Fluorescence Monitoring of Cationic Photopolymerizations: Divinyl Ether Polymerizations Photosensitized by Anthracene Derivatives

Abstract

Cationic photopolymerizations of vinyl ethers were investigated using in situ, time-resolved fluorescence spectroscopy. Due to its short intrinsic time scale, fluorescence spectroscopy provides a means to characterize these polymerizations which are too rapid to be monitored by traditional methods. The fluorescence intensity of the photosensitizer (anthracene or its derivatives) was monitored as a function of time with spectra collected in intervals as short as 2 ms. An observed reduction in fluorescence intensity was attributed to consumption of the photosensitizer, providing a means to monitor the production of active cationic centers. The reaction rate increased as the initiator or photosensitizer concentrations were increased. Also, reactions photosensitized by anthracene and 9,10-dimethylanthracene produced the fastest rates, followed by 9-vinylanthracene. The polymerization rate for 9,10-diphenylanthracene was considerably slower due to steric hindrance or resonance effects. These results illustrate the tremendous potential of in situ, timeresolved fluorescence spectroscopy for monitoring polymerizations.

UV‐initiated free radical and cationic photopolymerizations of acrylate/epoxide and acrylate/vinyl ether hybrid systems with and without photosensitizer

“…This interpretation is supported by the observation that this postreaction did not occur near the bottom of the samples. 5,14 In comparing reactivity, as expected, the RS exhibited a shorter induction time (which is related to the efficiency of the photoinitiator) and a lower peak maximum as well as higher R p,max than did the CS, which implies that the polymerization reactivity of the RS is much faster than that of the CS. The HSs were also shown to polymerize faster than the CS.…”

“…The better performance of formulations HS1-P and HS2-P is due to photosensitization: the efficiency of the photoinitiator was improved to give more active species. 5 This photosensitization occurs via an excited state complex (exciplex) as a result of a direct interaction between an excited state of a photosensitizer and the photoinitiator and proceeds by an energy-or electron-transfer mechanism to form a radical cation that is capable of initiating free radical and cationic photopolymerizations. 14 -16,20,21 In general, thioxanthones have been used to photosensitize both free radical and cationic photopolymerizations.…”

“…However, acrylates are relatively volatile, inhibited by oxygen, have an unpleasant odor, exhibit high viscosities, and present potential health hazards, including carcinogenicity. [5][6][7] Therefore, acrylate monomers are being substituted in many formulations by vinyl ethers (VEs). The main advantages of using VE with acrylate are lower odor and skin irritancy, without sacrificing cure speed relative to the common acrylate monomers.…”

Evaluation of the curing process of UV resins in a 1,1,1,3,3-pentafluoropropane gas environment by photo differential scanning calorimetry and Fourier transform infrared spectroscopy

“…9 The curing of radical UV-curable resins is usually more rapid than that of cationic UV-curable resins 10 but the former is inhibited by oxygen, 11,12 while the latter is not. 9 The curing of radical UV-curable resins is usually more rapid than that of cationic UV-curable resins 10 but the former is inhibited by oxygen, 11,12 while the latter is not.…”

Development and characterization of novel photopolymerizable formulations for stereolithography

“…Moreover, cationic polymerization kinetics are complex and strongly affected by resin formulation. Therefore, a simple, coherent, kinetic expression of general validity, as those proposed for many thermoanalytical data [5], is not available for cationic polymerizations [6]. In order to combine the advantages of both kinds of resins, limiting their disadvantages, novel photopolymerizable formulations for SL, based on a dual kinetic mechanism, radical and cationic, are proposed and characterized.…”