A study of the structure, properties and synthesis of block copolymers

The mechanical properties of a styrene–butadiene–styrene block copolymer (Shell Cariflex K101) have been found to be dependent upon the morphology of the polymer, which could be altered by thermal or solvent treatments. Films cast from toluene, methylene chloride and methyl cyclohexane and moulded samples are compared. Small-angle X-ray scattering, electron microscopic and swelling techniques have been used to determine the morphology of the samples. Macro-lattice models based on the microphase separation of the two chemical species into domains and matrix have been proposed for the toluene and methylene chloride cast samples. Properties which have been found to differ are the dynamic mechanical spectra, stress-strain behaviour, stress relaxation and creep. The dynamic mechanical apparatus as described by Bowman has been improved and modified and has been used to measure the Young's temperature moduli and loss tangent of the (-150°C to +120°C) and frequency samples over a wide range (0.01Hz to 1000Hz). The network characteristic of this system has been attributed to the entanglements of the polybutadiene chains, the physical adsorption of the polybutadiene chains onto the domain surface and the polybutadiene–polystyrene junctions. The ultimate properties have been shown to be those of the rubbery matrix but are highly enhanced by the polystyrene domains acting as reinforcing fillers. Preliminary work has been carried out in the synthesis of the XYX type of block copolymer where X is a crystalline segment (poly 3,3-bis(chloromethyl) oxetane) and Y is an elastomeric segment (tetrahydrofuran/3,3-bis(chloromethyl) oxetane copolymer).