@article{HoffmannMachatschekLendlein2022,
  author    = {Hoffmann, Falk and Machatschek, Rainhard Gabriel and Lendlein, Andreas},
  title     = {Analytical model and Monte Carlo simulations of polymer degradation with improved chain cut statistics},
  series = {Journal of materials research : JMR},
  volume    = {37},
  journal   = {Journal of materials research : JMR},
  number    = {5},
  publisher = {Springer},
  address   = {Heidelberg},
  issn      = {0884-2914},
  doi       = {10.1557/s43578-022-00495-4},
  pages     = {1093 -- 1101},
  year      = {2022},
  abstract  = {The degradation of polymers is described by mathematical models based on bond cleavage statistics including the decreasing probability of chain cuts with decreasing average chain length. We derive equations for the degradation of chains under a random chain cut and a chain end cut mechanism, which are compared to existing models. The results are used to predict the influence of internal molecular parameters. It is shown that both chain cut mechanisms lead to a similar shape of the mass or molecular mass loss curve. A characteristic time is derived, which can be used to extract the maximum length of soluble fragments l of the polymer. We show that the complete description is needed to extract the degradation rate constant k from the molecular mass loss curve and that l can be used to design polymers that lose less mechanical stability before entering the mass loss phase.},
  language  = {en}
}
@article{MachatschekHeuchelLendlein2021,
  author    = {Machatschek, Rainhard Gabriel and Heuchel, Matthias and Lendlein, Andreas},
  title     = {Hydrolytic stability of polyetherimide investigated in ultrathin films},
  series = {Journal of materials research : JMR / Materials Research Society},
  volume    = {36},
  journal   = {Journal of materials research : JMR / Materials Research Society},
  number    = {14},
  publisher = {Springer},
  address   = {Berlin},
  issn      = {0884-2914},
  doi       = {10.1557/s43578-021-00267-6},
  pages     = {2987 -- 2994},
  year      = {2021},
  abstract  = {Increasing the surface hydrophilicity of polyetherimide (PEI) through partial hydrolysis of the imide groups while maintaining the length of the main-chain was explored for adjusting its function in biomedical and membrane applications. The outcome of the polymer analogous reaction, i.e., the degree of ring opening and chain cleavage, is difficult to address in bulk and microstructured systems, as these changes only occur at the interface. Here, the reaction was studied at the air-water interface using the Langmuir technique, assisted by atomic force microscopy and vibrational spectroscopy. Slow PEI hydrolysis sets in at pH > 12. At pH = 14, the ring opening is nearly instantaneous. Reduction of the layer viscosity with time at pH = 14 suggested moderate chain cleavage. No hydrolysis was observed at pH = 1. Hydrolyzed PEI films had a much more cohesive structure, suggesting that the nanoporous morphology of PEI can be tuned via hydrolysis.},
  language  = {en}
}
@article{MachatschekHeuchelLendlein2021,
  author    = {Machatschek, Rainhard Gabriel and Heuchel, Matthias and Lendlein, Andreas},
  title     = {Thin-layer studies on surface functionalization of polyetherimide},
  series = {Journal of materials research : JMR / Materials Research Society},
  volume    = {37},
  journal   = {Journal of materials research : JMR / Materials Research Society},
  number    = {1},
  publisher = {Springer},
  address   = {Berlin},
  issn      = {0884-2914},
  doi       = {10.1557/s43578-021-00339-7},
  pages     = {67 -- 76},
  year      = {2021},
  abstract  = {Among the high-performance and engineering polymers, polyimides and the closely related polyetherimide (PEI) stand out by their capability to react with nucleophiles under relatively mild conditions. By targeting the phthalimide groups in the chain backbone, post-functionalization offers a pathway to adjust surface properties such as hydrophilicity, solvent resistance, and porosity. Here, we use ultrathin PEI films on a Langmuir trough as a model system to investigate the surface functionalization with ethylene diamine and tetrakis(4-aminophenyl)porphyrin as multivalent nucleophiles. By means of AFM, Raman spectroscopy, and interfacial rheology, we show that hydrolysis enhances the chemical and mechanical stability of ultrathin films and allows for the formation of EDC/NHS-activated esters. Direct amidation of PEI was achieved in the presence of a Lewis acid catalyst, resulting in free amine groups rather than cross-linking. When comparing amidation with hydrolysis, we find a greater influence of the latter on material properties.},
  language  = {en}
}
@article{BehlBalkLuetzowetal.2021,
  author    = {Behl, Marc and Balk, Maria and L{\"u}tzow, Karola and Lendlein, Andreas},
