Electron‐beam initiated polymerization of acrylate compositions, 2. Simulation of thermal effects in thin films

The thermal effects taking place during the electron beam‐induced polymerization of acrylate type formulations were numerically simulated on the basis of the general heat equation applied to a one‐dimensional system. The nature, the dimensions and the environment of the polymerizing medium were defined for representing the actual conditions of kinetic experiments performed with a 175 kV laboratory accelerator and FTIR monitoring. The modeled system was constituted of a polymerizable composition coated onto a NaCl plate, initially at 20°C in gaseous nitrogen at the same constant temperature, with or without a PET film covering the reactive layer. Polymerization profiles describing the progress of the reaction as a function of dose were modeled on a phenomenological basis from actual data obtained by discontinuous FTIR monitoring of typical epoxy acrylate or polyurethane acrylate compositions. The influence of the reactive layer thickness (10/100 μm), dose rate (10–110 kGy·s^–1), maximum polymerization heat (200–400 J·g^–1) on the temperature‐time variations was examined for continuous irradiation. In spite of the relatively small thickness of the reactive layer, significant temperature rise is simulated when heat production is large and fast compared to energy dissipation at the reactive layer boundaries. The obtained data substantiate the fact that upon fractionated EB‐treatment with small dose increments (down to 0.6 kGy per pass) at low dose rate (down to 10 kGy·s^–1) the heat release can be considered weak and without noticeable influence on the conversion data processed for a detailed kinetic analysis. For example, a maximal temperature rise of 6°C was calculated for a fractionated irradiation of 2 kGy increments at 19 kGy·s^–1 applied to a polymerizable formulation releasing a maximum enthalpy of 300 J·g^–1.     

Anionic polymerization of methyl methacrylate and tert-butyl acrylate initiated with the YCl3/lithium amide/nBuLi systems

The anionic polymerization of methyl methacrylate (MMA) was initiated with a mixture of lithium amide of various secondary amines and nBuLi in the presence of YCl₃, where an Y-ate complex was formed and an amide ligand on Y attacked MMA nucleophilically. In THF at −78 °C, PMMAs with narrow molecular weight distributions were obtained in high yields. The presence of a secondary amino group derived from the initiator at the polymer chain end was confirmed by MALDI-TOF-MS analyses. The initiating system using indoline as a secondary amine was effective for block copolymerization of MMA with tert-butyl acrylate (tBA), giving poly(MMA-b-tBA)s with narrow molecular weight distributions.     

Kinetics of retarded polymerization: Investigation of the retardation of V5+–thiourea initiated polymerization of methyl acrylate by phenol

The kinetics and mechanism of the retarding action of phenol on the V⁵⁺–thiourea initiated polymerization of methyl acrylate (MA) have been studied within the temperature range of 30–50°C. The effects of retarder (phenol), metal ion (V⁵⁺), monomer (MA), sulfuric acid, some organic solvents and inorganic salts on the percentage and rate of polymerization have been studied. The remarkable observation of the present study is the positive intercept obtained from the plot of [M]/R_p vs. 1/[M]. This type of observation is significantly different from previous studies on retarded polymerization. The values of composite rate constants k₀k_t/k_ik_pkK have been calculated from plots of [M]/R_p vs. 1/[M]. On the basis of experimental findings a reaction mechanism has been suggested, and a suitable rate expression has been proposed and explained.     

γ-radiation-initiated emulsion polymerization of n-butyl acrylate and of methyl methacrylate

We have investigated the γ-radiation-initiated polymerization of n-butyl acrylate (BA) and of methyl methacrylate (MMA) in aqueous emulsions stabilized with sodium lauryl sulfate (SLS). The reaction rate, as measured by a nonabsolute thermocouple technique, varies as the square root of emulsifier concentration for both monomers. In the case of BA, the dose rate exponent of the reaction rate is 0.7 ± 0.3, whereas the corresponding value for MMA is approximately 0.4. The overall activation energy of the BA polymerization is close to zero, whereas for MMA a value of 4.8 ± 2.1 kcal/mole has been found. The poly(butyl acrylate) molecular weight is effectively independent of soap concentration and of dose rate but decreases as the reaction temperature is increased in the range 30–70°C. The general conclusion drawn from this work is that these radiation-induced emulsion polymerizations differ little from conventionally initiated systems insofar as the reaction kinetics are concerned. Poly(butyl acrylate-g-methyl methacrylate) copolymers have been prepared by a direct irradiation method involving a poly(butyl acrylate) prepolymer seed latex. Some physical properties of this material have been examined.     

