Polystyrene mechanical anisotropy

There are relatively few measurements on amorphous polymers, where the degree of mechanical anisotropy is much less than in crystalline polymers. Early studies include those of Hennig [92] on polyvinyl chloride, polymethylmethacrylate and polystyrene and Robertson and Buenker [93] on bisphenol A polycarbonate. The results are summarised in Table 8.8. Hennig s measurements on 533 and 5n were obtained from dynamic testing at... 

A peculiarity of polystyrene in bulk is the fact that it has a negative optical anisotropy. The optical anisotropy is revealed, for instance, by birefringence when the material is strained. Let us consider a uniaxial strain produced by a mechanical tension 3. For small deformations, the difference Sn of the indices for directions parallel and perpendicular to the axis vary linearly with respect to F... 

Is the mean length of the glass fibre reinforcement in injection-moulded polypropylene (fig. 4.28a) sufficient enough to give optimal stress transfer to the fibres Explain how the stiffness anisotropy in such a moulding arises. What new mechanisms of energy absorption arise when polystyrene is converted into a low density closed cell foam, and how can the compressive yield stress be controlled over a range of values ... 

In many instances orientation is produced deliberately. In onedimensional articles such as fibres and monofils the mechanical properties are, in general, only of importance in one direction and therefore a high anisotropy is desirable. In two-dimensional objects such as sheets and films good properties are required in two or even in only one direction, dependent on the application. Biaxial orientation may be beneficial to improve strength and toughness. A biaxially oriented thick polystyrene sheet, for instance, can be so flexible and tough, that it can be bent through... 

Conformation and Chemical Shifts.—Chemical shifts have been correlated with conformation for H shifts in polystyrene and poly(vinyl chloride) and C shifts in model compounds of polypropylene. In all these papers, the chemical shift is related empirically to the occurrence of three- and four-bond steric interactions, similar to those used in the rotational isomeric state treatment of polymer statistical mechanics, " and the shift is expressed as a sum of compositional and conformational increments. The origin of the shielding contributions (magnetic anisotropy, electric field effects, etc.) is not stated, except for polystyrene in which the magnetic anistropy of the aromatic rings are incorporated... 

---