TY - JOUR A1 - Bothe, Martin A1 - Pretsch, Thorsten T1 - Two-way shape changes of a shape-memory poly(ester urethane) N2 - Phase-segregated PEU exhibits two-way shape changes under various constant stresses. Most distinct actuation (expansion on cooling and contraction on heating) can be detected between +60 and -20 °C when the maximum stress applied during a thermo-mechanical pretreatment approached the point where deformation-induced crystallization of the PBA soft segment sets in. The driving forces for the strain-related two-way shape changes consist of PBA crystallization and PBA melting-induced entropy elasticity. At low constant stresses (<1.5 MPa), entropy elasticity also contributes to specimen expansion on cooling. The results of multiple- cycling experiments imply that PEU is an appropriate candidate for the fabrication of thermoresponsive actuators working under constant stress conditions. KW - Actuation KW - Entropy elasticity KW - Mechanical properties KW - Phase change KW - Polymorphism KW - Poly(ester urethane) KW - Poly(1,4-butylene adipate) KW - Semi-crystallinity KW - Shape memory polymers KW - Stimuli-sensitive polymers KW - Stress KW - Two-way actuator KW - Two-way shape memory PY - 2012 DO - https://doi.org/10.1002/macp.201200096 SN - 1022-1352 SN - 1521-3935 VL - 213 IS - 22 SP - 2378 EP - 2385 PB - Wiley-VCH Verl. CY - Weinheim AN - OPUS4-27074 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Bothe, Martin A1 - Pretsch, Thorsten T1 - Bidirectional actuation of a thermoplastic polyurethane elastomer N2 - Herein, we report on how to teach a thermoplastic polyurethane elastomer completely stress-free, bidirectional motion. Briefly spoken, we applied training, consisting of extensive tensile deformation in the specimen's viscoelastic state, initiating deformation-induced crystallization. Once unloaded, thermo-reversible specimen expansion and contraction could be detected. Following the microstructural evolution of such a trained specimen by in situ wide-angle X-ray scattering gave evidence for progressive growth of oriented crystallites during cooling. Upon heating, crystallite melting resulted in structural disorder. Beyond this, modification of the training method was used to introduce a geometrically more complex crystalline order. Here, actuation in the form of a decrease and an increase in sample thickness and specimen twisting and untwisting were witnessed. The novel semi-crystalline polymer actuator highlights an enormous potential for realizing versatile reversible shape changes in elastomers. KW - Bidrectional actuation KW - Thermoplastic polyurethane elastomer KW - Shape memory polymer KW - Training KW - Reversible shape changes KW - In situ wide-angle X-ray scattering KW - Hermann's orientation function KW - Mechanical properties KW - Phase change KW - Polymorphism KW - Poly(ester urethane) KW - Poly(1,4-butylene adipate) KW - Semi-crystallinity KW - Stimuli-sensitive polymer KW - Two-way actuator KW - Two-way shape memory KW - Microscopic model PY - 2013 DO - https://doi.org/10.1039/c3ta13414h SN - 2050-7496 SN - 2050-7488 VL - 1 IS - 46 SP - 14491 EP - 14497 PB - RSC CY - London [u.a.] AN - OPUS4-29641 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - THES A1 - Bothe, Martin T1 - Shape Memory and Actuation Behavior of Semicrystalline Polymer Networks N2 - Formgedächtnispolymere (FGPe) können unter Einwirkung eines geeigneten Stimulus ihre Form verändern. Um dieses Verhalten zu ermöglichen, wird eine Deformation mittels ‘Programmierungs’- Verfahren fixiert, wobei das FGP eine stabile, temporäre Form einnimmt. In thermoresponsiven FGPen löst anschließendes Erwärmen entropieelastische Rückstellung in die ursprüngliche Form aus. Um thermoreversible Zweiwege-Aktuation zu realisieren, kann eine zusätzliche Formänderung beim Abkühlen durch ein Kristallisationsphänomen hervorgerufen werden. Mittels zyklischer thermomechanischer Messungen wurden (1) die Formgedächtniseigenschaften (FGEen) und (2) das thermoreversible Aktuationsverhalten sowohl unter konstanter Auflast als auch unter spannungsfreien Bedingungen quantifiziert. Sternförmige Hybridpolymernetzwerke, chemisch quervernetzt durch polyedrisches oligomeres Silsesquioxan und Polyurethan (SPOSSPU) und physikalisch quervernetzte Poly(ester urethan)-Blockcopolymere (PEUe) wurden im Bereich der Schmelz- und Kristallisationstemperaturen ihrer Polyesterweichsegmente untersucht. (1) Insbesondere die SPOSS-PUs mit hoher Quervernetzungsdichte zeigten Formfixier- und Formrückstellbarkeiten von nahezu 100%, während PEUs ausgeprägte FGEen bei hohem eichsegmentanteil aufwiesen. In zweifach programmierten SPOSS-PUs ließen sich darüber hinaus zwei thermisch separierte Rückstellungen induzieren. Selbst eine Einschnürung, die sich während der Verformung von SPOSS-PUs mit hohem Weichsegmentanteil gebildet hatte, war reversibel. (2) Global orientierte