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The effects of solvent polarity and pKa on the absorption of solvents into poly(glutaric acid-glycerol) films

Victor T. Wyatt
Journal of applied polymer science 2014 v.131 no.13 pp. -
absorption, acetic acid, aqueous solutions, chloroform, dimethyl sulfoxide, ethanol, ethyl acetate, ethylene glycol, films (materials), glutaric acid, glycerol, polymers, pyridines, solvents
In this study, solvent absorption into the matrices of poly(glutaric acid-glycerol) films has been evaluated. It was determined that the combined effects of polarity and the size and shape of the solvent molecule, rather than pKa, have the most significant influence on absorption into the films. Polar aprotic solvents (with solvent polarity index values >4) such as 1,4-dioxane (absorbed 163.8% 6 0.3% [w/w] of the original weight of the polymer), pyridine (200.4% 6 3.5%), and dimethyl sulfoxide (186.0% 6 11.4%) were among the highest absorbed solvents into the polymer matrix. Solvents with polarity index values 4.0 were absorbed poorly (5.3% 6 1.5%). The polymer films only absorbed 26.5% 6 2.1% of their weight of most protic solvents (water and mono-alcohols) but absorbed 72.6% 6 6.5% of ethylene glycol, a diol. The only high absorbing polar protic solvent was acetic acid (131% 6 13.1%). Except for chloroform, ethyl acetate, and ethanol, all of the solvents examined displayed small increases in absorption (7.8%, on average) when the films were desorbed and used again to absorb solvent. Erosion of the films ranged from 0.0% 6 0.0% to 22.0% 6 3.2% after 2–10 h absorption cycles. Miscible (7.7% 6 2.3% to 15.1% 6 2.2%) and immiscible (12.3% 6 6.4% to 80.0% 6 1.9%) solvents were preferentially absorbed from aqueous solutions. However, up to approximately 5% of those absorption values could be from water absorption. VC 2014 Wiley Periodicals, Inc.† J. Appl. Polym. Sci. 2014, 131, 40434.