Langmuir-Blodgett films of block copolymers from cellulose triacetate and poly(ethylene glycol)

Surface modification with amphiphilic block copolymers is of importance for surface biocompatibility, wetting and adhesion. Such modification can be achieved by the selective adsorption of a copolymer from solution or by the Langmuir-Blodgett technique. This technique has the important advantage of offering control over both the surface coverage and molecular organisation in the film.; Various monofunctionalized low molecular weight cellulose triacetate (CTA) blocks are prepared by acid cleavage of commercial CTA and characterized by NMR, SEC, DSC and X-ray spectroscopy methods. NMR spectra indicate that no significant deacetylization occurs during the cleavage and the resulting blocks contain completely substituted anhydroglucose rings. Furthermore, the hydroxyl endgroup permits the characterization of the degree of polymerization by NMR.; These CTA blocks are used to synthesize of a series of amphiphilic block copolymers (AB) with different molar ratios by coupling to poly(ethylene glycol) (PEG) with diisocyanates. The success of the coupling reaction between the two blocks is determined by SEC, DSC, X-ray diffraction and NMR spectroscopy.; Stable surface layers of these block copolymers can be spread at the air-water interface from dilute solution. The monolayers at the air-water interface are characterised by surface pressure-area isotherms and PM-IRRAS spectroscopy. The results suggest when the PEG block is small relative to the CTA block, CTA controls the surface area and that the CTA backbone lies flat at the water surface with the PEG chains dangling in the water. When the PEG block becomes larger, interactions between PEG chains become important. In this case, both the CTA backbone and the PEG chains contribute to the surface area. Furthermore, and at high surface pressures this copolymer becomes dissolved in the water subphase.; PM-IRRAS results confirm that the cellulose backbone lies flat at the interface for all of the samples considered, whereas the PEG chains are absence at air/water interface for the block copolymers with the small PEG blocks. Surprisingly, PEG is present at the water surface for the sample with the larger PEG block and at high compression the polymer molecules are expelled from the surface. This important observation suggests that the mole fraction of components in block copolymers influence their properties at air/water interface.; The surface force apparatus technique was used to measure directly the attached PEG chain length in water as a function of the area occupied per PEG chain. Our results dearly show that for the product with the small PEG block the PEG layer thickness is a function of polymer surface coverage and PEG layer thicknesses in the brush region are in excellent agreement with chain lengths calculated by scaling theory. This important result shows that monolayer of these block copolymers when transferred to hydrophobic substrates could provide a new route to surface attached polyethylene glycol chains.; For the product with the larger PEG block the results are ambiguous. The PEG chain length remained constant in mushroom and brush regime. This result also could support our hypothesis concerning the partially dissolution of monolayer of product at subphase on function of monolayer compression.