@article{FangYanNoecheletal.2016,
  author    = {Fang, Liang and Yan, Wan and N{\"o}chel, Ulrich and Kratz, Karl and Lendlein, Andreas},
  title     = {Programming structural functions in phase-segregated polymers by implementing a defined thermomechanical history},
  series = {Polymer : the international journal for the science and technology of polymers},
  volume    = {102},
  journal   = {Polymer : the international journal for the science and technology of polymers},
  publisher = {Elsevier},
  address   = {Oxford},
  issn      = {0032-3861},
  doi       = {10.1016/j.polymer.2016.08.105},
  pages     = {54 -- 62},
  year      = {2016},
  abstract  = {Unwanted shrinkage behaviors or failure in structural functions such as mechanical strength or deformability of polymeric products related to their thermomechanical history are a major challenge in production of plastics. Here, we address the question whether we can turn this challenge into an opportunity by creating defined thermomechanical histories in polymers, represented by a specific morphology and nanostructure, to equip polymeric shaped bodies with desired functions, e.g. a temperature-memory, by hot, warm or cold deformation into multiblock copolymers having two partially overlapping melting transitions. A copolyesterurethane named PDLCL, consisting of poly(epsilon-caprolactone) (PCL) and poly(omega-pentadecalactone) (PPDL) crystalline domains, exhibiting a pronounced phase-segregated morphology and partially overlapping melting transitions was selected for this study. Different types of PCL and PPDL crystals as well as distinct degrees of orientation in both amorphous and crystalline domains were obtained after deformation at 20 or 40 degrees C and to a lower extent at 60 degrees C. The generated non-isotropic structures were stable at ambient temperature and represent the different stresses stored. Stress-free heating experiments showed that the relaxation in both amorphous and crystalline phases occurred predominantly with melting of PCL crystals. When the switching temperature, which was similar to the applied deformation temperature (temperature-memory), was exceeded in stress-free heating experiments, the implemented thermomechanical history could be reversed. In contrast, during constant-strain heating to 60 degrees C the generated structural features remained almost unchanged. These findings provide insights about the structure function relation in multiblock copolymers with two crystalline phases exhibiting a temperature-memory effect by implementation of specific thermomechanical histories, which might be a general principle for tailoring other functions like mechanical strength or deformability in polymers. (C) 2016 Elsevier Ltd. All rights reserved.},
  language  = {en}
}
@article{YanFangNoecheletal.2016,
  author    = {Yan, Wan and Fang, Liang and N{\"o}chel, Ulrich and Kratz, Karl and Lendlein, Andreas},
  title     = {Influence of programming strain rates on the shape-memory performance of semicrystalline multiblock copolymers},
  series = {Journal of polymer science : B, Polymer physics},
  volume    = {54},
  journal   = {Journal of polymer science : B, Polymer physics},
  publisher = {Wiley-Blackwell},
  address   = {Hoboken},
  issn      = {0887-6266},
  doi       = {10.1002/polb.24097},
  pages     = {1935 -- 1943},
  year      = {2016},
  abstract  = {Multiblock copolymers named PCL-PIBMD consisting of crystallizable poly(epsilon-caprolactone) segments and crystallizable poly[oligo(3S-iso-butylmorpholine-2,5-dione)] segments coupled by trimethyl hexamethylene diisocyanate provide a versatile molecular architecture for achieving shape-memory effects (SMEs) in polymers. The mechanical properties as well as the SME performance of PCL-PIBMD can be tailored by the variation of physical parameters during programming such as deformation strain or applied temperature protocols. In this study, we explored the influence of applying different strain rates during programming on the resulting nanostructure of PCL-PIBMD. Programming was conducted at 50 degrees C by elongation to epsilon(m)=50\% with strain rates of 1 or 10 or 50 mmmin(-1). The nanostructural changes were visualized by atomic force microscopy (AFM) measurements and investigated by in situ wide and small angle X-ray scattering experiments. With increasing the strain rate, a higher degree of orientation was observed in the amorphous domains. Simultaneously the strain-induced formation of new PIBMD crystals as well as the fragmentation of existing large PIBMD crystals occurred. The observed differences in shape fixity ratio and recovery stress of samples deformed with various strain rates can be attributed to their different nanostructures. The achieved findings can be relevant parameters for programming the shape-memory polymers with designed recovery forces. (c) 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 1935-1943},
  language  = {en}
}