Humidity-dependent dynamic infrared linear dichroism study of a poly(ester urethane)

Fourier transform infrared techniques, infrared difference spectroscopy and dynamic infrared linear dichroism (DIRLD), have been utilized to explore the effects of humidity and water absorption on a poly(ester urethane). An environmental infrared microbalance cell was used to measure the infrared spectra as a function of humidity and accompanying weight change for the absorption-desorption processes. The infrared difference data indicate that exposure to humidity affects the hydrogen-bonding interactions in the polymer. Dynamic infrared linear dichroism studies in tensile deformation mode as a function of humidity demonstrate how changes in water content affect the orientational response of functional groups. Complex behavior as a function of humidity for functional groups involved in hydrogen bonding indicates that water absorbed by the polymer affects the micro-environments near these functional groups.     

Shape memory poly(ester urethane) with improved hydrolytic stability

In two hydrolytic degradation studies the tensile (mechanical) and functional (thermo-mechanical) properties of a hydrolysis-stabilized shape memory poly(ester urethane) and its non-stabilized analog were investigated. Hydrolytic degradation was enforced by specimen immersion in de-ionized water at 80 °C. Significant differences in the fundamental shape memory parameters were monitored as function of aging time for the stabilized and non-stabilized polymer. This included the ability to recover strain (shape recoverability) and stress (stress recoverability) on heating after shape programming. Hydrolysis-related mechanical and functional changes were correlated with morphological ones, detected by differential scanning calorimetry (DSC). The shape memory poly(ester urethane), which was protected by a carbodiimide-based hydrolysis stabilizer, revealed significantly improved resistance towards hydrolysis with respect to various mechanical and shape memory parameters.     

Catalysts and temperature driven melt polycondensation reaction for helical poly(ester‐urethane)s based on natural L‐amino acids

Catalyst and temperature driven melt polycondensation reaction was developed for natural L‐amino acid monomers to produce new classes of poly(ester‐urethane)s. Wide ranges of catalysts from alkali, alkali earth metal, transition metal and lanthanides were developed for the condensation of amino acid monomers with diols to yield poly(ester‐urethane)s. A‐B Diblock and A‐B‐A triblock species were obtained by carefully choosing mono‐ or diols in model reactions. More than two dozens of transition metal and lanthanide catalysts were identified for the polycondensation to yield high molecular weight poly(ester‐urethane)s. Theoretical studies revealed that the carbonyl carbon in ester possessed low electron density compared to the carbonyl carbon in urethane which driven the thermo‐selective polymerization process. Optical purity of the L‐amino acid residues in the melt polycondensation process was investigated using D‐ and L‐isomers and the resultant products were analyzed by chiral‐HPLC and CD spectroscopy. CD analysis revealed that the amino acid based polymers were self‐assembled as β‐sheet and polyproline type II secondary structures. Electron and atomic force microscopic analysis confirmed the formation of helical nano‐fibrous morphology in poly(ester‐urethane)s. The newly developed melt polycondensation process is very efficient and optimized for wide range of catalysts to produce diverse polymer structures from natural L‐amino acids. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1065–1077     

Changes in charge density and softness of a poly(l-lactide) microcapsule surface in the hydrolytic degradation process

The changes in surface properties of poly(l-lactide) microcapsules caused by hydrolytic degradation have been studied with electrophoretic mobility measurements. An electrokinetic model has been applied to examine the electrophoretic mobility data, which were previously analyzed with a model that does not take into account the liquid flow inside the microcapsule membrane [K. Makino, H. Ohshima and T. Kondo, J. Microencapsulation, 4 (1987) 47]. The present new model involves two parameters, the charge density in the microcapsule membrane and a softness parameter, the latter of which characterizes the reciprocal of the frictional coefficient of the polymer exerted on the liquid flow. Information about the changes in charge density and in the softness of the poly(l-lactide) microcapsule surface have been newly obtained. The surface charge density increases by the cleavage of ester bonds in the polymer chain in the initial stage of the degradation process. It then gradually decreases down to the value for intact poly(l-lactide) microcapsules as a result of the release of degraded polymer segments from the microcapsule surface. Also, as the degradation proceeds, the softness parameter value increases, suggesting that the surface of the microcapsules becomes softer, probably because the surface becomes porous. The above change in the softness and the decrease in charge density at the later stage of the degradation both imply liberation of charged polymer segments. The degradation of poly(l-lactide) microcapsules proceeds by alternate repetition of cleavage of the ester bonds in the polymer chains and liberation of the degraded polymer segments from the surface.     

