Small band gaps simplify the use of polymers as semiconductors. Dye molecules can be used to construct semiconducting polymers with small band gaps. We use ab initio calculations to systematically design and study polymers derived from squaraine dyes. The calculated band gaps range from 2.3 eV to as low as 0.2 eV. Simple arguments based upon a Hückel analysis of the ab initio results enable us to identify the factors that control the size of the band gap. Squaraine polymers synthesized up till now fall into a class in which the band gap (≥1.3 eV) essentially reflects the HOMO/LUMO energy difference of the squaraine monomer fragment. We predict that a second class of polymer topology leads to much smaller band gaps. The reason for this is that band formation in the polymer shifts the energy of the highest occupied state of the polymer up with respect to the HOMO of the squaraine monomer, whereas the energy of the lowest unoccupied state of the polymer is fixed at the level of the monomer LUMO because of symmetry. New semiconducting polymers can be designed using such general principles as symmetry and topology.

Low molecular mass liquid-crystal materials can be aligned homogeneously by polymer layers that are rubbed. Therefore, the rubbing process is widely used in the mass production of liquid-crystal displays. The rubbing treatment orients the polymer molecules in the layer. The extent of orientation of rubbed polyimide layers was investigated, using uniaxially drawn polymer tapes as a reference. For this, the experimental results from optical phase retardation, infrared dichroism, and X-ray diffraction studies were combined with a molecular modeling study. The results indicate that the Hermans' orientation factor of the top of the rubbed polyimide layer, Le., the part directly contacting the rubbing cloth during the rubbing process, clearly exceeds 0.5. In view of the fact that the studied polyimide is an amorphous polymer, this factor is rather high, indicating that the rubbing process is an effective way to induce molecular orientation of a polymer layer. The rubbing process is found to be more effective to orient a solvent-free thin polyimide layer than uniaxial drawing.

Three isomeric liquid crystal (LC) acrylates l,4-bis ((4-((6-(acryloyloxy)hexyl)oxy)benzoyl)oxy (benzene, ((6-(acryloyloxy)hexyl)oxy)-4- ((4-((4-((6-(acryloyloxy)hexyl)oxy)benzoyl)oxy)benzoyl)oxy)benzene, and bis(4-((6-(acryloyloxy)hexyl)oxy)phenyl) terephthalate were Synthesized. The orientation of the ester links with respect to the central phenyl ring has a strong influence on the phase, optical, and dielectric behavior of the monomers.The polymerization behavior of the isomers was found to differ. Changes occurring in the microstructure during polymerization were studied using X-ray diffraction. In order to obtain an understanding of the observed differences, the phase behavior and polymerization behavior of various mixtures were studied. The results of the experiments and the molecular modeling suggested that the associations between the molecules is the origin of the formation of observed LC phases and the strength of the interactions determine whether the microstructure is preserved during polymerization.

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