Solid-state polymerization of long-chain vinyl compounds. VI. In-source polymerization of octadecyl acrylate by γ-ray irradiation

The in-source polymerization of octadecyl acrylate in the lamellar crystal (hexagonal packing) by γ-ray irradiation has been investigated, as compared with the two-step and one-step postpolymerizations. The viscosity-average molecular weight is very high even in the initial stage and is practically saturated after 3–5 hr, although the conversion increases successively with time. The molecular weight distribution of poly(octadecyl acrylate) obtained by in-source polymerization is very wide (M _w/M _n = 13.1, at 20°C). The results of in-source polymerization of the long-chain vinyl compounds can be interpreted using the cone model for polymerization probability, similar to those of one-step and two-step postpolymerizations.     

Studies on the polymerization of ethyl acrylate. I. Kinetic studies

Kinetic studies on the polymerization of ethyl acrylate have been carried out and the various rate constants and their corresponding activation energies determined.     

Photoinitiated polymerization of acrylate,methacrylate, and vinyl ether end‐functional polyisobutylene macromonomers

Polyisobutylene‐based UV cured networks potentially useful as sealants were synthesized by photopolymerization of well‐defined polyisobutylene methacrylate (PIB‐MA), acrylate (PIB‐A) and vinyl ether (PIB‐VE) di‐ and trifunctional macromonomers. The kinetics of photocrosslinking were measured using an optical pyrometer apparatus and optimized with respect to different experimental parameters. PIB‐MA/A macromonomers displayed enhanced reactivity in radical photopolymerization in the presence of a bis(acylphosphine) oxide photoinitator. PIB‐VE macromonomers exhibited a high rates of photopolymerization with (4‐n‐octyloxyphenyl)phenyliodonium hexafluroantimonate as the photoinitiator. The rates as well as the ultimate monomer conversions were increased by increasing the irradiation light intensity. The inherent induction period associated with oxygen inhibition in the photopolymerization of PIB‐MA was significantly reduced by optimizing the choice of photoinitiator. A detailed investigation of the concentration of MA/A/VE end groups revealed the presence of a prominent saturation effect in the photopolymerization of PIB‐A, which was absent with PIB‐MA and PIB‐VE. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

ESR studies on poly(vinyl chloride) irradiated at medium and high doses

Room temperature gamma irradiation at medium (1-100 kGy) or high (0.9-25 MGy) doses induces different radicals into pure or industrial poly(vinyl chloride) (PVC); the various ESR signals differ by their shapes and/or values of their g-factors and/or peak-to-peak widths but do not give precise information on the chemical structures of the different radicals as the spectra are only poorly resolved. However, looking at the ESR parameters of the different signals and their evolution during natural ageing of the samples, allows us to make correlations between the radio-induced lines in industrial PVC and the ones induced in pure PVC or in PVC additives.     

Studies on the polymerization of ethyl acrylate. II. Chain transfer studies

Transfer constants for different solvents representing hydrocarbons, halogenated compounds, alcohols, ketones, acids, and esters were determined in the thermal polymerization of ethyl acrylate at 80°C and they are compared with the available data on methyl acrylate and ethyl methacrylate. It was observed from the values of transfer constants that ethyl acrylate radicals are a little more effective than methyl acrylate or ethyl methacrylate in abstracting hydrogen atom from hydrocarbons and alcohols. In acetic and n-butyric acid media, it has been found, by the aid of endgroup analysis, that the derived solvent radicals from transfer reactions are not too efficient to start a new chain.     

NMR and ESR studies of the solid-state polymerization of vinyl monomers. I. Acrylamide

The kinetics of the solid-state polymerization of acrylamide, γ-irradiated at 77°K, has been studied by wide line NMR and by ESR at temperatures above 300°K. This reaction may be followed by the growth of a narrow line superimposed on the NMR spectrum of the monomer. The amplitude of this narrow line has been found to be proportional to the polymer yield. By long continued annealing, the conversion yield approaches a limiting value, generally lower than 50% under most of our experimental conditions. The activation energy of post-polymerization is 19 ± 1 kcal/mole. The radiochemical yield of radicals, determined by ESR, is 0.27 ± 0.03 at 77°K before warming. In the course of annealing above 300°K, the overall concentration of radicals is reduced to about one tenth of its initial value at 77°K. However, the local concentration of the remaining radicals is constant and equal to 1.2 × 10¹⁹ spins/g, i.e., more than 100 times their overall concentration. The recombination of radicals does not seem to intervene in the kinetics of post-polymerization, so that it may be assumed that only the radicals remaining after annealing, have actually contributed to the reaction.     

