Glass forming high polymers have been densified by application of high hydrostatic pressure (∼1.5 kbar) in the melt followed by cooling under pressure to ambient. A density increase of about 1% was induced in each of the following polymers: polyvinylchloride, polymethylmethacrylate, polystyrene, poly‐4‐chlorostyrene, poly‐3‐chlorostyrene, poly‐4‐methoxystyrene and poly‐4‐phenoxystyrene. Differential thermal analysis (DSC) and volume relaxation techniques were used to study the reversion of the densified glass to a more normal glass at a temperature ∼Tg – 15 K in general. Enthalpy relaxation (a change from glass I to glass II) in this region gives a peak or diffuse hump on the DSC scan prior to a normal glass transition temperature. It is considered that although the densified glasses may become thermodynamically stable at a sufficiently low temperature they are inherently unstable at ambient. Reversion to a more normal glass is kinetically too slow to measure at ambient in all cases studied except polymethylmethacrylate. Changes of dynamic Young's moduli and dielectric constant with densification are reported in detail for some systems and in summary for others. The densified glasses exhibit moduli higher by ∼6%, dielectric constant higher by ∼2% and depressed secondary mechanical and dielectric relaxation processes. Ultimate property studies are reported for PVC.

The study of polymer interfaces is of prime importance in the field of tyre technology due to the critical role these contribute to tyre operation. The paper reviews the main polymer interfaces present in a t y r e g l ) tyre/road (tyre wear or abrasion; tyre traction/skid resistance); (2) polymer/filler (carbon black; silica): (3) polymer/cord (brass coated steel wire; textilcrayon, nylon, polyester, aramid); (4) compound/compound (tack); (5) tyrepair (oxygen/ozone protection)-with respect to the criteria required, physical and chemical, to achieve optimum performance.

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