am9b10052_si_001.pdf (1.82 MB)
External Stress-Free Reversible Multiple Shape Memory Polymers
journal contribution
posted on 2019-08-17, 17:29 authored by Ya Nan Huang, Long Fei Fan, Min Zhi Rong, Ming Qiu Zhang, Yu Ming GaoThe
present work is focused on developing external stress-free two-way
triple shape memory polymers (SMPs). Accordingly, a series of
innovative approaches are proposed for the material design and preparation.
Polyurethane prepolymers carrying crystalline polytetrahydrofuran
(PTMEG) and poly(ε-caprolactone) (PCL) as the switching phases
are respectively synthesized in advance and then cross-linked to produce
the target material. The stepwise method is believed to be conducive
to manipulation of the relative contribution of PCL and PTMEG. Moreover,
the chain extender, 2-amino-5-(2-hydroxyethyl)-6-methylpyrimidin-4-ol
(UPy), is incorporated to establish hydrogen bonds among the macromolecules.
By straightforward stretching treatment at different temperatures,
the hydrogen bond networks are successfully converted into an internal
stress provider, which overcomes the challenge of stress relaxation
of the melted low melting temperature polymer (i.e., PTMEG) and increases
the efficiency of stress transfer. Meanwhile, the contraction force
of the switching phases is tuned to match the internal tensile stress.
As a result, the internal stress provider can closely collaborate
with melting/recrystallization of the crystalline domains, leading
to the repeated multiple shape memory effects. The cross-linked
polyurethane is thus able to reversibly morph among three shapes and
displays its potentials as soft robot and actuator. The strategy reported
here has the advantages of easily accessible raw materials, simple
reaction, and facile programing/deprograming/reprograming, so that
it possesses wide applicability.