Thermal bulk polymerization of cholesteryl acrylate

The thermal bulk polymerization of cholesteryl acrylate was carried out in the solid phase, the mesomorphic phase, and the liquid phase to study the effect of monomer ordering on polymerization rate and polymer properties. The rate increased with decreasing ordering (or enhanced mobility) of the monomer. Formation of inhibitive by-products during the polymerization limited conversions to 35%. The sedimentation constant S₀ = 6.2 S was the same for the polymers obtained in the three phases. The weight-average molecular weight (M?_w) was 480,000 as determined by ultracentrifugation. Poly-(cholesteryl acrylate) formed in bulk is randomly coiled when dissolved in tetrahydrofuran. The thermal properties of the monomer are given.     

Calorimetric study of the kinetics of the bulk polymerization of ethyl acrylate

The bulk polymerization of ethyl acrylate using 1-1′-azobisisobutyronitrile as initiator at several temperatures has been studied by DTA. The order with respect to the monomer and the apparent activation energy of the polymerization process have been determined.     

Studies on bulk polymerization of methyl methacrylate. I. Thermal polymerization

The thermal bulk polymerization of methyl methacrylate (MMA) in a wide range of temperatures has been studied using a dilatometric reactor. It is shown that, irrespective of the care taken to purify the MMA, the evolution of the time-conversion curve can be explained only if we account for the presence of an impurity associated with the monomer acting as a free radical initiator. The activation energy for the decomposition of this impurity has been estimated as 98 kJ/mol. Having accounted for this impurity, the activation energy for the real thermal polymerization of the MMA has been estimated to be 75 kJ/mol. © 1993 John Wiley & Sons, Inc.     

Benzophenone/triethylamine-photoinitiated polymerization of methyl acrylate

Benzophenone-sensitized photopolymerization of methyl acrylate was shown to be remarkably enhanced by the addition of small amounts of triethylamine. This was attributed to the efficient formation of an electron-transfer complex between photoactivated benzophenone and ground-state amine. Ketyl and amine free radicals derived from this complex were postulated to be the chain-initiating species. Quantum yield experiments indicated that methyl acrylate itself was also a quencher of the benzophenone triplet state.     

Pulsed laser terpolymerization of styrene,methyl methacrylate and methyl acrylate

The propagation rate coefficient of the terpolymerization of styrene, methyl methacrylate and methyl acrylate in bulk was successfully determined at three different monomer compositions. The temperature was varied between 18 and 80°C. The resulting data at 50°C were not in agreement with predictions according to the terminal model with binary reactivity ratios that have been determined by fitting copolymer composition data with the terminal model. This indicates that here also the penultimate unit affects the kinetics.     

Atmospheric ozonolysis study of methyl acrylate and methyl 3-methyl acrylate

Detailed reaction mechanisms of methyl acrylate (MA) and methyl 3-methyl acrylate (M3MA) with ozone have been investigated using quantum chemistry calculations based on the CCSD(T)/6-31G(d)+CF//B3LYP/6-31+G(d,p) level of theory. Possible reaction channels and products have been presented and discussed. The temperature-dependent and pressure-independent overall and site-specific rate constants are calculated by employing multichannel RRKM theory. The obtained overall rate constants (in cm³ molecule^?1 s^?1) based on the CCSD(T)+CF energies can be described as: $ k_{{({\text{MA}} + {\text{O}}_{ 3} )}} = 3. 7 4 \times 10^{ - 1 3} { \exp }\,( - 3 7 4 6. 1 2/T) $ and $ k_{{({\text{M3MA}} + {\text{O}}_{ 3} )}} = 5. 1 2 \times 10^{ - 1 3} { \exp }( - 3 3 5 4. 8 7/T) $ at 200–400 K and 760 Torr. Under atmospheric conditions, the dominant products of ozonolysis of MA and M3MA are methyl glyoxylate and formaldehyde, methyl glyoxylate and acetaldehyde, respectively. The results of theoretical study are in good agreement with the available experimental measurements. Researches on branching ratios and atmospheric lifetimes also have been obtained as complement to the experimental results.     

Photoinitiated polymerization of methyl methacrylate and methyl acrylate with 14C-labeled benzoin methyl ethers

Three ¹⁴C-labeled benzoin methyl ether (α-methoxy-α-phenylacetophenone) derivatives were utilized as photoinitiators in the polymerization of methyl methacrylate (MMA) and methyl acrylate (MA). The results of polymer end-group analysis are in accord with a mechanism of benzoin ether photocleavage into initiator radicals and dispute earlier labeling studies which were interpreted as evidence for copolymerization of excited-state benzoin ethers with reactive monomers. In MMA polymerization, the results indicate a preference for termination by disproportionation (～60%) and provide evidence for primary radical termination at 0.041M photoinitiator (optically dense solutions) in neat MMA. Evidence for chain branching by initiator radical hydrogen abstraction from poly(methyl acrylate) (PMA) is also presented. The benzoyl and α-methoxybenzyl radicals, produced on photolysis of benzoin methyl ether, appear to be equally effective in both initiation and hydrogen-abstraction processes. Quantum yields at 366 and 313 nm indicate the absence of a wavelength effect.     

Gamma radiation-induced bulk polymerization of some methyl aryloxymethacrylates

The kinetics of γ-radiation-induced bulk polymerization of methyl phenoxymethacrylate and methyl paracresoxymethacrylate was studied at dose rates of 0.3 and 0.075 Mrad/h and at temperatures of 0 and 30°C. The polymerization was first order with respect to the monomers and the rate of polymerization had a direct dependence on dose rate. The activation energy value for the polymerization of methyl phenoxymethacrylate was 1.2 and 0.7 kcal/mol for methyl paracresoxymethacrylate. The polymerization proceeded predominantly by an ionic mechanism.     

Microstructural study of poly(methyl methacrylate-co-n-propyl acrylate) by 13C NMR

Analysis of carbonyl and β-CH₂ signals in the 100?MHz ¹³C NMR spectra of poly(methyl methacrylate-co-n-propyl acrylate) (PMMA/nPrA), provided distribution of configurational-compositional sequences for a series of the copolymer samples of different composition at pentad level for carbonyl signal and hexad level for the backbone methylene carbons. Computer simulation of the spectra based on incremental calculation of the chemical shifts for individual sequences provided very good agreement with the experimental spectra.     

Kinetics of copolymerization—II. Kinetic investigation of the polymerization of methyl acrylate in solution

The kinetics of methyl acrylate polymerization initiated by azobisisobutyronitrile were investigated in dimethylformamide at 40–60. The polymerization was 1/2 order with respect to initiator; the rate of initiation was independent of the initial concentration of monomer. The rate and the overall rate constant of polymerization strongly depend on the medium: the overall rate constant decreases with increase of solvent concentration. The solvent dependence of overall rate constant can adequately be described by the hot radical theory.     

Anionic graft polymerization of methyl acrylate to protein functional groups

Graft polymerization of methyl acrylate to functional groups in proteins was studied with model compounds and with whole gluten proteins. Polymerization was carried out in the presence of sodium hydride or sodium in dimethyl sulfoxide. Initiation proceeds by an anionic mechanism, and the rate-determining step is the production of the initially formed carbanion. The rate of disappearance of methyl acrylate was followed via gas chromatography. Amino acid analyses indicated that the functional groups of the amino acids, as well as the peptide bonds, were acting as the initiation sites in proteins. Reaction rates of the functional groups were determined on model compounds in the presence of sodium and sodium hydride. With both the model compounds and the proteins, polymerization was initially rapid and then leveled off, although rates depended on the concentration of activator and acrylate. Methoxyl group analyses of modified model compounds and proteins indicated that from 5 to 10 methyl acrylate residues were introduced per reactive site.     

Kinetics of radical polymerization—XLIII. Investigation of the polymerization of methyl acrylate in solution by the rotating sector method

The solvent effect on the chain propagation (k?₂) and chain termination (k₄) rate constants was studied for the polymerization of MA in benzene at 50°. Absolute values of the rate constants were determined from the classical polymerizations published earlier and from rotating sector measurements. The value of k₄ was found constant within the limits of experimental error, while k?₂ greatly depends on the monomer concentration, its variation can be quantitatively described in terms of the hot radical theory.     

Triad distributions of 1,1-diphenylethylene–methyl acrylate copolymer determined from NMR study

The triad distributions of 1,1-diphenylethylene (D)–methyl acrylate (M) copolymers have been determined from NMR measurements and examined according to the terminal and penultimate models of copolymerization theory. As expected from the diamagnetic shielding by the phenyl rings of the nearest D units, the methoxy proton resonances were found to appear as three resolved peaks at 6.4–6.6 τ, 6.7–7.0 τ, and 7.2 τ, and have been assigned to the central M units of the triads MMM, MMD or DMM and DMD, respectively. The copolymer composition and the triad distributions observed are shown to agree better with the terminal model with the methyl acrylate reactivity ratio of 0.092 ± 0.010 than with the penultimate model.     

