PMSE 98 |
| It has recently become possible for the first time to produce intimately mixed blends of two or more polymers that are generally believed to be incompatible or immiscible. Intimate molecular-level mixing is achieved by the formation of and coalescence from the non-covalent inclusion compounds (ICs) between the cyclic starch hosts, cyclodextrins (CDs), and guest polymers. The only current limitations of this blending method are the requirement of a solvent common for the component polymers in the blend and their ability to thread the ~ 0.5 – 1.0 nm diameter CD cavities. A large number of inherently immiscible polymers have been molecularly blended by this approach, and they include amorphous, crystalline, and mixed amorphous and crystalline polymer pairs and triplets. This nano-scale approach to blending polymers has also been applied to block copolymers containing incompatible blocks, where significant molecular mixing of normally phase-segregated blocks was achieved when all blocks were included in and coalesced from their CD-ICs. Formation of block copolymer CD-ICs with different CDs was demonstrated to provide control of copolymer block phase segregation. Block copolymers containing thin, narrow and thick,wide blocks that can and cannot, respectively, thread the host CD employed to form the block copolymer-CD-IC, alpha-CD for example, were found to exhibit a degree of block segregation that is greater than a solution-cast sample, while employing a larger CD host, such as gamma-CD that can be threaded by all blocks, resulted in a well-mixed coalesced block copolymer, with reduced segregation of its blocks. Preliminary observations of homopolymer blends and block copolymers obtained by CD-processing have indicated that their reorganized and well-mixed structures evidence considerable thermal and temporal stabilities. Heating them for substantial periods of time above the Tgs and Tms of their components did not generally result in de-mixing and phase segregation. |
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Block Copolymers as Nanoscale Materials
8:00 AM-11:20 AM, Monday, 11 September 2006 San Francisco Marriott -- Salon 7, Oral
Division of Polymeric Materials: Science & Engineering |