ESR study of NiIII complexes with nitrosonaphthols and dithio acids

Mixed-ligand Ni^III complexes with -nitroso--naphthol, -nitroso--naphthol,o-ethylxanthate, andN,N-diethyldithiocarbamate as ligands have been studied by ESR in liquid and frozen solutions. The degrees of symmetry distortion for the first coordination sphere of these complexes have been determined. It is shown that the transition from planar square Ni^IIL₂ complexes to more stable octahedral Ni^IIIL₂L and Ni^IIILL₂ complexes occursvia the radical addition mechanism. A method for trapping short-lived radicals is suggested on the basis of the complex formation scheme.Translted fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1513–1515, August, 1995.The work was financially supported by the Russian Foundation for Basic Research (Project No. 93-03-5050)     

Effects of 2‐hydroxyalkyl methacrylates on the styrene miniemulsion polymerizations stabilized by SDS and alkyl methacrylates

The effects of 2‐hydroxyalkyl methacrylates (HEMA and HPMA) on the styrene miniemulsion polymerizations stabilized by SDS/lauryl methacrylate (LMA) or SDS/stearyl methacrylate (SMA) were investigated. A mixed mode of particle nucleation (monomer droplet nucleation and homogeneous nucleation) is operative during polymerization. Homogeneous nucleation plays a crucial role in the polymerizations stabilized by SDS/LMA, whereas monomer droplet nucleation becomes more important in the polymerizations stabilized by SDS/SMA. The polymerization kinetics is insensitive to the type of 2‐hydroxyalkyl methacrylates, but the difference in the relative importance of monomer droplet nucleation and homogeneous nucleation is detected. Incorporation of 1‐pentanol (C₅OH) into the reaction mixture also shows a significant influence on the polymerizations stabilized by SDS/LMA or SDS/SMA. This is attributed to the formation of a close‐packed structure of SDS and C₅OH on the droplet surface, which acts as a barrier to the incoming oligomeric radicals. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 3188–3199, 2000     

NMR and ESR studies of the solid-state polymerization of vinyl monomers. III. Methacrylic acid

The kinetics of postpolymerization of γ-irradiated methacrylic acid at 77°K has been investigated by wide-line NMR and by ESR spectroscopy. The conversion yield was continuously measured in the temperature range of 260–280°K, from the narrowing of the NMR spectrum due to the progressive “amorphization” of the matrix, releasing the motion of monomer molecules. The rate of postpolymerization decays exponentially with time, independently of the recombination of free radicals. The local concentration of radicals remaining after prolonged annealing is actually the same as initially, showing that no recombination occurs in the microdomains of polymerization. The ¹³C NMR study of the poly(methacrylic acid) formed by solid-state polymerization shows a predominent syndiotactic character, with an increasing contribution of isotactic sequences as the postpolymerization temperature is lowered.     

NMR and ESR studies of the solid-state polymerization of vinyl monomers. II. Acrylic acid

The post-polymerization of acrylic acid, γ-irradiated at 77°K, has been studied by broad-line NMR and ESR between 240°K and 286°K (mp). The changes in the structure of NMR spectra during the polymerization has been related to the conversion yield checked by gravimetry of the polymer formed. The very fast reaction occurring above ?270°K has been followed simultaneously by NMR and thermal analysis. This last method indicates an activation energy of chain propagation of 18.6 ± 2 kcal/mole in satisfactory agreement with the value given by the initial slope of the conversion—time curves. ESR experiments show that, while the average radical concentration decays by a factor of about ten between 77°K and 240°K, the local concentration of radicals persisting after prolonged annealing at T > 240°K, remains the same as at 77°K, i.e., 1.4 × 10¹⁹ spins/g. A kinetic scheme, assuming an exponential decay of propagation and termination rate constants with chain length, has been proposed to explain the shape of conversion—time curves as well as the almost constancy of the local concentration of growing polymer chains.     

Ylide mediated polymerization of methacrylates and acrylates in the presence of tetraphenylphosphonium cation 3

Triphenylmethide tetraphenylphosphonium (TPM, TPP) or methylisobutyrate tetraphenylphosphonium (MIB, TPP) formed by ion exchange reactions of TPP chloride(TPPCl) with the TPM or MB potassium salts in THF, initiate the living polymerization of MMA producing PMMA's with narrow MW distributions (below 1.3) at ambient temperatures.     

