SUMMARY:Bis[(4'-cyanobiphenyl~-yl)oxy-n-alkyl]norbo~-5-ene-2,3-~~boxylates with alkyl chain lengths rn = 2-12 were synthesized. Most of the monomers exhibit thermodynamically metastable liquid crystalline phases with respect to the crystalline phases. Polymers were prepared by ring-opening metathesis polymerization (ROMP) using the molybdenum carbene initiator [Mo(CH-t-Bu) (NAr) (t-BuO),] (t-Bu = tert-butyl) with NAr = 2,6-diisopropylaniline. All polymers show thermotropic liquid crystalline phases. Results on characteristic phases and the influence of the number of methylene units m in the flexible spacer on the thermal behaviour (glass transition temperature, isotropization temperature, odd-even effect, enthalpy change) of these new side chain liquid crystal polymers (SCLCP's) are given. They are compared to monosubstituted polynorbornene derivatives and to SCLCP's with other backbones.

The polymerization of acetylene monomers using homogeneous Schrock-type initiators of the general formula Mo(CHR‘)(NAr)(OR)2 with different substitution patterns was investigated. The influence of the ligands at the molybdenum center and of donor functions at the β-position with respect to the monomer's triple bond on the polymerization was studied by means of NMR spectroscopy and size exclusion chromatography. The results clearly indicate that kinetics and mechanism of the metathesis reaction strongly depend on the structures of monomer and initiator. The use of partially fluorinated alkoxy ligands instead of aliphatic alkoxides leads to a change of the regiochemistry of the insertion. Ether functions in the monomer tend to slow the reaction, giving rise to polymers with a narrow molecular weight distribution probably due to coordination of the oxygen atom to the metal center.

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The ring opening metathesis polymerisation (ROMP) of (*)-and (-)-exo, endo-bis[(4'-cyanobiphenyl-4-yl)oxyalkyl]norborn-5-ene-2,3-dicarboxylates using three different Schrock type molybdenum alkylidene complexes ([Mo(NA~)(CH-~-BU)(OR)~] with R3C(CH3)3, -C(CH3)*(CF3) or -C(CH3)(CF3),) resulted in the formation of side chain liquid crystalline polymers (SCLCP's). The different initiators caused changes in the backbone tacticity which were determined by means of NMR techniques. The influence of the type of tacticity on the thermotropic behaviour of the SCLCP's was investigated. The thermal properties were determined by differential scanning calorimetry (DSC). The transition temperatures increased with rising molecular weight up to a degree of polymerisation of about 40. Above this value the thermal properties remained constant with increasing molecular weight. The types of phases for the liquid crystalline polymers were elucidated by polarising optical microscopy (POM). In general, the highly tactic polymers showed a broader thermal range of the LC phase. The kind of initiator used caused changes of the thermal and thermotropic behaviour of the SCLCP's. A grafting ratio model is introduced to explain the findings. From the experimental data a structure/property relationship is developed which might help to predict liquid crystalline properties of unknown polymers.

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Molybdenum carbene complexes supported on Al2O3/methylaluminoxane/ diol based carriers were tested in continuous metathesis reactions. For investigations on the stability of the heterogenized complexes, a small tubular reactor filled with catalyst powder was used. When mixing cyclic monomers with chain-transfer agents, we were able to run ring-opening metathesis polymerization (ROMP) via the supported carbenes in a continuous process. Furthermore, continuous acyclic metathesis reaction (ACM) and ring-closing metathesis reaction (RCM) were investigated. Results show that the stability of these molybdenum carbene complexes depends on the concentration of methylidene carbenes formed during the reactions.