TY  - JOUR
A1  - Sauter, Tilman
A1  - Kratz, Karl
A1  - Lendlein, Andreas
T1  - Pore-size distribution controls shape-memory properties on the macro- and microscale of polymeric foams
JF  - Macromolecular chemistry and physics
N2  - Open porous foams with identical foam density but different pore-size distributions (bimodal or monomodal) are prepared from a shape-memory polyetherurethane (PEU) by thermally induced phase separation. The shape-memory effect of the two PEU foams is explored by cyclic thermomechanical compression tests and microstructural analysis. The obtained results reveal that the PEU foam with a bimodal pore-size distribution exhibits an increased shape-recovery under stress-free conditions, both on the macro- (foam level) as well as the microscale (pore level). While bimodal pore-size distributions induce microscale bending during compression, buckling occurs in foams with monomodal pore-size distributions, leading to both a reduced and delayed shape recovery.
KW  - microstructure
KW  - morphology
KW  - polymer foams
KW  - pore-size distribution
KW  - shape-memory polymers
Y1  - 2013
U6  - https://doi.org/10.1002/macp.201300062
SN  - 1022-1352
VL  - 214
IS  - 11
SP  - 1184
EP  - 1188
PB  - Wiley-VCH
CY  - Weinheim
ER  - 
TY  - JOUR
A1  - Julich-Gruner, Konstanze K.
A1  - Löwenberg, Candy
A1  - Neffe, Axel T.
A1  - Behl, Marc
A1  - Lendlein, Andreas
T1  - Recent trends in the chemistry of shape-memory polymers
JF  - Macromolecular chemistry and physics
N2  - Shape-memory polymers (SMPs) are stimuli-sensitive materials capable of performing complex movements on demand, which makes them interesting candidates for various applications, for example, in biomedicine or aerospace. This trend article highlights current approaches in the chemistry of SMPs, such as tailored segment chemistry to integrate additional functions and novel synthetic routes toward permanent and temporary netpoints. Multiphase polymer networks and multimaterial systems illustrate that SMPs can be constructed as a modular system of different building blocks and netpoints. Future developments are aiming at multifunctional and multistimuli-sensitive SMPs.
KW  - multifunctional polymers
KW  - networks
KW  - shape-memory polymers
KW  - stimuli-sensitive polymers
KW  - triple-shape effect
Y1  - 2013
U6  - https://doi.org/10.1002/macp.201200607
SN  - 1022-1352
VL  - 214
IS  - 5
SP  - 527
EP  - 536
PB  - Wiley-VCH
CY  - Weinheim
ER  - 
TY  - JOUR
A1  - Liu, Yue
A1  - Gould, Oliver E. C.
A1  - Rudolph, Tobias
A1  - Fang, Liang
A1  - Kratz, Karl
A1  - Lendlein, Andreas
T1  - Polymeric microcuboids programmable for temperature-memory
JF  - Macromolecular materials and engineering
N2  - Microobjects with programmable mechanical functionality are highly desirable for the creation of flexible electronics, sensors, and microfluidic systems, where fabrication/programming and quantification methods are required to fully control and implement dynamic physical behavior. Here, programmable microcuboids with defined geometries are prepared by a template-based method from crosslinked poly[ethylene-co-(vinyl acetate)] elastomers. These microobjects could be programmed to exhibit a temperature-memory effect or a shape-memory polymer actuation capability. Switching temperaturesT(sw)during shape recovery of 55 +/- 2, 68 +/- 2, 80 +/- 2, and 86 +/- 2 degrees C are achieved by tuning programming temperatures to 55, 70, 85, and 100 degrees C, respectively. Actuation is achieved with a reversible strain of 2.9 +/- 0.2% to 6.7 +/- 0.1%, whereby greater compression ratios and higher separation temperatures induce a more pronounced actuation. Micro-geometry change is quantified using optical microscopy and atomic force microscopy. The realization and quantification of microparticles, capable of a tunable temperature responsive shape-change or reversible actuation, represent a key development in the creation of soft microscale devices for drug delivery or microrobotics.
KW  - actuation
KW  - atomic force microscopy
KW  - biomaterials
KW  - microparticles
KW  - shape-memory polymers
Y1  - 2020
U6  - https://doi.org/10.1002/mame.202000333
SN  - 1438-7492
SN  - 1439-2054
VL  - 305
IS  - 10
PB  - Wiley-VCH
CY  - Weinheim
ER  -