| UV-curing technology has been widely applied in coating, ink and adhesive due to its high efficiency, energy saving and environmental friendly. Nevertheless, there are some disadvantages in UV-curing process. Photoinitiator is usually excessively added into the UV-curing formulation to deal with the ubiquitous oxygen inhibition to polymerization, and the residual conventional photoinitiator trapped in the polymer network would generally jeopardize the weather-resistance and health assurance of the cured materials. The aromatic aldehyde possibly generated from the photolysis of photoinitiator usually leads to odor. The problems aforementioned could be overcome with macromolecular or polymeric photoinitiator in previous report. In the work, a kind of photosensitive cross-linked polyurethane microspheres, free of traditional photoinitiation moieties, was prepare dexploratively through the emulsified Michael’s addition of diethylene glycol diacetoacetate (DEDAA) with multi-functional polyurethane acrylate including polyurethane diacrylate (2FPUA), polyurethane triacrylate (3FPUA) and polyurethane hexa-acrylate (6FPUA). The obtained polyurethane microspheres bearing with photosentive dicarbonyl substituted quaternary carbon moiety could be employed as swollen microparticle photoinitiator as well as polymer filler to improve the performance of UV-cured materials.In the paper, the researches mainly include three parts:1. DEDAA, a crosslinking agent used to prepare photosensitive polyurethane microspheres, was produced through transesterification with the aid of microwave enhancement, and then identified with1H NMR and LC-MS.2. An amphiphilic diblocked copolymer to be used as macromolecular emulsifier was prepared with addition-fragmentation chain transfer (RAFT) living/controlled radical polymerization. Another amphiphilic oligomer to be employed as co-emulsifier was also synthesized via the reaction of diisocyanate and Span-80. In the firstly proposed non-aqueous emulsion polymerization for preparing polyurethane microspheres, both of the RAFT macromolecular emulsifier and the urethane modified Spane-80could not individually stabilize the polyurethane acrylate/DEDAA dispersion in petroleum ether. With the combination of the two synthesized emulsifiers, the Michael’s addition product could not be dispersed very well even though moderate dispersion was obtained in early stage. 3. In the secondary proposed conventional emulsion polymerization in water, three kinds of polyurethane acrylate with different functionality and DEDAA were used to prepare the photosensitive polyurethane microspheres with SDBS, Span-80and OP-10as the combinational emulsifier. The influences of emulsifier combination and its loading percentage on the reaction dispersion effect and photography were investigated. It was found that, for2FPUA Michael’s addition, the combined emulsifier of Span-80/SDBS (7/3) led moderate reaction dispersion in the dosage rang of40-60%, and dispersible polyurethane particle with diameter of60-100μm was produced in spite of being soft and viscous. For the3FPUA Michael’s addition, it was fail to get any stable dispersion with the combined emulsifier of Span-80/SDBS (7/3). However, dry-powder like and touch soft polyurethane microsphere (100-200μm) was finally obtained with the combined emulsifier of OP-10/SDBS (5/5) in50-60%loading. Due to rapid crosslinking, it was very difficult to get satisfied reaction dispersion for6FPUA Michael’s addition regardless of any emulsifier combination and loading percentage. The obtained dry powder was identified with FTIR and its swollen performance was tested with acrylic acid. It was showed that the swollen ratio could reach200%. The monomer inside the polyurethane microsphere could undergo photopolymerization upon UV exposure. |
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