TY - JOUR A1 - Bothe, Martin A1 - Mya, K.Y. A1 - Lin, E.M.J. A1 - Yeo, C. C. A1 - Lu, X. A1 - He, C. A1 - Pretsch, Thorsten T1 - Triple-shape properties of star-shaped POSS-polycaprolactone polyurethane networks JF - Soft matter N2 - Here, we present an investigation of the triple-shape properties of star-shaped polyhedral oligomeric silsesquioxane-poly(ε-caprolactone) polyurethanes (SPOSS-PUs), which have three-dimensional network structures. In a typical 'triple-shape functionalization process', mostly consisting of two tensile deformations at different temperatures, chain immobilization of the polymer network component poly(ε-caprolactone) (PCL) was successfully realized first through crystallization and then through vitrification. Subsequently, large parts of the respective strains were released under stress-free recovery conditions. The two-fold fixed ('programmed') specimens responded to heating with two independent length contractions (switching steps); the first shape change was associated with PCL devitrification and the second one with the melting of hitherto crystalline PCL. It was revealed that the triple-shape properties of SPOSS-PU networks considerably depend on PCL network chain length. When applying exactly the same 'triple-shape creation procedure', larger strain releases were detected in the first transition for polymers with a higher PCL network chain length, whereas the second transition was more accentuated for SPOSS-PU networks with a shorter PCL chain length. In the course of thermo-mechanical cycling, the formation of a neck during the second tensile deformation was repeatedly detected for SPOSS-PUs with higher PCL network chain length; in the subsequent recovery process the specimens even exhibited the highest total strain recoverability. Finally, gradual strain release could be achieved at temperatures below the PCL melting transition through the selection of up to four temperature holding steps, at which every time stable shapes were formed. KW - Shape memory polymer KW - Active polymer KW - Triple-shape polymer KW - Hybrid star-shaped polymer KW - POSS-polycaprolactone polyurethanes KW - Thermo-mechanical properties PY - 2012 DO - https://doi.org/10.1039/c1sm06474f SN - 1744-683X VL - 8 IS - 4 SP - 965 EP - 972 PB - RSC Publ. CY - Cambridge AN - OPUS4-25260 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Mya, K.Y. A1 - Gose, H.B. A1 - Pretsch, Thorsten A1 - Bothe, Martin A1 - He, C. T1 - Star-shaped POSS-polycaprolactone polyurethanes and their shape memory performance JF - Journal of materials chemistry N2 - Star-shaped polyhedral oligomeric silsesquioxane (SPOSS)-based multi-arm poly(ε-caprolactones) (PCLs) with various arm lengths were synthesized by ring opening polymerization of ε-caprolactone. Increasing the PCL arm lengths was observed to increase the melting temperature and also the melt crystallization temperature in SPOSS-PCLs. Star-shaped POSS-PCL polyurethanes (SPOSS-PUs) were then prepared by cross-linking SPOSS-PCLs with hexamethylene diisocyanate (HMDI) and their shape memory (SM) behaviour was determined. For this purpose two cyclic thermo-mechanical testing concepts with similar programming (deformation and shape fixing) but different recovery strategies (free strain versus fixed-strain constrained stress recovery) were used and the synthesized polymers were systematically investigated around the crystallization and melting temperatures of PCL. SPOSS-PU with the highest POSS content exhibited remarkable cycles-averaged (N = 2–5) shape fixities and strain recoverabilities of 98% and stress recoverabilities close to 100%. The main structural factors that were expected to reduce the SM performances with increasing PCL arm lengths were a lowering of cross-link density (content of octasubstituted POSS) and an increase in chain flexibility/molecular mobility. KW - Shape memory polymer KW - Active polymer KW - Hybrid star-shaped polymer KW - POSS-polycaprolactone polyurethanes KW - Thermo-mechanical properties PY - 2011 DO - https://doi.org/10.1039/c0jm04459h SN - 0959-9428 SN - 1364-5501 VL - 21 IS - 13 SP - 4827 EP - 4836 PB - Royal Society of Chemistry CY - Cambridge AN - OPUS4-23479 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -