Photopolymerization initiated by charge-transfer complex. VI. Photopolymerization of methyl methacrylate with the use of isoquinoline–chlorine charge-transfer complex

Polymerization of methyl methacrylate in visible light was studied at 30°C using the isoquino-line–chlorine charge-transfer complex as the photoinitiator. Analyses of kinetic and other data indicate that the polymerization proceeds via a radical mechanism and the termination is initiator dependent. Chain termination via degradative chain (initiator) transfer appears to be significant.     

Photopolymerization of methyl methacrylate initiated by sulphur dioxide

In catalytic concentrations (10^?5?10^?4 mol l^?1) sulphur dioxide induces polymerization of MMA, particularly on photoactivation. The effective initiating species appears to be the monomer-SO₂ complex rather than free SO₂. A mechanism involving biradical initiation by decomposition of the initiating species, linear propagation in two directions, and significant termination of growing chains by chain transfer with initiating species has been suggested. The initiator transfer constant is 1.6 at 40°.     

Photopolymerization initiated by charge transfer complex. II. Photopolymerization of methyl methacrylate with the use of γ-picoline–bromine charge transfer complex as photoinitiator

Polymerization of MMA was carried out in the presence of visible light (440 nm) with the use of γ-picoline-bromine charge transfer complex as the initiator. The rate of polymerization R_p increases with increasing monomer concentration and the monomer exponent was computed to be unity. The rate of polymerization increases with increasing initiator concentration. The initiator exponent was computed to be 0.5. The reaction was carried out at three different temperatures and the overall activation energy was calculated to be 4.5 kcal/mol. The polymerization was inhibited in the presence of hydroquinone. 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.     

Photopolymerization of methyl methacrylate using a morpholine–sulfur dioxide charge-transfer complex as the photoinitiator

Photopolymerization of the vinyl monomer (M) of methyl methacrylate (MMA) was kinetically studied by using near-UV/visible light at 40°C and employing a morpholine (MOR)–sulfur dioxide (SO₂) charge-transfer (C-T) complex as the photoinitiator. The rate of polymerization (R_P) was found to be dependent on the morpholine: sulfur dioxide mole ratio; the 1 : 2 (MOR–SO₂) complex acted as the latent initiator complex C which underwent further complexation with the monomer molecules to give the actual initiating complex I. Using the 1 : 2 (MOR–SO₂) C-T complex as the latent initiator, the observed kinetics may be expressed as R_P [MOR–SO₂]^0.27[M]^1.10. Benzoquinone behaved as a strong inhibitor. Polymers obtained tested positive for the incorporation of a sulphonate-type end group. Polymerization followed a radical mechanism. Kinetic nonideality as revealed by a low initiator exponent and monomer exponent of greater than unity was explained on the basis of a prominent primary radical termination effect. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1973–1979, 1998     

Photopolymerization of methyl methacrylate with the use of tetrahydrofuran–bromine charge-transfer complex as the photoinitiator

The polymerization of MMA was kinetically studied in the presence of visible light (using a 125-W high-pressure mercury vapor lamp with fluorescent coating, without a filter), a THF—bromine charge-transfer complex being used as the photoinitiator. The initiator exponent was 0.5 in bulk polymerization. The monomer exponent varied from about 1.2 to about 2.5, depending on the nature of the solvent used; the initiator exponent also varied in diluted systems, depending on the nature and proportion of the solvent, the variation being from a value of 0.5 in bulk system to zero or almost zero at about 25% (v/v) solvent concentration. Other kinetic parameters, viz., k_p²/k_t and the activation energy for polymerization, were determined and are reported. Kinetic and other evidence indicates that the photopolymerization takes place by a radical mechanism and termination is bimolecular in nature in bulk systems; in dilute systems, termination by initiator complex assumes predominance, particularly at high solvent concentrations (≥25% v/v).     

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     

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 in solution initiated with benzophenone derivatives

Theoretical and Experimental Chemistry -     

Photopolymerization initiated by charge-transfer complex. I. Photopolymerization of methylmethacrylate with the use of quinaldine-bromine and lutidine–bromine charge-transfer complexes as photoinitiator

Photopolymerization of MMA was carried out with quinaldine–bromine (QN–Br₂) and lutidine–bromine (LU–Br₂) charge-transfer complexes as initiators. The rate of polymerization R_p increased with rising monomer concentration and the monomer exponent was computed as unity. At first the rate of polymerization accelerated and then reduced as the initiator concentration was increased. The initiator exponent was 0.5. The reaction was carried out at three different temperatures and overall activation energy was calculated at 4.0 kcal/mol. The kinetic data and other evidence indicate that the overall polymerization takes place in a radical mechanism. A suitable mechanism is suggested.     

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.     

