Use of an Internal Keto-Imino Compound as the Photoinitiator in the Polymerization of Methyl Methacrylate

Photopolymerization of MMA in visible light was studied at 40°C using acridone as the photoinitiator. The polymerization was found to proceed via a free radical mechanism and the radical generation process was considered to follow an initial complexation reaction between monomer and acridone. Kinetic data indicated a lower order dependence of R_p on the initiator concentration (initiator exponent < 0.5). Initiator-dependent chain termination was significant along with the usual bimolecular mode of chain termination. The monomer exponent varied from about 1.0 to 1.5, depending on the nature of the solvent used. The nonidealities in this case were also analyzed.     

Photopolymerization of Methyl Methacrylate Using the Benzil-Dimethylaniline Combination as the Photoinitiator

Benzil (BZL)-dimethylaniline (DMA) exciplex interaction has been utilized to initiate the photopolymerization of methyl methacrylate at 40°C in bulk and in solution. Depending on the nature of the solvent used, the monomer exponent values varied between 0.47 to 2.76. Initiator exponent values were found to be 0.29 and 0.15 with respect to [BZL] and [DMA], respectively. A low value of k_p ²/k_t and the high initiator transfer constant values indicated significant initiator-dependent termination. The semipinacol radical formed during irradiation is thought to be mainly responsible for primary radical termination while the generated ion radicals are presumed to participate in degradative initiator transfer.     

Kinetic Investigation on the Photopolymerization of Methyl Methacrylate Using Iodine Trichloride as Initiator

The photopolymerization of MMA in visible light was studied at 45°C using IC1₃ as the photoinitiator. The initiator exponent was found to be 0.16 and the monomer exponent varied between 1.0 to 1.50, depending on the nature of the solvent. Analysis of the data revealed that the polymerization was induced by a free radical mechanism. Nonideality of the kinetics was explained on the basis of 1) Monomer-dependent chain initiation and 2) Initiator-dependent chain termination via degradative initiator transfer.     

Polymerization of Methyl Methacrylate Using Acridone-Bromine Combination as the Photoinitiator

The photopolymerization of methyl methacrylate (MMA) in visible light was studied at 40°C using the acridone-bromine (acridone-Br₂) combination as the photoinitiator. The polymerization was found to proceed via a free radical mechanism, and the radical generation process was considered to follow an initial complexation reaction between monomer and each initiator component (acridone and Br₂), followed by further interaction between these two initiator-monomer complexes. Kinetic data indicated a lower-order dependence of R on initiator concentrations (initiator exponent < 0.5). Initiator-dependent chain termination was signifi-cant along with the usual bimolecular mode of chain termination. The monomer exponent varied from about 1.00 to 2.00, depending on the nature of solvents used. The nonidealities in this system were also analyzed.     

Polymerization of methyl methacrylate using isatoic anhydride–bromine donor–acceptor complex as the photoinitiator

Isatoic anhydride (IA) alone did not initiate photopolymerization of methyl metacrylate (MMA) at 40°C when exposed to visible light for about 180 min. But IA, when used in combination with bromine (Br₂) as the initiator, initiated the photopolymerization of MMA readily under the same conditions. This behavior was explained by the formation of a donor-acceptor type of complex between IA and Br₂ in the presence of MMA. The polymerization was found to proceed via a free radical mechanism and the radical generation process was considered to follow an initial complexation reaction between the initiator components and monomer. The complex initiator showed nonideal kinetics for the present system (initiator exponent < 0.5) and was analyzed. The monomer exponents varied from 0.83 to 1.15 normally depending on the nature of solvent used. Initiator-dependent chain termination was significant as well as the bimolecular mode of chain termination. © 1993 John Wiley & Sons, Inc.     

Non-ideality in vinyl polymerization—IV. Kinetics of polymerization of vinyl acetate in benzene initiated by azo-bis isobutyronitrile (AIBN)

Vinyl acetate was polymerized in bulk and in benzene at 50°C using a wide range of concentrations of azobisisobutyronitrile. Values of f_k (the efficiency of initiator) and k_prt/k_ik_p (the characteristic constant of primary radical termination) were found to be 0.53 and 2.00 × 10⁴ respectively from data for bulk polymerization. In solution polymerization, the initiator exponent is a function of initiator concentration ranging from 0.35 at high concentration to- about 0.65 at low concentration. This result has been explained on the basis of degradative chain transfer to solvent and primary radical termination. The results have been treated according to mathematical formulations already developed; the characteristic constant of degradative chain transfer and the transfer constant of the solvent have been determined. The results have been compared with literature values and discrepancies explained.     

