Page 163 - Biodegradable Polyesters

6.2 Shape Memory Polymer Systems 141

Temperature SMCP-2s-I SMCP-2s-II SMCP-1s Shapes

1 1 1 (0°)
70 °C Shape C

2 2
40 °C (90°)
Shape B

0 °C (180°)
t t t Shape A
(a)
T high = 70 °C T high = 40 °C T low = 0 °C

1 2 3 4

Magnetite core
Silica shell
PCLDIMA PEGMA SNP
(b) Shape C Shape B Shape A

Figure 6.5 (a) Schematic representations functionalized polyethylene glycol, PCLDIMA:
of the different SM creation procedures poly(ε-caprolactone) dimethacrylate. Phase
applied for bending of the nanocomposites. structure – orange: amorphous PCL chain
Two-step programming methods: SMCP- segments, light blue: amorphous PEG chain
2s-I, SMCP-2s-II, as well as single-step pro- segments, red: crystalline PCL chain seg-
gramming procedure: SMCP-1s. (b) Molec- ments, dark blue: crystalline PEG chain seg-
ular mechanism for graft polymer network ments, gray: amorphous poly(methacrylate)
composites during SM creation procedure. chain segments. (Ref. [40], reproduced with
Abbreviations – PEGMA: methacrylate permission of BME-PT.)

afterward. This development targeted the reduction of water sensitivity and
improvement of the flexibility and surface properties of the polymer whereby
∘
maintaining the switch function of the PCL phase (T trans = 80 C). Note that PCL
∘
∘
exhibits T =−60 C, whereas polydimethylsiloxane has a T =−125 C.
g g
Bio-based polyesters composed of 1,3-propanediol, sebacic acid, and itaconic
acid in various ratios showed excellent SM properties after cross-linking with per-
∘
oxide. T could be tuned by the composition between 12 and 54 C [46].
trans
The feasibility of the Diels–Alder coupling was shown on the example of
biodegradable polyester by Ninh and Bettinger [47]. In this case, hyperbranched
poly(glycerol-co-sebacate) with pendant furan groups was coupled with a bifunc-
tional maleimide cross-linker to produce an elastomeric material. POSS moieties
may serve as cross-linking sites, as well. Ishida et al. [48] have shown how a