Polystyrene continuous morphologies

Extreme differences in PB block length curiously appear to extend the range in PS block heterogeneity in which polystyrene-continuous morphologies are possible. For example, Figure 13 shows a straight blend of linear SBS polymers in which both kinds of blocks vary tenfold in length (composition F) ... 

In the time interval between phase inversion and gelation of the polystyrene continuous phase, the final morphological features such as size average and size distribution of elastomer domains become fixed. Since these morphological changes affect properties such as modulus and impact resistance, the characteristics of the system at and just after phase inversion and before gelation demand the closest scrutiny. The open time interval was found to decrease as the polyester prepolymer content increases, probably because higher polystyrene conversions are required for the system to reach suitable phase inversion conditions. 

Electron micrographs of compositions D and E are shown in Figures 9 and 10. It is evident that in E polybutadiene is the continuous phase (with some rubber in the polystyrene domains) while D represents a transition from lamellar to polybutadiene-continuous morphology. Again the dynamic mechanical data (Table II) are consistent with these obser-... 

Since the last edition several new materials have been aimounced. Many of these are based on metallocene catalyst technology. Besides the more obvious materials such as metallocene-catalysed polyethylene and polypropylene these also include syndiotactic polystyrenes, ethylene-styrene copolymers and cycloolefin polymers. Developments also continue with condensation polymers with several new polyester-type materials of interest for bottle-blowing and/or degradable plastics. New phenolic-type resins have also been announced. As with previous editions I have tried to explain the properties of these new materials in terms of their structure and morphology involving the principles laid down in the earlier chapters. 

This simplified representation of the morphology shows spheres of polystyrene embedded in a continuous soft elastomeric polybutadiene phase. Here the polystyrene domains act as pseudo crosslinks and the polybutadiene conveys elasticity to the material. When heated above the Tg of polystyrene, the domains soften, disassociate, and the material can be made to flow. When cooled, the polystyrene domains reform and elastomeric behaviour returns. 

Figure 4.2 An Archimedean tile morphology for blends of poly(2-vinylpyridine-/)-isoprene-/)-vinylpyridine) with poly(styrene-/)-4-hydroxystyrene) in a 2 1 vinylpyridine/hydroxystyrene blend. The vinylpyridine/hydroxystyrene domains are the cylinders at the vertices of polystyrene hexagons within a polyisoprene continuous phase. Reprinted from Asari et al. (2006). Copyright 2006 American Chemical Society.

As shown in Figures 5 and 7 the nature of the solvent does not appear to have any effect on T0 within experimental error. However, the solvent can have a profound influence on the morphology of cast block copolymer specimens. Thus, instead of the continuous polybutadiene phase normally observed, a continuous polystyrene phase appears to exist in Kraton 101 films cast from solution in MEK/THF mixtures (2). Methyl ethyl ketone has a solubility parameter of 9.3, only slightly higher than that of the solvents used in our work. It is clear from the data presented here that our films must have had continuous polybutadiene phases. 

SBM) as a compatibilizer. As a result of the particular thermodynamic interaction between the relevant blocks and the blend components, a discontinuous and nanoscale distribution of the elastomer at the interface, the so-called raspberry morphology, is observed (Fig. 15). Similar morphologies have also been observed when using triblock terpolymers with hydrogenated middle blocks (polystyrene-W<9ck-poly(ethylene-C0-butylene)-Wock-poly(methyl methacrylate), SEBM). It is this discontinuous interfacial coverage by the elastomer as compared to a continuous layer which allows one to minimize the loss in modulus and to ensure toughening of the PPE/SAN blend [69],... 

---