Insights into Shape-Memory Poly(蔚-caprolactone) Materials by Solid-State NMR

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• 作者：Silvia Borsacchi ; Katia Paderni ; Massimo Messori ; Maurizio Toselli ; Francesco Pilati ; Marco Geppi
• 刊名：Macromolecules
• 出版年：2014
• 出版时间：June 10, 2014
• 年：2014
• 卷：47
• 期：11
• 页码：3544-3552
• 全文大小：370K
• 年卷期：v.47,no.11(June 10, 2014)
• ISSN：1520-5835

文摘

Polymeric materials showing shape-memory behavior are attracting large interest especially in the field of biomaterials. Despite the large number of studies aimed at charaterizing macroscopic features, detailed investigations of properties at the nanometric scale and molecular level are still very few. In this work we present a multinuclear and multitechnique solid-state NMR investigation on recently developed hybrid materials formed by sol鈥揼el cross-linked alkoxysilane terminated poly(蔚-caprolactone), showing very interesting shape-memory behavior. By investigating several spectral and relaxation properties of ²⁹Si, ¹³C, and ¹H nuclei present in the hybrid material, we could characterize and compare the structural, dynamic, and phase properties of a sample fixed in a stretched temporary shape with those of a sample in the permanent shape. Interesting differences could be observed: in particular, the sample fixed in the temporary shape showed a larger amount (40% instead of 35%) of crystalline phase and amorphous domains in which polymeric chains experienced a more restricted molecular mobility, as inferred from proton T₂ values. Moreover, from ¹³C spectra recorded by varying the orientation of the sample with respect to the direction of the magnetic field, it was possible to clearly detect that about 90% of PCL chains, mainly in the crystalline domains, but also in the amorphous ones, were strongly aligned along the stretching direction. If subjected to heating, so to remove the temporary shape, the sample showed a melting temperature a few degrees higher, a sligthly more rigid melt phase, and a complete loss of molecular alignment.