Synthesis And Properties Of UV-curable PCL Polyurethane Acrylate

In this paper,polycaprolactone（PCL）diol was synthesized by addition reaction.Polyurethane acrylate（PUA）was synthesized by bulk method and used as oligomer to prepare UV light-curable coating.The research content and results of the paper are as follows:（1）Using hydroquinone bis（2-hydroxyethyl）ether（HQEE）andε-caprolactone as raw materials,polycaprolactone（PCL）diol was synthesized by addition polymerization.The effects of catalyst types,reaction temperature and reaction time on the molecular weight of the synthesized product and its distribution were investigated.The results showed that the obtained PCL-diol can reach the designed molecular weight of 882 and has a narrow molecular weight distribution of 1.28 when the reaction time was 5 hours,the reaction temperature was 150°C,and the catalyst organic bismuth dosage was 0.1%（the mass fraction ofε-caprolactone）;The results of FT-IR analysis showed that the carbonyl absorption peak ofε-caprolactone shifted from 1722 cm^-1 to 1732 cm^-1,indicating that the ring-opening reaction between HQEE andε-caprolactone had occurred;The results of ¹H-NMR analysis showed that 3.95 ppm belonged to the methylene proton absorption peak connected to the ether bond of PCL,and 2.20 ppm belonged to the methylene proton absorption peak that PCL connected to the carbonyl of the main chain,which also indicated thatε-caprolactone reacted with the hydroxyl group of HQEE;The results of ¹³C-NMR analysis showed that the resonance absorption peak at 173.42 ppm was attributed to the carbonyl carbon on the PCL chain,and the resonance absorption peak at 63.99 ppm was attributed to the resonance absorption peak of connecting oxygen and methylene carbon,which were consistent with the analysis results of FT-IR and ¹H-NMR;The results of DSC analysis showed that with the increase of the molecular weight of PCL-diol,the melting point gradually increased from 36℃to 36.8℃,and the enthalpy value also increased.（2）Using the PCL-diol obtained above,isophorone diisocyanate（IPDI）and hydroxyethyl acrylate（HEA）as raw materials,and dibutyltin laurate as a catalyst,PUA was synthesized by adopting the method of first capping and then chain extension.The effects of catalyst dosage and reaction temperature on the synthesis process were investigated.The results showed that,when the reaction temperature of the first step was 55°C,the reaction time was 240 min（including the dropwise addition time of 90 min）,and the amount of catalyst was 0.05%（mass fraction of end-capping agent）;The reaction temperature of the second step was 65°C,the catalyst dosage was 0.05%（the mass fraction of chain extender）,and the reaction time was 300 min（including the dropwise addition time of 90 min）,The molecular weight of the synthesized urethane acrylate was consistent with the theoretical value and had a narrow molecular weight distribution;The results of FT-IR analysis showed that the characteristic peak of NCO at 2240～2275cm^-1disappeared,indicating that the NCO group had completely reacted;The results of ¹H-NMR analysis showed that the proton absorption peak at 6.32 ppm was attributed to the secondary amino bond,indicating that the NCO group in the reactant reacted with the hydroxyl group;The results of ¹³C-NMR analysis showed that the resonance absorption peak at 152.95ppm was attributed to the carbonyl carbon attached to the secondary amino group,indicating that the NCO group and the hydroxyl group in the reactants had reacted,which were consistent with the analysis results of FT-IR and ¹H-NMR;The results of DSC analysis showed that with the increasing molecular weight of PUA,the melting point gradually increased from 41.49℃to 47.77℃,and the enthalpy value also increased.（3）Using the above PUA as the UV light-curing oligomer,the formulation of the UV light-curing coating was optimized,and the optimized coating formulation was obtained:45 parts of PUA oligomer,5 parts of epoxy acrylate,36 parts of reactive diluent 1,6-Hexylene glycol diacrylate（HDDA）,10 parts reactive diluent trimethylolpropane triacrylate（TMPTA）,2 parts photoinitiator 2-hydroxy-2-methyl-1-phenylacetone（1173）,2 parts Photoinitiator methyl benzoylformate（MBF）;When using PCL-diol synthesized with HQEE,and urethane acrylate synthesized with IPDI and HEA as the PUA resin in the formula,excellent UV light curing experimental results could be obtained:Curing time was12s,hardness was 3H,and flexibility was 1.5mm,the abrasion resistance was0.028/g,the adhesion was grade 1,and the chemical resistance was excellent;The results of FT-IR analysis showed that the stretching vibration of the acrylate C=C double bond at 1633cm^-1and the out-of-plane bending vibration of CH on the CH=CH double bond near 814cm^-1 had disappeared,and the C=C double bond has disappeared.Effectively participate in the photocuring process,and the coating film was completely cured;SEM results showed that the surface of the cured film was smooth and dense.