| Abstract
| - FT-IR spectroscopy, synchrotron SAXS, and dynamic rheometry havebeen employed tomonitor, in-situ, structure development during the reactiveprocessing of model flexible polyurethanefoam systems. The following combinations of components wereinvestigated: (I) diisocyanate, polyetherpolyol, and water and (II) diisocyanate, polyether monol, and water.The formation of urethane, solubleurea, and hydrogen-bonded urea species during the fast bulkcopolymerization has been studied usingthe adiabatic reactor method and forced-adiabatic, time-resolved FT-IRspectroscopy. The decay ofisocyanate is correlated with the polymerization kinetics, and theevolution of hydrogen-bonded urea isanalyzed emphasizing the onset of microphase separation of urea hardsegment sequences. FT-IRspectroscopy indicated that the microphase separation transition (MST)occurred at a critical conversionof isocyanate functional groups and followed the kinetics associatedwith nucleation and growth. Thedynamics of microphase separation during the fast bulk copolymerizationhave also been investigatedemploying forced-adiabatic, time-resolved synchrotron SAXS experiments.Microphase separation wasobserved to occur at a critical conversion of isocyanate functionalgroups and is shown to follow the kineticsassociated with spinodal decomposition. Forced-adiabaticrheological measurements have been conductedduring the fast bulk copolymerization. Four main regions ofrheological development during the formationof polyurethane foam were identified. These were: (I) bubblenucleation, (II) liquid foam and microphaseseparation, (III) physical gelation, and (IV) foamed elastomer.The use of model systems demonstratedthat the presence of covalent cross-links delay the onset of microphaseseparation of the urea hard segmentsequence lengths. Although foam stability is not dependent uponthe formation of urethane covalentcross-links in the early part of the foaming reaction, molecularconnectivity between the microphases viaurethane covalent cross-links is an essential requirement with regardto long-term dimensional stabilityand the mechanical/physical properties of the foam.
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