Soft Segment Matrix Research Articles

Microstructure of N-Picolylpolyurethane Transition Metal Complexes

Spectroscopic methods are used to investigate coordination structure of N-picolylpolyurethane transition metal complexes (PUPYM, M = Co2+ and Ni2+). Geometrical arrangement of ligands in first-shell coordination sphere of metal ions is postulated to be tetrahedral CoL2Cl2 and octahedral NiL2Cl2Z2, where L is the picolyl group and Z is a hydrate. From extended X-ray absorption fine structure (EXAFS) analysis, bond lengths for metal−chlorine and metal−ligand of PUPYM are similar to those of small molecular weight transition metal complexes. A two-phase model of PUPYM, which best describes the experimental data of DMTA and SAXS, is proposed. One microphase is the hard domain of self-segregated hard segments brought about by metal−ligand interaction, and the other phase is the matrix of soft segments. Transition metal ion−ligand moieties and their interactions dominate the macroscopic thermal behavior of PUPYM. The ligand field stabilization energy difference (ΔLFSE) between metal d-electrons in complexes with two picolyl ligands in the coordination sphere of metal ions and complexes maintaining one picolyl ligand as coordination pendent group is calculated on the basis of observed coordination structure, and it represents the energy supplied to split coordination cross-links. ΔLFSE of polyurethane nickel(II) complex is larger than that of the cobalt(II) complex. Since the mobility of hard segments is in inverse proportion to the strength of coordination cross-links, a higher α-transition temperature of PUPYNi2+ with respect to PUPYCo2+ is found as expected.

Effect of the structure of chain extenders on the dynamic mechanical behaviour of polyurethane

The dynamic mechanical behaviors of polyurethanes with different types of non-linear chain extenders are compared with those of corresponding linear chain extender. The Tg of the soft segment matrix showed much variation depending on the type of the chain extenders. The use of non-linear chain extender results in at least 30°C shift toward the higher temperature compared with the sample with 1,4-butanediol. The softening temperature of the hard segment domains is dependent on the detailed structure of the chain extender. Cyclic chain extender and some chain extenders with pendent groups showed a quite significant increase in the softening temperature and well-developed rubbery plateau regions. In tan δ peaks, the peak representing the soft segment matrix becomes much sharper and larger when non-linear chain extenders are employed.

Influence of chain extenders and chain end groups on properties of segmented polyurethanes. I. Phase morphology

Segmented polyurethanes from oligotetramethylene glycol 1000, 4,4′-diphenylmethane diisocyanate and different chain extenders were characterized by specific heat capacity (temperature interval 130–450 K) and small-angle X-ray scattering measurements. A regular macrolattice of uniform-size micro-domains of stiff segments spanning a continuous matrix of soft segments was observed for the sample chain-extended with dihydrazide of isophthalipc acid, DIPA. The distribution of microdomains by sizes remained unchanged, whereas the overall degree of micropahase separation (DMS) increased due to dilution of DIPA and/or blocking of chain ends with crown ether-containing di- and monohydrazides. The distribution of microdomains by sizes broadened, whereas the DMS either remained unchanged or slightly decreased on dilution of DIPA with hydroxyl-containing chain extenders [1,4-di-N-oxy-2,3-bis-(oxymethyl)-quinoxaline and 1,4-butane-diol, respectively].

Polymers by “criss‐cross”‐cycloaddition, 7. Segmented block copolymers

Abstract“Criss‐cross”‐cycloaddition of 4,4′‐diisocyanatodiphenyl ether and 4‐methoxybenzaldazine was used to synthesize α,ω‐diisocyanato telechelics of molecular weights between 1 600 and 3 900. These precursors were reacted with different α,ω‐dihydroxy functionalized aliphatic polyethers to produce segmented block copolymers in which the precursors obtained by cycloaddition reaction provide hard segment domains embedded in a polyether soft segment matrix. The resulting materials were soluble in common organic solvents such as tetrahydrofuran and chloroform and were characterized by spectroscopic techniques (1H‐, 13C NMR, IR spectroscopy) as well as gel permeation chromatography (GPC) for molar mass determination. The block copolymers were molded in a hot stage press, and the resulting samples were characterized by differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA) and stress‐strain measurement. The materials with a hard segment fraction below 0.36 and a molecular weight above M̄n = 90 000 were elastomers with ultimate elongations above 700%.

