The photopolymerization behavior and reaction kinetics of ethylhexyl methacrylate (EHMA) and ethylene glycol dimethacrylate (EGDMA) monomers in styrene−butadiene−styrene block copolymer (SBS) were studied. For both monomers, di- and tetrafunctional, reaction diffusion was found to be the only mechanism of termination when the polymerization is carried out in this polymeric medium, that is, reaction diffusion controls the termination reaction from the beginning of the reaction. The polymerization of EGDMA in polystyrene and polybutadiene showed similar behavior to that in SBS. Also, the relationship between the individual rate constants k t and k p was studied, and a constant ratio of these kinetic constants was found.

Relative reactivities of radicals derived from several p-dimethylanilines toward the polymerization of butyl acrylate have been calculated. It was observed that the reactivity of the radicals increases as the electron-withdrawing character of the groups attached in the para position increases. The experimental efficiency factor if) has been found to be proportional to the value defined in the Hammett equation. The dependence of the reactivities on the nature of the radicals has also been explained through their frontier orbital characteristics. The high similarity of the behavior of /versus and/versus £somo led us to conclude that the simple perturbative molecular orbital calculations can be used to predict the relative reactivity of initiating radicals with similar structure toward the polymerization of acrylic monomers.

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The kinetics and mechanism of the photoinitiated polymerization of tetrafunctional and difunctional methacrylate monomers (di-, hexa-, and decamethylene dimethacrylates; and ethylhexyl and dodecyl methacrylates) in a styrene−butadiene−styrene (SBS) block copolymer matrix have been studied. Reaction diffusion was found to be the only termination mechanism for tetrafunctional monomers when the monomer concentration in the matrix is below 30−40%; for higher monomer concentrations, reaction diffusion controls the termination process only after approximately 10% conversion was reached. The values of both the propagation kinetic constant and the overall double bond conversion for the three tetrafunctional monomers studied showed the following order:  deca- > hexa- > dimethylene dimethacrylate. The termination process in the photoinitiated polymerization of difunctional methacrylate monomers is clearly controlled by reaction diffusion right from the beginning of the polymerization reaction only at a very low monomer concentration in the matrix (10−15%); for medium monomer concentrations (20−40%), a combination of both mechanisms, segmental diffusion-controlled (autoaccelerated kinetics) and reaction diffusion, was observed until reaching a double bond conversion of 20%, from which point reaction diffusion predominated; for higher monomer concentrations (60−90%), the termination kinetic constant values at low conversions (<30%) were close to those corresponding with standard polymerizations, observing the Trommsdorff effect (autoacceleration) at higher double bond conversions. The SBS matrix participates appreciably in the polymerization process through the direct addition of the macroradical or the primary radical to the double bond of the polybutadiene moiety and through hydrogen abstraction from the matrix with the formation of benzylic and allylic radicals.

The kinetics and mechanism of the photoinitiated polymerization of tetrafunctional and difunctional methacrylic monomers [1,6‐hexanediol dimethacylate (HDDMA) and 2‐ethylhexyl methacrylate (EHMA)] in a polybutadiene matrix (PB) have been studied. The maximum double‐bond conversion, the maximum polymerization rate, the intrinsic reactivity, and the kinetic constants for propagation and termination have been calculated. Unlike the behavior followed by the SBS‐HDDMA and PS‐HDDMA systems, where a reaction‐diffusion mechanism occurs from the start of the polymerization at low monomer concentrations (<30–40%), in the PB‐HDDMA system the reaction diffusion controls the termination process only after approximately 10% conversion is reached, as for the bulk polymerization of polyfunctional methacrylic monomers. Before reaching 10% conversion the behavior observed can be better explained by a combination of segmental diffusion‐controlled (autoaccelerated) and reaction‐diffusion mechanisms. This is probably a consequence of the lower force of attraction between the monomer and the matrix and between the growing macroradical and the matrix than those corresponding to the other systems mentioned. For the PB‐EHMA system, the termination mechanism is principally diffusion‐controlled from the beginning of the polymerization for monomer concentrations below 30–40%, and for higher monomer concentrations, a standard termination mechanism takes place (kt ≈ 106) at low double‐bond conversions, which is diffusion‐controlled for high conversions (>40%). For PB‐HDDMA and PB‐EHMA systems, crosslinked polymerized products are obtained as a result of the participation of the double bonds of the matrix in the polymerization process. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2444–2453, 2001

