Aqueous polypropylene glycol induces swelling and severe plasticization of high Tg amphiphilic copolymers containing hexafluoroisopropanol groups

Abstract

Poly(ethylene glycol) (PEG) tends to be considered low fouling, which has led to its use in a wide variety of applications. Amphiphilic polyols, such as Antifoam 204, are commonly used as surfactants in fermentation processes due to their limited toxicity and low cost, but these polyols in aqueous solutions can unexpectedly swell membranes. Here we examine the interactions of PEG or poly(propylene glycol) (PPG) with amphiphilic substituted norbornene copolymers through swelling in dilute aqueous solution. The effect of molecular mass (M_n) of the polyol (PEG and PPG) in aqueous (1 wt% butanol) solution on the swelling and mechanical properties of a series of poly(alkyl norbornene-co-hexafluoroisopropanol norbornene) is systematically investigated using a quartz crystal microbalance with dissipation. At 10 ppm of PEG, the swelling is less than 20% for all of the copolymers examined and the swelling is independent of PEG M_n. Although PPG at the lowest M_n examined leads to similar swelling to PEG, the swelling induced by PPG increases with M_n to reach a maximum at M_n = 3.1 kg mol⁻¹. Pluronic L121 is similar compositionally to Antifoam 204, but the equilibrium swelling is decreased by nearly a factor of 2, which is attributed to the higher M_n of Pluronic L121. The limited dependence on the alkyl chain in the copolymer suggest that the interactions between the polyol and hexafluoroisopropanol moiety in the copolymer drive the uptake by the membrane through bound water with the unassociated ether in the PPG that increases swelling with increasing M_n, but a finite size effect limits the swelling for sufficiently large polymer additives.