AFM monitoring of the cut surface of a segmented polyurethane unveils a microtome-engraving induced growth process of oriented hard domains

We report on nanoscale order-disorder transitions of hard segments and their domains composed of 4,4′-methylenebis(phenyl isocyanate) - 1,4-butanediol (MDI-BD), in polycaprolactone-based (Mn = 2000 g/mol) polyurethanes (PCL-PUs), when the free surface is pre-oriented by cryo-microtoming of the material. Morphological variations of the hard domains as a function of temperature and the anisotropy of surface morphology features are captured by employing Atomic Force Microscopy (AFM) stiffness imaging by PeakForce Quantitative Nanomechanical Mapping (PF-QNM). The AFM imaging is supported by WAXS, SAXS, FTIR, and DSC measurements. The experimental results show that hard domains initially grown at the surface break apart at elevated temperatures (65 °C) and cannot be re-grown upon cooling. They require new microtoming to repeat the growth scenario. The detailed step-by-step submicron scale observations of the surfaces serve to show importance of the influence that microtoming and the time after its completion have on surface morphology, and that these shall be considered when studying polymer materials microscopically.</p

Kinetic aspects of formation and processing of polycaprolactone polyurethanes: In situ from a blocked isocyanate

In order to produce segmented polyurethane polymers (PU) that can be processed readily into elastomeric thin films, a thermally labile blocking agent was used to form an isocyanate prepolymer and prevent reaction with moisture while facilitating the formation of the polymers by bulk thermal polymerization. The approach is to react a polymeric diol and isocyanate to form a prepolymer, end cap or 'block' the isocyanate, combine it with a chain extender, and form films that then thermally polymerize when the blocking agent dissociates and evaporates. A major advantage of this process is that the blocked isocyanate prepolymer is completely stable and unreactive on exposure to incidental moisture. Film polymerization kinetic studies were performed with the blocked isocyanate at a series of temperatures and reaction times. The extent of reaction was followed by proton NMR and the molecular weights of the resulting films were characterized by gel permeation chromatography (GPC). The data indicate how both temperature and reaction time are important for the formation of high molecular weight polyurethanes and that a catalyst is required to facilitate the reaction. Films with high molar masses and excellent mechanical properties were obtained. High resolution quantitative atomic force microscopy (AFM) imaging disclosed interesting features of the polymer morphology at the nanoscale that relate directly to the polymer mechanical properties

Properties and Phase Structure of Polycaprolactone-Based Segmented Polyurethanes with Varying Hard and Soft Segments: Effects of Processing Conditions

A series of segmented polycaprolactone polyurethane (PU) polymers is synthesized. One set of polymers ranges in composition from 0 to 100 wt% hard segments (HSs). The syntheses are carried out in solution and the polymers are melt-processed by compression molding. Another subset of polymers is formed in bulk from a blocked isocyanate prepolymer. The blocked polymer's thermal and mechanical properties are compared with the melt-processed materials. The emphasis in this paper is on the effects of varying the chemical structures of the PUs on their phase structures and physical cross-linking due to nanocrystalline hard domains. The thermal properties indicate that nanophase separation and the formation of hard domains occur at HS contents above ≈8 wt%. Property differences resulting from varying the hard segment amounts are directly related to differences in morphology at the nanoscale. Atomic force microscopy images show that the best elastomeric mechanical properties are found when nanocrystallites are 4-5 nm in size

Post-Synthetic Modification of Ionic Liquids Using Ligand-Exchange and Redox Coordination Chemistry

Ionic liquids (ILs) derive their useful properties from molecularly tunable compositions, but methods to diversify anion identities and probe ion speciation remain limited. Here, we demonstrate post-synthetic modification of perhalometallate anions to achieve ionic liquid-to-ionic liquid transformations. Rheological measurements of the metal-containing ILs indicate that minor alterations to anion coordination spheres induces considerable changes to IL viscosities. UV-vis spectra confirm the purities for most ILs, while revealing a surprising cation dependence of perchlorovanadate speciation and supramolecular structure. The intermolecular interactions studied here span a wide range from dispersion to covalent bonding, permitting their impact on IL viscosity to be decoupled and quantified. Together, synthetic strategies from coordination chemistry paired with conventional UV-vis spectroscopy provide a powerful tool for expanding IL compositions and investigating fundamental nanoscale behavior

Inflammatory reaction and capillary leak syndrome related to cardiopulmonary bypass in neonates undergoing cardiac operations

We studied the inflammatory reaction related to cardiopulmonary bypass in 24 neonates (median age 6 days) undergoing the arterial switch operation for simple transposition of the great arteries, with respect to the development of postoperative capillary leak syndrome. Complement proteins, leukocyte count, tumor necrosis factor-α, and histamine levels were determined before, during, and after cardiopulmonary bypass. Additionally, protein movement from the intravascular into the extravascular space during cardiopulmonary bypass was assessed by the measurement of plasma concentrations of proteins with molecular weights ranging from 21,200 to 718,000. Capillary leak syndrome developed in 13 of the 24 neonates. Patients with capillary leak syndrome, as compared with those without, had preoperatively higher C5a levels (C5a, 3.0 ± 0.6 μg/L vs 0.9 ± 0.2 μg/L) (mean ± standard error of the mean) (p < 0.05) and higher leukocyte counts (leukocytes, 17.9 ± 2.1 x 10 3 cells/ml versus 11.7 ± 0.8 x 10 3 cells/ml) (p < 0.05), suggesting in these neonates a preoperative inflammatory state. Preoperative clinical and operative data were identical in both patient groups. Before cardiopulmonary bypass, serum protein concentrations were similar in all patients. Ten minutes after institution of cardiopulmonary bypass, protein concentrations fell to significantly lower values in patients with capillary leak syndrome than in those without: albumin (19% ± 1.5% vs 30% ± 6% of the prebypass value, p < 0.05), immunoglobulin G (17% ± 1.5% vs 29% ± 5.5%, p < 0.001), and α 2-macroglobulin (15% ± 1.2% vs 25% ± 4%, p < 0.02). During cardiopulmonary bypass, albumin concentrations remained significantly lower in patients with capillary leak syndrome than in those without, whereas hematocrit values were similar in both groups. During cardiopulmonary bypass, patients with capillary leak syndrome also had lower concentrations of complement proteins C3 and C4 but not C1 inhibitor. C3d/C3 ratio and C5a levels were similar in both patient groups. In contrast, histamine liberation during cardiopulmonary bypass was significantly more pronounced in patients with capillary leak syndrome than in those without (725.2 ± 396.7 pg/ml vs -54.1 ± 58.4 pg/ml, p < 0.05). Tumor necrosis factor-α levels after protamine administration were also significantly higher in patients with capillary leak syndrome (38.1 ± 10.0 pg/ml vs 15.3 ± 3.4 pg/ml, p < 0.05). Leukocyte count during and after cardiopulmonary bypass was similar in both patient groups. This study demonstrates increased protein leakage as early as 10 minutes after initiation of cardiopulmonary bypass in patients having clinical signs of postoperative capillary leak syndrome. Patients with capillary leak syndrome displayed more pronounced histamine liberation and tumor necrosis factor-α liberation than patients without capillary leak syndrome, suggesting a relationship between cardiopulmonary bypass-related inflammatory reaction and perioperative capillary damage. A preoperative inflammatory state in patients with capillary leak syndrome could have enhanced the inflammatory response to cardiopulmonary bypass