Structural and end‐group effects on bulk and surface properties of hyperbranched poly(urea urethane)s

The hydroxy end groups of aromatic and aliphatic hyperbranched poly‐(urea urethane)s prepared with an AA* + B*B₂ one‐pot method were modified with phenylisocyanate, butylisocyanate, and stearylisocyanate. The success of the modification reaction was verified with ¹H NMR and IR spectroscopy. Linear model poly‐(urea urethane)s were prepared, too, for comparison. The bulk properties of OH functionalized hyperbranched poly(urea urethane)s, compared with those of linear analogues and modified hyperbranched poly(urea urethane)s, were studied with differential scanning calorimetry, thermogravimetric analysis, and temperature‐dependent Fourier transform infrared measurements. Transparent and smooth thin films could be prepared from all polymer samples and were examined with a light microscope, a microglider, and an atomic force microscope. The properties of the polymer surface were examined by measurements of the contact angle and zeta potential. For all samples, the properties were mainly governed by the strong interactions of the urea and urethane units within the backbone, whereas the influence of the nature of the end groups and of the branched structure was reduced in comparison with other hyperbranched polymer systems. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3376–3393, 2005     

Conformational changes of fibrinogen after adsorption

The adsorption behavior of fibrinogen to two biomedical polyurethanes and a perfluorinated polymer has been investigated. Changes in the secondary structure of adsorbed fibrinogen were monitored using attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) and sum frequency generation vibrational spectroscopy (SFG). SFG measurements were performed in the amide I range as well as in the C-H/N-H stretching range. Amide I signals from SFG demonstrate that fibrinogen has post-adsorption conformational changes that are dependent upon the polymer surface properties. For example, strong attenuation of the amide I and N-H stretching signals with increasing residence time was observed for fibrinogen adsorbed to poly(ether urethane) but not for the other two polymers. This change is not readily observed by ATR-FTIR. Differences in the observed spectral changes for fibrinogen adsorbed to each polymer are explained by different initial binding mechanisms and post-adsorption conformational changes.     

Polyurethane elastomers with hydrolytic and thermooxidative stability. I. Polyurethanes with N-alkylated polyamide soft blocks

Segmented polyurethanes with N-alkylated amides as soft blocks as prepared. Comparisons are made with both a poly(ester urethane) and a poly(ether urethane) with the same hard block; the poly(amide urethane) is more hydrolytically stable than the polyester containing material and demonstrates greater thermooxidative stability than that with the polyether moiety. The aliphatic poly(amide urethane)s remain transparent upon exposure to uv light.     

Thermosensitive biodegradable polydepsipeptide

A poly(N-isopropylacrylamide) (PNIPAAm)-like biodegradable thermosensitive polydepsipeptide, poly[Glc-Asn(N-isopropyl)], was synthesized by introducing an isopropyl amide group into poly[Glc-Asn]. Poly[Glc-Asn(N-isopropyl)] was degraded in vitro by cleavage of the ester bonds in the main chain in water at room temperature. The non-toxic nature of the polymer and its degradation products, coupled with a cloud point at 29 degrees C in water, make this polymer attractive for biomedical implant applications.     

