Synthesis and characterization of poly N-isopropylacrylamide-co-acrylic acid and their binary blend films properties

In past decades, the combination of polymers to obtain blends in film shapes has been a very effective strategy to meet the needs of the increasingly demanding market. In this sense, pH- and thermo-sensitive (PHT) polymers have recently drawn the attention of researchers for their countless applications. However, binary mixtures of typical PHTs like polyacrylic acid (p-AAc) and poly-N-isopropylacrylamide (p-NIPAm) were unable to form films. In this sense, it was hypothesized that NIPAm copolymerized with AAc monomers can yield blends with virtually the same functional group composition of binary mixtures of p-NIPAm and p-AAc homopolymers but with different properties of film formation. For this, a copolymeric radical synthesis and the subsequent analytical studies were complemented to get a broad description of these materials. P-NIPAm and p-AAc homopolymers and different proportions of copolymers p-NIPAm-co-AAc were obtained and thoroughly characterized by Fourier Transform Infrared Spectroscopy (FT-IR), Size Exclusion Chromatography (SEC), acid-basic titration, and rotational rheology. Among the samples, the solutions of p-AAc with p-NIPAm and p-NIPAm-co-AAc copolymers with a higher proportion of NIPAm units (0.8 and 0.6 NIPAm/AAc) precipitated as interpolymer complexes. Since it was expected, the combination with p-NIPAm-co-AAc 40/60 copolymer, which has a higher proportion of AAc groups and pH sensitivity, allowed obtaining blends suitable for the preparation of films. Furthermore, despite the fact that the combinations of p-NIPAm-co-AAc 40/60 with p-NIPAm-co-AAc 80/20 or p-NIPAm were successful, the mechanical properties of the films are worse compared to the other blends, leaving this issue open for subsequent studies.