ISSN:
1436-2449
Source:
Springer Online Journal Archives 1860-2000
Topics:
Chemistry and Pharmacology
,
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
,
Physics
Notes:
Summary If isocyanate groups are in excess networks prepared from poly(oxypropylene)triols (PPT) and 4,4′-diphenylmethanediisocyanate (MDI) in the presence of an organotin catalyst have higher values of the equilibrium modulus G and of the gel fraction wg compared with theoretical predictions in which only the formation of urethane bonds is considered. If however, the NCO groups in excess were reacted with monofunctional phenyl isocyanate keeping the molar ratio [OH]/[NCO]=1 constant, networks with a wide range of crosslinking density were obtained, for which the G and wg values were in a good accord with the theory. The probable cause of departures in the PPT-MDI systems with NCO groups in excess consists in the formation of allophanate groups. An analysis of the equilibrium elastic behaviour of these net-works has shown that the trapped entanglement contribution to the equilibrium modulus is likely to occur.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00264926
