Phase Transition Behavior of Main Chain Nematic Liquid-Crystalline Polymers Based on 2-methyl-1,4-bis[4-(4-pentenyloxy)b
- PDF / 241,696 Bytes
- 6 Pages / 432 x 648 pts Page_size
- 3 Downloads / 243 Views
Phase Transition Behavior of Main Chain Nematic Liquid-Crystalline Polymers Based on 2-methyl-1,4-bis[4-(4-pentenyloxy)benzoyl]hydroquinone and 2-tert-butyl-1,4-bis[4-(4-pentenyloxy)benzoyl]hydroquinone C. Melchert1,2, M. Behl1,2, and A. Lendlein1,2 1
Center for Biomaterial Development and Berlin Brandenburg Center for Regenerative Therapies, Institute of Polymer Research, Helmholtz-Zentrum Geesthacht, Kantstr. 55, 14513 Teltow, Germany 2 Institute of Chemistry, University of Potsdam, Potsdam-Golm, Germany ABSTRACT The control of phase transition behavior in liquid crystalline polymers could enable potential application in the field of actuators and sensors by enabling a higher actuator performance of liquid crystalline elastomers (LCE). In this context the phase transition behavior of siloxane based liquid crystalline copolymers synthesized from 1,1,3,3-tetramethyldisiloxane, 2-methyl-1,4-bis[4-(4-pentenyloxy)benzoyl]hydroquinone (M-MeHq), and 2-tert-butyl-1,4bis[4-(4-pentenyloxy)benzoyl]hydroquinone (M-tBHq) was explored. The selected monomers provided different thermal stabilities of the nematic phase, while the non-flexible siloxane spacer suppressed a smectic phase. The mesogenic properties were studied by means of differential scanning calorimetry (DSC), polarizing optical microscopy (POM), and wide angle X-ray scattering (WAXS). With increasing fraction of M-MeHq the nematic phase of the copolymer was stabilized and a tailoring of relatively low TNI was achieved. INTRODUCTION Liquid crystalline polymers attracted the attention of researchers since many years due to their unique abilities related to the combination of the thermal and mechanical properties of polymers with the optical properties of liquid crystals. This enabled a broad range of applications, spanning e.g. from flat panel displays to sensors and actuators [1]. Main chain liquid crystalline polymers (MCLCP) are a very interesting class among the various liquid crystalline polymers. MCLCP feature mesogens incorporated in the polymer backbone, which are connected by spacers providing variable flexibility. The mechanical and mesomorphic properties such as the nematic to isotropic phase transition temperature (TNI) are determined by the chemical structure of the mesogen and the flexibility of the spacer [2, 3]. Liquid crystal elastomers (LCE) could be obtained by weak crosslinking of MCLCP and were capable of a spontaneous uniaxial contraction at the nematic to isotropic phase transition [4]. This transition could be triggered by different stimuli, e.g. temperature [5], light [6], and alternating magnetic fields [7]. The process was shown to be reversible and resulted from the combination of the flexible polymer backbone and the anisotropy resulting from the mesogens [8]. Main chain LCE exhibited an enhanced coupling of elasticity and anisotropy compared to LCE consisting of mesogens attached to the side chain of the polymer backbone [9]. For these reasons nematic MCLCP are an important class of LCE. However, the high phase transition temperature of
Data Loading...