Brillouin-scattering determination of the acoustic properties and their pressure dependence for three polymeric elastomers

The acoustic properties of three polymer elastomers, a cross-linked poly(dimethylsiloxane) (Sylgard 184), a cross-linked terpolymer poly(ethylene-vinyl acetate-vinyl alcohol), and a segmented thermoplastic poly(ester urethane) copolymer (Estane 5703), have been measured from ambient pressure to approximately 12 GPa by using Brillouin scattering in high-pressure diamond anvil cells. The Brillouin-scattering technique is a powerful tool for aiding in the determination of equations of state for a variety of materials, but to date has not been applied to polymers at pressures exceeding a few kilobars. For the three elastomers, both transverse and longitudinal acoustic modes were observed, though the transverse modes were observed only at elevated pressures (>0.7 GPa) in all cases. From the Brillouin frequency shifts, longitudinal and transverse sound speeds were calculated, as were the C(11) and C(12) elastic constants, bulk, shear, and Young's moduli, and Poisson's ratios, and their respective pressure dependencies. P-V isotherms were then constructed, and fit to several empirical/semiempirical equations of state to extract the isothermal bulk modulus and its pressure derivative for each material. Finally, the lack of shear waves observed for any polymer at ambient pressure, and the pressure dependency of their appearance is discussed with regard to instrumental and material considerations.     

Long branching in poly(vinyl acetate) and poly(vinyl alcohol). I. Crosslinking and crosslinking cleavage of poly(vinyl acetate)

A crosslinked network was formed by the reaction of partially saponified poly(vinyl acetate) and toluylene diisocyanate in benzene. The yield of gel was markedly dependent on the degree of saponification and the concentrations of polymer and diisocyanate. Crosslinked poly(vinyl alcohol) was obtained by treating the poly(vinyl acetate) with a catalytic amount of sodium hydroxide in methanol without any change of the urethane crosslinks. The crosslink based on the urethane linkage was quantitatively cleaved by acids, especially by hydrobromic acid, releasing polymers of the same molecular weight as the original.     

Poly(caprolactone) containing highly branched segmented poly(ester urethane)s via A2 with oligomeric B3 polymerization

Highly branched, poly(caprolactone) (PCL) containing segmented poly(ester urethane)s were synthesized via polymerization of A₂ and oligomeric B₃ type monomers. An isocyanate functional butanediol‐based A₂ hard segment was synthesized and immediately reacted with a poly(caprolactone)‐based trifunctional (B₃) soft segment. Characterization of thermal properties using DMA and DSC analysis demonstrated that the PCL segment remained amorphous in branched poly(ester urethane)s. Conversely, the crystallinity of PCL segment was retained to some extent in a linear analogue with equivalent soft segment molecular weight. Tensile testing revealed a slight decrease in Young's modulus and tensile strength for the highly branched polymers compared with a linear analogue. However, highly branched poly(ester urethane)s demonstrated lower hysteresis. In addition to synthesis of highly branched polymers, poly(ester urethane) networks were synthesized from a highly branched hydroxyl‐terminated precursor and a low molar mass diisocyanate as the crosslinking agent. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6285–6295, 2008     

Spectroscopic Ellipsometry for Characterization of Thin Films of Polymer Blends

Morphology, composition, miscibility, interdiffusion, and interactions at interfaces are important quantities of polymer blends. Many of these parameters can be probed with spectroscopic ellipsometry. Ellipsometry in the visible spectral range is very suitable for determination of thicknesses and the high frequency refractive indices of thin organic films. However the spectral contrast is low for many polymers in comparison to infrared spectroscopic ellipsometry (IRSE) where specific contributions of the molecular vibrations are probed. In the presented study the infrared optical constants of a double layer (206.6 nm in total) of poly(n-butyl methacrylate) (PnBMA) and poly(vinyl chloride) (PVC) and of the films of the single compounds have been determined with optical simulations using layer models. The multiple layer model served for simulation of the ellipsometric spectra taken after an annealing induced mixing process in a polymeric double layer. The ellipsometric spectra of a not completely mixed sample could be fitted in a three-layer model, in which a mixed interphase in between the two layers of the polymers is formed due to interdiffusion.     