Preparation and characterization of fluorinated acrylate copolymer latexes by miniemulsion polymerization under microwave irradiation

Fluoroacrylate copolymer miniemulsion was prepared by miniemulsion polymerization under microwave irradiation. The composition of the copolymer was determined by FTIR, DSC, ¹H NMR and ¹⁹F NMR. The morphology, size, and size distribution of the latex particles as well as changes in the size during polymerization were characterized by TEM and photon correlation spectroscopy (PCS). The effects of kinetic parameters on the polymerization were evaluated. The particle size of latex underwent almost no change during microwave irradiation polymerization. The diameters of latex particles prepared by microwave irradiation were smaller and more monodispersed than those prepared by conventional heating and the latex had good centrifugal stability. Polymerization under microwave irradiation had a higher reaction rate and higher conversion than traditional heating. By using 10 wt% fluoromonomer, the surface energy of the latex film could be reduced from 27.24 mJ/m² (latex film of fluorine-free) to 17.59 mJ/m² and the decomposition temperature increased by 25 °C.     

Emulsion polymerization of butyl acrylate: Spin trapping and EPR study

The propagating radical in the emulsion polymerization reaction of butyl acrylate was detected by Electron Paramagnetic Resonance (EPR) spectroscopy using two spin-trapping agents, 2-methyl-2-nitrosopropane (MNP) and α-(4-pyridyl 1-oxide)-N-tert-butylnitrone (PyOBN). Through analysis of hyperfine structure of the spectra obtainedfrom the trapped radicals, the propagating radical is inferred to be the well known acrylate radical, ? [CH₂? CH(COOC₄H₉)]_n? CH₂? CH(COOC₄H₉)? . © 1994 John Wiley & Sons, Inc.     

Comparative study of the absolute reactivity of vinyl monomers: Kinetics of polymerization of vinyl monomers initiated by Mn3+–thiodiglycolic acid redox system

The kinetics and mechanism of polymerization of methacrylic acid (MAA) and ethyl acrylate (EA) initiated by the redox system, Mn³⁺–thiodiglycolic acid (TDGA) were investigated in the 15–35°C temperature range. The polymerization kinetics of both the monomers followed the same mechanism, viz., initiation by primary radical and termination by Mn³⁺–thiodiglycolic acid complex. The rate coefficients k_i/k₀ and k_p/k_t were related to the monomer reactivity and polymer radical reactivity, respectively. It was observed that both monomer reactivity and polymer radical reactivity followed the same order, viz., EA > MAA. The polymer radical reactivity varied inversely with the Q values of the monomers.     

A computational study on the reactivity enhancement in the free radical polymerization of alkyl α‐hydroxymethacrylate and acrylate derivatives

The free radical polimerizability behavior of alkyl α‐hydroxymethacrylate (RHMA) derivatives ( M1–M3 ) has been modeled by considering the propagation of the dimeric units of the compounds of interest. All the transition structures in this class of monomers are stabilized by long‐range C?O…H? C interactions. The RHMA monomer bearing the ester functionality ( M2 ) polymerizes slightly faster than the one with the ether functionality ( M1 ) because of stronger electrostatic interactions between the C?O and H? C groups. 2‐(Methoxycarbonyl)allyl benzoate ( M3 ) shows higher reactivity as compared to M1 and M2 due to stronger electrostatic interactions. The same type of study has been carried out for hexyl ( M4 ), benzyl ( M5 ), and phenyl ( M6 ) acrylate derivatives whose increasing reactivity has been attributed to the presence of C?O…H? C, C?O…H‐? as well as π–π stabilizing interactions, respectively. While B3LYP/6‐31+G(d) has been used to locate the stationary points along the free radical polymerization of nonaromatic species, long‐range stabilizing interactions have only been detected with M06‐2X/6‐31+G(d). The kinetics that we obtain with this latter methodology for the free radical polymerization reactions of M1 – M6 agree well qualitatively with experiment. An implicit solvent model has reproduced the kinetics of M1–M3 in benzene the best. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

The reactivity of 3-methyl- and 5-methyl-1-vinylpyrazoles in free-radical polymerization

3-Methyl-l-vinylpyrazole (M3VP) and 5-methyl-1-vinylpyrazole (M5VP) were isolated as individual substances by vacuum rectification of their mixture (M3VP: M5VP 60 40). For each of them the kinetics of free-radical polymerization in MeOH were measured at low conversions. In both cases the rate of polymerization is proportional to 0.5 order with respect to the initiator (AIBN) concentration. On the other hand, a first order of reaction with respect to monomer concentration is observed only when the latter is relatively low (3M). At higher initial concentrations of monomers the order of reaction becomes less than unity. The overall rate of polymerization for M5VP was higher than for M3VP, whereas the initiation rate remained constant in the whole range of monomer concentrations and did not depend on the exact structure of the monomer. The difference in the rates of polymerization observed for M3VP and M5VP is probably connected with the difference in the key parameterk _p/k _t ^1/2 for each of the two isomers. It is concluded that the correct kinetic information about homo- and co-polymerization of M3VP and M5VP cannot be obtained without their adequate separation.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 413–415, February, 1993.     

