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Issue 4, 2012
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Triple-shape properties of star-shaped POSS-polycaprolactone polyurethane networks

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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.

Graphical abstract: Triple-shape properties of star-shaped POSS-polycaprolactone polyurethane networks

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Publication details

The article was received on 01 Aug 2011, accepted on 19 Oct 2011 and first published on 15 Nov 2011

Article type: Paper
DOI: 10.1039/C1SM06474F
Citation: Soft Matter, 2012,8, 965-972

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    Triple-shape properties of star-shaped POSS-polycaprolactone polyurethane networks

    M. Bothe, K. Y. Mya, E. M. Jie Lin, C. C. Yeo, X. Lu, C. He and T. Pretsch, Soft Matter, 2012, 8, 965
    DOI: 10.1039/C1SM06474F

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