The effect of soft segment molecular weight and chemical structure on the morphology and final properties of segmented thermoplastic polyurethanes containing various hard segment contents has been investigated from the viewpoint of the degree of microphase separation. Vegetable oil‐based polyesters and corn sugar‐based chain extender have been used as renewable resources. The synthesis has been carried out in bulk without catalyst using a two‐step polymerization process. Physicochemical, thermal and mechanical properties, and also morphology, have been studied using Fourier transform infrared spectroscopy, differential scanning calorimetry, dynamic mechanical analysis, atomic force microscopy, X‐ray diffraction and mechanical testing. Chemical structure and molecular weight of polyols strongly affect the properties of the synthesized segmented thermoplastic polyurethanes. An increase in soft segment molecular weight leads to an increase of the degree of soft segment crystallinity and microphase separation, thus giving enhanced mechanical properties and higher thermal stability. Copyright © 2012 Society of Chemical Industry

Spider silk is an icon of supertough energy absorbing polymeric material which its macromolecular multiblock composition has been attributed to be responsible for such remarkable properties. As in spider silk, polyurethanes can be synthesized with two distinct block which can differ in nature, combining properties like deformability and relatively high strengths. Here we synthesized and studied four different block polyurethanes with two different soft segments (SS) and two different hard segments (HS), with the aim of discovering the best molecular architecture to develop best mechanical performance after macromolecular alignment. The difference between soft segments is the crystalline nature, one in the rubbery state (T g, SS < T room ) and the other in the semicrystalline state at room temperature (T room < T m, SS ). In parallel one hard segment was amorphous in the glassy state (T room < T g, HS ) and the other semicrystalline (T g, HS < T room < T m, HS ). Results indicate that polyurethane with crystalline soft segments produce stronger materials after drawing than polyurethanes with rubbery soft segments, but the most exciting finding is the influence that hard segment has on the mechanical performance of predrawn materials, having polyurethanes prepared with semicrystalline hard segments more capability to undergo macromolecular alignment than materials with glassy segments, developing stiffer, stronger, and tougher materials.

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Since polyol is one of the major components in polyurethane foam synthesis, introducing renewably sourced polyols in the foam formulation leads to materials with high renewable carbon content. A series of flexible polyurethane foams with variations in polyol composition were synthesized with castor oil based Lupranol Balance ® 50 polyether polyol and corn based polytrimethylene ether glycol mixtures. Water was used as the unique and eco-friendly blowing agent. The effect of the relative amount of each polyol on the structure and properties was analyzed by optical microscopy, Fourier transform infrared spectroscopy, thermogravimetric analysis, tensile and compressive tests, dynamic mechanical analysis and atomic force microscopy. The average molecular weight and hydroxyl number of the polyol components showed to influence the foaming reaction and hence the structure and properties of the polyurethane foam. The newly developed peak force quantitative nano-mechanics technique was used to map the elastic modulus values of foam cell struts and it seemed to be adequate to assess the purity of the different phases.

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