Synthesis and kinetics of polymerization of unsaturated monomers with OH groups in their structure: I.3-hydroxyneopentyl acrylate

The synthesis of new unsaturated monomers containing functional groups has been theoretically analyzed by considering a simple kinetic scheme. In the reactions between acetyl and acryloyl chloride with neopentylglycol, it was shown that the comparison between theoretical and experimental results, does not allow us to conclude that the two rate constants controlling the reactions are equivalent. Kinetic experiments of the polymerization of 3-hydroxyneopentyl acrylate were carried out in benzene and 1,4-dioxane solution at different temperatures. Dilatometric techniques and nonlinear least-squares methods were used to obtain kinetic data and to determine the kinetic constants, respectively. The values of $k_p /k_t^{1/2}$ for this monomer were found higher in dioxane than in benzene due, probably, to the fact that in the last solvent the polymerization is heterogeneous. The activation energy, determined by using different values of $k_p /k_t^{1/2}$ was found 7.6 kcal/mol. The stereostructure of the polymers derived from 3-hydroxyneopentyl acrylate and 3-acetoxyneopentyl acrylate was determined by ¹³C-NMR spectroscopy from the analysis of the resonance signals belonging to the carbonyl groups, obtaining values for the fraction of isotactic dyads in the range 0.36 ± 0.03 for both polymers. Finally, the glass transition temperatures of both polymers, determined calorimetrically, were found 281 and 255 K, respectively. © 1994 John Wiley & Sons, Inc.     

Anionic polymerization of acrylates. II. Polymerization of 2-ethylhexyl acrylate initiated by butyllithium/lithium-tert-butoxide system in tetrahydrofuran and its mixtures with toluene

The anionic polymerization of 2-ethylhexyl acrylate (EtHA) initiated with the complex butyllithium/lithium-tert-butoxide (BuLi/t-BuOLi) was investigated at ?60°C in a medium of various solvating power, i.e., in mixtures of toluene and tetrahydrofuran and in neat tetrahydrofuran. With increasing amount of THF in the mixture the attainable limiting conversion of polymerization decreases; the monomer can be polymerized quantitatively only in a toluene/THF mixture (9/1). Molecular weights of the polymers thus obtained, their distribution, and initiator efficiency are not appreciably affected by the polymerization medium. The molecular weight distribution of the products is medium-broad (M_w/M_n = 2–2.4), with a hint of bimodality. The ¹H-¹³C-NMR, and IR spectra suggest that during the polymerization there is neither any perceptible reesterification of the polymer with the alkoxide nor transmetalation of the monomer with the initiator. In a suitable medium, autotermination of propagation proceeds to a limited extent only, predominantly via intramolecular cyclization of propagating chains; in a medium with a higher content of polar THF, it prevails and terminates propagation before the polymerization of the monomer has been completed. © 1992 John Wiley & Sons, Inc.     

Radical polymerization and copolymerization of methyl α-(2-carbomethoxyethyl)acrylate,a dimer of methyl acrylate,as a polymerizable α-substituted acrylate

Polymerization and copolymerization of methyl α-(2-carbomethoxyethyl)acrylate (MMEA), which is known as a dimer of methyl acrylate, were studied in relation to steric hindrance-assisted polymerization. The propagating polymer radical from MMEA was detected as a five-line spectrum and quantified by ESR spectroscopy during the bulk polymerization at 40–80°C. The absolute rate constants of propagation and termination (κ_p and κ_t) for MMEA at 60°C (κ_p = 19 L/mol s and κ_t = 5.1 × 10⁵ L/mol s) were evaluated using the concentration of the propagating radical at the steady state. The balance of the propagation and termination rates allows polymer formation from MMEA. The polymerization rate of MMEA at 60°C was less than that of MMA by a factor of about 4 at a constant monomer concentration. Although no influence of ceiling temperature was observed at a temperature ranging from 40 to 70°C, addition-fragmentation in competition with propagation reduced the molecular weight of the polymer. The content of the unsaturated end group was estimated to be 0.1% at 60°C to the total amount of the monomer units consisting of the main chain. MMEA exhibited reactivities almost similar to those of MMA toward polymer radicals. It is concluded that MMEA is one of the polymerizable acrylates bearing a substituted alkyl group as an α-substituent. Characterization of poly(MMEA) was also carried out. © 1996 John Wiley & Sons, Inc.     