Volatile evolution induced by energetic He++ ions in a poly(ester) based polyurethane

Irradiation of polymer samples using an accelerated beam of He⁺⁺ ions passed through a 10 μm thick window of havar foil has been performed. Such an irradiation simulates the effects of large α radiation doses. The experimental set up was designed so that the irradiated material was contained within a small sample chamber, which was isolated from the main vacuum chamber of the ion beam by means of the foil window. A mass spectrometer linked directly to the sample chamber facilitated analysis of gaseous products evolved from the materials as a consequence of irradiation. Samples of a poly(ester) based poly(urethane) polymer evolved mainly CO₂ along with a number of higher mass volatile species. Assignment of chemical structures to the main molecular ions has allowed deductions about the chemical processes underlying radiation induced change to be made. Furthermore, identification of trends in volatile production affords information about radiation induced crosslinking reactions, which do not directly result in the production of volatile species to be deduced.     

Poly(ester urethane acrylates) and holographic properties of formulations on their basis

Poly(ester urethane acrylates) with unsaturated bonds in stiff blocks have been synthesized from oligo(ester acrylates) containing functional groups. The structure and mechanical properties of the block copolymers thus prepared have been studied before and after UV cure. On the basis of the said poly(ester urethane acrylates), light-sensitive formulations for holographic recording have been designed. The formation of holographic gratings under illumination by an Ar laser light has been investigated. The formations under study offer promise as photostructuring media for holography.     

Topologically interpenetrating elastomeric networks

Several partially interpenetrating polymeric networks (IPN) were made by combining chemically different linear elastomers. The polymer combinations were deposited as films from aqueous emulsions made by mixing the individual emulsions in equal proportions. The films were crosslinked to form two superimposed networks. In two cases, the networks were cleanly separated by hydrolysis of one of the component networks to demonstrate that there was no chemical interaction between the polymers. Measurement of crosslink density showed that, in most cases, partial interpenetration does occur as evidenced by an effective crosslink density of the IPN's greater than the arithmetic mean of the crosslink densities of the component networks. The swelling ratios, densities, and stress–strain properties were determined. For one of the network combinations, a poly(urethane–urea) and a poly(butadiene–acrylonitrile), a series of IPN's varying in polymer composition was made. The swelling ratios and densities are close to the arithmetic means; however, both the tensile strength and crosslink density exhibit a maximum at about 70% poly(butadiene-acrylonitrile). The maximum tensile strength is actually significantly higher than that of either of the component polymers. The elongations all approach that of the poly(urethane–urea), the more extensible material, except for compositions approaching 100% poly(butadiene–acrylonitrile), which exhibit a very low extensibility.     

Synthesis and biodegradation of poly(ester amide)s containing amino acid residues: The effect of the stereoisomeric composition of L‐ and D‐phenylalanines on the enzymatic degradation of the polymers

Biodegradable poly(ester amide)s that contained phenylalanine residues in the main chains were synthesized by the polycondensation of di‐p‐nitrophenyl sebacate and phenylalanine 2‐aminoethyl ester. The stereoisomeric composition (L /D ratio) of the phenylalanine residue in the monomer did not affect the yield and molecular weight of the polymer much. From the optical rotations of the polymers, it was found that the L /D ratio of the phenylalanine residue in the polymer was almost equal to the L /D ratio of the phenylalanine residue in the monomer. The biodegradability of the poly(ester amide)s was studied in aqueous solutions with proteases as catalysts. The polymer with 100% L ‐phenylalanine residue was effectively degraded by α‐chymotrypsin or subtilisins. However, the replacement of 10% L ‐phenylalanine with D ‐isomer resulted in a dramatic decrease in degradability. The polymers with less than 30% L ‐isomer were hardly degraded by the enzymes. Gel permeation chromatography studies suggested that the solubility of the degradation products in water greatly affected the rate and extent of biodegradation. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 40: 385–392, 2002     

