Study On Synthesis And Modification Of UV-cured Polyurethane Acrylate Films

Ultraviolet (UV) curing technology could be used to synthesize high performance vanish coatings because of its rapid prototyping, easy precessing, energy saving, environmental friendly and suitable for large scaled industrial production. In UV-curable coating field, cycloaliphatie polyurethane acrylate (CPUA) oligomer is an important UV-curable resin, which combines advantages of polyurethane and polyacrylate and has good adhesion, flexibility, wear resistance and low temperature resistance. Phenyl group is substituted by cyclohexyl group in its molecule, improving etiolation resistance and weather resistance of its UV-cured film. In this dissertation the effects of four soft segment polyether diols polyethylene glycol1000(PEG1000), polyoxytetramethylene glycol1000(PTMG1000), polypropylene glycol1000(PPG1000), polypropylene glycol2000(PPG2000) on the properties of alicyclic polyurethane acrylate films were discussed, and cycloaliphatic polyurethane acrylate/cycloaliphatic epoxy acrylate(CEA) UV-cured blend films, cycloaliphatic polyurethane acrylate (CPUA)/cycloaliphatic epoxy resin (CER) UV-cured blend films and cycloaliphatic polyurethane acrylate (CPUA)/cycloaliphatic epoxy resin (CER)/small molecular weight silicon-containind acrylate KH570UV-cured blend films were prepared on the basis of polyether cycloaliphatic polyurethane acrylate with the best overall properties, and the relationships between micro-morphologies, phase structures and thermal stabilities, mechanical properties, apparent properties of the UV-cured blend films were investigated. In addition, dynamic genesises and phase separation behaviors of Interpenetrating Polymer Network (IPN) system UTC-3prepared by free-radical/cationic hybrid UV curing technique were carefully analyzed. The main research works and conclusions are as follows:1. Four different cycloaliphatic polyether polyurethane acrylate UV-cured films CPUA-1, CPUA-2, CPUA-3and CPUA-4were prepared by using isophorone diisocyanate (IPDI) and hydroxyethyl methacrylate (HEMA) as hard segments and polyether diols PEG1000, PTMG1000, PPG1000and PPG2000as soft segments, respectively. Most of their properies were not obviously different, in which CPUA-1UV-cured film had better pencil hardness due to the regular chain structure and good crystallinity of PEG1000molecule, while higher viscosity, and poor wash-resistant due to its higher content of ether bonds; UV-cured film CPUA-3showed the best comprehensive properties especially lower viscosity of its oligomer because PPG1000molecule with side methyl groups reduced the crystallinity of UV-cured film, more suitable for large scale industrial production. According to the analyses of relationship between molecular structure of polyether diols and the properties of corresponding polyurethane acrylates UV-cured films, the content and structure of soft segment could be considered as determined important factors:the softer the soft segment, the easier the crystallization, the better the hardness and heat resistance; the greater molecular weight of soft segment, the lower content of hard segment, the poor hardness.2. In cycloaliphatic polyurethane acrylate and cycloaliphatic epoxy acrylate modified blend UV-cured films, CPUA-3, CEA and reactive diluent TMPTMA with excellent compatibility, copolymerized with each other by free-radical mechnism, surffering no obvious phase separation. Scanning Electron Microscope (SEM) pictures showed the cross section of film UEAT-2(the mass ratio of CPUA-3, CEA and TMPTMA is30:20:50), prepared by liquid nitrogen quenching, presented long fault zones, smooth fault surface, indicatng good flexibility of the film. Moreover, the film had the best comprehensive properties with good pencil hardness, pendulum hardness, tensile properties and heat resistance and smooth surface without defects.3. In cycloaliphatic polyurethane acrylate and cycloaliphatic epoxy resin modified blend UV-curable systems, cycloaliphatic urethane acrylate CPUA-3, the alicyclic epoxy resin CER and reactive diluent trimethylolpropane triacrylate (TMPTMA) had good compatibility. During the UV curing process, CPUA-3and TMPTMA reacted via free-radical copolymerization with relatively higher polymerization rate; CER was polymerized via cationic photopolymerization with relatively lower polymerization rate. Two different types of photo-polymerization initiated micro-phase separation, and the system exhibited an obvious two-phase structure. When the weight percentages of CER were in the range from50%to70%, the two phases formed into IPN structures. UV-cured film UTC-3(the mass ratio of CPUA-3, TMPTMA and CER was15:15:70) with IPN structure exhibited the best overall performance, including better mechanical properties, thermal stability and surface properties, because of synergistic effect of the dual-phase polymers. There were a lot of hydrogen bonds between the two cross-linked network polymer molecular chains, leading to good compatibility between the two phases, which was proved by the performance of Dynamic Thermomechanical Analysis (DMA) curve with a single peak situation.4. In the free-radical/cationic modified blend UV-curable systems initiated by photopolymerization-induced phase separation, Differential Scanning Calorimetry (DSC) curves of the unreacted systems, corresponding glass transition temperature Tg, viscous flow temperature Tf and initial polymerization temperature Ti were investigated, and temperature change phase diagram of the blend systems was established. With the increase of CER content, the phase structures went through three stages:sea-islands structure (â… ), bicontinuous structure and sea-islands structure (â…¡). Due to the different viscosity of CPUA and CER, the phase transition process was asymmetry. The UV-cured IPN film UTC-3with best properties was considered as the research object and SEM photos was used to track evolution of phase separation process of UTC-3blend system which was changed with time. It was found that the phase separation behavior of CPUA-3/TMPTMA/CER blend system was affected by the modulus, viscosity, curing reaction rates of two phase polymers. Based on the above analysis of the free-radical/cationic UV curing induced phase separation process, a triangle metastable phase diagram was established, and a conclusion was proposed that the phase separation process of free-radical/cationic UV-curable system was divided into several stages:starting phase separation, UV-curable free-radical photo-polymeric dominant period, modulus controlled phase separation period of UV-curable free-radical/cationic co-photopolymerization, UV-curable cationic photo-polymeric dominant period, phase separation termination.5. In UV-curable UTC-3and a small molecule silicon-containing acrylate KH570modified blend UV-curable systems, KH570had certain compatibility with UTC-3modified system. When mass percentage of KH570is less than1.0wt.%o, four components could be miscible with each other. The introduction of additive KH570with single double bond decreased the density of cross-linked networks, provided flowing space for photo-initiators, oligomers and unreacted monomers, accelerated the polymerization rate of free-radical/cationic hybrid curing systems, and increased the final conversions. As observed in SEM images, microstructure of UV-cured IPN film became complicated structures containing a large number of holes and gaps, which was attributed to the steric effect of KH570. However, with the increase of the content of KH570, hydrogen bond effect between molecules was dominant, and the cross section become smooth and contact. Compared with the UTC-3UV-cured film, the mechanical properties of UTC-3/KH570blend UV-cured systems were decreased, while breaking elongation was increased, damping properties and thermal stability has obviously been improved, wetting resistance was also improved. Furthermore, as shown in the Atomic Force Microscope (AFM) images and X-ray Photoelectron Spectroscopy (XPS) spectra, the content of KH570on the surface of UTC-3UV-cured film was much higher than the addition ratio to the unreactive systems, indicating that the migration phenomenon during photopolymerization process, and the bulk density was lower than the density of UV-cured film surface.