The reciprocity law concerning light dose relationships applied to BisGMA/TEGDMA photopolymers: theoretical analysis and experimental characterization.

Objectives: A model BisGMA/TEGDMA unfilled resin was utilized to investigate the effect of varied irradiation intensity on the photopolymerization kinetics and shrinkage stress evolution, as a means for evaluation of the reciprocity relationship.

Methods: Functional group conversion was determined by FTIR spectroscopy and polymerization shrinkage stress was obtained by a tensometer. Samples were polymerized with UV light from an EXFO Acticure with 0.

Enhanced Two-Stage Reactive Polymer Network Forming Systems.

In this study, we develop thiol/acrylate two-stage reactive network forming polymer systems that exhibit two distinct and orthogonal stages of curing. Using a thiol-acrylate system with excess acrylate functional groups, a first stage polymer network is formed via a 1 to 1 stoichiometric thiol-acrylate Michael addition reaction (stage 1). At a later point in time, the excess acrylate functional groups are homopolymerized via a photoinitiated free radical polymerization to form a second stage polymer network (stage 2).

Using hyperbranched oligomer functionalized glass fillers to reduce shrinkage stress.

Objective: Fillers are widely utilized to enhance the mechanical properties of polymer resins. However, polymerization stress has the potential to increase due to the higher elastic modulus achieved upon filler addition. Here, we demonstrate a hyperbranched oligomer functionalized glass filler UV curable resin composite which is able to reduce the shrinkage stress without sacrificing mechanical properties.

Reaction Kinetics and Reduced Shrinkage Stress of Thiol-Yne-Methacrylate and Thiol-Yne-Acrylate Ternary Systems.

Thiol-yne-methacrylate and thiol-yne-acrylate ternary systems were investigated for polymerization kinetics and material properties and compared to the analogous pure thiol-yne and (meth)acrylate systems. Both thiol-yne-methacrylate and thiol-yne-acrylate systems were demonstrated to reduce polymerization induced shrinkage stress while simultaneously achieving high glass transition temperatures (T(g)) and modulius. Formulations with 70 wt% methacrylate increased the T(g) from 51 ± 2 to 75 ± 1 °C and the modulus from 1800 ± 100 to 3200 ± 400 MPa (44% increase) over the pure thiol-yne system.

Induction Curing of Thiol-acrylate and Thiolene Composite Systems.

Induction curing is demonstrated as a novel type of in situ radiation curing that maintains most of the advantages of photocuring while eliminating the restriction of light accessibility. Induction curing is utilized to polymerize opaque composites comprised of thiol-acrylate and thiol-ene resins, nanoscale magnetic particles, and carbon nanotubes. Nanoscale magnetic particles are dispersed in the resin and upon exposure to the magnetic field, these particles lead to induction heating that rapidly initiates the polymerization.

Soft-lithography fabrication of microfluidic features using thiol-ene formulations.

In this work, a novel thiol-ene based photopolymerizable resin formulation was shown to exhibit highly desirable characteristics, such as low cure time and the ability to overcome oxygen inhibition, for the photolithographic fabrication of microfluidic devices. The feature fidelity, as well as various aspects of the feature shape and quality, were assessed as functions of various resin attributes, particularly the exposure conditions, initiator concentration and inhibitor to initiator ratio. An optical technique was utilized to evaluate the feature fidelity as well as the feature shape and quality.

Thiol-ene-methacrylate composites as dental restorative materials.

Objectives: The objective of this study was to evaluate composite methacrylate-thiol-ene formulations with varying thiol:ene stoichiometry relative to composite dimethacrylate control formulations. It was hypothesized that the methacrylate-thiol-ene systems would exhibit superior properties relative to the dimethacrylate control resins and that excess thiol relative to ene would further enhance shrinkage and conversion associated properties.

Methods: Polymerization kinetics and functional group conversions were determined by Fourier transform infrared spectroscopy (FTIR).

Photopolymerized Thiol-Ene Systems as Shape Memory Polymers.

In this study we introduce the use of thiol-ene photopolymers as shape memory polymer systems. The thiol-ene polymer networks are compared to a commonly utilized acrylic shape memory polymer and shown to have significantly improved properties for two different thiol-ene based polymer formulations. Using thermomechanical and mechanical analysis, we demonstrate that thiol-ene based shape memory polymer systems have comparable thermomechanical properties while also exhibiting a number of advantageous properties due to the thiol-ene polymerization mechanism which results in the formation of a homogenous polymer network with low shrinkage stress and negligible oxygen inhibition.

Properties of methacrylate-thiol-ene formulations as dental restorative materials.

Objectives: The objective of this study was to evaluate ternary methacrylate-thiol-ene systems, with varying thiol-ene content and thiol:ene stoichiometry, as dental restorative resin materials. It was hypothesized that an off-stoichiometric thiol-ene component would enhance interactions between the methacrylate and thiol-ene processes to reduce shrinkage stress while maintaining equivalent mechanical properties.

Methods: Polymerization kinetics and functional group conversions were determined by Fourier transform infrared spectroscopy (FTIR).

Investigation of thiol-ene and thiol-ene-methacrylate based resins as dental restorative materials.

Objectives: The objective of this work was to evaluate thiol-norbornene and thiol-ene-methacrylate systems as the resin phase of dental restorative materials and demonstrate their superior performance as compared to dimethacrylate materials.

Methods: Polymerization kinetics and overall functional group conversions were determined by Fourier transform infrared spectroscopy (FTIR). Flexural strength and modulus were determined with a 3-point flexural test.

Rapid Solid-State Photopolymerization of Cyclic Acetal-Containing Acrylates.

A cyclic acetal-functionalized urethane acrylate monomer is synthesized here and polymerized in a crystalline state without the polymerization kinetics being deleteriously affected by the solid state. Depending on the processing conditions, the cyclic acetal urethane acrylate monomer exists in either a metastable liquid state or a crystalline state at ambient conditions. Due to mobility restrictions, extremely poor polymerization kinetics and functional group conversions are typically achieved in solid state polymerizations.

Evaluation of highly reactive mono-methacrylates as reactive diluents for BisGMA-based dental composites.

Objectives: This study evaluates the performance of highly reactive novel monomethacrylates characterized by various secondary moieties as reactive diluent alternatives to TEGDMA in BisGMA filled dental resins. We hypothesize that these monomers improve material properties and kinetics over TEGDMA because of their unique polymerization behavior.

Methods: The cure rates and final double bond conversion of the resins were measured using real-time FTIR spectroscopy.