Phase behavior of mesoporous nanostructures templated by amphiphilic crystalline-crystalline diblock copolymers of poly (ethylene oxide-b-epsilon-caprolactone)

A crystalline-crystalline diblock copolymer, poly(ethylene oxide-b-epsilon-caprolactone) (PEO-b-PCL), was synthesized through ring-opening polymerization using monomethoxy-poly(ethylene oxide) as a macro-initiator. The amphiphilic double-crystalline diblock copolymer was used as a template to prepare highly-ordered mesoporous silicas and phenolic resins using an evaporation-induced self-assembly (EISA) method. The mesophase transformation of mesoporous nanostructures, which contained different tetraethyl orthosilicate (TEOS) and phenolic resin contents, was investigated using small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM) analyses. The SAXS profiles revealed a sharp primary peak and highly long-range order reflections such as a cylinder or gyroid structures, at certain compositions of TEOS and phenolic resins, which was consistent with the TEM images. Fourier transform infrared spectroscopy (FTIR) analyses provided positive evidence that the ether group of PEO is a stronger hydrogen bond acceptor than the carbonyl of PCL with the hydroxyl group of TEOS or phenolic resin, resulting in the excluded and confined PCL phase. This is the first report suggesting that differential scanning calorimeter (DSC) analysis could be utilized as a convenient method to differentiate the morphology of mesoporous nanostructures in a crystalline-crystalline diblock copolymer.