Undersøgelse af vandbinding i vandige opløsninger af polyethylenglykol, polypropylenglykol og symmetriske treblok copolymerer af polyethylenglykol og polypropylenglykol
Translated title
Investigation of Water Binding in Aqueous Solutions of Poly(ethylene glycol), Poly(propylene glycol) and Symmetric Triblock Copolymers of Poly(ethylene glycol) and Poly(propylene glycol)
Author
Stoltze, Andreas Stensgaard
Term
4. term
Education
Publication year
2009
Pages
42
Abstract
Dette projekt undersøger, hvordan vand binder sig i vandige opløsninger af polyethylenglykol (PEG), polypropylenglykol (PPG) og amfifile, symmetriske treblok-copolymerer af PEG og PPG. Vandbindingen blev vurderet ved at måle vandaktivitet (et mål for, hvor tilgængeligt vandet er i opløsningen) som funktion af temperatur og koncentration. Derudover blev differential skanningskalorimetri (DSC) brugt til at bestemme den kritiske micelletemperatur (CMT), den temperatur hvor polymererne begynder at danne miceller (små aggregater). Otte forskellige PEG-polymerer, én PPG-polymer og tre treblok-copolymerer blev testet; PPG-polymeren blev dog udeladt, fordi den ikke opløstes tilstrækkeligt. Målingerne viste, at vandaktiviteten stiger med stigende temperatur og faldende polymerkoncentration. Det betyder, at vand bliver et dårligere opløsningsmiddel ved højere temperatur, fordi interaktionerne mellem polymer og vand svækkes. Ud fra vandaktivitetsdata blev overskudsentalpier for vandbinding beregnet, men disse er sandsynligvis for høje på grund af utilstrækkelig ligevægtstid i systemet. DSC-målingerne viste, at ved en given koncentration stiger CMT med stigende hydrofil karakter (mere vand-elskende) af copolymeren.
This project examines how water binds in aqueous solutions of polyethylene glycol (PEG), polypropylene glycol (PPG), and amphiphilic, symmetric triblock copolymers of PEG and PPG. Water binding was assessed by measuring water activity (a measure of how available water is in the solution) as a function of temperature and concentration. Differential scanning calorimetry (DSC) was used to determine the critical micelle temperature (CMT), the temperature at which the polymers start forming micelles (small aggregates). Eight PEG polymers, one PPG polymer, and three triblock copolymers were tested; the PPG polymer was excluded because it did not dissolve adequately. The measurements showed that water activity increases with higher temperature and lower polymer concentration. This indicates that water becomes a poorer solvent at higher temperatures because polymer–water interactions weaken. From the water activity data, excess enthalpies of water binding were calculated, but these values are likely too high due to insufficient equilibration time in the system. DSC measurements showed that, at a given concentration, the CMT increases with the copolymer’s hydrophilic character (more water-loving).
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