A new crosslinker for polyurethane

DDP (N-［(1

1-dimethyl-2-acetyl)ethyl］-β-dihydroxyethylamino propanamide)

was synthesized by Michael reaction between diethanolamine (DEA) and diacetone acrylamide (DAAM).Self-crosslinkable aqueous polyurethane emulsion containing active keto groups was obtained using isophorone isocyanate (IPDI)

poly(tetramethylene oxide) (PTMG1000)

dimethylol propionic acid (DMPA) and trimethylol propane (TMP) as main materials

both dihydroxyketon N-［(1

1-dimethyl-2-acetyl)ethyl］-β-dihydroxyethylamino propanamide (DDP) and 1

4-butanediol (BDO) as chain expanders

γ-aminopropyltriethoxysilane (KH550) as end capping agent and then adipic acid dihydrazide (ADH) was added into the emulsion.The structures of the crosslinker DDP and films were characterized by ATR-FTIR and NMR.The tests results confirm the formation and reaction of DDP.The result of ATR-FTIR also shows that the crosslinking reaction between ketone group and the hydrazine group has happened during the film curing.The effects of n(—NHNH2)/n(—CO—)

n(NCO)/n(OH) and DDP content on the properties of the films were studied.The results show that

water absorption of polyurethane films without adipic dihydrazide(ADH) increases with the increase of DDP content; it is difficult to emulsify polyurethane polymer and the stability of the emulsion is deteriorated significantly in the case of n(NCO)/n(OH)﹥1.40.Under the optimal ratios (n(—NHNH2)/n(—CO—) = 1

n(NCO)/n(OH) = 1.40)

when DDP content increases from 0% to 7.22%

water absorption of the films decreases from 39.36% to 18.92% also with higher performance in solvent resistance

crosslinking degree increases from 51.49% to 90.23%

tensile strength increases from 20.09 MPa to 28.26 MPa

pencil hardness is 2H.Thermogravimetic analysis (TGA) indicates that the Ketone-Hydrazide crosslinking structure can improve thermal stability of the films.