57
4.3 Shape Memory PU
Shape memory PUs are an evolving class of smart polymers (Pal 2019). Tailoring
the molecular design and functionality can alter the recovery processes involved.
Initially, shape memory PUs have thermally induced effects, and then, moisture-,
pH- and pressure-sensitive PUs have been studied. Keeping this in mind, Chen et al.
(2010) prepared pyridine containing supramolecular PUs. These authors synthesized PU using 1,4-butanediol, hexamethylene diisocyanate and N,N-bis(2hydroxylethyl)isonicotinamine (Fig.  4.1). The low N,N-bis(2-hydroxylethyl)
isonicotinamine content resulted in a fine shape memory property of PU materials.
The soft and hard PU segments were formed by H-bonding between the urethane
and pyridine groups. H-bonds between urethane groups acted as physical net points
for the shape memory effect, while molecular switches were formed by interactions
between pyridine rings (Jiang et al. 2019). Usually, the hard segments are related to
N
N
HO
HO
N,N-bis(2-hydroxylethyl) isonicotinamine
N
C
O
N
C
O
hexamethylene diisocyanate
HO
OH
1,4-butanediol
N
N
H
N
C
O
N
C
O
O
O
O
O
H
O
n
N
N
H
N C
N
C
O
O
O
O
O
H
O
n
H
N C
N
C
O
O
H
O
m
Fig. 4.1 PU synthesis
4 Carbon Nanoparticle-Loaded Shape Memory Polyurethanes: Design…