Nanotube functionalization with 4-hydroxymethylaniline (HMA) via the diazonium salt method has been done on SWNT produced by the CoMoCAT process. Thermal analysis indicates 1 out of every 33 C atoms remains functionalized. Raman, FTIR, and optical absorption spectroscopy confirm the side-wall functionalization and show that it can be reversed by thermolysis. The OH group that is generated from the functionalization was used to start the ring-opening polymerization of ε-caprolactone. The polymer thus produced (PCL) remains grafted to the nanotube as demonstrated by FTIR and a dramatic increase in suspendibility in chloroform. By combining several techniques (TGA, TPD, and TPO) a quantification of the number of polymer chains attached to the nanotube and their average length has been attempted.

A commercially available aliphatic thermoplastic polyurethane formulated with a methylene bis(cyclohexyl) diisocyanate hard segment and a poly(tetramethylene oxide) soft segment and chain‐extended with 1,4‐butanediol was dissolved in dimethylformamide and mixed with dispersed single‐walled carbon nanotubes. The properties of composites made with unfunctionalized nanotubes were compared with the properties of composites made with nanotubes functionalized to contain hydroxyl groups. Functionalization almost eliminated the conductivity of the tubes according to the conductivity of the composites above the percolation threshold. In most cases, functionalized and unfunctionalized tubes yielded composites with statistically identical mechanical properties. However, composites made with functionalized tubes did have a slightly higher modulus in the rubbery plateau region at higher nanotube fractions. Small‐angle X‐ray scattering patterns indicated that the dispersion reached a plateau in the unfunctionalized composites that was consistent with the plateau in the rubbery plateau region. The room‐temperature modulus and tensile strength increase was proportionally higher than almost all increases seen previously in thermoplastic polyurethanes; however, the increase was still an order of magnitude below what has been reported for the best nanotube–polymer systems. Nanotube addition increased the hard‐segment glass transition temperature slightly, whereas the soft‐segment glass transition was so diffuse that no conclusions could be drawn. Unfunctionalized tubes suppressed the crystallization of the hard segment; whereas functionalized tubes had no effect. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 490–501, 2007

Two series of biomedical segmented polyurethanes (SPU) based on poly(epsilon-caprolactone) diol (PCL diol), 1,6-hexamethylene diisocyanate (HDI) or L: -lysine methyl ester diisocyanate (LDI) and three novel chain extenders, were synthesized and characterized. Chain extenders containing urea groups or an aromatic amino-acid derivative were incorporated in the SPU formulation to strengthen the hard segment interactions through either bidentate hydrogen bonding or pi-stacking interactions, respectively. By varying the composition of the hard segment (diisocyanate and chain extender), its structure was varied to investigate the structure-property relationships. The different chemical composition and symmetry of hard segment modulated the phase separation of soft and hard domains, as demonstrated by the thermal behavior. Hard segment association was more enhanced by using a combination of symmetric diisocyanate and urea-diol chain extenders. The hard segment cohesion had an important effect on the observed mechanical behavior. Polyurethanes synthesized using HDI (Series H) were stronger than those obtained using LDI (Series L). The latter SPU exhibited no tendency to undergo cold-drawing and the lowest ultimate properties. Incorporation of the aromatic chain extender produced opposite effects, resulting in polyurethanes with the highest elongation and tearing energy (Series H) and the lowest strain at break (Series L). Since the synthesized biodegradable SPU possess a range of thermal and mechanical properties, these materials may hold potential for use in soft tissue engineering scaffold applications.

The development of biomimetic highly-porous scaffolds is essential for successful tissue engineering. Segmented poly(ester urethane)s and poly(ester urethane urea)s have been infrequently used for the fabrication of electrospun nanofibrous tissues, which is surprising because these polymers represent a very large variety of materials with tailored properties. This study reports the preparation of new electrospun elastomeric polyurethane scaffolds. Two novel segmented polyurethanes (SPU), synthesized from poly(epsilon-caprolactone) diol, 1,6-hexamethylene diisocyanate, and diester-diphenol or diurea-diol chain extenders, were used (Caracciolo et al. in J Mater Sci Mater Med 20:145-155, 2009). The spinnability and the morphology of the electrospun SPU scaffolds were investigated and discussed. The electrospinning parameters such as solution properties (polymer concentration and solvent) and processing parameters (applied electric field, needle to collector distance and solution flow rate) were optimized to achieve smooth, uniform bead-free fibers with diameter (~700 nm) mimicking the protein fibers of native extracellular matrix (ECM). The obtained elastomeric polyurethane scaffolds could be appropriate for soft tissue-engineering applications.

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The development of elastomeric, bioresorbable, and biocompatible segmented polyurethanes (SPUs) for use in tissue‐engineering applications has attracted considerable interest in recent years. In this work, nonporous films and microfiber/nanofiber scaffolds, which were prepared from two different poly(ϵ‐caprolactone)‐based SPUs previously synthesized from 1,6‐hexamethylene diisocyanate and novel chain extenders containing urea groups or an aromatic amino acid derivative, were studied. Their thermal properties were influenced by both the different chemical structures of the hard segments and the processing conditions. The mechanical properties of the scaffolds (the elastic modulus, ultimate strain, and tensile stress) were adequate for engineered soft‐tissue constructs (e.g., myocardial tissue). The film samples displayed a low swelling degree (<2 wt %) in a phosphate‐buffered solution at 37°C. The introduction of the amino acid derivative chain extender with hydrolyzable ester bonds contributed to greater degradation. The fibrous scaffolds exhibited higher hydrolytic stability than the films after short assay times because of their more crystalline structures and higher degrees of association by hydrogen bonding, but they also experienced higher mass losses under accelerated conditions (70°C). This suggested that the degradation rate was not constant but depended on the degradation time and the processing technique. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Unsaturated polyester prepolymers were synthesized with different chemical compositions and molecular weights. Cloud-point curves (CPC) were measured in St-UP quasibinary solutions, showing UCST behavior in all cases. The miscibility of the first UP samples series in St comonomer was enhanced when AA chemical comonomer concentration in UP prepolymer increased. In the second series, UP prepolymer miscibility increased with the molecular weight up to a maximum and, after that, the miscibility decreased. A thermodynamic analysis of experimental CPCs was performed using the Flory-Huggins (F-H) theory for polydisperse polymer solutions. A simple relationship between the interaction parameter and the temperature inverse could fit the measured CPCs in wide concentrations and molecular weight ranges. In the temperature interval where this fit took place, the positive enthalpic contribution to the interaction parameters determined the miscibility dependence with temperature in both UP sample series. The St-UP miscibility behavior was also correlated with UPs structural chemical parameters as: (a) the final HOÀ À and HOOCÀ À high polar groups concentration, (b) the chain backbone polar adipate and phthalate groups concentration, and (c) the UP size dependent mixing entropy. All these parameters are molecular weight dependent.