Aging of a medical device surface following cold plasma treatment: Influence of low molecular weight compounds on surface recovery

The surface of medical devices is of great importance for biocompatibility. Surface properties can evolve with a material treatment, time, and storage conditions. In this work, poly(urethane) catheters sterilised by cold nitrogen plasma treatment, were subjected to air and temperature aging in order to evaluate the influence of humidity and temperature on surface recovery. The surface of catheters was analysed by contact angle measurements and XPS. Faster surface changes upon aging were observed at high temperature (45 °C) and relative humidity (90%). For the commercial poly(urethane) catheters analysed in this work, the importance of the nature and polymorphism of additives added to the polymer (lubricant, antioxidant) in the recovery process was demonstrated. Indeed, DSC and TSC showed that additive transitions (relaxation, melting…) could govern the aging process.     

Hyaluronic Acid/Poly(β‐Amino Ester) Polymer Nanogels for Cancer‐Cell‐Specific NIR Fluorescence Switch

Cancer‐cell‐specific pH‐activatable polymer nanogels consisting of CD44‐receptor‐targeting hyaluronic acid (HA), pH‐sensitive poly(β‐amino ester) (PBAE), and near‐infrared (NIR) fluorescent indocyanine green (ICG) were synthesized and used to detect cancer cells. The HA/PBAE/ICG‐polymer‐nanogel‐based NIR probe was nonfluorescent outside of tumor cells. After internalization by CD44‐receptor‐mediated endocytosis, the probe accumulated in the late endosomes or lysosomes where the acidic pH solubilized the PBAE and caused instant disassembly of the polymer nanogel. During endosomal maturation, the encapsulated ICG was released from its quenched state, inducing strong NIR fluorescence recovery. The nanogels generate a highly tumor‐specific NIR signal with a reduced background signal.     

Molecular parameters for the prediction of polyurethane structures

Recent efforts to determine the structures of poly(MDI/diol) hard segments in polyurethane elastomers have relied on the structures determined by single-crystal x-ray methods for diphenylmethane urethane model compounds. We have surveyed the structure of six model compounds, and have derived average values for the bond lengths, bond angles, and bond torsion angles for use in future analyses. The applicability of these averages to polymer structures is discussed, and the data are used to derive models for the poly(MDI-butanediol) chain which are found to be consistent with the fiber repeat determine by x-ray methods.     

Nuclear magnetic resonance studies of polymer solutions. I. Poly(methyl methacrylates)

The microscopic interactions of solvent with the diastereoisomeric units of isotactic and syndiotactic poly(methyl methacrylate) have been studied by high-resolution nuclear magnetic resonance. The changes in chemical shifts in various solvents were compared with those of low molecular weight analogs, methyl acetate, and methyl propionate. These changes are caused mainly by the ring-current effect, which has been found to be larger for the low molecular weight analogs than for the polymer. This is especially true when the protons on the polymer backbone are compared with the corresponding ones in the low molecular weight compounds. As one changes from a chloroform solvent to an aromatic solvent, the displacements of the chemical shifts of the polymer can be expressed as percentages of the corresponding shifts of methyl acetate. For syndiotactic poly(methyl methacrylate) in chlorobenzene, benzene, and α-chloronaphthalene, respectively, the percentages are 82, 93, 75 for ester protons; 35, 29, 17 for the backbone methylene protons; and 18, 6.7, 0 for the backbone α-methyl protons. For isotactic poly(methyl methacrylate) in chlorobenzene and benzene, respectively, the percentages are 71, 76 for the ester protons; 41, 38 for the backbone methylene protons; and 41, 32 for the backbone α-methyl protons. These results are discussed in terms of the local stereochemistry of the polymer systems. The exploitation of procedures of this sort in revealing details of polymer behavior in solution indicates dramatic possibilities for future investigations.