學 生：符昌中 指導老師：王振乾 老師

Introduction Waterborne polyurethanes (WPUs) have excellent mechanical properties and are environment-friendly. WPU resins have poor resistance against water and chemicals compared with the crosslinked two-pack solvent-based urethanes. A separate polymer could be incorporated to polyurethane to form a multiphase structure in the dispersions through various techniques such as blending, seeded emulsion polymerization.

Introduction Using epoxy resin to modify WPU can combine the advantages of both of these materials and results in improved film performance. Epoxy resin and a blocked NCO prepolymer were mixed to avoid the high viscosity of precrosslinked poly- urethane and the difficulty of emulsification. In this work, we explored a novel postcrosslinking method to form crosslinked polyurethane–epoxy hybrid emulsion.

Materials 2,4-Toluene diisocyanate (TDI, 80/20) Polyether diol (PED) with a molecular weight of 1000 Da(N210) Dimethylol propionic acid (DMPA) Epikote 1001 (hereinaftercalled type 1 epoxy)

Materials 1,4-Butanediol Diethylene triamine Acetone 1-methyl-2-pyrrolidone(NMP) Isopropanol Triethylamine (TEA)

Unmodified polyurethane dispersion TDI, PED, 1,4-butanediol,and DMPA/NMP 70 ℃ 3 h Isopropanol 40 ℃ Triethylamine Ethylene diamine The unmodified aqueous polyurethane dispersion was thus obtained. Neutralizing Chain extension Blocking agent ‚ ƒ

Epoxy resin-modified polyurethane dispersion Precrossinking TDI, PED,1,4-butanediol, and DMPA /NMP 70 ℃ 3 h ℃ 2-3 h Type 1 epoxy /NMP Isopropanol Triethylamine Neutralizing Primary diamines Chain extension An aqueous dispersion of polyurethane ionomer was thus obtained.  ‚ ƒ „ Blocking agent

Epoxy resin-modified polyurethane dispersion Postcrossinking TDI, PED,1,4-butanediol, and DMPA /NMP 70 ℃ 3 h  ‚ Isopropanol Blocking agent Type 1 epoxy /NMP 30 ℃ Triethylamine Neutralizing ƒ Diethylene triamine Chain extension 80 ℃ 2 h „ The crosslinked polyurethane–epoxy hybrid emulsion was thus obtained.

Results and discussion Fig. 2: IR spectra of emulsion before chain extension by amine Fig. 3: IR spectra of emulsion after chain extension by amine N–H stretching of polyurethane was shifted to 3294 cm -1. The band at 1745 cm -1 was C=O stretching of the urethane group. The band at 1223–1267 cm -1 corresponded to the stretching vibrations of C=O combined with NH. The absorption peaks of epoxy group and free isocyanate group at 917 and 2277 cm -1 vanished after chain extension in, which indicated that a chain extender reaction occured between the isocyanate group, epoxide groups, and amine chain extender. The bands at 1533–1539 cm -1 correspond to carbamate.

There were two endothermic peaks at about 100 and 150 ℃, which represented the epoxide group curing and the deblocking of isocyanate, respectively. Fig. 4,5: DSC thermogram of PUPE1,2(before chain-extension) Results and discussion

Fig. 6: DSC thermogram of PUPE3(after chain extension) Fig. 7: DSC thermogram of PUPE4(after chain extension) Fig. 8: DSC thermogram of PUPE4 cured at 180 ℃ for 2 h Results and discussion

Fig. 9: TEM images of (a) polyurethane emulsion, (b)emulsion prepared with precrosslinking, and (c) emulsion prepared with postcrosslinking Results and discussion

Since the crosslinking density of the films increased with an increase in epoxy content, the ratio of the rigid segment in resin was enhanced. Results and discussion

Conclusions The postcrosslinking method could improve the film performance and the emulsion stability, and did not result in increased viscosity of the prepolymer before phase inversion because the epoxy resin did not react with prepolymer. The type of amine chain extender significantly affected the stability of emulsion. The molar ratio of NH/NCO at 1:1 showed the best film performance, and the optimal reaction temperature of amine extending chain was around 80 ℃.