Novel solvent effects in the photopolymerization of methyl methacrylate by use of quinoline–bromine charge-transfer complex as photoinitiator

Photopolymerization of MMA was carried out at 40°C in diluted systems by use of quinolinebromine (Q–Br₂) charge-transfer complex as the initiator and chloroform, carbon tetrachloride, chlorobenzene, dioxane, THF, acetone, benzene, toluene, quinoline, and pyridine as solvents. The results showed variable monomer exponents ranging from 1 to 3. For chloroform, carbon tetrachloride, and chlorobenzene, the monomer exponent observed was unity; for other solvents used, the value of the same exponent was much higher (between 2 and 3). Initiation of polymerization is considered to take place through radicals generated in the polymerization systems by the photodecomposition of (Q–Br₂)–monomer complex (C) formed instantaneously in situ on addition of the Q–Br₂ complex in monomer. The kinetic feature of high monomer exponent is considered to be due to higher order of stabilization of the initiating complex (C) in presence of the respective solvents. In the presence of the retarding solvents, very low or zero initiator exponents were also observed, depending on the nature and concentration of the solvents used. The deviation from the square-root dependence of rate on initiator concentration becomes higher at high solvent and initiator concentrations in general. This novel deviation is explained on the basis of initiator termination, probably via degradative chain transfer involving the solvent-modified initiating complexes and the propagating radicals.     

Studies on the polymerization of methyl methacrylate activated by azobisisobutyramidine

Kinetic studies on methyl methacrylate polymerization were carried out with watersoluble 2,2′-azobisisobutyramidine (ABA). The rate of polymerization was proportional to the square root of the initiator concentration in the solvents chloroform, methanol, and dimethyl sulfoxide (DMSO), which confirms the bimolecular nature of the termination reaction. The monomer exponent was unity in chloroform but in methanol and DMSO the rate of polymerization passed through a maximum when plotted against the monmer concentration. This behavior in methanol has been attributed to be due to the enhanced rate of production of radical with increasing proportion of methanol. The rate of decomposition of the ABA has been observed to be faster in methanol than in chloroform. The situation becomes more complicated with DMSO, which was found to reduce the value of δ = (2k_t)^1/2/k_p in methyl methacrylate polymerization. The rate of polymerization was observed to be highly dependent on the nature of the solvent, the rate increasing with increased electrophilicity of the solvent. The dependence of R_p on the solvent has been explained in the light of the stabilization of the transition state due to increased solvation of the basic amidine group of the initiator with the increased electrophilicity of the solvent.     

Effect of pyridine on the kinetics of polymerization of styrene initiated by benzoyl peroxide and azobisisobutyronitrile at 60°C

Kinetics of solution polymerization of styrene was studied using pyridine as solvent and BZ₂O₂ and azobisisobutyronitrile (AIBN) as initiators at 60°C. Normal kinetic features (R_p ∝ [AIBN]^0.5 · [styrene]^1.0) were observed for the AIBN-initiated polymerization, with pyridine playing the role of an inert diluent; but in the BZ₂O₂-initiated polymerization, the monomer exponent was found to vary from a low value of 0.45 at a relatively low initiator concentration (1 × 10^?2 mole/liter) to a value higher than the usual value of unity (1.18) at a much higher concentration of the initiator (16 × 10^?2 mole/liter). The initiator exponent value was found to be 0.5 (usual) up to 20% v/v dilution with pyridine, but it showed a tendency to decrease with increase in pyridine content beyond 20% v/v. The k/k_t value for each initiator system, however, was found to remain constant over the whole concentration range of pyridine. The unusual kinetic features were explained on the basis of predominance of one or the other of two competitive reactions in BZ₂O₂-initiated system: (a) higher rate of decomposition of BZ₂O₂ in pyridine and (b) primary radical depletion by reaction with pyridine, depending upon the concentration of BZ₂O₂ and pyridine.     

Photopolymerization of methyl methacrylate by use of a quinoline–bromine charge-transfer complex as the photoinitiator

Polymerization of MMA was carried out in presence of visible light (440 nm), quinoline-bromine charge-transfer complex being used as the photoinitiator. The initiator exponent was observed to be 0.5 up to 0.014 M initiator concentration; when chloroform was used as the solvent, the monomer exponent was found to be unity. The polymerization was inhibited in presence of hydroquinone but little inhibitory effect was observed in the presence of air. An average value of k²_p/k_t for this photopolymerization system was found to be (1.08 ± 0.22) × 10^-2. Kinetic and other evidence indicates that the overall polymerization takes place by a radical mechanism.     

