Monomer Exponent Research Articles

Aqueous polymerization of methyl methacrylate using quinoline‐sulfur dioxide complex and tetrahydrofuran‐sulfur dioxide complex as initiators

AbstractAqueous polymerization of MMA was kinetically studied using separately two complexes of sulfur dioxide as initiators, namely, quinoline‐sulfur dioxide (Q‐SO2) complex and tetrahydrofuran‐sulfur dioxide (THF‐SO2) complex. In each case the initiator exponent was 0,5 and the monomer exponent was 1,5. Kinetic data, inhibitory effect of hydroquinone, and incorporation of sulfoxy end groups in the polymers indicate a radical mechanism of polymerization with first order dependence on monomer for the rate of initiation while termination appears to take place bimolecularly.

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

AbstractSolution 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 k2p/kt Value increased in both cases with an increase in pyridine concentration in the system. This was explained in terms of an increase in the kp 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 kt value for the diffusion‐controlled termination reaction due to an increase in the medium viscosity and pyridine content.

Photopolymerization of methyl methacrylate using tetrahydrofuran sulphur dioxide complex as photoinitiator

Photopolymerization of MMA in visible light was studied at 40 using THF-SO 2 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 hydrogen peroxide as the photoinitiator

AbstractPhotopolymerization 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.

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

AbstractKinetics of solution polymerization of styrene was studied using pyridine as solvent and BZ2O2 and azobisisobutyronitrile (AIBN) as initiators at 60°C. Normal kinetic features (Rp ∝ [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/kt 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 methylmethacrylate using triethylamine-benzoylperoxide redox initiator system

Photopolymerization of MMA was studied kinetically at 35° using TEA-BZ 2O 2 redox system as initiator. The initiator exponent is 0.34 but the monomer exponent depends on the solvent. Solvents (acetonitrile, pyridine and bromobenzene) giving negative or fractional monomer exponent show a rate enhancing effect through actively influencing the initiation step; benzene and chloroform give first order dependence of rate on [monomer] and behave as normal (inert) diluents. Initiation of polymerization takes place through radicals generated by photodecomposition of TEA-BZ 2O 2 complex formed in situ, the radical generation step being solvent or monomer dependent. Kinetic non-idealities are interpreted in terms of significant initiator dependent termination via degradative chain transfer.

Studies on the kinetics of polymerization of vinyl acetate by benzoyl peroxide at 60° using pyridine as solvent

Kinetics of Bz 2O 2-initiated polymerization of VAC in pyridine at 60° were investigated. The polymerization was significantly retarded by pyridine. The monomer exponent decreased from 2.5 at a relatively low [Bz 2O 2] (1.0 × 10 −2 M) to 2.0 at [Bz 2O 2] ⩾ 4.0 × 10 −2 M. The observed kinetic features were explained on the basis of degradative chain transfer and copolymerization with pyridine.

Photopolymerization of methyl methacrylate with the use of iodine monobromide as photoinitiator

AbstractIodine monobromide easily induces photopolymerization of methyl methacrylate (MMA) at 40°C under visible light. Initiator exponent and monomer exponent values were found to be 0.5 and 2, respectively, at low initiator concentrations, while the corresponding values at high initiator concentration conditions were zero and 3. The chain transfer constant of IBr at 40°C was found to be 13.0. Kinetic and other data indicate a radical polymerization mechanism involving complexation of monomer molecules with iodine monobromide prior to radical generation, and termination is believed to take place biomolecularly at low IBr concentrations and unimolecularly, involving reaction with the initiator, at high IBr concentrations (initiator termination).

Metal chelates in vinyl polymerization. I. Ferric dipivaloylmethide as an initiator

AbstractThe behavior of the chelate, ferric dipivaloylmethide, Fe(DPM)3, in vinyl polymerization systems was investigated. The polymerization was found to be of free‐radical nature. The rate of polymerization was proportional to the square root of the concentration of the chelate. The monomer exponent was close to 1.5 for the Fe(DPM)3‐initiated polymerization of styrene and methyl methacrylate. The kinetic and transfer constants and activation energies for these systems have been evaluated. Spectral studies revealed the possibility of a complex formation between the chelate and the monomer. A kinetic scheme for the Fe(DPM)3‐initiated polymerization is derived based on this initial complex formation.

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

AbstractPhotopolymerization 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.

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

AbstractThe 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., kp2/kt 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 and other vinyl monomers with the use of N‐bromosuccinimide as photoinitiator

AbstractPolymerization of MMA was done in the presence of visible light (440 nm) with the use of N‐bromosuccinimide (NBS) as the photoinitiator. The initiator exponent and intensity exponent were 0.5, and the monomer exponent was found to be unity. The polymerization was inhibited in the presence of hydroquinone. The average kp2/kt for this photopolymerization system was found to be 0.296 × 10−2 and the activation energy of photopolymerization was 4.67 kcal/mole. Kinetic and other evidence indicate that the overall polymerization takes place by a radical mechanism. With NBS as the photoinitiator, the order of polymerizability at 40°C was MMA, EMA ≫ MA ≃ VA, and styrene could not be polymerized under similar conditions.

