Dataset Information

Stress Relaxation by Addition-Fragmentation Chain Transfer in Highly Crosslinked Thiol-Yne Networks.

ABSTRACT: Radical mediated addition-fragmentation chain transfer of mid-chain allyl sulfide functional groups was utilized to reduce polymerization-induced shrinkage stress in thiol-yne step-growth photopolymerization reactions. In previous studies, the addition-fragmentation of allyl sulfide during the polymerization of a step-growth thiol-ene network demonstrated reduced polymerization stress; however, the glass transition temperature of the material was well below room temperature (~ -20°C). Many applications require super-ambient glass transition temperatures, such as microelectronics and dental materials. Polymerization reactions utilizing thiol-yne functional groups have many of the advantageous attributes of the thiol-ene-based materials, such as possessing a delayed gel-point, resistant to oxygen inhibition, and fast reaction kinetics, while also possessing a high glass transition temperature. Here we incorporate allyl sulfide functional groups into a highly crosslinked thiol-yne network to reduce polymerization-induced shrinkage stress. Simultaneous shrinkage stress and functional group conversion measurements were performed during polymerization using a cantilever-type tensometer coupled with a FTIR spectrometer. The resulting networks were highly crosslinked, possessed super-ambient glass transition temperatures, and exhibited significantly reduced polymerization-induced shrinkage stress when compared with analogous propyl sulfide-containing materials that are incapable of addition-fragmentation.

SUBMITTER: Park HY

PROVIDER: S-EPMC3134880 | biostudies-literature | 2010

REPOSITORIES: biostudies-literature

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Stress Relaxation by Addition-Fragmentation Chain Transfer in Highly Crosslinked Thiol-Yne Networks.

Park Hee Young HY Kloxin Christopher J CJ Scott Timothy F TF Bowman Christopher N CN

Macromolecules 20100101 24

Radical mediated addition-fragmentation chain transfer of mid-chain allyl sulfide functional groups was utilized to reduce polymerization-induced shrinkage stress in thiol-yne step-growth photopolymerization reactions. In previous studies, the addition-fragmentation of allyl sulfide during the polymerization of a step-growth thiol-ene network demonstrated reduced polymerization stress; however, the glass transition temperature of the material was well below room temperature (~ -20°C). Many appli ...[more]

PMID: 21765551

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Project description:To reduce shrinkage stress which arises during the polymerization of crosslinked polymers, allyl sulfide functional groups were incorporated into methacrylate polymerizations to determine their effect on stress relaxation via addition-fragmentation chain transfer (AFCT). Additionally, stoichiometrically balanced thiol and allyl sulfide-containing norbornene monomers were incorporated into the methacrylate resin to maximize the overall functional group conversion and promote AFCT while also enhancing the polymer's mechanical properties. Shrinkage stress and reaction kinetics for each of the various functional groups were measured by tensometry and Fourier-transform infrared (FTIR) spectroscopy, respectively. The glass transition temperature (T(g)) and elastic moduli (E') were measured using dynamic mechanical analysis. When the allyl sulfide functional group was incorporated into dimethacrylates, the polymerization-induced shrinkage stress was not relieved as compared with analogous propyl sulfide-containing resins. These analogous propyl sulfide containing monomers are incapable of undergoing AFCT while having similar chemical structure and crosslink density to the allyl sulfide containing methacrylates. Here, a monomethacrylate monomer that also contains a cyclic allyl sulfide (PAS) was found to increase the crosslinking density nearly 20 times as compared to an analogous monomethacrylate in which the allyl sulfide was replaced with an ethyl sulfide. Despite the much higher crosslink density, the PAS formulation exhibited no concomitant increase in stress. Thiol-norbornene resins were copolymerized in PAS to promote AFCT as well as to synergistically combine the ring opening benefits associated with the thiol-ene reaction. AFCT resulted in a 63% reduction of polymerization stress and a 45°C enhancement of the glass transition temperature in the allyl sulfide-containing thiol-norbornene-methacrylate system compared with rubbery dimethacrylates. When compared with conventional glassy dimethacrylates, this combined system has less than 10% of the typical shrinkage stress level while having similarly excellent mechanical properties.

Dataset Information

Stress Relaxation by Addition-Fragmentation Chain Transfer in Highly Crosslinked Thiol-Yne Networks.

Publications

Stress Relaxation by Addition-Fragmentation Chain Transfer in Highly Crosslinked Thiol-Yne Networks.

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