Abstract
During the past several years my students and I have been utilizing certain small-molecule hosts to create nanostructured polymers. This is accomplished by first forming noncovalently bonded inclusion complexes (ICs) between these small-molecule hosts and guest polymers, followed by the careful removal of the host crystalline lattice to obtain a coalesced bulk polymer. We have repeatedly observed that such coalesced polymer samples behave distinctly from those produced from their solutions or melts. Coalesced amorphous homopolymers exhibit higher glass-transition temperatures, while crystallizable homopolymers coalesced from their ICs display higher melting and crystallization temperatures, and sometimes different crystalline polymorphs. When ICs are formed with block copolymers or with two or more different homopolymers, the resulting coalesced samples can exhibit intimate mixing between the copolymer blocks, or between entire homopolymer chains. Each of the distinct behaviors observed for polymers coalesced from their ICs is a consequence of the structural organization of the polymer–host-ICs. Polymer chains in host-IC crystals are confined to occupy narrow channels (diameter ~0.5–1.0 nm) formed by the small-molecule hosts around the included guest polymers during IC crystallization. This results in the separation and high extension of the included guest polymer chains, which leads, following the careful removal of the host molecule lattice, to unique behaviors for the bulk coalesced polymer samples. Apparently, substantial degrees of the extended and unentangled natures of the IC-included chains are retained upon coalescence. In this review we summarize the behaviors and uses of coalesced polymers, and attempt to draw conclusions on the relationship between their behavior and the organization/structures/conformations of the constituent polymer chains achieved upon coalescence from their ICs.
Highlights
The behaviors and properties of polymer materials are closely related to the organizations, structures, and morphologies of their constituent chains, which can be significantly altered during their processing, unlike the case of atomic and small molecule solids
In polymer inclusion complexes (ICs) formed with CDs and other small-molecule hosts, such as urea, thiourea, cyclotriphosphazenes, and perhydrotriphenylenes, the polymer guests are included in very narrow channels (~0.5–1.0 nm in diameter) of the crystalline lattice formed by the host molecules
We have attempted to demonstrate the utility of restructuring polymers, through nanoconfinement in and subsequent release/ coalescence from their noncovalently bonded inclusion compounds, for the reorganization of their resulting bulk samples, thereby improving their properties
Summary
The behaviors and properties of polymer materials are closely related to the organizations, structures, and morphologies of their constituent chains, which can be significantly altered during their processing, unlike the case of atomic and small molecule solids. Their characterization is accomplished by the same experimental means mentioned above for polymer–CD ICs. In addition, details of the polarizing micrographs, permeabilities, mechanical properties, and rheological behaviors of the c-polymer samples discussed here may be found in references [8,64,65,68,69,70].
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