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Synthesis and Properties of Uv-Curable Polyurethane acrylate ...

By Theresa Brooks,2014-09-18 23:36
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Synthesis and Properties of Uv-Curable Polyurethane acrylate ...Synt

자외선 경화형 폴리우레탄 아크릴레이트 수지의 분리 팽윤현상

    전종호, 서종철, 조기윤, 한학수

    연세대학교 화학공학과

    Phase Separation and Swelling behavior of UV-Curable Polyurethane Acrylates

    Jongho Jeon, Jongchul Seo, Kiyun Cho, and Haksoo Han

    Dept. of Chem. Eng., Yonsei University

Introduction

    Polyurethanes are a unique class of polymers that have a wide range of applications because their properties can be readily modified by the variations of their component. Polyurethane materials possess very attractive bulk mechanical properties due to the presence of phase-separated structures. Conventionally, polyurethanes are extensively used as foams, coatings, adhesives, elastomers, and fibers. However, polyurethanes are prepared in organic solvent-based system, and these solvents are very expensive, and highly toxic. Therefore, many researchers study uv-curing system. The advantages of this uv-curing system include higher throughput, savings energy and reduced or eliminated solvent emission in comparison with solvent-based systems, since most formulations are 100% reactive oligomeric liquid and diluents. A uv-curable system is typically composed of reactive urethane oligomer, reactive diluents, and photoinitiator. Reactive urethane oligomer is the most important component in determining the ultimate physical properties of uv-cured coatings. Typically it is a segmented polyurethane oligomer tipped with acrylic functionality, combined with vinyl monomers, which are added to make harder products and to reduce the viscosity of the precursor liquid to obtain better processability.

    In this study, uv-curable polyurethane acrylates were prepared from poly(propylene glycol) (PPG), toluene diisocyanate (TDI), and 2-hydroxyethyl acrylate (HEA). Effects of molecular weight of polyol, chemical structure of reactive diluent and the contents of reactive diluent were studied in terms of thermal properties,

    solvent resistance, and morphological structure of cured films. The relationships between the soft-segment molecular weight and ultimate properties were also investigated as a function of reactive diluent and phase-separation.

Experimental

     Extra pure grade 2,4-toluene diisocyanate (TDI), 2-hydroxyethyl acrylate (HEA), benzophenone, and N-methyldiethanolamine (MDEA) were used without further purification. Various molecular weight polyols, poly(propylene glycol) were dried and degassed at 80?C and 1-2 mmHg pressure until no bubbling was observed. Molecular weight of polyol is from 725 to 4000. Four reactive diluents, 1-vinyl-2-pyrrolodinone (NVP), lauryl methacrylate (LMA), hydroxypropyl methacrylate (HPMA), and poly(ethylene glycol) diacrylate (PEGDA) were used as received.

     Uv-curable polyurethane acrylates were synthesized using a two-step reaction procedure. Polyol and diisocyanate (1:2 by mole) were charged into a 500 mL round-bottom flask equipped with a mechanical stirrer, thermometer, and condenser with drying tube. The urethane forming reaction proceeded at 90?C for 1

    hour, and the reaction mixture was cooled down to 40?C and HEA was added

    dropwise. NCO-terminated prepolymer with HEA was done for 3 hour below 45?C

    and for 0.5 hour at 60?C. Then the mixture of urethane acrylate, 1.4 wt%

    benzophenone, 1.4 wt% MDEA, and reactive diluent were heated to 90?C for 20

    minutes.

     Polyurethane acrylate films were prepared approximately 0.5-1.0 mm in thickness, and these samples were irradiated from both sides with 40 W-UV (365 nm) lamp for 3 min at room temperature.

     For the morphological structure of cured polyurethane acrylate films, wide-angle X-ray diffraction (WAXD) patterns were obtained by using a Rigaku horizontal X-ray diffraction apparatus with nickel-filtered radiation. The CuK radiation source ;

    (=1.54Å) was operated at 35kV and 40mA and all measurements were carried out

    -1/2 mode. Each sample (20?1 mg) was cooled to 123?C at 40?C min, and its DSC

    thermogram obtained over the range 123?C to 117?C (or 217?C), at a heating rate of

    -1-120?C min and a sensitivity of 5mcal sec and under a He purge. IR spectra was

    -1taken before and after u.v. irradiation using. The resolution was 2.0 cm. Swelling

    test of cured films was performed for various solvents (NMP, xylene, and

cyclohexanone) at room temperature for 24 hours.

Results and Discussion

     Morphology of uv-cured polyurethane acrylate films was measured as a function of reactive diluents, molecular weight of polyols. Increase in the molecular weight of the polyol allows greater phase separation, resulting in higher phase purity and lower T of the soft-segment phase. The glass transition temperature of the hard-g

    segment phase slightly decreased as the soft-segment molecular weight increase. With increasing soft-segment molecular weight, solvent resistance was decreased. With increasing reactive diluent amount, solvent resistance was increased.

Acknowledgment

     We would like to thank Mukunghwa industrial Co. for the financial support of this work.

References

    [1] B. K. Kim, S. H. Paik, J. Polym. Sci., Polym. Chem., 37, 2703 (1999) [2] K. Mitsunobu, K. S. Kirk Hwang, J. Mater. Sci., 17, 1447 (1982) [3] B. K. Kim, K. H. Lee, H. D. Kim, J. Appl. Polym. Sci., 60, 799 (1996) [4] T. A. Speckhard, K. K. S. Hwang, J. Appl. Polym. Sci., 30, 647 (1985) [5] S. Nakazato, T. Amari, T. Yamaoka, J. Appl. Polym. Sci., 38, 628 (1989)

    Swelling Ratio

    2 1.81.6 1.41.2L-RatioTDI-PPG 2000 system 1 RatioW-Ratio0.80.6 0.40.2 0

     T.P2000.L10T.P2000.L20 SampleT.P2000.L20(TEA)T.P2000.N10 Swelling RatioT.P2000.N20T.P2000.P10 1.6T.P2000.P201.4 1.21 L-RatioTDI-PPG 725 system 0.8RatioW-Ratio0.6 0.4 0.20

    T.P725.L10 SampleT.P725.L15T.P725.L20 Swelling RatioT.P725.N10T.P725.N20 3.5T.P725.P103T.P725.P20

    2.5 2L-RatioTDI-PPG 4000 system RatioW-Ratio1.5

    1

    0.5

    0

    T.P4000.L10T.P4000.L20T.P4000.N10SampleT.P4000.N20T.P4000.P10(opacity X)T.P4000.P20(opacity X)

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