Synthesis and characterization of two-armed poly(ɛ-caprolactone) polymers initiated by the Schiffʹs base complexes of copper(II) and nickel(II)

Two-armed poly(ɛ-caprolactone) (TAPCL) polymers were successfully synthesized via the ring opening polymerization (ROP) of ɛ-caprolactone (ɛ-CL) using the Schiffʹs base complexes [Cu(SAEE)2] (1) and [Ni(SAEE)2] (2), which have two hydroxyl functional groups, as the two-site initiators and tin(II) 2-ethylhexanoate (Sn(Oct)2) as the catalyst in bulk at 115 °C. The Schiffʹs base complexes (1 and 2) were synthesized by utilizing the concentrated template synthesis method starting from salicyl aldehyde, 2-(2-aminoethoxy) ethanol and related metal acetate salts. The synthesized TAPCL polymers were characterized by GPC, FTIR, UV–vis, and electron paramagnetic resonance (EPR). The molecular weights of TAPCL polymers linearly increased with increasing molar ratio of the monomer to the initiator. The results obtained from FTIR, UV–vis, and EPR studies indicated that TAPCL polymers had the Schiffʹs base complexes at the junction point of PCL arms. The crystallization behavior of TAPCL was studied by using differential scanning calorimetry (DSC) and polarizing optical microscopy (POM). Thermal behavior of TAPCL was also investigated by thermogravimetrical analysis (TGA).