Water uptake is measured for approximate to 100 nm and approximate to 60 m thick quaternized comb-shaped poly(2,6-dimethyl-1,4-phenylene oxide) (QA-PPO) polymers with 0, 6, 10, and 16 carbon alkyl side chains to probe the influence of thin film confinement. The thin film modulus is measured to probe the effect of side chain length on the thin film modulus and the ensuing water uptake. Increasing the alkyl side chain length results in increased modulus, decreased swelling strain, and decreased water uptake due to the lengthening of the n-alkyl side chains. Confinement effects on the comb-shaped QA-PPO water uptake are expressed through increased water uptake in the thin film compared to the bulk membrane. The thin films also exhibit a different water sorption mechanism consistent with two types of water compared to the bulk membranes that exhibit a single type of water sorption.