Synthesis and dissociation of amine‐blocked diisocyanates and polyurethane prepolymers

Abstract

Substituted N‐methylanilines are shown to act as blocking agents for toluenediisocyanate. N‐methylaniline‐, N‐methyl‐p‐anisidine‐ and N‐methyl‐p‐nitroaniline‐blocked toluene diisocyanates have been prepared and characterized by FTIR, 1H NMR and 13C NMR spectroscopies, and nitrogen content analysis. A new method for determining the minimum deblocking temperature of the blocked isocyanate is described. The method has advantages in that it can be used to find the minimum deblocking temperature of even non‐volatile blocking agents. The minimum deblocking temperature of the adducts is found to be in the following order: N‐methyl‐p‐anisidine–TDI adduct < N‐methyaniline–TDI adduct < N‐methyl‐p‐nitroaniline–TDI adduct. The anilines exhibit the same trend when they block a polyurethane prepolymer prepared using polypropylene glycol of molecular weight 2000 g mol−1 and tolylene‐2,6‐diisocyanate. The deblocking temperatures are lower in the case of blocked prepolymers than in the blocked adducts. The blocked adducts and prepolymers are reacted with pyromellitic dianhydride (PMDA) in dimethylpropylene urea (DMPU) and the evolution of carbon dioxide is monitored to study the completion of imidization. The reaction time is in accordance with the deblocking ability of the adducts. The regeneration of the blocking agent is confirmed by gas chromatography. © 2002 Society of Chemical Industry

On the Versatility of Urethane/Urea Bonds: Reversibility, Blocked Isocyanate, and Non-isocyanate Polyurethane

“…158 Similar compounds were heated with pyromellitic dianhydride (43, Scheme 38) by TGA and in that case, the deblocking temperature increased as 40 > 37 > 41. 174 As predicted by the proposed mechanism (Scheme 37), the electron-withdrawing groups (phenyl, naphthyl group attached on the nitrogen atom, or nitro group on the aromatic ring) drain the electrons from the nitrogen atom hindering the hydrogen abstraction. Conversely, the electron-releasing groups such as methyl and nitro group strengthen the electron density on nitrogen and so enhance the autocatalytic effect.…”

Properties and morphology of interpenetrating polymer networks based on poly(urethane-imide) and epoxy resin

“…The disappearance of IR absorption peak for the isocyanate groups (2270 cm -1 ) was used to ascertain the Table I completion of the reaction. 18 From the Figure 2(a), it can be clearly seen that there is a strong sharp peak at 2270 cm -1 in the curve before cured, while after completely cured, this above peak has disappeared suggesting the formation of grafted epoxy-poly(urethane-imide) IPN. In addition, the strong IR absorbance at 1780 and 1830 cm -1 in the Figure 2(b) proves the imides segments were successfully introduced into the IPN.…”

Preparation of carbon nanotube and polyurethane‐imide hybrid composites by sol–gel reaction

“…Considering Table , by addition of CNTS, thermal characteristics (char residue and maximum degradation temperature) were improved for all the hybrid composites. Also, by using heterocyclic imide structure as the chain extender, char residue and T max increased more than the hybrid composites formed from BD as chain extender .…”