Formation, characterization and dynamics of polymer-cyclodextrin inclusion compounds

Certain small molecules, such as urea (U), perhydrophenylene (PHTP) and cyclodextrins (CDs), can be cocrystallized with polymers to form inclusion compounds (ICs). The guest polymer chains are confined to narrow, cylindrical channels created by the host, small-molecular lattice. The number and conformation of included polymer chains depend on the relative cross-sectional dimensions of polymer chains and the host diameter. Cyclodextrins (CDs) are cyclic molecules consisting of six to eight glucose units joined by α-1,4-glycosidic linkages. For the host α-CD (D ≈ 4.9 Å), only highly extended single chains can be squeezed inside the channel and are separated from neighbouring polymer chains by the IC channel walls composed exclusively of the small-molecule lattice. However, for the host γ-CD (D ≈ 7.9 Å), two side-by-side, parallel extended polymer chains can be incorporated inside the channel, and thus, are also decoupled from all other neighbouring chains by the channel walls. Therefore, the unique solid-state environment for polymers residing in IC channels can be utilized as model systems for ordered, bulk polymer phases; The inclusion compounds between cyclodextrins (CDs) and high molecular weight homopolymers, such as poly(ϵ-caprolactone) (PCL) and poly(ethylene oxide) (PEO), and blockcopolymer PCL-PEOPCL have been successfully prepared and studied in this dissertation. Several methods including DSC, TGA, X-ray diffraction, FTIR and solid-state 13C NMR have been developed to characterize and confirm that polymer chains have been successfully included inside the IC narrow channels formed by the cyclodextrins.; The conformation, structure and molecular dynamics of polymer inclusion compounds have been further investigated by solid-state NMR. The 13 C CP/MAS/DD spectra show that the included polymer chains adopt conformations as highly extended conformation as their conformations in their bulk crystalline phases. The length scales of mixing between polymers and cyclodextrins have been measured by T_1ρ(H) and 2D heteronuclear correlation experiments. The 2D heteronuclear correlation experiment is demonstrated to be a more powerful and straightforward method to measure the homogeneity of these kinds of materials. Furthermore, the dynamics have been tested by T₁(13C), T_1ρ (13C) and 2D WIM/WISE experiments. Localized molecular motions in the megahertz regime for the included polymer chains are much more facile than in the bulk, crystalline polymers. The cooperative, longer chain motions in the mid-kilohertz regime for included polymer chains are also more facile than in the bulk polymers. The difference in dynamics for pairs of polymer chains included inside the γ-CD channels and single polymer chains inside the α-CD channels have also been observed. Based on the above experimental results, we are able to elucidate the behavior of single, isolated and stretched polymer chains, the interaction between adjacent side-by-side parallel chains and overall cooperative, interchain interactions. This leads us to a better molecular level understanding of the properties of ordered, bulk polymers.; Finally, an example of the potential application of IC technology has been given. An inclusion compound has been successfully formed between the antibiotic triclosan and β-CD, and embedded into biodegradable/bioabsorbable PCL films. When the embedded polymer-additive composite is used as the adhesive for laminating cotton fabrics, we observe that the resulting cotton laminates are resistant to the growth of E. coli bacteria, which indicates the possibility to fabricate antibacterial polymer films and fabrics by means of simple melt-processing with antibacterial inclusion complexes.