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 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 U6 - 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 -