Electrochemical bulk polymerization of methyl methacrylate in the presence of nitric acid

The electroinitiated polymerization of methyl methacrylate in the presence of nitric acid has been investigated on platinum and graphite anodes. The dependence of yields and molecular weights on parameters such as current density, temperature, speed of stirring, and HNO₃ concentration was determined. Under continuous electrolysis conditions a stationary state takes place and the rate of polymerization exhibits zero order with respect to monomer and a 1.5 order with respect to current. On the other hand, under postpolymerization conditions a kinetic gel effect occurs, which limits the termination rate and leads to the typical acceleration in the conversion–time curves. The effect of postpolymerization is so marked, even after supplying small amounts of charge, that the formation of long-lived radical chains is believed to be possible. In this respect HNO₃ would play a fundamental role by stabilizing the growing radicals.     

Kinetics of radical polymerization—XXXIX Investigation of the polymerizations of butyl acrylate and methyl acrylate in solution

The kinetics of free radical polymerizations of methyl and butyl acrylate were studied in benzene at 50°. The initiation rate constant determined by the inhibition method was found to be constant over the whole monomer-solvent composition range in both systems. The polymerization rate was investigated as a function of initiator and monomer concentrations. In accordance with theory, an initiator order of 0.5 was obtained for both systems; monomer orders > 1 were found. This solvent effect could not be explained either in terms of the diffusion theory or by the theory of EDA complexes; complete agreement was found between experimental results and the theory of hot radicals.     

Pulsed NMR study of the structure of poly(vinyl alcohol)-poly(sodium acrylate) composite hydrogel

The heterogeneous structure of poly(vinyl alcohol)-poly(sodium acrylate) composite hydrogels (PVA-PAA gels), prepared by repeatedly freezing and thawing mixed aqueous solutions of PVA and PAA, has been studied using pulsed NMR. The free induction decay (FID) signals of the transverse magnetization for the PVA-PAA gels were measured by both Carr-Purcell-Meiboom-Gill and solid-echo pulse sequences. The FID signal was decomposed into two or three decaying signals with various spin-spin relaxation times, based upon differences in the molecular mobility that reflected structural heterogeneity. The structural heterogeneity of the PVA-PAA gel is quite different from that of PVA gel free of PAA. We have made observations on “crosslinked” domains in the PVA-PAA gels. They are formed by PVA solid chains, probably phase-separated in the freezing-thawing process. The formation of crosslinked domains is influenced by the number of freezing-thawing cycles. © 1994 John Wiley & Sons, Inc.     

Kinetics of radical polymerization-XXXVI: Investigation of molecule-inhibitors in the radical polymerization of methyl acrylate

A study was made on the effect of novel molecule-inhibitors (nitroso-benzene and N-substituted p-nitroso-aniline derivatives, as well as phenothiazine) on the radical polymerization of methyl acrylate initiated by AIBN at 50°. The investigated compounds are strong inhibitors, in contrast to the “traditional” molecule-inhibitors, which only retard the polymerization of MA. The relative reactivities of the inhibitors and the stoichiometric coefficients of the inhibition reactions were determined. Phenothiazine is even more reactive than the nitroso-compounds, but the inhibition is accompanied by some chain-regeneration.     

Vinyl polymerization by cobaltic ions in aqueous solution. Part II. Polymerization of acrylonitrile and methyl acrylate

Polymerization of methyl acrylate in HClO₄ and HNO₃ was studied in the temperature range 10–15°C. The kinetics of the polymerization were found to be very simple, involving initiation and termination by cobaltic ions. Kinetic studies on polymerization of acrylonitrile in HClO₄ and HNO₃ revealed that water oxidation, and monomer oxidation were side reactions as in the case of methyl methacrylate. Experimental evidence favored the simultaneous initiation by Co³⁺ and CoOH²⁺ species. In H₂SO₄, certain unusual features were encountered. At low [Co³⁺], linear termination as well as termination by mutual combination occurred. Another interesting aspect was that CoSO₄⁺ initiated at low [Co³⁺]. This was unlike the case of other monomers in H₂SO₄. The rates of polymerization and rates of cobaltic ion disappearance were measured with respect to changes in [M], [Co³⁺], [H⁺], temperature, etc. The various rate constants were evaluated.