Kristallisation führte bei Abkühlung zur Expansion der PEU-Proben, vor allem bei hohem Weichsegmentanteil und nach dem Aufbringen einer starken Deformation. Schmelzen revidierte die Orientierung; die PEU-Probe kontrahierte und komplettierte damit den thermoreversiblen Aktuationszyklus. Unter Auflast konnten multiple Phasenübergänge im polymorphen Weichsegment zwei aufeinander folgende Expansions- und Kontraktionsschritte auslösen, während spannungsfrei verschiedene Formänderungen, z.B. die Zu- und Abnahme von Probenlänge und -dicke sowie Ver- und Entdrehen einer Probe experimentell belegt werden konnten. Die vorgestellte Aktuatortechnologie ermöglicht völlig neue Anwendungen, die bidirektionale, organische Bewegungen nachahmen und wiederholen können. N2 - Shape memory polymers (SMPs) can change their shape on application of a suitable stimulus. To enable such behavior, a ‘programming’ procedure fixes a deformation, yielding a stable temporary shape. In thermoresponsive SMPs, subsequent heating triggers entropy-elastic recovery of the initial shape. An additional shape change on cooling, i.e. thermoreversible two-way actuation, can be stimulated by a crystallization phenomenon. In this thesis, cyclic thermomechanical measurements systematically determined (1) the shape memory and (2) the actuation behavior under constant load as well as under stress-free conditions. Chemically cross-linked, star-shaped polyhedral oligomeric silsesquioxane polyurethane (SPOSS-PU) hybrid polymer networks and physically cross-linked poly(ester urethane) (PEU) block copolymers were investigated around the melting and crystallization temperatures of their polyester soft segments. (1) The SPOSS-PUs showed excellent shape fixities and recoverabilities of almost 100% at high cross-linking density, while PEUs exhibited pronounced shape memory properties at increased soft segment content. Furthermore, two-fold programmed SPOSS-PU specimens were able to recover their initial shape in two thermally separated events. Even a neck, which formed during deformation of SPOSS-PUs with high soft segment content, was reversed. (2) In PEUs, globally oriented crystallization on cooling drove expansion of the sample, in particular at high soft segment content and after application of a strong deformation. Melting reversed that orientation; the PEU sample contracted and thereby completed the thermoreversible actuation cycle. Under load, multiple polymorphic phase transitions enabled two successive expansion and contraction steps, while under stress-free conditions various geometric shape changes, including the increase and decrease of PEU sample length and thickness as well as twisting and untwisting could be experimentally witnessed. Such actuation technology allows for entirely new applications, enabling mimicry of reversible, bidirectional and repeated organic movements. T3 - BAM Dissertationsreihe - 121 KW - Shape Memory Polymers KW - Polymorphism KW - Semicrystalline KW - Actuation KW - Training PY - 2014 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-372 SN - 978-3-9816668-1-6 SN - 1613-4249 VL - 121 SP - 1 EP - 139 PB - Bundesanstalt für Materialforschung und -prüfung (BAM) CY - Berlin AN - OPUS4-37 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Bothe, Martin A1 - Emmerling, Franziska A1 - Pretsch, Thorsten T1 - Poly(ester urethane) with varying polyester chain length: Polymorphism and shape-memory behavior N2 - The swelling, viscoelastic, and mechanical behavior of phase-segregated poly(ester urethane) (PEU) block copolymers, composed of 4,4'-methylenediphenyl diisocyanate, 1,4-butanediol as a chain extender, and crystallizable poly(1,4-butylene adipate) (PBA) with molecular weights between 1330 and 4120 g mol-1, are investigated. Wide-angle X-ray scattering (WAXS) is employed to study the overall PEU crystallinity, which increases from 8.6 to 13.6% at higher PBA contents. The existence of two crystalline, polymorphic PBA phases, a thermodynamically stable α phase and a metastable β phase, is confirmed by further WAXS measurements. Calorimetric and thermomechanical investigations give evidence for controllable PBA polymorphic behavior. The crystallization conditions, like the cooling rate, affect the emerging polymorphic mixture, whereas the storage conditions either promote or inhibit the polymorphic (β to α) transition. The introduced concepts represent a new approach for gaining control over programmable thermo­responsiveness, which may be transferable to other shape-memory polymers with polymorphic switching segments. KW - Shape-memory polymers KW - Stimuli-sensitive polymers KW - Poly(ester urethane) KW - Polymorphism PY - 2013 DO - https://doi.org/10.1002/macp.201300464 SN - 1022-1352 SN - 1521-3935 VL - 214 IS - 23 SP - 2683 EP - 2693 PB - Wiley-VCH Verl. CY - Weinheim AN - OPUS4-29892 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -