(284m) Quantifying Specific Interactions in CO2 - Polymer Systems

A number of studies have shown that CO2 and polymers such as poly(methyl methacrylate) (PMMA) exhibit evidence of Lewis acid-base interactions between the ?electron poor? carbon atom of CO2 and the ?electron rich ?oxygen atom of carbonyl group in the polymer. It has been suggested that such interactions give rise to many of the attractive properties of polymers such as PMMA. Unfortunately, quantitative estimates for specific interactions have only been obtained in a small number of cases. In addition, ab initio estimates of the strength of these interactions often differ significantly from experimental results. We have quantified specific interactions between carbon dioxide (CO2) and carbonyl polymers such as poly (methyl methacrylate) (PMMA), poly (vinyl acetate) (PVAc), poly (lactide) (PLA) and poly (lactide-co-glycolide) (PLGA) via in-situ ATR-FTIR measurements on polymer films exposed to high pressure CO2. Shifts in the carbonyl group stretching band at 1700 cm-1 and the CO2 bending mode at 660 cm-1 were studied. The carbonyl stretching band was found to shift to higher wave number (blue shift) which can be attributed to dielectric effects according to the Kirkwood - Bauer - Magat (KBM) equation. The CO2 bending mode was used to quantify the strength of specific interaction between the polymer and CO2 via an equilibrium constant for the association reaction.