Kinetic and ESR studies on radical polymerization of methyl methacrylate in the presence of fullerene

The effect of fullerene (C₆₀) on the radical polymerization of methyl methacrylate (MMA) in benzene was studied kinetically and by means of ESR, where dimethyl 2,2′-azobis(isobutyrate) (MAIB) was used as initiator. The polymerization rate (R_p) and the molecular weight of resulting poly(MMA) decreased with increasing C₆₀ concentration ((0–2.11) × 10⁻⁴ mol/L). The molecular weight of polymer tended to increase with time at higher C₆₀ concentrations. R_p at 50°C in the presence of C₆₀ (7.0 × 10⁻⁵ mol/L) was expressed by R_p = k[MAIB]^0.5[MMA]^1.25. The overall activation energy of polymerization at 7.0 × 10⁻⁵ mol/L of C₆₀ concentration was calculated to be 23.2 kcal/mol. Persistent fullerene radicals were observed by ESR in the polymerization system. The concentration of fullerene radicals was found to increase linearly with time and then be saturated. The rate of fullerene radical formation increased with MAIB concentration. Thermal polymerization of styrene (St) in the presence of resulting poly(MMA) seemed to yield a starlike copolymer carrying poly(MMA) and poly(St) arms. The results (r₁ = 0.53, r₂ = 0.56) of copolymerization of MMA and St with MAIB at 60°C in the presence of C₆₀ (7.15 × 10⁻⁵ mol/L) were similar to those (r₁ = 0.46, r₂ = 0.52) in the absence of C₆₀. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 2905–2912, 1998     

Solid-state polymerization of long-chain vinyl compounds. IV. Effects of chain length on the polymorphic behavior and postpolymerization of n-alkyl methacrylates

Polymorphic behavior and γ-ray-initiated postpolymerization of the even-numbered long-chain Methacrylates (C₁₈-C₁₂) have been investigated. Phase transition behaviors of octadecyl, hexadecyl, tetradecyl, and dodecyl methacrylates are respectively, which become simpler with shortening of the chain length. The methacrylate monomers with sufficiently long hydrocarbon chains, such as octadecyl and hexadecyl, can be polymerized rapidly in the α-form crystal (hexagonal packing) by a fully two-dimensional mechanism, whereas in the β-form crystal (triclinic packing), polymerization can hardly occur. In the case of dodecyl methacrylate, however, an accelerated polymerization in the β form occurs after an induction period of several hours and the resultant polymer is gel-like. This can be interpreted by the propagation reaction across the polymer chain already formed. It has been found that the solid-state post-polymerization of n-alkyl methacrylates is affected by the chain length through the packing mode of the monomer molecules and also by the aggregation state of side chains in the resultant comblike polymer.     

Solid-state polymerization of long-chain vinyl compounds. II. Effect of molecular arrangement on polymerizability of octadecyl acrylate

To clarify the effect of a molecular arrangement of long-chain monomers on polymerizability, γ-ray-initiated postpolymerization of polymorphic crystals of octadecyl acrylate and the melt has been investigated. According to thermal, x-ray, and infrared (IR) analyses octadecyl acrylate exhibit three crystalline modifications similar to, but different in transition behavior from, those of octadecyl methacrylate. The α-form is stable in the range of 19–32°C (mp) and at lower temperatures the β-form is stable, whereas the sub-α-form appears transiently in α → β transition. The monomer molecules in triclinic packing (α-form) show little tendency to polymerize, whereas those in hexagonal packing (β-form) have high polymerizability that increases with temperature. The polymerizability in the molten state at fairly high temperatures is rather low, however. Thus the polymerization rate, saturated conversion, and polymer molecular weight exhibit maxima just above the melting point of α-form. It is concluded that the hexagonal packing of monomer molecules with particular orientation in the layered structure and rotational freedom around the molecular axis, together with some conformational freedom of functional group, is favorable to the polymerization reaction. In addition, the mechanism of polymerization in the layered structure is discussed, assuming a cone-type distribution for the polymerization probability.     

