Synthesis and mesomorphic properties of side chain liquid-crystalline biphenyl-phenyl polyacrylates

Abstract

A síntese e a caracterização de dois cristais líquidos poliacrilatos, de cadeia lateral contendo o sistema bifenil-fenila como unidade central são descritos. A cadeia terminal é derivada da L-isoleucina. Em cada caso, o espaçador undecila foi utilizado para conectar o grupo mesogênico e a cadeia polimérica. Ambos os polímeros apresentaram mesofase esmética A. Encontrou-se uma dependência entre as propriedades transicionais e parâmetros estruturais, tais como, flexibilidade da cadeia polimérica e conectividade da cadeia terminal quiral.The synthesis and characterization of two chiral side-chain liquid crystal based on polyacrylates having a biphenyl-phenyl system as a core unit are described. The chiral terminal chain is derived from L-isoleucine. In each case an undecyl spacer was used to connect the mesogenic group to the backbone. Smectic A phase was found for both polymers. The transitional properties were dependent on structural parameters such as backbone flexibility and chiral terminal chain connectivity. Keywords: chiral polyacrylates, L-isoleucine, synthesis, liquid crystal IntroductionLiquid crystals science is a field of human knowledge that emerged at the end of the 19 th century when the Austrian botanist Friedrich Reinitzer 1 reported from his microscopic observation the unusual thermal behavior of the molten sample of cholesteryl benzoate. This first observation of optical anisotropies phenomena in organic compounds opened a new and fascinating class of soft materials which combines extraordinary optical, elastic and viscous properties.Liquid crystals are systems that can self-organize due to mesogenic groups which show short and long range collective interactions among them. This is the origin of interesting liquid crystals properties which were exploited extensively in the earlier 70's in TN-LC technology. 2,3 Nowadays, the LC displays are found everywhere such as watches, clocks, calculators, portable notebooks computers, vehicle clocks, speedometers, navigation and positional aids, mobile phones, flat desktop monitors, wave plates, polarizers, notch filters, etc. The LC technology has dominated the display market due to their compactness, low weight, low-voltage operation, and lower power consumption. In our technological society, LC displays provide an interface between humans and machines and are expected to play an even bigger role in the future as the need of displaying information grows. The need of developing LC materials, batteries, polarizers, electrodes, semi-conductor, compensation films, spacers, etc for those applications mentioned before has been the main driving force behind LC research. LC science growth was dependent on the parallel progress and development of other fields of science such as synthetic organic chemistry, electronics, physics and device engineering.Concerning LC materials, there are basically two types of concepts related to the design and synthesis: (i) development of non-polymeric liquid crystals which are extensively used in LC displays as fast active devices w...

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