46
tailored around body temperature by controlling the soft segment/hard segment
ratio in the system. Currently, SMPU-based materials are used as catheters, drug
delivery systems, fracture fixation, orthopedic surgery, etc (Burke and Hasirci 2004;
Grapski and Cooper 2001; Lendlein et al. 2010; Yakacki and Gall 2009) SMPUs
could also be used for aerospace and automotive applications (Paik et al. 2006).
3.4.3 Shape Memory Resins (SMRs)
SMRs are another important type of SMP. These materials have been continuously
developed, due to their excellent electrical insulation and mechanical performance,
and thermal and corrosion resistance. Charles (1953) first reported the development
of radiation-crosslinked poly(vinyl chloride) (PVC)-based SMRs as a packaging
material. Following Hu et al. (2005b), these radiation-crosslinked PVC-based
retractable packaging membranes have the advantages of a relatively high transparency and good shrinkage properties.
Poly(norbornene)-based SMRs are one of the first industrialized products as
SMPs, and are obtained via Diels-Alder reaction from cyclopentane and ethylene.
These SMRs are marketed under the name NORSOREX, and their Mw is around
3 × 10
6
of Da, i.e. they have a Mw of 100 times greater than the convectional polymers, and their T g is 35 °C. In these SMRs, the crosslinking sites act as a stationary
phase, while the amorphous polymer chains are used as a reversible phase (和郎中
山 1990). Poly (norbornene)-based SMRs compared to other types of SMPs, have
the following characteristics (Bogue 2009; Serrano and Ameer 2012):
1. They can be processed by calendering, injection extrusion and vacuum forming.
However, the processing is difficult due to their high Mw.
2. Poly(norbornene)’s Tg is close to human body temperature. Therefore, it can be
used as raw material for biomaterial manufacturing. However, this temperature
is difficult to control.
3. Poly(norbornene) has excellent oil absorption capacity, which is from 5 to 100
times its own weight. It could thus be used as a reusable device for oil spills.
After oil absorption, elastomeric resins could be obtained from them, as well as
they could be turned into low hardness rubber (15 JIS grade, hard), which results
in excellent materials after being properly treated.
Trans-poly(isoprene) (TPI) is a crystalline polymer under ambient conditions,
which can be vulcanized/crosslinked like any ordinary rubber, thus resulting in
SMRs. The stationary phase is the network structure after the crosslinking reaction,
while the reversible phase is made up of crystalline structures, which can be melted
(Ni and Sun 2006). TPI-based SMRs have high deformation and recovery rates
between 46 and 76 °C. As a result, at low temperatures could be applied as thermal
control switches (Ni and Sun 2006). However, TPI-based SMRs have poor thermal
resistance and weatherability, and low shape memory temperature (30–50 °C), thus
restricting their potential applications. Radiation-crosslinked poly(ethylene) (PE)Z. Gao and G. Gao
tailored around body temperature by controlling the soft segment/hard segment
ratio in the system. Currently, SMPU-based materials are used as catheters, drug
delivery systems, fracture fixation, orthopedic surgery, etc (Burke and Hasirci 2004;
Grapski and Cooper 2001; Lendlein et al. 2010; Yakacki and Gall 2009) SMPUs
could also be used for aerospace and automotive applications (Paik et al. 2006).
3.4.3 Shape Memory Resins (SMRs)
SMRs are another important type of SMP. These materials have been continuously
developed, due to their excellent electrical insulation and mechanical performance,
and thermal and corrosion resistance. Charles (1953) first reported the development
of radiation-crosslinked poly(vinyl chloride) (PVC)-based SMRs as a packaging
material. Following Hu et al. (2005b), these radiation-crosslinked PVC-based
retractable packaging membranes have the advantages of a relatively high transparency and good shrinkage properties.
Poly(norbornene)-based SMRs are one of the first industrialized products as
SMPs, and are obtained via Diels-Alder reaction from cyclopentane and ethylene.
These SMRs are marketed under the name NORSOREX, and their Mw is around
3 × 10
6
of Da, i.e. they have a Mw of 100 times greater than the convectional polymers, and their T g is 35 °C. In these SMRs, the crosslinking sites act as a stationary
phase, while the amorphous polymer chains are used as a reversible phase (和郎中
山 1990). Poly (norbornene)-based SMRs compared to other types of SMPs, have
the following characteristics (Bogue 2009; Serrano and Ameer 2012):
1. They can be processed by calendering, injection extrusion and vacuum forming.
However, the processing is difficult due to their high Mw.
2. Poly(norbornene)’s Tg is close to human body temperature. Therefore, it can be
used as raw material for biomaterial manufacturing. However, this temperature
is difficult to control.
3. Poly(norbornene) has excellent oil absorption capacity, which is from 5 to 100
times its own weight. It could thus be used as a reusable device for oil spills.
After oil absorption, elastomeric resins could be obtained from them, as well as
they could be turned into low hardness rubber (15 JIS grade, hard), which results
in excellent materials after being properly treated.
Trans-poly(isoprene) (TPI) is a crystalline polymer under ambient conditions,
which can be vulcanized/crosslinked like any ordinary rubber, thus resulting in
SMRs. The stationary phase is the network structure after the crosslinking reaction,
while the reversible phase is made up of crystalline structures, which can be melted
(Ni and Sun 2006). TPI-based SMRs have high deformation and recovery rates
between 46 and 76 °C. As a result, at low temperatures could be applied as thermal
control switches (Ni and Sun 2006). However, TPI-based SMRs have poor thermal
resistance and weatherability, and low shape memory temperature (30–50 °C), thus
restricting their potential applications. Radiation-crosslinked poly(ethylene) (PE)Z. Gao and G. Gao