(Photo)crosslinkable Smectic LC Main‐Chain Polymers

Abstract

This paper presents the synthetic route to SmA LC main‐chain polymers, that can be (photo)crosslinked without solvent in the bulk phase. They are based on soluble polymalonates, in which higher ordered phases can be suppressed by copolymerization with a laterally brominated biphenyl. Two routes were developed to incorporate the crosslinkable groups into the polyester backbone. The first consists in the incorporation of phenols into the polyester. These phenols are not reactive enough to participate in the transesterification reaction used to build up the polymer, but they can be esterified afterwards with acrylates. Thermally or photochemically created radicals then start the crosslinking. The second route is based on the incorporation of benzophenone as side group. It allows a photochemical crosslinking. Crosslinked fibers (monodomains) show the potential of the smectic LC main‐chain elastomers as actuators.magnified image

Nanosized Shape‐Changing Colloids from Liquid Crystalline Elastomers

“…The corresponding syntheses have been published elsewhere. [20] Main-chain LC polymers show notoriously high phase transition temperatures. However, due to practical reasons, an actuation at more ambient conditions is desirable.…”

“…The employed main-chain polymer was a polyester made from diethyl malonate derivatives and bis(hydroxyoxyhexyl) bisphenyl derivatives [20,21] (see Scheme 1). The corresponding syntheses have been published elsewhere.…”

Liquid Crystalline Elastomers as Actuators and Sensors

“…Here, the liquid crystalline prepolymer already contains crosslinkable groups. These can for example be photoreactive benzophenone units which attach to C–H σ ‐bonds after UV irradiation in an H‐abstraction mechanism,34 allowing a crosslinking to aliphatic parts of the polymer 35–37 . Figure shows a system introduced by Beyer.…”

Actuators based on liquid crystalline elastomer materials

“…Another example for mechanical orientation is the drawing of fibres from a polymeric liquid crystal and a quick crosslinking afterwards, before the obtained orientation is lost. This can be manually done [20, 26], or in a more sophisticated electrospinning process [27, 38]. These LCEs are easily prepared and highly ordered, and to some extent mimic natural muscles.…”