  title     = {Impact of block sequence on the phase morphology of multiblock copolymers obtained by high-throughput robotic synthesis},
  series = {European polymer journal : EPJ},
  volume    = {143},
  journal   = {European polymer journal : EPJ},
  publisher = {Elsevier},
  address   = {Oxford},
  issn      = {0014-3057},
  doi       = {10.1016/j.eurpolymj.2020.110207},
  pages     = {9},
  year      = {2021},
  abstract  = {The chemical nature, the number length of integrated building blocks, as well as their sequence structure impact the phase morphology of multiblock copolymers (MBC) consisting of two non-miscible block types. We hypothesized that a strictly alternating sequence should favour phase segregation and in this way the elastic properties. A library of well-defined MBCs composed of two different hydrophobic, semi-crystalline blocks providing domains with well-separated melting temperatures (T(m)s) were synthesized from the same type of precursor building blocks as strictly alternating (MBCsalt) or random (MBCsran) MBCs and compared. Three different series of MBCsalt or MBCsran were synthesized by high-throughput synthesis by coupling oligo(e-caprolactone) (OCL) of different molecular weights (2, 4, and 8 kDa) with oligotetrahydrofuran (OTHF, 2.9 kDa) via Steglich esterification in which the molar ratio of the reaction partners was slightly adjusted. Maximum of weight average molecular weight (M-w) were 65,000 g center dot mol(-1), 165,000 g center dot mol(-1), and 168,000 g center dot mol(-1) for MBCsalt and 80,500 g center dot mol(-1), 100,000 g center dot mol(-1), and 147,600 g center dot mol(-1) for MBCsran. When Mw increased, a decrease of both Tms associated to the melting of the OCL and OTHF domains was observed for all MBCs. T-m (OTHF) of MBCsran was always higher than Tm (OTHF) of MBCsalt, which was attributed to a better phase segregation. In addition, the elongation at break of MBCsalt was almost half as high when compared to MBCsran. In this way this study elucidates role of the block length and sequence structure in MBCs and enables a quantitative discussion of the structure-function relationship when two semi-crystalline block segments are utilized for the design of block copolymers.},
  language  = {en}
}
@article{BaeckemoLiuLendlein2021,
  author    = {B{\"a}ckemo, Johan Dag Valentin and Liu, Yue and Lendlein, Andreas},
  title     = {Bio-inspired and computer-supported design of modulated shape changes in polymer materials},
  series = {MRS communications / a publication of the Materials Research Society},
  volume    = {11},
  journal   = {MRS communications / a publication of the Materials Research Society},
  number    = {4},
  publisher = {Springer},
  address   = {Berlin},
  issn      = {2159-6867},
  doi       = {10.1557/s43579-021-00056-6},
  pages     = {462 -- 469},
  year      = {2021},
  abstract  = {The Venus flytrap is a fascinating plant with a finely tuned mechanical bi-stable system, which can switch between mono- and bi-stability. Here, we combine geometrical design of compliant mechanics and the function of shape-memory polymers to enable switching between bi- and mono-stable states. Digital design and modelling using the Chained Beam Constraint Model forecasted two geometries, which were experimentally realized as structured films of cross-linked poly[ethylene-co-(vinyl acetate)] supported by digital manufacturing. Mechanical evaluation confirmed our predicted features. We demonstrated that a shape-memory effect could switch between bi- and mono-stability for the same construct, effectively imitating the Venus flytrap.},
  language  = {en}
}
@article{FarhanBehlKratzetal.2021,
  author    = {Farhan, Muhammad and Behl, Marc and Kratz, Karl and Lendlein, Andreas},
  title     = {Origami hand for soft robotics driven by thermally controlled polymeric fiber actuators},
  series = {MRS communications / a publication of the Materials Research Society},
  volume    = {11},
  journal   = {MRS communications / a publication of the Materials Research Society},
  number    = {4},
  publisher = {Springer},
  address   = {Berlin},
  issn      = {2159-6859},
  doi       = {10.1557/s43579-021-00058-4},
  pages     = {476 -- 482},
  year      = {2021},
  abstract  = {Active fibers can serve as artificial muscles in robotics or components of smart textiles. Here, we present an origami hand robot, where single fibers control the reversible movement of the fingers. A recovery/contracting force of 0.2 N with a work capacity of 0.175 kJ kg(-1) was observed in crosslinked poly[ethylene-co-(vinyl acetate)] (cPEVA) fibers, which could enable the bending movement of the fingers by contraction upon heating. The reversible opening of the fingers was attributed to a combination of elastic recovery force of the origami structure and crystallization-induced elongation of the fibers upon cooling.},
  language  = {en}
}