Premium
Cure‐reaction kinetics of amine‐blocked polyisocyanates with alcohol using hot‐stage Fourier transform infrared spectroscopy
Author(s) -
Sankar Govindarajan,
Nasar A. Sultan
Publication year - 2008
Publication title -
journal of applied polymer science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.575
H-Index - 166
eISSN - 1097-4628
pISSN - 0021-8995
DOI - 10.1002/app.28172
Subject(s) - chemistry , isocyanate , fourier transform infrared spectroscopy , polymer chemistry , kinetics , polyurethane , infrared spectroscopy , order of reaction , reaction rate constant , organic chemistry , chemical engineering , physics , quantum mechanics , engineering
Cure reaction between a series of N ‐methylaniline‐blocked polyisocyanates, based on 4,4′‐methylenebis(phenyl isocyanate), poly(tetrahydrofuran) and several substituted N ‐methylanilines, and n ‐decanol has been studied. The solid‐state isothermal cure reaction was carried out using hot‐stage FTIR spectroscopy, in the temperature range of 125–145°C. The urea carbonyl absorption band of blocked polyisocyanate moiety was used to monitor the conversion of blocked polyisocyanate into polyurethane. Kinetic and thermodynamic parameters were calculated using normalized conversion curves. The overall order of cure reaction, for each of the blocked polyisocyanates was found to be first order. Based on the results of kinetics and reaction conditions used in this study, the elimination‐addition (S N 1 ) mechanism was suggested for the cure reaction between N ‐methylaniline‐blocked polyisocyanates and n ‐decanol. The effect of substituents present in the blocking agents on the cure reaction of N ‐methylaniline‐blocked polyisocyanates was investigated and found that the cure reaction of N ‐methylaniline‐blocked polyisocyanates was retarded by electron‐donating substituents and facilitated by electron withdrawing substituents. The observed high negative entropy of activation value supports the formation of a four‐centered, intramolecularly hydrogen‐bonded ring structure during transition state of the cure reaction. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008