Change in the molecular weight distribution of poly(ethylene oxide) caused by the complexation with poly(acrylic acid)

The complexation between poly(ethylene oxide) (PEO) and poly(acrylic acid) (PAA) was made by using double the molar quantity of either polymer component at pH 2 where the resulting complex completely precipitates. After the removal of the precipitate, PEO or PAA remaining in the supernatant was subjected to gel permeation chromatography to investigate the change in the molecular weight distribution (MWD) caused by the complexation. No remarkable difference is observed in the MWD curves for PEO1] (M_w=1.37 × 10⁴) before and after the complexation with PAA1] (M_w=1.10 × 10³) and PAA2] (M_w=4.16 × 10⁵). However, the MWD curves of PEO2] (M_w=1.26 × 10⁵) and PAA2] become shortened and shift to the low molecular weight side after the complexation with PAA1] or 2] and PEO2], respectively. This tendency is enhanced by increasing the complexation temperature. From these results, it is indicated that the complexation between PEO and PAA deals with an equilibrium reaction, and the equilibrium constant is dependent on the chain length of both polymer components and also on the complexation temperature.