Thermoresponsive Semicrystalline
Poly(ε-caprolactone)
Networks: Exploiting Cross-linking with Cinnamoyl Moieties to Design
Polymers with Tunable Shape Memory
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Abstract
The overall goal of this study was to synthesize semicrystalline
poly(ε-caprolactone) (PCL) copolymer networks with stimuli-responsive
shape memory behavior. Herein, we investigate the influence of a cinnamoyl
moiety to design shape memory polymer networks with tunable transition
temperatures. The effect of various copolymer architectures (random
or ABA triblock), the molecular weight of the crystalline domains,
PCL diol, <i>(M</i><sub>w</sub> 1250 or 2000 g mol<sup>–1</sup>) and its composition in the triblock (50 or 80 mol %) were also
investigated. The polymer microstructures were confirmed by NMR, DSC,
WAXS and UV–vis spectroscopic techniques. The thermal and mechanical
properties and the cross-linking density of the networks were characterized
by DSC, tensile testing and solvent swelling, respectively. Detailed
thermomechanical investigations conducted using DMA showed that shape
memory behavior was obtained only in the ABA triblock copolymers.
The best shape memory fixity, <i>R</i><sub>f</sub> of ∼99%
and shape recovery, <i>R</i><sub>r</sub> of ∼99%
was obtained when PCL diol with <i>M</i><sub>w</sub> 2000
g mol<sup>–1</sup> was incorporated in the triblock copolymer
at a concentration of 50 mol %. The series of triblock copolymers
with PCL at 50 mol % also showed mechanical properties with tunable
shape memory transition temperatures, ranging from 54 °C to close
to body temperature. Our work establishes a general design concept
for inducing a shape memory effect into any semicrystalline polyester
network. More specifically, it can be applied to systems which have
the highest transition temperature closest to the application temperature.
An advantage of our novel copolymers is their ability to be cross-linked
with UV radiation without any initiator or chemical cross-linker.
Possible applications are envisioned in the area of endovascular treatment
of ischemic stroke and cerebrovascular aneurysms, and for femoral
stents