The polymerization mechanism of the ternary thiol−allyl ether−methacrylate monomer system has been investigated. The effects of various factors including the thiol concentration, functionality, and structure on the polymerization mechanism, the polymer network structure, and mechanical properties were examined. The thiol−allyl ether−methacrylate ternary system uniquely exhibits two different polymerization regimes:  a methacrylate homopolymerization dominated regime coupled with chain transfer to thiol followed by a second thiol−ene polymerization dominated regime. This polymerization mechanism is primarily due to the chemical nature of the methacrylate and allyl ether double bonds. Because methacrylate homopolymerization with chain transfer reactions to thiols dominates the initial stage of polymerization (up to 60% of the methacrylate conversion), the concentration and structure of the thiol significantly affect the polymerization processes and polymer network structure. The methacrylate chain length significantly decreases from 20 to 1.5 with increasing thiol content, and the methacrylate conversion rate during the first polymerization regime depends linearly on the [SH]0/[methacrylate]0 ratio. The overall polymerization rates and glass transition temperature increase significantly with increasing thiol functionality, while the methacrylate final conversion decreases more than 20% due to the formation of the highly cross-linked network.

The evolution of the polymerization-induced shrinkage stress and mechanical properties of thiol−allyl ether−methacrylate ternary systems and their relationship to the polymerization kinetics have been investigated. Because of the two distinct polymerization regimes of the ternary systemsa methacrylate homopolymerization regime followed by a thiol−ene polymerization dominated regimethe mechanism for the evolution of polymerization induced shrinkage stress is unique as compared to other thiol−ene and methacrylate systems. During the first polymerization stage, only intermediate molecular weight methacrylate oligomers are produced, resulting in delayed gelation and near zero shrinkage stress. Immediately following the first polymerization stage, the allyl ether begins to polymerize, and shrinkage stress increases in correspondence with the increased allyl ether conversion. It is observed that the shrinkage stress of the ternary systems exhibits ∼50% of the shrinkage stress of the current dental restoration systems. Also, because of the two polymerization regimes, the mechanical properties evolve uniquely as compared to other ternary systems. It is noted that glass transition temperatures of the ternary systems (∼100 °C) are much higher than traditional thiol−ene polymers and comparable to the current polymeric composites for dental restorations, indicating that the thiol−allyl ether−methacrylate systems are an excellent candidate for dental restorations.

This paper describes the synthesis and systematic study of substituted acenes that have differences in conjugation both along their long axes (by the number of fused benzene or thiophene rings) and along their short axes (by the number of arylethynyl substituents). These acenes include what we believe to be the first reported examples of five new subclasses of substituted acenes. Systematic analyses of data obtained using absorbance and fluorescence spectroscopies, cyclic voltammetry, and DFT calculations reveal clear correlations between these common structural perturbations to acene structure and the key parameters, such as HOMO-LUMO gap, frontier molecular orbital energies, and reactivity with singlet oxygen.

This paper describes a series of thiophene-based conjugated polymers that become insoluble upon irradiation with ultraviolet light. Stille or Suzuki reactions of appropriately substituted 2,5-bromothiophene derivatives yielded terthiophene and polythiophene derivatives with either o-nitrobenzyl (ONB) ester or ONB ether photolabile side chains with n-octyl substituents. Light-induced cleavage of these ONB side chains with ultraviolet light at 365 nm cleaves the octyl chains responsible for solubilization of the polymers away from the conjugated main chains, rendering them insoluble. Consistent with the accepted mechanism of ONB photolysis, those structural modifications that would yield a more stable benzylic radical methyl substitution on the benzylic position, replacement of the ester with an ether, or bothyielded more efficient photolyses as determined by (i) quantum yields of photolysis of ONB-substituted terthiophenes, and (ii) the percentage of polymer that persists in UV-irradiated thin films upon rinsing with chloroform. These polymers behave as negative-tone photoresists, enabling both direct photopatterning of conjugated polymers, and fabrication of multilayer conjugated polymer films by irradiating with UV light after each spin-casting step. Although hole-mobility values of these polymers in thin film transistors were only ∼10 −5 cm 2 V −1 s −1 , photolysis and rinsing did not cause significant degradation in performance.

This letter describes thiophene-based materials that undergo photoinduced aggregation or precipitation upon irradiation with UV light. The only solubilizing side chains on these materials are photocleavable by connection through photolabile nitrobenzyl esters. While quaterthiophene oligomers yield diacids that remain soluble in dichloromethane at micromolar concentrations upon exposure to ultraviolet light, the polymeric analog shows both red-shifted absorbance and heavily quenched fluorescence, consistent with aggregation due to photochemical cleavage of solubilizing alkyl chains. Thin films of this polymer also resisted dissolution in organic solvent upon irradiation, suggesting applicability in the construction of multilayer solid-state devices.