Investigation Of The Effect Of Thiols On Polymerization Kinetics Of Vinyl Acrylate

Tai Yeon Lee; Charles E Hoyle; Todd M Roper; C Allan Guymon; E Sonny Jonsson

Traditionally, methodology for film formation by exposing reactive resins to UV light has involved use of monomer mixtures from a single class of reactive functional groups. In some cases, multiple components such as mixtures of acrylates and unsaturated esters or acrylates and vinyl ethers have been used to provide rapid curing materials that give films with multidimensional properties that combine many of the features of each type of reactive monomer. In virtually all of the systems to date employed in industrial applications, there is a requirement of adding an external photoinitiator to absorb light and efficiently initiate the free-radical chain process that results in film formation. Molecular systems that incorporate multifunctional monomers that have two groups with different reactivity and photoinitiate their own polymerization without the addition of external initiators would be advantageous in many applications, in particular where elimination of extractable components in the final crosslinked film is desirable. The use of monomers that have multiple types of reactive functional groups, one of which is photoreactive and capable of initiating freeradical polymerization, has been reported by Hult et al. Herein we report on the free-radical polymerization of vinyl acrylate which potentially has two reactive functional groups that can participate in free-radical polymerization, the acrylate group and the vinyl group. In this system, no initiator is required as the vinyl acrylate group self-initiates its own polymerization by a cleavage of the carbonyl carbon-oxygen bond in the ester group to produce initiating radicals. The basic photopolymerization of vinyl acrylate will first be discussed with emphasis on the mechanism of film formation. In addition the photopolymerization of vinyl acrylate in the presence of a multifunctional thiol will be presented: this multicomponent system involves the unusual situation of curing by dual free-radical chain processes, making it virtually unique among free-radical film formation processes. One hallmark of thiol-ene photopolymerization processes is the ability to achieve rapid free-radical polymerizations in the presence and absence of oxygen. Polymerization kinetics of ethyl acrylate/tri-thiol and vinyl propionate/tri-thiol systems are also reported as a model for the vinyl acrylate polymerization.

Investigation Of The Effect Of Thiols On Polymerization Kinetics Of Vinyl Acrylate

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