Polymer Mixtures and Their Solutions

Block Copolymer Solutions.—Random copolymers are more conveniently considered in parallel with polymer mixtures and their solutions. The only solutions of block copol3mers that appear to have received any attention concern triblock (ABA) copolymers. These systems are included in reviews by Blanks and by Tager. They have been considered in detail by Hco and Williams who present a scheme for classifying the phase behaviour that covers both macro-and micro-phasic characteristics. Motivated by the desire to find a completely compatible tri block-solvent system they exhibit examples of their categorization with one triblock copolymer and various solvents. 

In another paper Pico and Williams extend the thermodynamic theory of Leary and Williams for ABA block copolymers to obtain an expression for free energy of mixing. Supported by data their model appears to deal with microphase separation, but can not account for macrophase separation or preferential block precipitation in its present form. 

Polymer Mixtures and Their Solutions.—Polymer mixtures have been widely reviewed - - -1 . with the main emphasis directed at their phase behaviour (compatibility, see Chapter 4). Nagarajan remarks that the subject is widely discussed but vaguely understood having undergone technical rather than scientific development , a comment perhaps illustrated by the theoretical 

Coleman et suggest that poly(vinylidine fluoride)-poly(methyl methacrylate) offers one of the most interesting polymer pairs in view of the highly crystallizable nature of the first component and consequent occurrence of specific interactions (complex formation). Naito et on the other hand, have inferred that the system poly(methyl methacrylamide)-copoly(styrene-acrylonitrile) exhibits almost regular solution behaviour, which should make it interesting from a theoretical point of view. 

Robard et a/.. claim that, in addition to ia, AAr = goi—g i is the significant interaction variable - their so called AJf -effect . When A.Y is lar phase separation can result even if is small (or negative) and the polymers are compatible. Furthermore Aj)T, unlike gn, is expected to have a con- 

---