@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} } @article{ZhangSauterFangetal.2015, author = {Zhang, Quanchao and Sauter, Tilman and Fang, Liang and Kratz, Karl and Lendlein, Andreas}, title = {Shape-Memory Capability of Copolyetheresterurethane Microparticles Prepared via Electrospraying}, series = {Macromolecular materials and engineering}, volume = {300}, journal = {Macromolecular materials and engineering}, number = {5}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {1438-7492}, doi = {10.1002/mame.201400267}, pages = {522 -- 530}, year = {2015}, abstract = {Multifunctional thermo-responsive and degradable microparticles exhibiting a shapememory effect (SME) have attracted widespread interest in biomedicine as switchable delivery vehicles or microactuators. In this work almost spherical solid microparticles with an average diameter of 3.9 +/- 0.9 mm are prepared via electrospraying of a copolyetheresterurethane named PDC, which is composed of crystallizable oligo(p-dioxanone) (OPDO) hard and oligo(e-caprolactone) (OCL) switching segments. The PDC microparticles are programmed via compression at different pressures and their shapememory capability is explored by off-line and online heating experiments. When a low programming pressure of 0.2 MPa is applied a pronounced thermally-induced shape-memory effect is achieved with a shape recovery ratio about 80\%, while a high programming pressure of 100 MPa resulted in a weak shape-memory performance. Finally, it is demonstrated that an array of PDC microparticles deposited on a polypropylene (PP) substrate can be successfully programmed into a smart temporary film, which disintegrates upon heating to 60 degrees C.}, language = {en} } @article{MiasnikovaLaschewsky2012, author = {Miasnikova, Anna and Laschewsky, Andr{\´e}}, title = {Influencing the phase transition temperature of poly(methoxy diethylene glycol acrylate) by molar mass, end groups, and polymer architecture}, series = {Journal of polymer science : A, Polymer chemistry}, volume = {50}, journal = {Journal of polymer science : A, Polymer chemistry}, number = {16}, publisher = {Wiley-Blackwell}, address = {Hoboken}, issn = {0887-624X}, doi = {10.1002/pola.26116}, pages = {3313 -- 3323}, year = {2012}, abstract = {The easily accessible, but virtually overlooked monomer methoxy diethylene glycol acrylate was polymerized by the RAFT method using monofunctional, difunctional, and trifunctional trithiocarbonates to afford thermoresponsive polymers exhibiting lower critical solution temperature-type phase transitions in aqueous solution. The use of the appropriate RAFT agent allowed for the preparation and systematic variation of polymers with defined molar mass, end-groups, and architecture, including amphiphilic diblock, symmetrical triblock, and triarm star-block copolymers, containing polystyrene as permanently hydrophobic constituent. The cloud points (CPs) of the various polymers proved to be sensitive to all varied parameters, namely molar mass, nature, and number of the end-groups, and the architecture, up to relatively high molar masses. Thus, CPs of the polymers can be adjusted within the physiological interesting range of 2040 degrees C. Remarkably, CPs increased with the molar mass, even when hydrophilic end groups were attached to the polymers.}, language = {en} } @article{MelchertBehlNoecheletal.2012, author = {Melchert, Christian and Behl, Marc and N{\"o}chel, Ulrich and Lendlein, Andreas}, title = {Influence of Comesogens on the Thermal and Actuation Properties of 2-tert-Butyl-1,4-bis[4-(4-pentenyloxy)benzoyl]hydroquinone Based Nematic Main-Chain Liquid Crystalline Elastomers}, series = {Macromolecular materials and engineering}, volume = {297}, journal = {Macromolecular materials and engineering}, number = {12}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {1438-7492}, doi = {10.1002/mame.201200238}, pages = {1203 -- 1212}, year = {2012}, abstract = {Although the shape-changing capabilities of LCEs hold great potential for applications ranging from micropumps to artificial muscles, customization of the LCE functionality to the applications' requirements is still a challenge. It is studied whether the orientation of NMC-LCPs and NMC-LCEs based on 2-tert-butyl-1,4-bis[4-(4-pentenyloxy)benzoyl]hydroquinone can be enhanced by copolymerization with 2-methyl-1,4-bis[4-(4-pentenyloxy)benzoyl]hydroquinone or 2,6-bis[4-(4-pentenyl-oxy)-benzoyl]anthracene. An increasing content of the comonomers stabilizes the nematic phase, which enables a tailoring of T-NI for the NMC-LCP between 45 and 68 degrees C, while for the NMC-LCE T-NI ranges between 69 and 76 degrees C. In addition, NMC-LCE show an increased actuation performance.}, language = {en} } @article{JulichGrunerLoewenbergNeffeetal.2013, author = {Julich-Gruner, Konstanze K. and L{\"o}wenberg, Candy and Neffe, Axel T. and Behl, Marc and Lendlein, Andreas}, title = {Recent trends in the chemistry of shape-memory polymers}, series = {Macromolecular chemistry and physics}, volume = {214}, journal = {Macromolecular chemistry and physics}, number = {5}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {1022-1352}, doi = {10.1002/macp.201200607}, pages = {527 -- 536}, year = {2013}, abstract = {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.}, language = {en} } @article{GhobadiHeuchelKratzetal.2013, author = {Ghobadi, Ehsan and Heuchel, Matthias and Kratz, Karl and Lendlein, Andreas}, title = {Simulating the shape-Memory behavior of amorphous switching domains of Poly(L-lactide) by molecular dynamics}, series = {Macromolecular chemistry and physics}, volume = {214}, journal = {Macromolecular chemistry and physics}, number = {11}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {1022-1352}, doi = {10.1002/macp.201200450}, pages = {1273 -- 1283}, year = {2013}, abstract = {The thermally induced shape-memory effect of polymers is typically characterized by cyclic uniaxial thermomechanical tests. Here, a molecular-dynamics (MD) simulation approach of such a cyclic uniaxial thermomechanical test is presented for amorphous switching domains of poly(L-lactide) (PLLA). Uniaxial deformation of the constructed PLLA models is simulated with a Parinello-Rahman scheme, as well as a pragmatic geometrical approach. We are able to describe two subsequent test cycles using the presented simulation approach. The obtained simulated shape-memory properties in both test cycles are similar and independent of the applied deformation protocols. The simulated PLLA shows high shape fixity ratios (Rf 94\%), but only a moderate shape recovery ratio is obtained (Rr 30\%). Finally, the structural changes during the simulated test are characterized by analysis of the changes in the dihedral angle distributions.}, language = {en} }