Evaluation of hydroxyl terminated polybutadiene‐isophorone diisocyanate gel formation during crosslinking process

Abstract

Crosslinking reaction of hydroxyl-terminated polybutadiene (HTPB)/isophorone di-isocyanate (IPDI) was monitored by infrared spectroscopy, dynamic mechanical analysis (DMA), swelling measurements, and by relaxation time (T 2 ) measurements obtained by low-field NMR technique. Chemical reaction monitored by FTIR shows that urethane bonds were predominantly formed throughout the whole reaction period while DMA and swelling became only effective once the three-dimensional network was formed. NMR results allow differentiating between relaxation-processes associated with different fractions of the reactants in the mixture prior to the network formation. The most important finding in this study is that two of the relaxation processes were found to decline whereas a new fraction with a short relaxation time which emerged specifically at an early stage of reaction and progressed along with advancement of the reaction. All results pointed out to a change in the mixture behavior around 30 h of crosslinking reaction at 60 C, reflecting an important restriction in molecules diffusion and mobilities which were attributed to the gel point formation.

Biocomposites From Switchgrass and Lignin Hybrid and Poly(butylene succinate) Bioplastic: Studies on Reactive Compatibilization and Performance Evaluation

“…Broad COC stretching peaks appear at 1 040–1 060 cm −1 which indicate the presence of ether groups (from lignin) in the composite materials . No characteristic peak for the NCO (isocyanate) group at 2 260 cm −1 appears in the spectra of composites which indicate a complete reaction of isocyanate groups into urethane functionality. As NH stretching appears at 3 500–3 300 cm −1 overlapping with hydrogen bonded OH stretching peaks, it is difficult to identify them in this region.…”

Plasticizer effect on network structure and hydrolytic degradation

“…Hence, T 1 and T 2 decrease when the crosslink density of the system increases [32,33], whereas they are shown to increase with the chain flexibility and mobility [33].…”

Designing a Highly Energetic PCL-GAP-PCL-based PU Elastomer; Investigation of the Effect of Plasticizers on Its Properties

“…PUEs are formed from soft segment and hard segment sequences. The soft segments are derived from a polyol, while the hard segments are derived from a di-isocyanate and a chain extender [5]. PUEs may be modified by various methods, such as using specific di-isocyanates, polyols and chain extenders, to provide new features.…”