Styrene has been copolymerized at low conversion with minor quantities of p‐divinyl‐benzene (p‐DVB) in (10–15%) solution in toluene and cyclohexane. Under these conditions the molecular weight of the polystyrene formed in the absence of p‐DVB was controlled by chain transfer, and the copolymerization coefficients of the styrene and the p‐DVB agreed with previous work. Polymer molecular weights were studied as a function of conversion. At very low conversions the number‐average (2.2 × 105) and the weight‐average (4.4 × 105) molecular weights were unaffected by substituting some of the styrene by p‐DVB, but as the reaction continued M̄n increased slowly and M̄w much faster. On the other hand, even at the lowest conversions the intrinsic viscosity was drastically reduced by the introduction of p‐DVB, and the radius of gyration, as measured by light scattering, fell. Infrared studies on the polymer show that the concentration of pendent double bonds in low‐conversion copolymers is about half of the doubly substituted phenyl groups. It is concluded that the first polymer chains formed are extensively cyclized with the formation of a relatively large number of small rings.

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A new generation of hip replacements has been designed incorporating compliant layers to promote fluid film lubrication when the joints are implanted in patients. Tests in the Durham hip function simulator show that the friction in these joints is up to an order of magnitude lower than in currently used prostheses, and because this is due to complete separation of the rubbing surfaces, wear ought to be vastly reduced. Experiments have shown that the best results are achieved with compliant surfaces of hardness between 4 and 8 N/mm2. Such surfaces produce coefficients of friction of the order of 5 × 10-3.

An experimental study of the lubrication mechanisms existing in prototype artificial hip joints which have compliant surface linings, has shown that for a lining with a hardness of about 4N/mm2, fluid film lubrication can be achieved even with the low viscosity synovial fluid present in diseased joints after surgery. In tests, a synthetic lubricant was used in place of the synovial fluid. The best results seem to be produced with a 2 mm thick layer.

synopsisThe effect of temperature and strain rate on the compressive yield behavior of polystyrene is compared with the effect of the same variables on crazing in tension. The results support the conclusion of other, more extensive work, which shows that crazing involves the same types of molecular processes as those which occur during deformation under compression and shear. An improved method of measuring compressive stressstrain curves is then described, and the compressive yield stress is also compared with an extrapolated tensile yield stress. The difference between the two is in line with concepts which assume a dependence of yield stress on the state of hydrostatic tension (or compression).A p plication of this criterion also enables a theoretical stress strain curve in tension to be derived from other results in compression. Comparison of the tensile stress-strain curve so obtained with those which can be directly measured with other plastics, supports the hypothesis that crazing is favored by a marked decline in engineering stress during tensile elongation (plastic instability). It can be adequately described by the Mohr-Coulomb yield criterion.