Page 155 - Biodegradable Polyesters

6.2 Shape Memory Polymer Systems 133

R f = 100% 3 2
1 Shaping
R f < 100%
2 Shape fixing
Deformation 3 Deloading

4
1 4 Recovery

Stress
or T
T g m Temperature
R r = 100%
R r < 100%

Figure 6.1 Schematic representation of single SM cycles of one-way SM polymers.

quantification of SM behavior in cyclic thermomechanical tests was compiled by
Sauter et al.[7].
SMPs and related composite systems are grouped differently. The classification
may consider the SM mechanisms, the morphology, the type (one-way, two-way),
the activation mode (e.g., thermal, photo, chemical sensitive) among others.
Biodegradable polymers play a prominent role in the family of SMPs. This is due
to their biodegradability because in many of the medical applications the related
“devices” with SM function (e.g., sutures, catheters, stents) should be present only
temporarily in the human body. The other, not less important, aspect is that the
switch temperature for shape programming (T trans ) can well be matched with that
of the body.
Next we shall give an overview on SMP systems which are composed fully or
partly from biodegradable polyesters. To give a comprehensive review is beyond
our intention owing to large body of the related works available both in the open
and patent literatures. On the other hand, the reader will get a structured overview
of the basic strategies followed to tailor the structure and performance of SMPs
in order to meet the requirements of given applications.

6.2
Shape Memory Polymer Systems

The grouping followed is according to the basic compositions of the SMPs treated,
that is, homopolymers, copolymers, blends, and polymers with thermosetting
resins. In order to deliver an adequate review, systems containing biodegradable
polyesters are also included. Accordingly, polyurethane (PU) systems composed
of polyester building blocks are also reported in a very concise manner. Further,
each group of the above SMPs is divided into two subgroups, namely, linear