Photopolymerization of methyl methacrylate using tetrahydrofuran sulphur dioxide complex as photoinitiator

Photopolymerization of MMA in visible light was studied at 40 using THF-SO₂ complex as the photoinitiator. Initiator exponent was 0.19 and monomer exponent lay between 1.0 and 1.5, depending on thenature of solvent. Analysis of kinetic and other data indicate that the polymerization proceeds by a radical mechanism and termination is initiator dependent. Chain termination via degradative chain (initiator) transfer appears to be significant feature.     

Chain length‐dependent termination in pulsed‐laser polymerization. VIII. The temperature dependence of the rate coefficient of bimolecular termination in the bulk polymerization of styrene

The photosensitized polymerization of styrene in bulk was investigated in the temperature range of 25–70°C with respect to the average rate coefficient of bimolecular chain termination k̄_t, especially its chain length dependence at low conversions, by means of pulsed laser polymerization (PLP). Three methods were applied: two of them were based on equations originally derived for chain length independent termination taking the quantity k_t contained therein as an average k̄_t, while the third one consisted in a nonlinear fit of the experimental chain length distribution (CLD) obtained at very low pulse frequencies (LF‐PLP) to a theoretical equation. The exponent b characterizing the extent of chain length dependence was unanimously found to decrease from about 0.17–0.20 at 25°C to 0.08–0.11 at 70°C, slightly depending on which of the three methods was chosen. This trend toward more “ideal” polymerization kinetics with rise of polymerization temperature is tentatively ascribed to a quite general type of polymer solution behavior that consists in a (slow) approach to a lower critical solution temperature (LCST), which is associated with a decrease of the solvent quality of the monomer toward the polymer, an effect that should be accompanied with a decrease of the parameter b. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 697–705, 2000     

Photopolymerization of methyl methacrylate with the use of morpholine-chlorine charge transfer complex as the photoinitiator

Polymerization of methyl methacrylate (MMA) was kinetically studied under photo condition using near UV visible light at 40°C and employing morpholine (MOR)–chlorine (Cl₂) charge transfer (C-T) complex as the photoinitiator. The rate of polymerization (R_p) was dependent on morpholine/chlorine mole ratio; the 1 : 2 (MOR–Cl₂) C-T complex acted as the latent initiator complex, C, which underwent further complexation with the monomer molecules to give the actual initiator complex, I. Using 1 : 2 (MOR-Cl₂) C-T complex as the latent initiator, the initiator exponent evaluated for bulk photopolymerization of MMA was 0.071 and monomer exponent determined from studies of photopolymerization in benzene diluted system was 1.10. Benzoquinone behaved as a strong inhibitor and the polymers tested positive for the incorporation of chlorine atom end groups. Polymerization followed a radical mechanism. Kinetic nonideality as revealed by low (≪0.5) initiator exponent and a monomer exponent of greater than unity were explained in terms of primary radical termination effect. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 1681–1687, 1997     

Effect of pyridine on the kinetics of polymerization of methyl methacrylate initiated by benzoyl peroxide and azobisisobutyronitrile at 60°C

Solution polymerization of MMA, with pyridine as the solvent and BZ₂O₂ and AIBN as thermal initiators, was studied kinetically at 60°C. The monomer exponent varied from 0.45 to 0.91 as [BZ₂O₂] was increased from 1 × 10^?2 to 30 × 10^?2 mole/liter in a concentration range of 8.3-4.6 mole/liter for MMA. For AIBN-initiated polymerization the monomer exponent remained constant at 0.69 as [AIBN] varied from 0.4 × 10^?2 to 1.0 × 10^?2 mole/liter in the same concentration range for MMA. The k²_p/k_t Value increased in both cases with an increase in pyridine concentration in the system. This was explained in terms of an increase in the k_p value, which was due presumably to the increased reactivity of the chain radicals by donor-acceptor interaction between the molecules of solvent pyridine and propagating PMMA radicals and in terms of lowering the k_t value for the diffusion-controlled termination reaction due to an increase in the medium viscosity and pyridine content.     

Studies on polymerization of vinyl acetate using ylide as an initiator and degradative transfer agent

Polymerization of vinyl acetate initiated by β-picolinium p-chlorophenacylide was carried out at 30, 35, and 40°C, using conventional dilatometric technique. The initiator and the monomer exponent values were 0.80 ± 0.15 and unity, respectively. The polymerization was inhibited in the presence of hydroquinone, but was favored by nonpolar solvent and polymerization temperature. The energy of activation was 90.3 KJ mol^?1. An average value of k/k_t for the present system was found to be 0.37 × 10^?2. The results are explained in terms of a radical mode of polymerization with degradative initiator transfer; the principal mode of termination, however, was bimolecular.     

