Structure-property relationship and epoxy resin compatibility of poly(2-alkyl/aryl-2-oxazoline)s, alongside rheological properties of their blends

Official URL: https://dx.doi.org/10.1002/pen.27208

The utilization of polyoxazolines (POZs) in different fields can be more vigorously explored to take advantage of their unique properties, such as chemical stability, straightforward synthesis, and the versatility of the chemical structure and functionalities. This paper aims to investigate the structure-property relationship of several POZ homopolymers before their intended use in the formulation of thermoset resins and composite manufacturing. For this goal, poly(2-alkyl/aryl-2-oxazoline) homopolymers with three molar masses (1000, 2000, and 5000 g/mol) were synthesized using 2-ethyl/propyl/pentyl/phenyl-2-oxazoline monomers. 1H NMR, FTIR, and SEC results verified the successful synthesis of the monomers and homopolymers at targeted molar masses and low dispersity values (Ð). DSC and TGA analyses revealed the effects of molar mass and the structure of the homopolymers on their thermal behavior. DSC analysis showed that the homopolymers exhibited either amorphous or semi-crystalline behavior, with their Tg values ranging from −4 to 100°C. TGA analysis revealed that higher molar masses and longer alkyl pendant groups led to increased decomposition temperatures. Furthermore, the effects of the molar masses and chemical structure of the POZ homopolymers on their compatibility with epoxy resin were investigated using rheology, demonstrating that longer alkyl chains, higher molar masses, and aromatic groups improved miscibility with DGEBA, as evidenced by higher viscosity values. The hydrophilicity of the homopolymers was estimated by calculating their hydrophilic-lipophilic balance (HLB) values, which confirmed that PEOZ is hydrophilic, whereas PPrOZ, PPeOZ, and PPhOZ are lipophilic. HLB values decreased with increasing alkyl length, with the lowest value observed for PPhOZ (lower than 7.8). This study offers valuable insights into the properties exhibited by different POZ homopolymers when incorporated into epoxy resins, thereby advancing their potential application in one-component epoxy formulations. Highlights: Structure–property relationship of polyoxazolines (POZs) was investigated. Calculated HLB values and solubility behavior of POZs correlate well. Hydrophilicity and hydrophobicity were governed by POZ type and molar mass. Thermal and rheological properties were influenced by POZ type and molar mass. Tg values of POZs were tunable within a range of −4 to 100°C.