| Due to excellent performance of environment and waterborne polyurethane acrylate resin has received much concern.Relative to mono-functional resin,the multi-functional acrylate polyurethane overcome the shortages of slow curing rate and the weak hardness.Pentaerythritol triacrylate is one of important diluent and reactive monomer for preparation of multifunctional polyurethane acrylate.Currently,the traditional method for synthesize and later processing of pentaerythritol triacrylate is fussy and environmental unfriendly.Therefore,it is prospect to develop the environmental friendly technology for preparation process of pentaerythritol triacrylate and the waterborne UV-curable polyurethane acrylate with high performance.In this paper,the preparation of pentaerythritol triacrylate has been explored;and the esterification process directly from acrylic acid with pentaerythritol was selected to be main object.The effects of catalyst type and dosage,the molar ratio of acrylic acid to pentaerythritol and other reaction condition on the conversion of esterification have been investigated.The modification on the later processing has been made to the current method.Because p-vinyl benzene sulfonic acid can be UV cured and the sodium salt of p-vinyl benzene sulfonic acid and the polymer are a kind of surfactants,the p-vinyl benzene sulfonic acid has been used to promote the esterification of acrylic acid with pentaerythritol to produce pentaerythritol acrylates with different content of hydroxyl group,then the acrylatesdirectly reacted with NCO terminated polyurethane prepolymer formatted by reaction of isophorone diisocyanate with polyethylene glycol.The UV-curable waterborne polyurethane acrylates were prepared by alkalization of polyurethane acrylates.The obtained products were characterized by FT-IR and ~1H NMR.The effect of temperature,dosage of the p-vinyl sulfonic acid,the molar ratio of acrylic acid to pentaerythritol,the length of flexible chain,and other factors on esterification and the performance of UV-curable resin were evaluated.At molar ratio of acid to alcohol being 3 and 115~120℃for 2.5 h,the conversion of esterification of pentaerythritol with acrylic acid reached up to 97%using 4 wt%p-vinyl benzene sulfonic acid as catalyst and 40 wt%of toluene as water-carrying agent.The esterification of pentaerythritol with acrylic acid generates the pentaerythritol acrylates mixture,which contains pentaerythritol mono-acrylate,di-acrylate,tri-acrylate and tetra-acylate.The distribution of the different acrylate depends on the molar ratio of pentaerythritol to acrylic acid.At the molar ratio of acrylic acid to pentaerythritol in the range of 2.9~3.5,the mass fraction of pentaerythritol mono-acrylate and pentaerythritol di-acrylate decline with increase of molar ratio,while the mass fraction of pentaerythritol tri-acrylate risings first,and then decline,the mass fraction of pentaerythritol tetra-acrylate risings.At the molar ratio of acrylic acid to pentaerythritol being 3,the content of pentaerythritol tri-acrylate is highest to 61.2 wt%,and the weight content of mono-acrylate,di-acrylate,and tetra-acylate are 3.8 wt%,10.8 wt%,and 24.2 wt%,respectively.The pentaerythritol acrylate resin with weight content of mono,di,tri,and tetra-acylate being 1.7,6.9,46.2 and 45.2wt%,which is coming from the esterification of pentaerythritol with acrylic acid at molar ratio of 3.2 under promotion of 4 wt%p-vinyl benzene sulfonic acid,reacted with the-NCO terminated polyurethane prepolymer with PEG-600 as soft segment to produce polyurethane acrylate.The so prepared polyurethane acrylate was neutralized with the alkali solution to give the waterborne polyurethane acrylate.The prescription of UV glue was of 82 wt%WPUA,15 wt%HDDA and 3 wt%1173.At film thickness of 100~150μm,the comprehensive performance of cured film was the best.The hardness and the flexibility of film were 5H was 0.5 mm,respectively. |
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