Studies on vinyl photopolymerization using a macromolecular C.T. Complex between poly(N-vinyl carbazole) and bromine as the photoinitiator

Photopolymerization of methyl methacrylate (MMA) was studied at 40°C using a macromolecular C.T. Complex between poly(N-vinyl carbazole) and bromine, expressed in brief as (PNVC–Br₂) complex, as the photoinitiator. Initiator exponent was 0.40 for [PNVC–Br₂] ≤ 2.5 × 10^?3 mol L^?1 and practically zero for [PNVC–Br₂] > 2.5 × 10^?3 mol L^?1. Monomer exponent in different diluent systems such as benzene, carbon tetrachloride, and acetone was close to 1.0. Low initiator exponent (<0.5) is explained on the basis of an initiator-dependent termination mechanism, in addition to the usual bimolecular termination. Analysis of kinetic data indicates that the initiator-dependent termination is primarily due to degradative initiator transfer and that due to primary radicals is considered inconsequential in view of monomer exponent being close to unity. The non-ideal termination process assumes over-whelming prominence at high [PNVC–Br₂].     

Studies on polymerization of vinyl acetate using ylide as an initiator and degradative transfer agent

The polymerization of vinyl acetate initiated by β-picolinium-p-chlorophenacylide was carried out at 30, 35, and 40°C, using the conventional dilatometric technique. The initiator and the monomer exponent values were 0.80 ± 0.15 and unity, respectively. The polymerization was inhibited in the presence of hydroquinone, but was favored by nonpolar solvent and polymerization temperature. The energy of activation was 90.3 kJ mol^?1. An average value of k/k_t for the present system was found to be 0.37 × 10^?2 L mol^?1 s^?1. The results are explained in terms of radical mode of polymerization with degradative initiator transfer; the principal mode of termination, however, was biomolecular.     

Photopolymerization of methyl methacrylate using hydrogen peroxide as the photoinitiator

Photopolymerization of MMA with the use of H₂O₂ as the photoinitiator under visible light at 30°C was studied. Kinetic features in bulk monomer and in the presence of different diluents differ significantly. Usual free radical kinetics with square-root dependence of rate on initiator, indicating bimolecular termination of chain radicals, were observed for bulk polymerization. On dilution with various solvents polymerization was found to be retarded to different (usual and more than usual) extents, the observed monomer exponent value being much higher than unity in many cases. This deviation from normal kinetics has been interpreted in terms of the predominance of degradative initiator transfer in the diluted systems.     

Homogeneous free‐radical polymerization of styrene in supercritical CO2

The free‐radical polymerization of styrene has been studied in the homogeneous phase of supercritical (sc) CO₂ at 80°C and pressures between 200 and 1 500 bar. 2,2'‐Azobisisobutyronitrile is used as initiator and CBr₄ as chain‐transfer agent. The polymerization is monitored by means of online FT‐IR/NIR spectroscopy. In the presence of CO₂ a solution polymerization may be carried out up to a considerable degree of monomer conversion. At 500 bar, for example, maximum styrene conversions of 34.4 and 11.9% may be reached in homogeneous phase at CO₂ contents of 16.8 and 44.5 wt.‐%, respectively. Analysis of the measured conversion‐time profiles yields termination rate coefficients, k_t, which are by one order of magnitude larger than k_t for styrene bulk polymerizations at identical temperature and pressure. The enhanced termination rate in fluid CO₂ is assigned to the poor solvent quality of scCO₂ for polystyrene.     

Photopolymerization of methyl methacrylate and some other vinyl monomers with the use of a pyridine–bromine charge-transfer complex as photoinitiator

Polymerization of MMA was carried out under visible light (440 nm) with the use of pyridine–bromine (Py–Br₂) charge-transfer (CT) complex as the photoinitiator. Initiator exponent and intensity exponent were 0.5 and 0.43, respectively, and the monomer exponent was found to be dependent on the nature of the solvent or diluent used. The Polymerization was inhibited in the presence of hydroquinone, but oxygen had very little inhibitory effect. An average value of k_p²/k_t for this polymerization system was 1.19 × 10^?2, and the activation energy of photopolymerization was 4.95 kcal/mole. Kinetic data and other evidence indicate that the overall polymerization takes place by a radical mechanism. With Py–Br₂ complex as the photoinitiator, the order of polymerizability at 40°C was found to be MMA, EMA ? Sty, MA.