A series of thermoplastic polyurethane elastomers based on polycarbonate diol, 4,4′‐diphenylmethane diisocyanate and 1,4‐butanediol was synthesized in bulk by two‐step polymerization varying polycarbonate diol soft segment molecular weight and chemical structure, and also hard segment content, and their effects on the thermal and mechanical properties were investigated. Dynamic mechanical analysis termogravimetric analysis, differential scanning calorimetry, Fourier transform infrared‐attenuated total reflection spectroscopy and mechanical tests were employed to characterize the polyurethanes. Thermal and mechanical properties are discussed from the viewpoint of microphase domain separation of hard and soft segments. On one hand, an increase in soft segment length, and on the other hand an increase in the hard segment content, i.e., hard segment molecular weight, was accompanied by an increase in the microphase separation degree, hard domain order and crystallinity, and stiffness. In phase separated systems more developed reinforcing hard domain structure is observed. These hard segment structures, in addition to the elastic nature of soft segment, provide enough physical crosslink sites to have elastomeric behavior. POLYM. ENG. SCI., 2008. © 2007 Society of Plastics Engineers

Novel epoxy-based blends containing 30 wt % star styrene-b-butadiene block copolymers epoxidized at several degrees (SepB) have been investigated in order to analyze the effect of epoxidation degree on the ability of these copolymers to produce nanostructures inside the epoxy matrix as well as their effect on the network structure of the matrix. For neat styrene−butadiene (SB) and SepB15-modified systems, macroscopic phase separation was observed. The SepB epoxidized at 40−76 mol %, however, yielded hexagonally ordered nanostructures formed by PS cylinders arranged in the matrix containing also the epoxidized and nonepoxidized butadiene units. DSC analysis indicates that the slight differences observed in self-assembling of the mixture containing the 40 wt % epoxidized block copolymer with respect to those for the blends with higher epoxidation degrees could be related with reactivity differences of the epoxidized copolymers with the curing agent. It is envisaged that these novel nanostructured blends may lead to novel materials with excellent optical properties and enhanced fracture toughness.

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Novel nanostructured thermosetting materials have been prepared by modification of an epoxy resin with a semifluorinated diblock copolymer, poly(heptadecafluorodecyl acrylate)-b-poly(caprolactone), PaFb-PCL. In a first step, the phase behavior and linear viscoelasticity of PaF-b-PCL were investigated. According to the segregation regime, no order-order transitions were detected, being the order-disorder transition temperature beyond the degradation temperature. Atomic force microscopy (AFM) images of the block copolymer after different thermal treatments revealed that self-assembly takes place into spherical nanodomains, which is consistent with the copolymer composition. This block copolymer was further used to prepare a nanostructured thermoset blend with an epoxy resin. DSC and DMA analysis reveals microphase separation of PaF block from the epoxy-rich phase after curing. The PaF block self-assembled into wormlike and spherical micelles in the thermoset system. This nanostructured blend presented unique surface properties showing high hydrophobicity (υ ) 109°) and low surface energy (17 mN/m).