Covalent adaptable networks as dental restorative resins: Stress relaxation by addition–fragmentation chain transfer in allyl sulfide-containing resins

Park, Hee Young; Kloxin, Christopher J.; Scott, Timothy F.; Bowman, Christopher N.

doi:10.1016/j.dental.2010.06.007

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Volume 26, Issue 10 , Pages 1010-1016, October 2010

Covalent adaptable networks as dental restorative resins: Stress relaxation by addition–fragmentation chain transfer in allyl sulfide-containing resins

Hee Young Park
- Department of Chemical and Biological Engineering, Engineering Center, ECCH 111, University of Colorado, Boulder, CO 80309-0424, USA
Christopher J. Kloxin
- Department of Chemical and Biological Engineering, Engineering Center, ECCH 111, University of Colorado, Boulder, CO 80309-0424, USA
Timothy F. Scott
- Department of Mechanical Engineering, Engineering Center, ECME 114, University of Colorado, Boulder, CO 80309-0427, USA
Christopher N. Bowman
- Department of Chemical and Biological Engineering, Engineering Center, ECCH 111, University of Colorado, Boulder, CO 80309-0424, USA
- Biomaterials Research Center, School of Dentistry, University of Colorado Health Sciences Center, Aurora, CO 80045, USA
- Corresponding author at: Department of Chemical and Biological Engineering, Engineering Center, ECCH 111, University of Colorado, Boulder, CO 80309-0424, USA. Tel.: +1 303 492 3247; fax: +1 303 492 4341.

Received 1 December 2009; received in revised form 19 May 2010; accepted 25 June 2010.

Abstract

Objectives

The aim is to demonstrate significant polymerization shrinkage stress reduction in model resins through incorporation of addition–fragmentation chain transfer moieties that promote network stress accommodation by molecular rearrangement. Monomers containing allyl sulfide linkages are incorporated to affect the shrinkage stress that arises during photopolymerization of model resins that contain an initiator and dimethacrylates. Radical-mediated allyl sulfide addition–fragmentation is enabled during polymerization. We hypothesize that allyl sulfide incorporation into methacrylate polymerizations promotes stress relaxation by enabling network adaptation.

Methods

A 1:2 mixture of tetrathiol and allyl sulfide-containing divinyl ethers is formulated with glass-forming dimethacrylates and compared to controls where the allyl sulfide is replaced with a propyl sulfide that is incapable of undergoing addition–fragmentation. Simultaneous shrinkage stress and functional group conversion measurements are performed. The T_g is determined by DMA.

Results

Increasing allyl sulfide concentration reduces the relative stress by up to 75% in the resins containing the maximum amount of allyl sulfide. In glassy systems, at much lower allyl sulfide concentrations, the stress is reduced by up to 20% as compared to propyl sulfide-containing systems incapable of undergoing addition–fragmentation chain transfer.

Significance

Shrinkage stress reduction, typically accompanying free-radical polymerization, is a primary focus in dental materials research and new product development. Allyl sulfide addition–fragmentation chain transfer is utilized as a novel approach to reduce stress in ternary thiol-ene-methacrylate polymerizations. The stress reduction effect depends directly on the allyl sulfide concentration in the given ternary systems, with stress reduction observed even in systems possessing super-ambient T_gs and low allyl sulfide concentrations.

Keywords: Shrinkage stress, Stress relaxation, Polymer networks, Allyl sulfide, Addition–fragmentation chain transfer, Photopolymerization