The strategic aims of the project include the following:
Synthesis and evaluation of suitable mesogenic structures with different functional groups to provide structure property relationships to control and predict the phase behaviour in a wide range of curing conditions.
Investigation of the morphology of the thermosets as a function of chemical structure and extent of reaction.
Determination of relevant mechanical properties of the thermosets in relation to the structure of the thermosets, modelling of network formation.
The processing of the new materials will be the same as that of conventional thermosets.
The functional liquid crystalline monomers based on diad and triad mesogens have been synthesised and characterised and a chemical selection has taken place. Monomers have been characterised by chromatographic, spectroscopic and thermal analytical techniques. Polymerisations form an anisotropic phase that is retained in the crosslinked polymer. Advances have been made in the type of reactions that can yield anisotropic networks. In total 65 new monomers have been reported along with fundamental scientific work on 15 new model compounds. New chemistry to produce anisotropic networks, the reaction of isocyanates with liquid crystalline epoxies has yielded a new class of anisotropic oxazolidinone materials. The CLTE's of a large number of mesogenic networks have been measured. No materials have been made which meet the stringent requirement of CLTE < 20 ppm. The analysis of machineability and long-term stability was delayed. Ultimately no materials passed the OCÉ thermal expansion coefficient test. A polymerisation model has been developed and applied to the reaction kinetics. The application of the model is reported for a number of systems. 10g quantities of a number of monomers have been characterised by X-ray diffraction and rheological techniques. Oriented networks have been made by polymerisation in a strong magnetic field. The time-resolved spectroscopy, rheology and X-ray diffraction experiments provide the data-base for the development of a process model. 100g quantities of monomer were processed into oriented and unoriented liquid crystalline networks whose structure and mechanical properties have been measured. The fracture toughness of the lc-network materials is twice that of the isotropic networks. The fracture toughness obtained exceeded the specification by a factor of ten. Collaboration between partners has lead to the development of mechanical testing protocols which limit the amounts of material required for the accurate determination of materials properties.
Inherent problems in processing and undesired orientation of thermoplastic liquid crystalline polymers require innovative solutions to overcome these drawbacks while maintaining their beneficial properties of high stiffness and strength allied to a low coefficient of thermal expansion.
The project has the goal of scientifically investigating the manufacture of self reinforcing thermosets by network formation from low molecular weight liquid crystalline compounds in a mesophase. The thermosets will consists of microscopic whereas the domains are randomly oriented and give a macroscopically isotropic material.
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