Influence of a Low Content of PEO Segment on the Thermal, Surface and Morphological Properties of Triblock and Diblock PCL Copolymers

Two series, one of triblock (PCL/PEO/PCL) and the other of diblock (PCL/PEO) copolymers were prepared by ring-opening polymerization of epsilon-caprolactone catalized with tin(II) octoate and by using dihydroxy or monohydroxy poly(ethylene oxide) as the macroinitiator. The PEO block length was fixed (M-n 1,000 g/mol) and the PCL block lengths (M-n 10,000-40,000 g/mol) were tailored by changing weight ratio of epsilon-CL/PEO. The copolymers' structure was confirmed by H-1 and quantitative C-13 NMR spectroscopy while their molecular weights were determined by GPC analysis. The thermal properties and the degree of crystallinity of the copolymers were investigated and compared by using DSC and WAXS. Both types of copolymers were semicrystalline with the orthorhombic PCL crystal lattice. The surface morphology of the copolymer films was investigated by using optical microscopy and AFM analysis, which confirmed the spherulitic lamellar structure with spherulites of different diameters. Data indicated that a low content of PEO segment had an influence on thermal degradation behavior, crystallinity and morphology of copolymers. Roughness of copolymer films was affected by the content of PEO and correlated with the spherulites' diameter. The small changes in water and moisture absorption properties of copolymers compared to homopolymer PCL were observed.