Step-growth Production of Nanogels for Use as Macromers with Dimethacrylate Monomers.

A series of functional nanogels were synthesized by a step-growth mechanism that involved diisocyanate addition to a modest stoichiometric excess of multi-thiols. Nanogels with sizes less than 10 nm were obtained as room temperature liquids with residual thiol groups used to attach methacrylate functionality. Depending on nanogel structure, bulk nanogel properties varied widely, as did the properties of the nanogel-derived and nanogel-modified polymers.

Evaporation of low-volatility components in polymeric dental resins.

Objectives: This study provides measurement of the volatility of selected photoinitiators and monomers used in dental adhesive resins. A detailed determination of the spatial and temporal character of camphorquinone (CQ) volatilization with respect to air flow conditions as well as media viscosity is assessed to gauge the effect of evaporative loss on the photopolymerization process and the photopolymers formed.

Methods: Vapor pressures of materials are measured by thermogravimetric analysis.

Spatial and Temporal Control of Thiol-Michael Addition via Photocaged Superbase in Photopatterning and Two-Stage Polymer Networks Formation.

Photochemical processes enable spatial and temporal control of reactions, which can be implemented as an accurate external control approach in both polymer synthesis and materials applications. "Click" reactions have also been employed as efficient tools in the same field. Herein, we combined photochemical processes and thiol-Michael "click" reactions to achieve a "photo-click" reaction that can be used in surface patterning and controlled polymer network formation, owing to the ease of spatial and temporal control through use of photolabile amines as appropriate catalysts.

Investigations of step-growth thiol-ene polymerizations for novel dental restoratives.

Objectives: The goal of this work was to investigate the feasibility of formulating novel dental restorative materials that utilize a step-growth thiol-ene photopolymerization. Particularly, we are aiming to significantly reduce the polymerization shrinkage and shrinkage stress while retaining adequate physical properties as compared to current dimethacrylatre-based systems.

Methods: The thiol-ene system is composed of a 4:3 molar mixture of triallyl-1,3,5-triazine-2,4,6-trione (TATATO) and pentaerythritol tetramercaptopropionate (PETMP).

Towards the elucidation of shrinkage stress development and relaxation in dental composites.

Objective: Although various photo-curing techniques aiming to partially relieve the shrinkage stress by flow have been proposed and investigated, the direct monitoring and observation of stress relaxation behavior received little attention. In this study, the elucidation of stress relaxation behavior and its impact on the overall stress development were investigated.

Methods: A novel experimental set-up capable of real-time, simultaneous shrinkage stress and double bond conversion measurements on the same sample was utilized.

Synthesis, characterization and evaluation of urethane derivatives of Bis-GMA.

Objectives: The aims of the study were to synthesize derivatives of Bis-GMA having pendant n-alkyl urethane substituents and to characterize and evaluate their physicochemical properties.

Methods: Stoichiometric amounts of Bis-GMA and n-alkyl isocyanates were reacted in dichloromethane with dibutyltin dilaurate as a catalyst. Volumetric shrinkage, water uptake, degree of vinyl conversion, refractive index and viscosity of resulting urethane monomers and those of Bis-GMA were measured.