The photopolymerization of several di‐ and tetrafunctional (meth)acrylic monomers in the presence of a styrene–butadiene–styrene polymeric matrix (SBS) has been studied. Electron spin resonance spectroscopy (ESR) and differential scanning photocalorimetry (photo‐DSC) were used as monitoring techniques to identify the photogenerated radicals and analyze photopolymerization profiles, radical environments, and radical secondary reactions. The study of the photopolymerization and/or photocrosslinking reactions of these monomers in the solid media was carried out by taking into consideration different factors, such as the influence of both monomer and photoinitiator structures on the hydrogen abstraction in the binder with formation of benzylic and allylic radicals, the polymerization of the monomers itself and the hydrogen abstraction reaction in the polymerized acrylic chains. Finally, irradiation of the system SBS/photoinitiator in the absence of monomer was also accomplished. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 2775–2783, 1998

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The initial rate of the polymerization of methyl acrylate photoinitiated by Cdimethylamino-4'-isopropylbenzophenone (2) varies linearly with monomer concentration and the square-root of light intensity. For small absorbances, the initial polymerization rate, %, varies linearly with the square-root of the photoinitiator concentration. For high absorbance values, I$ is independent of the photoinitiator concentration in a well-stirred system and decreases as the photoinitiator concentration increases in an unstirred system. This marked difference between the polymerization kinetics in well-stirred and unstirred systems is discussed. The ratio of the propagation rate constant and the square-root of the termination rate constant, $,/&I/*, and the quantum yield of photoinitiation were determined and related to the results previously obtained in a study on the photoreactivity of 2.Materials: Methyl acrylate (MA) from Fluka A 0 was washed 3 times with portions of 10 v01.-% aqueous sodium hydroxide to remove the inhibitor and then 3 times with distilled water. The monomer was dried over anhydrous MgSO, and then distilled under reduce pressure before using. 4-Dirnethylamino-4'-isopropylbenzophenone (2) was prepared according to the method described in ref.'). Benzene (fluorescence grade from Carlo Erba) was used without further purification.Polymerizution procedure: The required amounts of monomer, solvents and photoinitiator were charged into a dilatometer which was degassed under vacuum by the conventional freezeand-thaw technique and sealed off under vacuum (lo-, mmHg). The dilatometer, being constructed by attaching two capillary branches (internal diameter: 0,s mm) to a cylindrical reaction vessel (internal diameter: 2 cm; volume: 13 cm'), was placed into a constant temperature bath in which the cylindrical reaction vessel fitted perfectly into the space of the metallic base of the bath, provided with two parallel quartz windows. The bath was placed on an optical bench, including a Hg-He lamp (200 W Hanovia 901B1), quartz lens, and interference 365 nm filter (International Light NB-365). A radiometer was placed immediately behind the second quartz window which allowed changes in the light intensity to be measured. Aberchrome 540 (Edward Davis Chemical Laboratories) actinometry was used to relate the digital display of the radiometer to an absolute value for the number of incident quanta per unit time'). The polymerizations were carried out to low conversion (2-4%) and invariably at 30 f 0,Ol 'C; the reaction mixture in each run was removed from the dilatometer and the polymer precipitated into cold methanol. The polymer, isolated by filtration, was washed several times with methanol and then dried at 40 "C under vacuum. The rates of all photoinitiated polymerizations were corrected to allow for the changes from run to run of the incident light intensity, assuming in all cases a square-root dependence on the intensity.Viscosity measurements: Viscosity measurements were performed in a Ubbelohde viscometer at 30°C with b...