractions of different solubilities in water. The use of a gradual feeding technique, which included the sequential addition of more reactive GMA monomer into the reaction, yielded copolymers with much more homogeneous composition. The produced copolymers with 0.9 and 0.11 fractional GMA contents preserved their temperature‐responsive properties and precipitated from aqueous solutions when the temperature exceeded 31 °C. The GMA units in the VCL–GMA copolymers were capable of reacting with amino end‐functionalized poly(ethylene oxide) at room temperature to produce poly(N‐vinylcaprolactam)–poly(ethylene oxide) graft copolymers. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 183–191, 2006     

Influence of catalyst depletion or deactivation on polymerization kinetics. II. Nonsteady-state polymerization

The number-average and weight-average degrees of polymerization at the end of the polymerization process have been calculated in terms of the initial monomer concentration, initial catalyst concentration, and rate constants for various polymerization processes, all of which assume instantaneous initiation. The mechanisms differ among themselves in that there is either first-order catalyst deactivation, or transfer to monomer, or both. The calculation is greatly simplified if only the molecular weights at the end of polymerization are considered. The method given is particularly useful for systems where the calculation of the distribution function as a function of time is complicated. The fact that the monomer concentration and catalyst concentration have a marked effect on the molecular weight provides a good test of the validity of the mechanism under consideration. A comparison of the calculated and observed molecular weights obtained for the homogeneous polymerization of acrylonitrile with an organometallic catalyst will be given in a later communication.     

Radiation-induced heterogeneous polymerization of acrylamide in acetone and acetone–water mixtures

The effects of temperature, dose rate, and monomer concentration on the heterogeneous polymerization of acrylamide in acetone–water mixtures have been studied. Heterogeneous polymerization takes place in mixtures containing less than 60 vol-% water. The polymerization is steady in acetone and nonsteady in acetone an nonsteady in mixtures containing 10–50 vol-% water. The average rate of polymerization is highest in mixtures with about 20 vol-% water. Polymer molecular weight increases with the increasing water content in range 0–10 vol-% and does not change in the range of 30–70 vol-% water. For the polymerization in acetone and an acetone–water 60/40 mixture the activation energies are 2.3 and ?1.8 kcal/mole, the dose rate exponents of rate are 0.78 and 0.52, and the monomer concentration exponents of rate are 0.5 and 1.6, respectively. The polymer molecular weight increases with decreasing dose rate, decreasing temperature, and increasing monomer concentration. These results are discussed in connection with the mechanism of heterogeneous polymerization and the solvent effect.     

Studies of redox polymerization. I. Aqueous polymerization of acrylamide by an ascorbic acid–peroxydisulfate system

The polymerization of acrylamide initiated by an ascorbic acid–peroxydisulfate redox system was studied in aqueous solution at 35 ± 0.2°C in the presence of air. The concentrations studied were [monomer] = (2.0–15.0) × 10^?2 mole/liter; [peroxydisulfate] = (1.5–10.0) × 10^?3 mole/liter; and [ascorbic acid] = (2.84–28.4) × 10^?4 mole/liter; temperatures were between 25–50°C. Within these ranges the initial rate showed a half-order dependence on peroxydisulfate, a first-order dependence on an initial monomer concentration, and a first-order dependence on a low concentration of ascorbic acid [(2.84–8.54) × 10^?4 mole/liter]. At higher concentrations of ascorbic acid the rate remained constant in the concentration range (8.54–22.72) × 10^?4 mole/liter, then varied as an inverse halfpower at still higher concentrations of ascorbic acid [(22.72–28.4) × 10^?4 mole/liter]. The initial rate increased with an increase in polymerization temperature. The overall energy of activation was 12.203 kcal/mole in a temperature range of 25–50°C. Water-miscible organic solvents depressed the initial rate and the limiting conversion. The viscometric average molecular weight increased with an increase in temperature and initial monomer concentration but decreased with increasing concentration of peroxydisulfate and an additive, dimethyl formamide (DMF).     

Vinyl polymerization initiated by peroxydiphosphate. XII. Polymerization of acrylamide and acrylic acid by peroxydiphosphate–sodium thiosulfate redox system

The aqueous polymerization of acrylic acid and acrylamide initiated by peroxydiphosphate–sodium thiosulfate redox system was investigated within the temperature range of 25–35°C. The rates of polymerization were measured at different concentrations of oxidant, activator and monomer. The monomer and the initiator exponents were evaluated to be 1.12 and 0.51. The rate of polymerization decreases with increasing thiosulfate concentration. On the basis of the experimental observation of the dependence of the rate of polymerization, R_p, on various variables, a suitable kinetic scheme has been proposed and the rate parameters have been evaluated.     

