| Abstrakt: |
An attempt was made to clarify the mechanism of the reactions of acetone with propylenediamine (PDA) or ethylenediamine (EDA) for direct synthesis of poly(urethane-urea) (DSPUU reaction) by using the reaction products (masked diamines) and an isocyanate-terminated prepolymer. In the masking reaction of acetone with PDA at 40°C, 1-(N-isopropylidene)propanediamine (1), 2-(N-isopropylidene)propanediamine (1'), 2,2-dimethyl-4-methylimidazolidine (3) as main product, N,N'-diisopropylidenepropylenediamine (2) were formed in this order due to the dominant rate (k30=3.0 kg mol-1min-1) of the water-catalyzed reaction to form (3) in addition to the slow rate (k20=3.2×10-3kg mol-1min-1) of (2). The concentration of (1') remained lower than (1) because of the steric hindrance of the methyl group of the former. The formation reactions of (1) and (2) were more acid-catalyzed than the reverse reactions, leading to shorter equilibrated time and larger molar fractions of these compounds. The reaction profiles for acetone-EDA were analogous except for lower molar fraction of 2,2-dimethylimidazolidine (6) and larger N,N'-diisopropylideneethylenediamine. The rates of demasking reactions which are of importance in DSPUU reactions using masked EDAs were as follows; (i) the water- and acid-catalyzed ring opening reaction rate of (6), k-30and k-3=1.43 and 0.26 kg mol-1min-1and (ii) the acid-catalyzed hydrolysis reaction rates of the ketimine groups, k-1=5.09 and k-2=3.13 kg2mol-2min-1, respectively. |
