Joachim Rübner

Methacrylate networks containing chiral calamitic liquid crystalline side groups

A one-step copolymerization of ferroelectric methacrylate monomers leading to networks is presented. Oriented networks are obtained and electro-optical investigations are described. Smectic C * and another smectic phase are found in slightly crosslinked networks. For higher crosslinking densities, only the high temperature smectic C * phase was found. Electro-optical measurements were performed on the networks, and significant changes in the ferroelectrical properties were found. For crosslinking densities higher than 0.5 mol-%, switching times increased dramatically and the spontaneous polarization decreased. Networks with crosslinking densities of 2 mol-% did not exhibit ferroelectric properties.

New azo-dye containing side group copolymethacrylates

A new type of side group copolymethacrylates was synthesized, characterized and tested with rcspect to its behavior on irradiation with an Ar + -laser beam. The side groups consist of methylene spacer units with different length and of three-ring mesogens with an ester group between the first and the second aromatic ring and on the other hand of two-ring mesogens with an azo-structure between the aromatic rings, respectively. The azochromophoric structure contains different substituents in the terminal aromatic ring. The homopolymcrs of the azo-dye containing monomers do not display liquid crystalline (Ic) mesophases, but the three-ring mesogens induce lc-phases in opposition to the equimolaric copolymers with two-ring ester group mesogens. The Ic phases are important for the stability of the recorded change of birefringence (photorecording process) which is influenced by irradiation of thc polymers.

Thermal and Ferroelectric Stability of Liquid Crystalline Methacrylate Networks

Abstract A series of ferroelectric liquid crystalline methacrylate networks was synthesized via bulk copolymerization. Electro-optical investigations revealed ferroelectric behavior (spontaneous polarization (Ps), ferroelectric switching, tilt angles) up to a certain degree of crosslinking. In this contribution we present a study of the ferroelectric properties with regard to their long term stability. A considerable part of this work is focussed on the determination of the network structure, the degree of conversion and on the often unanswered question of the amount of monomer still present in the network, which cannot be extracted. We found that the crosslinking reaction reaches almost quantitative degrees of conversions. This was confirmed by infrared spectroscopy.

Polymer liquid crystals in solution

The great interest in the application of new materials with anisotropic properties since 1980 or so has led to the stormy development of polymer liquid crystals (PLCs). With the aim of optimizing certain mechanical, optical or electrical properties, many polymers with new structures have been synthesized and tested. To understand the relationship between the properties and the molecular and supermolecular structure of this class of polymers, systematic investigations of the materials have not kept up with this dramatic development. Especially the properties of these polymers in solution have been relatively little investigated until now, even though information concerning molecular parameters such as molar mass, degree of polymerization, molecular dimensions and shape, linearity and chain branching can be accessed only through the investigation of solutions. In addition to the anisometric shape of the repeating units, the properties of mesophases are due to strong interactions between the mesogens.

Zur kinetik der copolymerisation von methacrylaten mit entkoppelter seitengruppe

The copolymerization behaviour of methacrylate monomers CH 2 =C(Me)COO(CH 2 ) 6 OPh(R)-X-PhOMe (R= H, Br; X= COO, CONH, N=N) was studied depending on the structure of the linked mesogen. Some units (-N=N-, -CO-NH-) in the mesogen influence the copolymerization reaction in spite of the strong decoupling by a C 6 -spacer group and lead to retarding effects and to the preferred insertion of monomers with weaker mesogenic interactions. The liquid-crystalline behaviour of the copolymers was not affected due to the relatively small differences in the copolymerization parameters