Reactive blending approach to modify spin-coated epoxy film: Part I. Synthesis and characterization of star-shaped poly(e-caprolactone)

To effectively modify the properties of an epoxy, branched oligomers were synthesized from e-caprolactone (CL) and end-functionalized to realize network precursors that can be reactively blended with the epoxy. The ring-opening polymerization (ROP) of the CL in the presence of polyglycerol (PGL) initiator (3.9 and 9.1 mol %) and Sn(II) 2-ethylhexanoate catalyst yielded oligomers with hydroxyl end-groups, which were converted to carboxylic acid functionality by reaction with succinic anhydride. The functionalized oligomers had a four-armed structure and the molecular weight of the oligomers could be controlled by the ratio of CL to PGL in the feed. To achieve an adequately crosslinked network in the reactive blending, a dual-catalyzed reaction scheme was employed. First the oligomer was incorporated into the epoxy matrix in an imidazole-catalyzed reaction and then the crosslinking was completed with an acid-catalyzed ROP of the residual epoxies. Investigations showed that toughened coatings could be prepared from the inherently brittle epoxy through proper choice of the blending ratio of oligomer to epoxy. The blending increased surface hydrophobicity at high concentrations of functionalized oligomer, but did not have an adverse effect on the inherently advantageous endothelial cell spreading.