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Studies of the molecular dynamics in polyurethane networks with hyperbranched crosslinkers of different coordination numbers
Author(s) -
Czech Przemyslaw,
Okrasa Lidia,
Ulanski Jacek,
Boiteux Gisele,
Mechin Francoise,
Cassagnau Philippe
Publication year - 2007
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.26106
Subject(s) - polyurethane , trimethylolpropane , differential scanning calorimetry , polymer chemistry , materials science , relaxation (psychology) , glass transition , hydrogen bond , rheology , molecular dynamics , melting point , polyester , dielectric , atmospheric temperature range , chemical engineering , polymer , molecule , chemistry , composite material , thermodynamics , organic chemistry , computational chemistry , psychology , social psychology , physics , optoelectronics , engineering
Several new polyurethane networks based on hyperbranched polyesters (trade name Boltorn) were synthesized to investigate the influence of the hyperbranched crosslinking agent on the molecular dynamics of the linear segments containing urethane groups. For comparison, linear polyurethanes as well as polyurethanes crosslinked with the classical crosslinker trimethylolpropane were prepared. Broadband dielectric spectroscopy, dynamic mechanical analysis, and differential scanning calorimetry yielded consistent results concerning the molecular relaxation processes; however, dielectric spectroscopy appeared to be more sensitive concerning the secondary relaxation processes. In the temperature range up to 150°C, the molecular relaxations were very similar in all the investigated samples, despite considerable structural differences. The weak influence of the crosslinking on the molecular properties could be explained by the existence of hydrogen bonds forming a physical network, which was very dense in this temperature range in comparison with the chemical crosslinks and therefore dominated the molecular mobility in all the investigated systems. This hypothesis was confirmed by rheological measurements performed at temperatures above 150°C, when the hydrogen bonds should be thermally destroyed. At these temperatures, the effect of crosslinking was manifested by a strong shift of the flowing point: in the linear polyurethanes, this point occurred at much higher frequencies (and lower temperatures) than in the crosslinked analogues. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 105: 89–98, 2007