In Situ X-Ray Scattering Studies of Poly(Epsilon-caprolactone) Networks with Grafted Poly(ethylene glycol) Chains to Investigate Structural Changes during Dual- and Triple-Shape Effect


The dual- and triple-shape effects of multiphase polymer networks that contain two crystallizable chain segments have been assessed in situ by combining X-ray measurements with thermomechanical investigations. The studied polymer, named CLEG, is a multiphase polymer network of crystallizable poly(ε-caprolactone) (PCL) with grafted poly(ethylene glycol) (PEG) side chains. Wide-angle (WAXS) and small-angle X-ray scattering (SAXS) measurements were combined with temperature-controlled in situ tensile testing experiments. This integrated approach enables systematic investigation and interpretation of relevant structural features during the programming procedures and the thermally-induced recovery process. Main results concern the combined effect of PCL and PEG crystals on shape fixation, the specific role of low-melting PCL crystallites in the fixation of the low temperature temporary shape, and the different orientation behavior of PCL and PEG crystals during certain stages of the programming procedure. These results demonstrate that crystal orientation effects are dominant for the PCL crystals. The effects of the low temperature PCL crystals could only be investigated when synchrotron radiation was applied. These findings indicate the great potential of in situ X-ray investigations for the creation of design-relevant knowledge about the microscopic foundations of dual- and triple-shape effects in appropriate polymer systems.
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