Polymerization initiated by an electron donor–acceptor complex. VI. Polymerization of methyl methacrylate initiated by a liquid SO2–nicotine complex and carbon tetrachloride

A kinetic study has been made of polymerization of methyl methacrylate initiated by an electron donor–acceptor complex of liquid SO₂ (electron acceptor) and nicotine (donor) in the presence of carbon tetrachloride. It is concluded that the polymerization proceeds through free-radical intermediates similar to the cases of liquid SO₂–pyridine and liquid SO₂–poly(2-vinylpyridine) complexes. The overall rate of polymerization is proportional to the square root of both liquid SO₂ and nicotine concentrations, and the values of k_p/k_t^½ under various polymerization conditions are in satisfactory agreement with the literature values. For the activation energy of initiation, 13.6 kcal/mole is estimated from the k_p/k_t^½ values obtained at temperatures ranging from 0 to 80°C.     

Polymerization initiated by an electron donor–acceptor complex. Part IV. Kinetic study of polymerization of methyl methacrylate initiated by the charge-transfer complex consisting of poly-2-vinylpyridine and liquid sulfur dioxide

A kinetic study has been made of the polymerization of methyl methacrylate (MMA) initiated by a charge-transfer complex of poly-2-vinylpyridine (electron donor) and liquid sulfur dioxide (acceptor) in the presence of carbon tetrachloride. It is concluded that the polymerization proceeds through free-radical intermediates, as with the pyridine-liquid sulfur dioxide complex system. The association constants K of acceptor and polymer electron donors which range widely in their molecular weight were determined spectrophotometrically, and it has been found that both K and overall rate of polymerization R_p of MMA decrease with increasing molecular weight of polymer donor; contrary to this, molecular weight of PMMA formed increases with increasing molecular weight of the polymer donor. Other kinetic behaviors was essentially the same as in the pyridine–liquid sulfur dioxide system, i.e., R_p is proportional to the square root of the concentration of the complex and to the 3/2-order of the monomer concentration; R_p is clearly sensitive to the carbon tetrachloride concentration at low concentration of carbon tetrachloride, but for a higher concentration it is practically independent of the carbon tetrachloride concentration. It has been deduced from a kinetic mechanism for the initiation that a primary radical may be produced from the reduction of carbon tetrachloride by an associated complex consisting of liquid sulfur dioxide–polymer donor and the monomer.     

Polymerization initiated by an electron donor–acceptor complex. Part I. Polymerization of methyl methacrylate initiated by liquid sulfur dioxide–pyridine complex in the presence of carbon tetrachloride

The polymerization of methyl methacrylate can be initiated by a charge-transfer complex of liquid sulfur dioxide and pyridine in the presence of carbon tetrachloride. The molar ratio of sulfur dioxide and pyridine which participated in the complex was found from a spectrophotometric study to be 2:1. The polymerization proceeds through free-radical intermediates. The overall rate of polymerization is proportional to the square root of the concentration of the complex, and the values of k_p/k_t^1/2 under the various polymerization conditions were satisfactorily consistent with the literature value. For the activation energy of the overall reaction, 8.2 kcal./mole was obtained, and for initiation, 9.7 kcal./mole was evaluated from the values of k_p/k_t^1/2. It was deduced from a kinetic mechanism for the initiation that a primary radical may be produced from the reduction of carbon tetrachloride by an associated complex consisting of liquid sulfur dioxide–pyridine complex and the monomer.     

Photopolymerization of methyl methacrylate with the use of bromine as photoinitiator

Low concentrations of bromine (0.008–0.06M) were used to initiate photopolymerization of MMA in bulk and in diluted (near bulk) systems, the diluents or solvents used being benzene, toluene, dioxane, tetrahydrofuran, carbon tetrachloride, chloroform, methylene chloride, and methanol. Polymerization in bulk follows usual free-radical kinetics. Inert solvents (benzene, toluene) as well as the other solvents used enhance the rate of polymerization MMA even when used in the range of catalytic concentrations (0.04–0.4M). An initiation mechanism involving solvent molecules appears to be predominant in diluted systems.     

Polymerization of methyl methacrylate initiated by tri-n-butylborane–organic halide systems

The polymerization of methyl methacrylate (MMA) initiated by tri-n-butylborane (TBB) was studied in the presence of various organic halides (R′X). It was found that R′X accelerated the polymerization of MMA. Aliphatic halides were more effective than aromatic halides. Cocatalytic effects of butyl halides decreased in the order: n -BuI > n -BuBr > n -BuCl; n -BuBr ? sec-BuBr > i-BuBr > tert-BuBr. In the polymerization of MMA by TBB- n -BuI, the initial rate of polymerization was found to be proportional to the concentration of MMA and to the square root of the concentration of TBB-n-BuI. The apparent activation energy was 5.3 kcal/mole. From this and other results, it was assumed that the polymerization of MMA by this initiator system proceeds by a radical mechanism via a weak complex between TBB and R′X; alkyl radicals are formed by the interaction of R′X with TBB. The TBB–R′X system can initiate the polymerization of MMA and AN, but is ineffective in the polymerization of styrene.