Photocurable polythiol based (meth)acrylate resins stabilization: New powerful stabilizers and stabilization systems

Industry: Other
Z. Belbakra
Radical photopolymerized (meth)acrylate systems provide rapid cure on demand which is a particular processing advantage of thermosets. However (meth)acrylates are generally known to shrink when cured by UV light and to provide photocured materials with limited thermo-mechanical properties balance due partly to their relatively low functional group conversion. Other disadvantages related to photocured (meth)acrylate systems such as yellowing and surface tackiness (due to oxygen inhibition) are to be taken into account when developing new system, especially for visual and tactile applications [1–4]. Photopolymerized thiol-enes provide an excellent solution to the above mentioned problems. In fact, some articles have shown that thiol-ene photopolymerization suffers much less from the oxygen inhibition and showed an enhanced photoreactivity. Those effects are attributed to the generation of thiyl radicals which have a poor sensitivity toward the oxygen inhibition [5–8]. This advantage of thiol-ene systems goes along with other benefits as the formation of highly cross-linked polymer networks which could be formed with high functional group conversion, high polymerization rate and with lower shrinkage than conventional (meth)acrylate polymerization systems [9–14]. Thiol-ene application are used for different applications as dental resins, photo-curable coatings, adhesives, photoresists, ceramic materials for MEMS and microfluidic device, adhesives, optical components, and stereolithography as instance [5,15–22].

However, despite of all these advantages, one important drawback is limiting the use of thiol-ene chemistry. The dark premature polymerization giving rise to reduced pot-life of the thiol-ene resins is the main issue. Several solutions were proposed to overcome this difficulty but they are still not satisfactory because of their insufficient stabilization performance. In the present paper it is attempted to investigate other systems from which efficient stabilization of thiol-enes and more particularly of thiol-(meth)acrylate based resins at the level of industry requirement is likely to stem. Some stabilizers are selected according to a specific analysis of the state of the art results on the thiol-ene resins stabilization in particular and oxidation stabilizers in general. All the investigated stabilizers have different molecular functions and do not act according to the same mechanism. Therefore, synergies between different types of stabilizers are of course in the scope of the present work. The selected stabilizers and stabilization systems are then tested over a polythiol-(meth)acrylate based resin (TMBR) and the stabilization results are discussed. Finally, the impact of the most efficient selected stabilizers on the photoreactivity of the photocurable TMBR and on the thermo-mechanical properties of the photocured TMBR will be discussed.
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Contents:  13 pages