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

AbstractPolymerization 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 kp2/kt 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.

Nonideal Polymerization Kinetics of Styrene in Acetone

Abstract Deviations from the “ideal” behavior have been observed in the polymerization of styrene in acetone. Both monomer and initiator exponents differ from the expected values. The poor thermodynamic properties of acetone as a solvent for the polystyrene chain seem responsible for the decrease of the initiation rate exponent, owing to the presence of a noticeable primary termination reaction. The strong effect of the reaction medium on monomer exponent can be related to the electron-donating tendency of acetone. The sharp decrease of the fractional rate of polymerization as a function of dilution has been interpreted in terms of lowering of the propagation rate constant, presumably due to solvent complexation of the growing chains.

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

AbstractPolymerization 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 k2p/kt 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 with the use of iodine as the photoinitiator

AbstractKinetics of photopolymerization of MMA at 40°C with the use of iodine as the photoinitiator was studied. At low range of iodine concentration (< 0.0004M), the rate of polymerization was proportional to square root of iodine concentration and the monomer exponent was 2.5, while at a higher range of iodine concentration, (0.0005–0.002M) the initiator exponent and monomer exponent were zero and 3.6–3.8 (i.e., close to 4), respectively. The chain‐transfer constant of iodine at 40°C was found to be 6.0. Polymerization was found to be largely inhibited in the presence of relatively high concentrations of iodine (> 0.005M) and also in presence of hydroquinone. Kinetic and other data indicate a radical mechanism of polymerization involving complexation of monomer molecules with iodine prior to radical generation, and termination is believed to take place bimolecularly at low iodine concentrations and unimolecularly, involving reaction with iodine, at high iodine concentrations (initiator termination).

Kinetics of the benzoyl peroxide and azobis-isobutyronitrile initiated thermal polymerizations of N-vinylcarbazole in solution

Whereas the azobis-isobutyronitrile thermally initiated polymerization of N-vinylcarbazole in solution obeys the usual rate law for a free-radical polymerization, the rate law for the benzoyl peroxide initiated polymerization is found to have a monomer exponent of two and an initiator exponent of one; a partial charge-transfer mechanism of the polymerization is proposed.

Studies on the polymerization of methyl methacrylate activated by azobisisobutyramidine

AbstractKinetic 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 = (2kt)1/2/kp 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 Rp 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.

Ferrous-bromate redox as initiator of aqueous vinyl polymerization

Ferrous-bromate redox is a very efficient initiator for the aqueous polymerization of a number of vinyl monomers. With methylmethacrylate, polymerization takes place in dark and at temperatures starting from 0 °C onwards. Bromate, ferrous and monomer exponents are respectively 0.51, 0.43 and 1.32 and the overall activation energy is 7.47 Kcal/mole. Neutral salts depress the polymerization rate, while an emulsifier increases it. pH of the medium has not much influence on the polymerization rate upto the value of 2.32. However, at pH 1.39, rate is somewhat depressed. Endgroups incorporated are hydroxyl and bromine totalling to an average of one per chain. Based upon these findings suitable mechanisms of initiation and termination have been proposed.

Permanganate–oxalic acid as a redox initiator of acrylonitrile polymerization in aqueous media. Part III. Kinetics and DP

AbstractThe kinetics of the aqueous polymerization of acrylonitrile initiated by the permanganate–oxalic acid redox pair have been studied gravimetrically at 32 ± 0.2°C. The rate of polymerization is independent of oxalic acid concentration over a small range. The catalyst exponent varies continuously with the catalyst concentration, being 0.9 at low catalyst concentration and 0.27 at high catalyst concentration at a monomer concentration of 0.30M. The monomer exponent is nearly unity in the concentration range 0.30M and above. The molecular weight of the polymer is independent of oxalic acid concentration in the range where the rate of polymerization is independent of the oxalic acid concentration but decreases at higher concentration of oxalic acid with increasing concentration of catalyst and temperature. The overall activation energy was found to be 8.6 kcal./mole. Addition of salts such as Na2SO4 depresses the rate of polymerization, but the addition of MnSO4 at low concentrations increases the rate, whereas at higher concentration the initial rate falls. It has been suggested that hydrated Mn3+ ions cause oxidative chain termination of polyacrylonitrile radicals. Complexing agents, such as fluoride ions, ethylene‐diaminetetraacetic acid, etc., decrease the rate of polymerization, whereas addition of detergents enhances it.