Study on novel heat-resistant aqueous dispersion based on modified poly(phthalazinone ether nitrile ketone)s

Abstract

Poly(phthalazione ether nitrile ketone)s (PPENK), modified with NaOH, were studied in order to find a hydrophilic resin with could be used in heat-resistant water-borne coatings. The properties of hydrolysates — HPPENKa (0.5 hours), HPPENKb (1.5 hours) and HPPENKc (3.5 hours) — were measured by differential scanning calorimetry (DSC), thermo-gravimetric analysis (TGA), contract angle (water) and solubility. The structures of the hydrolysates were confirmed by FIIR (Fourier transform infrared spectroscopy) and1H-NMR. The results indicated that the conversion ration of the nitrile groups and the glass transition temperature (79) of the hydrolysates increased, whereas the weight loss ratio of HPPENK decreased as the hydrolysis time was prolonged As expected, the hydrophificity of HPPENK improved greatly (eg when the CN conversion ratio was 93.82%, and the water contact angles decreased from 75.3° for PPENK to 54.4° for HPPENK). By studying the effects of the different reactions of the co-solvents, the reaction temperature and the NaOH concentration on the hydrolysis, it could be concluded that the optimal synthetic technology was of a 6M NaOH solution with DMAc (N,N-dimethylacetamide) as co-solvent at 120°C. Aqueous dispersions based on three modified resins were prepared and their storage stability was as follows: HPPENKc >HPPENKb>HPPENKa. In particular, the HPPENKc dispersion had no settling for more than 30 days and provided good film-forming. The cured film properties of HPPENKc were as follows: pencil rigidity (six hours), thermal impact resistance (300°C, 24 hours), and adhesion (grade 1). Curing agents were applied to the dispersion, such as hexamethoxymethyl melamine (HMMM), epichlorohydrin (ECH), triethanolamine, and glycerol, etc. HMMM and ECH provided excellent curing properties. The co-operating emulsification of (Span) sorbate and (Tween) polyoxyethylene sorbate could improve the stability of the HPPENK dispersion.