Synthesis and Characterization of Fluorinated Acrylic Polymer and the Properties of Epoxy Thermosets Modified With It

A novel fluorinated acrylic polymer poly(2,2,3,4,4,4-hexafluorobutyl methacrylate)-r-poly(glycidyl methacrylate) (PHFMA-r-PGMA) was synthesized and used to modify the general performances of epoxy resin. Fourier transform infrared spectroscopy (FTIR) and ¹H nuclear magnetic resonance spectroscopy (¹H-NMR) successfully verified the synthesis of PHFMA-r-PGMA. In order to study the effect of epoxy groups in PHFMA-r-PGMA on the properties of modified epoxy resin, corresponding fluoropolymer without epoxy group (PHFMA) was also prepared, and the properties of epoxy thermosets modified by two kinds of fluoropolymers were comparatively studied. The contact angle measurements indicated that the PHFMA-r-PGMA and PHFMA modified thermosets both showed considerable hydrophobicity and lipophobicity. For further comparison, it was also found that the thermosets modified by PHFMA-r-PGMA had a little worse hydrophobicity and lipophobicity but better surface stability than which modified by PHFMA because the epoxy groups in PHFMA-r-PGMA “locked” more fluoropolymers in the bulk matrix of the thermosets, but PHFMA was more freely able to migrate to the surface of the thermosets. SEM images of the fracture surface of PHFMA-r-PGMA and PHFMA modified epoxy thermosets displayed “irregular ripples” or “protuberant island” structures, which suggesting both of these two copolymers could significantly toughen epoxy resin. The results of differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) showed that the thermosets modified by PHFMA-r-PGMA had better thermal stability than which modified by PHFMA due to the higher crosslinking density between PHFMA-r-PGMA and epoxy resin because of the epoxy groups in PHFMA-r-PGMA. The mechanical properties were investigated by tensile testing and impact testing. Although the tensile strength of the PHFMA-r-PGMA and PHFMA modified epoxy thermosets both declined slightly with growing the content of fluoropolymers, the elongation at break and impact strength both increased first and then decreased in the meantime, which indicated that the two kinds of modified thermosets had better toughness than pure epoxy resin. It may be because the macro-phase separation between the long fluorine carbon chain segments and epoxy resin during curing could absorb the impact energy effectively.