When the carbonyl groups in urethane are bonded to the N–H
groups by hydrogen bonding, the hard segments which contain
urethane group are placed next to each other and separated from
the soft segments. In this case, the so-called phase separation of
soft and hard segments would occur in polymer [11,30]. But when
the N–H group in urethane and the ether groups in polyol are connected
by hydrogen bonds, the hard and soft segments are mixed
and the phase mixing would be executed. As evident in Fig. 1,
the N–H absorption band in PU2 is sharper and its intensity
increased by BDA in polymer. This phenomenon is due to the
increased number of hydrogen bonds between the carbonyl groups
in urethane and N–H groups. This may reflect an increase in phase
separation and more affinity for the N–H groups to form hydrogen
bonds with urethane and urea carbonyl groups, and less affinity to
mix with ether groups in soft segments