Effect of sulfonated 3-pentadecyl phenyl acrylate as surfmer in the emulsion polymerization of styrene: synthesis and polymer properties

In this work, the evaluation of a newly developed anionic polymerizable surfactant (surfmer), viz., sulfonated 3-pentadecyl phenyl acrylate, in the emulsion polymerization of styrene and its effect on the polymer properties is reported. The results were compared with the commercially available non-reactive anionic surfactant sodium lauryl sulfate. The surfmer has a low critical micellar concentration value of 40.11 mg/L (8.7?×?10^?5?mol/L) in comparison to 2,400 mg/L (8.28?×?10^?3?mol/L) for sodium dodecyl sulfate. Nanosized polystyrene dispersions with varying concentration of this surfmer were prepared and characterized for conversion, particle size, and size distribution at a fixed monomer/water ratio of 0.1. The particle radii decreased from 560 nm for the surfactant-free dispersions to 45 nm for the dispersion with 2.3 mol% surfmer. Increasing surfmer content above this concentration did not further affect the particle size but increased the width of the particle size distribution. Transmission electron microscopy results along with particle size data show that with increasing surfmer content the particle size distribution broadens, and film formation is facilitated. The microstructure analysis of the copolymers using infrared and ¹H-NMR spectroscopy confirms that the surfmer is chemically attached to the polymer chains. The effect of the ionic sulfonate groups and the alkyl chains of the surfmer moieties on the polymer properties have been studied through measurement of dilute solution viscosity and thermal and viscoelastic properties. These results indicate that the behavior of surfmer-containing polymers resembles that of plasticized ionomers.     

Cationic polymerization of isobutene initiated by stannic chloride and phenols: Polymer endgroup studies

Low molecular weight polymers of isobutene produced with stannic chloride as catalyst and phenols as cocatalysts have been subjected to ultraviolet and NMR analysis. A high proportion of the endgroups are derived from the phenol cocatalyst when the concentration of free phenol in the reaction mixture at ?78.5°C is fairly large. At low concentrations of free phenol, termination to give vinylidene endgroups becomes more significant. The results lend support to the suggestion that an important mode of termination in this polymerization system involves the reaction between a growing carbonium ion and the phenol cocatalyst.     

Towards the control of the reactivity in high temperature anionic polymerization of styrene: retarded anionic polymerization. 3 – influence of triisobutylaluminum on the reactivity of polystyryllithium species

The addition of triisobutylaluminum to a lithiated‐based anionic polymerization of styrene leads to the formation of aluminate complexes and provokes a drastic reduction of the styrene polymerizability in relation with the Al/Li ratio used. The reaction is first order in monomer and active species and is stopped for iBu₃Al/PSLi > 1. From U.V. spectrometry, kinetic studies and viscometric measurements, it was possible to suggest the presence of various mixed complexes of different stoichiometries. The strong increase in the thermal stability of the new propagating species together with their much lower reactivity permits the controlled bulk polymerization of styrene at high temperature.     

Metal chelates in vinyl polymerization: Kinetics and mechanism of acrylonitrile polymerization initiated by Cu(II) imine complexes

The free radical polymerization of acrylonitrile (AN) initiated by Cu(II) 4-anilino 2-one [Cu(II) ANIPO] Cu(II), 4-p-toluedeno 3-pentene 2-one [Cu(II) TPO], and Cu(II) 4-p-nitroanilino 3-pentene 2-one [Cu(II) NAPO] was studied in benzene at 50 and 60°C and in carbon tetrachloride (CCl₄), dimethyl sulfoxide (DMSO), and methanol (MeOH) at 60°C. Although the polymerization proceeded in a heterogeneous phase, it followed the kinetics of a homogeneous process. The monomer exponents were ≥2 at two different temperatures and in different solvents. The square-root dependence of R_p on initiator concentration and higher monomer exponents accounted for a 1:2 complex formation between the chelate and monomer. The complex formation was shown by ultraviolet (UV) study. The activation energies, kinetics, and chain transfer constants were also evaluated.