The ability to prepare high Tg low shrinkage thiol–ene materials is attractive for applications such as coatings and dental restoratives. However, thiol and nonacrylated vinyl materials typically consist of a flexible backbone, limiting the utility of these polymers. Hence, it is of importance to synthesize and investigate thiol and vinyl materials of varying backbone chemistry and stiffness. Here, we investigate the effect of backbone chemistry and functionality of norbornene resins on polymerization kinetics and glass transition temperature (Tg) for several thiol–norbornene materials. Results indicate that Tgs as high as 94 °C are achievable in thiol–norbornene resins of appropriately controlled chemistry. Furthermore, both the backbone chemistry and the norbornene moiety are important factors in the development of high Tg materials. In particular, as much as a 70 °C increase in Tg was observed in a norbornene–thiol specimen when compared with a sample prepared using allyl ether monomer of analogous backbone chemistry. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5686–5696, 2007

The copolymerization behavior and the dark polymerization kinetics of highly reactive novel acrylic monomers were compared to traditional acrylate monomers. Copolymerization of thiol functionalities with novel acrylic monomers was characterized, and it was observed that the inclusion of secondary functionalities such as carbamates, carbonates, and cyclic carbonates, in acrylic monomers significantly alters the relative reactivity of the novel acrylates with thiols. While traditional aliphatic acrylates exhibited propagation to chain transfer ratios ranging between 0.8 (± 0.1)-1.5(± 0.2), the novel acrylates characterized by secondary functionalities exhibited much higher propagation to chain transfer ratios ranging from 2.8(± 0.2)-4(± 0.2). In the dark polymerization studies, the kinetics of the novel acrylates were evaluated following cessation of the UV light. The novel acrylates exhibited extensive polymerization in the dark compared to most traditional acrylates and diacrylates. For instance, cyclic carbonate acrylate was observed to attain 35 % additional conversion in the dark when the UV light was extinguished at 35 % conversion, whereas traditional acrylates such as hexyl acrylate attained only 3 % additional conversion when the UV light was extinguished at 35 %, and a diacrylate such as HDDA attained 15 % additional conversion when the UV light was extinguished at 40 % conversion. Also, through choice of appropriate monomers, the dark polymerization studies were performed such that the polymerization rate was approximately the same at the point the light was extinguished for all these monomers. The copolymerization and dark polymerization studies support the hypothesis that the nature of the propagating species in the novel acrylates is altered as compared to traditional acrylic monomers and polymerizations.

Formulations containing novel monovinyl methacrylates exhibit dramatically increased curing rates while also exhibiting superior or at least comparable composite polymer mechanical properties. Thus, these types of materials are attractive for use as reactive diluent alternatives to TEGDMA in dental formulations.

The impact of secondary functionalities on the radical‐vinyl chemistry of monoacrylates characterized by secondary functionalities that dramatically enhance their polymerization rate was elucidated utilizing experimental and computational techniques. Firstly, bulk interactions affecting the acrylate reactivity towards photopolymerization were removed by polymerizing at 5 wt % monomer in 1,4‐dioxane. Following deconvolution of bulk interactions impacting reactivity towards photopolymerization, a linear correlation between average polymerization rates and Michael addition reaction rate constants was observed on a logarithmic scale. This result indicates that the presence of the secondary functionality intramolecularly alters the monomer chemistry in a manner which impacts both of these distinct reaction types in a similar manner. These monomers exhibited reduced activation energies in both Michael addition and photopolymerization reactions as compared to hexyl acrylate. Reduction up to 20 ± 8 kJ mole−1was observed for Michael addition reactions and 12 ± 1 kJ mole−1 for photopolymerization reactions, thereby explaining the higher reactivity of the acrylates characterized by the secondary functionalities. Cyclic voltammetry experiments conducted to investigate the nature of the acrylic double bonds indicated that the rapidly polymerizing acrylates are more readily reduced as compared to traditional acrylates. Further, a distinct monotonic correlation of the irreversible cathodic peak potentials of the (meth)acrylates to photopolymerization and Michael addition reactivity was observed. The computationally estimated acrylic LUMO energies characterized by the secondary functionalities (−2.3 eV to −2.7 eV) were also found to be lower relative to hexyl acrylate (−2.2 eV). © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4859–4870, 2009

This study focuses on the design and development of novel monovinylic (meth)acrylate monomers with enhanced polymerization kinetics and the evaluation of their performance as reactive diluents in diacrylate systems. Novel (meth)acrylic monomers characterized by several new secondary functionalities are developed in this study and are shown to exhibit reactivities 10-70 fold greater than traditional monoacrylates such as hexyl acrylate. These monomers were designed based on our understanding of interactions between monomer structure, polymerizations kinetics, and polymer properties. Performance of these monovinyl monomers as reactive diluents is also investigated in this study. Copolymerization of these monomers with diacrylates enhanced both the reactivity and the mechanical properties of the diacrylate system. Specifically, while copolymerization of a diacrylate system with traditional monoacrylates such as hexyl acrylate decreases the overall reactivity of the system, its copolymerization with the novel monomers led to comonomer mixtures, that were 30-50% more reactive than either of the individual components, with initial polymerization rates increased by as much as 2 times the more reactive component. Further, the copolymerization of these novel monovinyl systems with diacrylates also enabled formation of polymers with enhanced mechanical properties over the corresponding diacrylates including a more homogeneous network structure as indicated by a glass transition temperature that was narrowed by up to 55 % while increasing the glass transition temperature by as much as 10°C.