Poly(l-lactic acid) Microdomain as a Nanopolarization Rotator in a Flexible, Elastic, and Transparent Polyurethane

Abstract

Chiral molecules have the ability to rotate the polarization plane of polarized light. Polymers that own a chiral segment are called optically active polymers, and a rigid backbone is usually required to maintain the chiral conformation, which also restricts their application mostly in the solution state. Polylactide acid is one of the most important biobased and biodegradable polymers, and its repeating unit could have left-handed and right-handed conformations. However, the utilization of its optical activity is mainly to improve its mechanical performance by forming a stereocomplex. In this work, we incorporate the poly­(l-lactic acid) (PLLA) diol in the soft segment of a polyurethane elastomer with high transparency and good recoverability. During the tensile process of in situ small-angle polarized light scattering, we find that the polarization plane of the incident light will be tuned periodically. The brightening process under the horizontal–vertical (Hv) mode always corresponds to the darkening procedure under the vertical–vertical (Vv) mode and vice versa. As the strain increases, the period where the scattering pattern changes from bright to dark also increases. Small-angle X-ray scattering/wide-angle X-ray scattering results exclude any periodic structural evolution in a length scale of 0.1–100 nm, and we conclude that the chiral PLLA segment induced such a polarization rotation phenomenon. The decrease of effective thickness of PLLA domains along the light path caused the periodic change in the polarization degree. Such a polyurethane elastomer can be used as a component in stretchable electronics and is very useful in tumor imaging and defect detection.

Chiroptical Elastomer Film Constructed by Chiral Helical Substituted Polyacetylene and Polydimethylsiloxane: Multiple Stimuli Responsivity and Chiral Amplification

“…As far as chiral polymers are concerned, the relevant research has mainly focused on conformation chirality and phase chirality. As relatively new types of chiral polymeric materials, chiral elastomers can be divided into chiral polymer-based elastomers and liquid crystal elastomers (LCE). − Besides, chiral helical substituted polyacetylenes are typical synthetic helical polymers with conformational chirality and a well-known chiral amplification effect. − In our previous studies, a series of chiral functional materials have been explored, taking advantage of the helical chirality of substituted polyacetylenes. − However, how to rationally combine chiral helical polymers with elastomers still remains highly challenging. The efforts along this research direction are expected to lead to some new chiroptical materials integrating the individual advantages of chiral helical polymers and elastomers.…”