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Formation of cross‐links during prepolymerisation reaction of methylene‐bis (4‐phenylisocyanate) with poly (tetramethyleneoxide) in N , N ‐Dimethylacetamide
Author(s) -
Kamide Kenji,
Hanahata Hiroyuki
Publication year - 1993
Publication title -
polymer international
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.592
H-Index - 105
eISSN - 1097-0126
pISSN - 0959-8103
DOI - 10.1002/pi.4990310204
Subject(s) - phenylisocyanate , biuret test , prepolymer , amidine , dimethylacetamide , chemistry , isocyanate , polymer chemistry , reaction mechanism , diborane , reaction rate , derivative (finance) , organic chemistry , urea , polyurethane , catalysis , solvent , financial economics , economics , boron
An attempt was made to investigate the cross‐linking reaction which occurs as a side reaction when an excess of methylene‐bis(4‐phenylisocyanate) (MDI) is reacted with polytetramethyleneoxide (PTMO) (number‐average molecular weight 2010) in N , N ‐dimethylacetamide (DMAc) prepolymerisation reaction) to give an isocyanate‐terminated prepolymer having urethane groups. Cross‐links existing in the prepolymer were shown to be of the biuret type by high performance liquid chromatography (HPLC) analysis on a product prepared by the raction of excess phenylisocyanate with n ‐butanol in DMAc. The biuret‐forming reaction, as well as the urethane reaction (i.e. the main reaction), is accelerated remarkably by an N , N ‐dimethyl‐ N '‐phenyl(phenylcarbamoyl)acetamidine derivative formed from a side reaction of MDI with DMAc, and the former reaction is suppressed dratically by neutralising the corresponding amidine with, for ecample, H 2 SO 4 . A novel kinetic model of the prepolymerisation reaction is proposed and reaction orders and rate constants are derived. Three heterocompetitive reactions are involved: (1) urethane groups formed from MDI with PRMOin the prepolymer, and subsequent formation of (2) biuret type cross‐links between isocyanates and urea groups formed from MDI with DMAc as a side reaction, and (3) the corresponding amidine derivative.