Linear vs Star polymers in Hydrogen-Bonded Assemblies

We report on the effect of the molecular architecture of poly(ethylene oxide), PEO (linear vs. 6-arm polymer, lPEO and sPEO, respectively) and molecular weight of poly(methacrylic acid) (PMAA) on hydrogen-bonding assembly of these polymers. Isothermal titration calorimetry studies (ITC) revealed the entropic nature of complex formation and complex strengthening with the increase of molecular weight of PMAA. At the same time, lPEO-containing and sPEO-containing complexes had a different stoichiometry of PMAA-to-PEO repeat units of 1 and 1.5 for PMAA/lPEO and PMAA/sPEO, respectively, suggesting possible formation of necklace-like complexes on a PMAA string. When the assembly was performed at surfaces, layer-by-layer (LbL) PMAA/PEO films constructed with linear PEO exhibited faster deposition of polymer mass as compared to films built with sPEO. Consistent with these results, neutron reflectometry revealed stronger molecular intermixing within films containing lPEO, suggesting faster diffusion of lPEO in LbL films as compared to the necklace-included sPEO polymer.