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We report synthesis of temperature-responsive linear and star poly(2-ureido aminoethyl methacrylates) (PUEMs) of matched molecular weights, their phase transitions in aqueous solutions and interactions with hydrogen bonding and hydrophobic small molecules. PUEMs with number of arms up to 8 were synthesized via the activator regenerated by electron transfer atom transfer radical polymerization (ARGET ATRP) technique using the core-first approach. The degrees of branching were determined using gel permeation chromatography (GPC) equipped with the multi-angle laser light scattering and viscometry detectors. The polymer molecular architecture had a neglectable effect on the upper critical solution temperature (UCST) behavior in aqueous solutions, while the presence of a strong hydrogen-bonded acceptor – dimethyl sulfoxide (DMSO) – suppressed the transition temperature for both linear and star UCST polymers. Importantly, star PUEMs showed an enhanced ability of trapping model drug molecules – proflavine and pyrene. In particular, an increase in polymer branching led to 4.5-fold more efficient proflavine trapping and stronger binding of pyrene molecules within the hydrophobic domains of star polymers below their UCST. The trapped molecules could be then fully released from the star polymers upon temperature increase, demonstrating potential for controlled delivery applications. 

This work establishes a correlation between the selectivity of hydrogen-bonding interactions and the functionality of micelle-containing layer-by-layer (LbL) assemblies. Specifically, we explore LbL films formed by assembly of poly(methacrylic acid) (PMAA) and upper critical solution temperature block copolymer micelles (UCSTMs) composed of poly(acrylamide- co -acrylonitrile) P(AAm- co -AN) cores and polyvinylpyrrolidone (PVP) coronae. UCSTMs had a hydrated diameter of ∼380 nm with a transition temperature between 45 and 50 °C, regardless of solution pH. Importantly, micelles were able to hydrogen-bond with PMAA, with the critical interaction pH being temperature dependent. To better understand the thermodynamic nature of these interactions, in depth studies using isothermal titration calorimetry (ITC) were conducted. ITC reveals opposite signs of enthalpies for binding of PMAA with micellar coronae vs. with the cores. Moreover, ITC indicates that pH directs the interactions of PMAA with micelles, selectively enabling binding with the micellar corona at pH 4 or with both the corona and the core at pH 3. We then explore UCSTM/PMAA LbL assemblies and show that the two distinct modes of PMAA interaction with the micelles ( i.e. whether or not PMAA binds with the core) had significant effects on the film composition, structure, and functionality. Consistent with PMAA hydrogen bonding with the P(AAm- co -AN) micellar cores, a significantly higher fraction of PMAA was found within the films assembled at pH 3 compared to pH 4 by both spectroscopic ellipsometry and neutron reflectometry. Selective interaction of PMAA with PVP coronae of the assembled micelles, achieved by the emergence of partial ionization of PMAA at pH 4 was critical for preserving film functionality demonstrated as temperature-controlled swelling and release of a model small molecule, pyrene. The work done here can be applied to a multitude of assembled polymer systems in order to predict suppression/retention of their stimuli-responsive behavior.