RESUMO
In this study, the surface morphologies of poly(2-vinyl pyridine-block-methyl methacrylate), P(2VP-MMA), copolymer films were analyzed by atomic force microscopy. P(2VP-MMA) samples varying in total molar mass and individual block length were evaluated for variations in the surface morphologies of films cast from toluene on Si wafers. The incorporation of AuNPs into the polymer domain significantly influenced the surface morphology of the films. Variations in the surface morphology as a function of the polarity of the casting solvent were also examined. In this context toluene (a non-polar solvent), chloroform (of intermediate polarity) and ethyl acetate (a polar solvent) were employed as casting solvents. Toluene is a good solvent for PMMA compared to P2VP, chloroform has no preferential solvation, while ethyl acetate is a good solvent for P2VP compared to PMMA. The morphology of the films cast on substrates of distinctly different polarities, such as mica, Si wafers, and HOPG, were studied to appraise their selectivity. Finally, a detailed study of the effects of thermal annealing on the surface morphologies of P(2VP-MMA) and P(2VP-MMA)-AuNPs was conducted.
RESUMO
Amphiphilic di- and tri-block copolymers based on poly(ethylene oxide) as a hydrophilic segment and poly(ε-caprolactone) as a hydrophobic part are synthesized by the ring-opening polymerization of ε-caprolactone while using poly(ethylene glycol)s and methoxy poly(ethylene glycol)s of varying molar masses as macro-initiators. The synthesized block copolymers are characterized with respect to their total relative molar mass and its distribution by size exclusion chromatography. Liquid chromatography at critical conditions of both blocks is established for the analysis of individual block lengths and tracking presence of unwanted homopolymers of both types in the block copolymer samples. New critical conditions of polycaprolactone on reversed phase column are reported using organic mobile phase. The established critical conditions of polycaprolactone extended the applicable molar mass range significantly compared to already reported critical conditions of polycaprolactone in aqueous mobile phase. Block copolymers are also analyzed at critical conditions of poly(ethylene glycol). Complete analysis of the di- and tri-block copolymers at corresponding critical conditions provided a fair estimate of molar mass of non-critical block besides information regarding presence of homopolymers of both types in the samples.
RESUMO
Star-shaped polymers exhibit lower hydrodynamic volume, glass transition temperature, critical micelles concentration (CMC), and higher viscosity and drug-loading capacity compared to their linear counterparts. In the present study, amphiphilic biodegradable 4-arm star-shaped block copolymers, based on poly(ethylene oxide) (PEO) as a hydrophilic part and poly(ε-caprolactone) (PCL) as a hydrophobic segment, are synthesized by ring-opening polymerization of ε-caprolactone employing pentaerythritol as an initiator and stannous octoate as a catalyst, followed by the coupling reaction with carboxyl-functionalized monomethoxy poly(ethylene oxide) (MeO-PEO-COOH). The structures of intermediates were deduced through 1H-NMR and FT-IR spectroscopy. Average chemical composition of the star block copolymer is determined by proton NMR. Information related to molar mass distribution of targeted products and their precursors is obtained by size exclusion chromatography (SEC). However, due to its inherent poor resolution SEC could not reveal whether all the parent homopolymers are coupled to each other or remained unattached to the other segment. In order to comprehensively characterize the synthesized star-block copolymers, liquid chromatography at critical conditions of both blocks is employed. The study allowed for separation of homopolymer precursors from targeted star-block copolymers. The study exposed heterogeneity of star block copolymers that was not possible by conventional techniques.