Reversible addition–fragmentation chain transfer polymerization of glycidyl methacrylate with 2‐cyanoprop‐2‐yl 1‐dithionaphthalate as a chain‐transfer agent

A reversible addition–fragmentation chain transfer (RAFT) agent, 2‐cyanoprop‐2‐yl 1‐dithionaphthalate (CPDN), was synthesized and applied to the RAFT polymerization of glycidyl methacrylate (GMA). The polymerization was conducted both in bulk and in a solvent with 2,2′‐azobisisobutyronitrile (AIBN) as the initiator at various temperatures. The results for both types of polymerizations showed that GMA could be polymerized in a controlled way by RAFT polymerization with CPDN as a RAFT agent; the polymerization rate was first‐order with respect to the monomer concentration, and the molecular weight increased linearly with the monomer conversion up to 96.7% at 60 °C, up to 98.9% at 80 °C in bulk, and up to 64.3% at 60 °C in a benzene solution. The polymerization rate of GMA in bulk was obviously faster than that in a benzene solution. The molecular weights obtained from gel permeation chromatography were close to the theoretical values, and the polydispersities of the polymer were relatively low up to high conversions in all cases. It was confirmed by a chain‐extension reaction that the AIBN‐initiated polymerizations of GMA with CPDN as a RAFT agent were well controlled and were consistent with the RAFT mechanism. The epoxy group remained intact in the polymers after the RAFT polymerization of GMA, as indicated by the ¹H NMR spectrum. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2558–2565, 2004     

Kinetics of copolymerization—I. Kinetic investigation of the polymerization of acrylonitrile in homogeneous phase

A detailed study was made of the kinetics of initiated homopolymerization of acrylonitrile in dimethylformamide and dimethylsulphoxide at 40–60°. The rate of polymerization was found to be proportional to the (initiator concentration)^1/2. The rate of initiation of polymerization was determined by the inhibition method, using three stable free radicals. Trends in the average rate of polymerization were also studied for various initial monomer and solvent concentrations. The overall rate constant (K) was strongly dependent on monomer concentration decreasing with decrease of monomer concentration. It has been shown that the hot radical theory describes accurately, without physical contradiction, the solvent dependence of rate constants of polymerization systems.     

Dispersion polymerization of styrene in alcohol media: Effect of initiator concentration,solvent polarity,and temperature on the rate of polymerization

The effects of three different variables (initiator concentration, polarity of the solvent and reaction temperature) on the rate of dispersion polymerization of styrene in alcohols have been investigated. It was found that the rate of polymerization increases with the initiator (AIBN) concentration at the 0% conversion level and becomes independent of it at higher monomer conversions. More significant was the result that the rate was also found to increase with solvent polarity. This is consistent with thermodynamic equilibrium calculations which account for the partitioning behavior of monomer and solvent in both the solution and the particle phases. The results further suggest the existence of two different kinetic regions: one at low conversions, where the reaction takes place primarily in the solution phase, and one at high conversions, where the reaction takes place primarily in the particle phase. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 2907–2915, 1997     

Photopolymerization of 2‐hydroxyethyl methacrylate: Effect of the medium properties on the polymerization rate

The effect of solvent properties on the polymerization rate of 2‐hydroxyethyl methacrylate (HEMA) was examined with the photoreaction of 4,4′‐azobis(2‐amidinopropane) and photoinduced electron transfer of a thioxanthone derivative and triethanolamine as the radical source. The polymerization rate of HEMA was markedly affected by pH and the medium polarity. The rate increased over a pH range of 6–8. The dependence of the polymerization rate on the amine concentration photoinitiated by the bimolecular system was different in water and acetonitrile as solvents. In aqueous medium, pH 9.5, the rate increased with the amine concentration reaching a constant value at 0.025 M amine; further amine addition inhibited the polymerization. In organic media the inhibition effect was not observed. Triethanolamine addition did not change the polymerization rate photoinitiated by the azo compound. Photochemical studies of the thioxanthone were carried out under the polymerization conditions. These studies allowed us to simulate the dependence of the polymerization rate on the amine concentration. The results are explained in terms of the interaction of the ketone excited states with the amine in the different media. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2368–2373, 2003     

Visible light‐induced living surface grafting polymerization for the potential biological applications

A novel visible light‐induced living surface grafting polymerization was developed by a strategy in which isopropyl thioxanthone (ITX) was first photoreduced under UV light and sequentially coupled onto the surface of polymeric substrates, and the produced isopropyl thioxanthone‐semipinacol (ITXSP) “dormant” groups were subsequently reactivated under visible light to initiate a surface grafting polymerization. By using glycidyl methacrylate (GMA) and low‐density polyethylene (LDPE) films as models, a “living” surface grafting polymerization initiated by ITXSP under visible light at room temperature was observed. Both the surface grafting chain length versus grafting conversion of monomer and the grafting polymerization rate versus monomer concentration demonstrated a linear dependence, which is in accord with the known characteristics of living polymerization. The livingness rendered it possible to accurately control the thickness of the grafted layer by simply altering the irradiation time. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Phys, 2009