Efkan Çatıker

Unperturbed dimensions and the theta temperature of dextran in ethylene glycol solutions

Abstract The unperturbed molecular dimensions of dextran samples (of different molecular weights) have been evaluated in ethylene glycol solutions from viscosity measurements at 25°C, 30°C, 35°C, 40°C and 45°C. The unperturbed dimension, K 0 , has been determined from extrapolation methods, i.e, Kurata–Stockmayer–Fixman (KSF), Berry and Inagaki–Suzuki–Kurata (ISK) equations. The hydrodynamic expansion factor, α η , as well as the unperturbed root-mean-square end-to-end distance, 〈 r 2 〉 0 1/2 , found for dextran samples in ethylene glycol solutions, indicated that the polymer coils are contracted as the temperature is raised from 25°C to 45°C. The long-range interaction parameter, B , was also evaluated and a significant decrease is found for the dextran/ethylene glycol system between 25°C and 45°C. The theta temperatures, Θ , were determined as 328.53, 328.02 and 325.93 K from the temperature dependence of the interaction parameter, respectively.

Novel hydrophobic macromonomers for potential amphiphilic block copolymers

Oligomers of 2-methyl nylon3 (2mN3) and 3-methyl nylon3 (3mN3) were synthesized by base-catalyzed hydrogen transfer polymerization (HTP) of methacrylamide and crotonamide, respectively. The detailed structural analyses of 2mN3 and 3mN3 were performed using MALDI-MS, 1H-NMR, elemental analysis and several end-group analyses to ascertain polymerization mechanism and exact chemical structures of final products. The structural analyses revealed that (1) base-catalyzed HTP of methacrylamide and crotonamide follows the sequence of: hydrogen abstraction from amide group of monomer by basic catalyst (NatBuO), addition of monomeric units to the anionic center, intramolecular hydrogen migration and finally, termination by hydrogen transfer from protonated catalyst (tBuOH) to anionic end-group, (2) both oligomeric products have olefinic chain-ends resulting from the initiation mechanism. The specific behavior of basic catalyst leads to the formation of olefinic chain-ends that are apt to possible end-group functionalization. Since the functional end-groups of a well-defined macromonomer are of importance in terms of chain extension, grafting, chemical modification, click chemistry, monolayer surface modification, etc., it was aimed to create more reactive functional end-groups by epoxylation and bromination. Disappearance of the signals belonging to the olefinic protons in 1H-NMR spectra of modified oligomers and existence of bromine and epoxy adducts in MALDI MS spectra of the modified oligomers were attributed to end-group modification as intended. Hence, four novel macromonomers of polyamidic backbone with functional chain-ends were synthesized successfully.

Synthesis and characterization of amphiphilic triblock copolymers including β-alanine/α-methyl-β-alanine and ethylene glycol by “click” chemistry

Terminally azide poly-β-alanine (PBA-Az) was directly obtained by hydrogen transfer polymerization of acrylamide in the presence of sodium azide as an initiator. However, terminally azide poly(α-methyl β-alanine) (PmBA-Az) was synthesized by the reaction between terminally bromo poly(α-methyl β-alanine) and sodium azide. Dipropargyllated polyethylene glycol (PEG-di-Pr) was synthesized by using the reaction of PEGs with different molecular weights and propargyl bromide. Synthesis of poly(β-alanine-b-ethylene glycol-b-β-alanine) and poly(α-methyl β-alanine-b-ethylene glycol-b-α-methyl β-alanine) amphiphilic ABA triblock copolymers was achieved via “click” chemistry of PBA-Az or PmBA-Az and PEG-di-Pr with different molecular weight. “Click” reaction parameters such as concentration and time were assessed. Macromonomers and the amphiphilic triblock copolymers were characterized by using 1H-NMR, FT-IR, MALDI-MS, TGA, and elemental analysis techniques. The multi-instruments studies of the obtained amphiphilic triblock copolymers reveal that the copolymers easily formed as a result of “click” chemistry.