Architectural effects on the stability limits of ABC block copolymers

✍ Scribed by Andreas Werner; Glenn H. Fredrickson

• Publisher: John Wiley and Sons
• Year: 1997
• Tongue: English
• Weight: 312 KB
• Volume: 35
• Category: Article
• ISSN: 0887-6266
• DOI: 10.1002/(sici)1099-0488(19970415)35:5<849::aid-polb14>3.0.co;2-a

✦ Synopsis

The random phase approximation has been used to extend the Leibler theory for the stability limit of a homogeneous melt of A-B diblock copolymers to examine the onset of microphase and macrophase separation in a variety of ABC block copolymer systems. The stability limit is located by the divergence of the collective structure factor of the melt. We introduce and analyze three models for ABC block copolymers: linear triblocks, random comb copolymers where a fixed number of A and B teeth are placed randomly along a C backbone, and statistical comb copolymers, with A or B teeth spaced regularly, but with sequences constructed using a two parameter Markov process. We compute order-disorder stability boundaries for the segregation strength parameter x AB N at threshold as a function of x AC N, x BC N, composition, and other model parameters, and compare the results for the three different architectural models. An interesting ''reentrant order-disorder transition'' is located in several model phase diagrams, and is associated with a peculiar situation in which more incompatibility causes less segregation. In the case of statistical combs, macrophase separation into two liquid phases can be favored over microphase separation.