Studies on diacetylenic vinyl compounds. II. Copolymerization of phenyl-4′-vinylphenylbutadiyne with styrene and methyl methacrylate

The copolymerizations of phenyl-4′-vinylphenylbutadiyne (PVPB) with styrene and methyl methacrylate were carried out under various conditions. PVPB was more readily incorporated in copolymerization than the comonomers, but the diacetylenic group of PVPB interacted with the propagating radical, decreasing the polymerization rate and the molecular weight of copolymer. When the polymerization system became very viscous, crosslinking took place giving light green luminescent gels. The thermal behaviors of copolymers were also studied.     

Energy transfer in luminescent complexes of EuIII and TbIII with homo- and copolymers of acrylic acid and alkyl methacrylates

The influence of the composition and structure of a macromolecular ligand on the efficiency of energy transfer in complexes of Eu^III and Tb^III with ligands based on acrylic acid has been studied. It has been found that a decrease in the size of an alkyl group of methacrylic esters and a low content of acrylic moieties of Eu^III complexes with copolymers increase the efficiency of Eu^III concentration quenching. Insertion of noncoordinative alkyl methacrylate into the polymeric chain results in an increase in the efficiency of energy transfer from Tb³⁺ to Eu³⁺.Translated fromIzvestiya Akademii Nauk. Seriya Klrimicheskaya, No. 6, pp. 1425–1428, June, 1996.     

Investigation of Pathogenic Mineralization on Human Heart Valves. II. ESR Spectroscopy

Pathogenic mineral precipitates on human heart valves (cardiolytes) were studied by electronic paramagnetic resonance (ESR) spectroscopy. Inorganic (CO ₂ ^– , CO ₃ ^3– ) and organic (CH₃, etc.) radicals were recorded in the valves under irradiation. The possibility for the spectrum of the CO ₂ ^– radical to be used for evaluating the relative amount of the crystalline apatite phase in cardiolyte was examined.     

Studies on polymers containing functional groups. VI. Kinetics of the polymerization and copolymerization behaviors of o-hydroxystyrene

Some kinetic studies were made of the homopolymerization of o-hydroxystyrene and its copolymerization behavior with styrene and methyl methacrylate in tetrahydrofuran using azobisisobutyronitrile as initiator were done. The rate of polymerization experimentally obtained is given by R_p = K[M][I]^0.72. Accordingly, it is likely that the growing chain radicals are terminated not only by mutual termination but also by a chain-transfer mechanism, the latter occupying a considerable portion. The latter is mostly attributed to the transfer to monomer, i.e., C_m for o-hydroxystyrene was 1.3 × 10^?2. Some transfer mechanisms were assumed, although it is difficult to elucidate the mechanism in detail, owing to its complexity. Effects of solvent on the rate of polymerization were examined, dioxane, methyl ethyl ketone, ethanol, and tetrahydrofuran being used. However, no differences were found among the solvents. The apparent activation energy of polymerization was found to be 21.5 kcal./mole. Monomer reactivity ratios and Alfrey-Price Q–e values for o-hydroxystyrene were determined. The Q–e values (Q = 1.41, e = ?1.13) are rather similar to those of p-methoxystyrene. Thus, the e value for o-hydroxystyrene is more negative than that for styrene.     

Kinetic and ESR studies on radical polymerization behavior of N‐(2‐phenylethoxycarbonyl)methacrylamide

Polymerization of N‐(2‐phenylethoxycarbonyl)methacrylamide (PECMA) with dimethyl 2,2′‐azobisisobutyrate (MAIB) was investigated in tetrahydrofuran (THF) kinetically and by means of electron spin resonance (ESR). The overall activation energy of the polymerization was calculated to be 58 kJ/mol. The initial polymerization rate (R_p) is expressed by R_p = k[MAIB]^0.3[PECMA]^2.3 at 60 °C. Such unusual kinetics may be ascribable to primary radical termination and to acceleration of propagation due to monomer association. Propagating poly(PECMA) radical was observed as a 13‐line spectrum by ESR under practical polymerization conditions. ESR‐determined rate constants of propagation (k_p, 4.7–10.5 L/mol s) and termination (k_t, 4.6 × 10⁴ L/ml s) at 60 °C are much lower than those of methacrylamide and methacrylate esters. The Arrhenius plots of k_p and k_t gave activation energies of propagation (24 kJ/mol) and termination (25 kJ/mol). The copolymerizations of PECMA with styrene (St) and acrylonitrile were examined at 60 °C in THF. Copolymerization parameters obtained for the PECMA (M₁) − St(M₂) system are as follows: r₁ = 0.58, r₂ = 0.60, Q₁ = 0.73, and e₁ = +0.22. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4264–4271, 2000