Dening Wang

Hydrogen bonding and crystallization behaviour of segmented polyurethaneurea : effects of hard segment concentration

Abstract I.r. spectroscopy, d.s.c., WAXD and optical microscopy were employed to investigate the differences between hydrogen bonding and crystallization behaviour depending on hard segment concentration in polyether- and polyester-based polyurethaneureas (PUUs). It has been found that the hard segment crystallization behaviour of polyether-based PUU is higher than polyester-based PUU for the same hard segment content. Hydrogen bonding in polyether-based PUU is formed mainly between hard segments, which promotes crystallization of hard segments. Hydrogen bonding in polyester-based PUU is formed mainly between soft and hard segments, which hinders the crystallization of hard segments.

Study on sequence distribution of segmented poly(urethane urea)s by 13C-NMR spectroscopy: Effect of polymerization procedures

The segmented poly(urethane urea) copolymers were synthesized by one- and two-step polymerization procedures. The copolymers were based on 4,4′-diphenylmethane diisocyanate, 3,5-diethyltoluene diamine, and ethylene oxide-capped poly(propylene oxide) diol. The mean sequence lengths of polyurethane soft block and polyurea hard block as well as the sequence distribution of the hard block in the copolymers were estimated from the signals of aromatic carbons in 13C-NMR spectra. The results indicated that two-step polymerization led to longer mean sequence lengths and broader hard block sequence distribution than one-step polymerization did.

Phase separation in segmented poly(urethane urea) copolymers during reaction injection molding (RIM) polymerization

In situ experiments were performed with a portable RIM (reaction injection molding) minimachine interfaced to an FTIR spectrophotometer to follow the reaction chemistry and monitor phase separation of copoly(urethane urea)s during RIM polymerization. The PUU copolymers were based on ethylene oxide-capped poly(propylene oxide) polyether diol, 3,5-diethyltoluenediamine (DETDA), and uretonimine liquefied 4,4′-diphenylmethane diisocyanate. The effect of catalyst concentration on the degree of phase separation in the as-molded RIM PUU copolymers was investigated by using differential scanning calorimetery and scanning electron microscopy as supplementary methods. The results suggested that an increase of degree of phase separation and a decrease of the size of hard-segment-rich domains take place with a rise of catalyst concentration. The morphological feature was a consequence in combination with the increase in relative rate of urethane formation and the ordering of hydrogen bonding through urea groups.