Photoinitiated Polymerization of Di- and Tetrafunctional Methacrylic Monomers in a SBS Matrix. Kinetic, Mechanistic, and Structural Aspects

Abstract

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.

Photopolymerization kinetics of 2-phenylethyl (meth)acrylates studied by photo DSC

“…The polymerization rate will however get reduced with time due to limitation in radical diffusion caused by an increase in viscosity of the system with conversion. The entire process is an outcome of the time dependant influence of translational, segmental and reaction diffusion (diffusion of mobility restricted macroradical) processes [2,8].…”

New fluorescent hyperbranched polymeric sensors as probes for monitoring photopolymerization reactions

“…For highly crosslinkable systems this happens at low conversions, and both propagating radicals and unreacted double bonds remain in the medium. Then, propagating radicals slowly add unreacted functional groups until encountering a second radical for termination [34]. This two-stage process is evident in Fig.…”

Physical and mechanical properties of photopolymerized SBS–methacrylic monomer systems

“…Decanodiol dimethacrylate (DDDMA) was prepared by reaction of methacrylic acid and 1,10-decanodiol, using p-toluensulfonic acid as the catalyst. 6 2,2-Dimethoxy-2-phenylacetophenone (DMPA) photoinitiator from Ciba Specialty Chemicals was used as received.…”

“…1), showing the polymethacrylate formed like a plasticizer despite the crosslinking produced in some extent during the photopolymerization 6 of the methacrylic monomers in the SBS matrix.…”

“…We have recently published several articles [5][6][7][8][9] about the photoinitiated polymerization of methacrylic monomers in polymeric matrices (styrene-butadienestyrene block copolymer, polystyrene, polybutadiene, and polymethyl methacrylate). The knowledge in detail of the mechanistic and kinetic behavior of the polymerization of methacrylic monomers in solid polymeric media is of interest to optimize conditions and compositions of reaction for these systems used in several applications as well as to design new others.…”