Mechanical hysteresis of a polyether polyurethane thermoplastic elastomer

AbstractThe mechanical hysteresis of a polyether polyurethane thermoplastic elastomer was studied as a function of temperature, percent strain, and deformation energy. Hysteresis values remained small at low temperatures when the extent of the sample deformation did not disrupt the glassy matrix. This was readily evident at temperatures below the glass transition temperature, Tg of the polymer where the material did not formally yield. At temperatures above the Tg of the polymer, hysteresis remained small even at substantial strains levels and demonstrated the capabilities of the hard segment domains to act as physical crosslinks. At elevated temperatures, percent hysteresis increased as the hydrogen‐bonded hard segment domains weakened. When mechanical hysteresis was considered on the basis of constant deformation energies, hysteresis values reached a maximum in the vicinity of the Tg of the polymer. These maxima existed as a consequence of two opposing trends: the decreasing resiliency of the polymer as it becomes a glass and the increase in the resistance of that glass to undergo deformations sufficient to cause plastic flow. Finally, a hysteresis response surface constructed as a function of deformation energy and temperature was found to be sensitive to both the strain‐induced crystallization of the rubbery soft segment matrix and to the strain‐induced yielding of the glassy soft segment matrix.

Extraction Kinetics of Uranium(VI) with Polyurethane Foam.

The extraction kinetics of uranium(VI) from aqueous nitrate solution with polyether-based polyurethane foam was investigated in a batch reactor with automatic squeezing. The extraction curves of uranium(VI) concentration in solution vs. extraction time exhibited a rather rapid exponential decay within the first few minutes, followed by a slower exponential decay during the remaining period. This phenomenon can be attributed to the presence of two-phase structure, hard segment domains and soft segment matrix in the polyurethane foam. A two-stage rate model expressed by a superposition of two exponential curves was proposed, according to which the experimental data were fitted by an optimization method. The extraction rate of uranium(VI) was also found to increase with increasing temperature, nitrate concentration, and hydration of the cation of nitrate salt.

親水性セグメント化ポリウレタンウレアからの抗菌剤徐放挙動

Blood-compatible segmented polyurethaneureas were evaluated as drug delivery matrices using crystal violet (CV), benzethonium chloride (AC) and acrinol (AC) as model drugs. The polymers were synthesized from ABA-type triblock copolyethers as prepolymers, where A stands for poly (oxyethylene) and B for poly (oxytetramethylene). Microphase separation was observed in the polyurethaneureas, including drug-doped ones. CV dissolved more in the hard segment domains than in the soft segment matrix, whereas BC easily dissolved in the soft segment matrix. AC dissolved in both phases. The drug release behaviors from these polymer films were analysed by the exponent relation Mt/M∞=ktn, where k and n are constants and Mt/M∞ is the fraction of drug released until time, t. The constant k increased with poly (oxyethylene) content, i.e. with the increase of swelling in water. The constant n was found to be ca. 0.5 in many samples, which suggests that the release of drugs from these polymers is explained by the Fickian diffusion model. However, the mechanism became non-Fickian with the increase of swelling of the devices in CV and BC systems. This observation seems to be due to the heterogeneous dissolution of drug in the microphase separated structure.

Structure and Properties of Fatigued Segmented Poly(urethaneurea)s IV. Dynamic Infrared Dichroism

Structure and orientational behavior of two kinds of segmented poly(urethaneurea)s, SPUUs, having different soft segment molecular weights, were investigated by dynamic infrared absorption dichroism (DIR). DIR is a rheo-optical technique and a powerful tool to study orientational behavior of individual segments on multi-phase polymers under sinusoidal mechanical stimuli. SPUUs, being multi-block copolymers, consist of hard segment domains and soft segment matrix. Analysis of the temperature and frequency dependence of the dynamic strain–dichroic ratio coefficient, L* disclosed the following: (1) both the hard and soft segments are deformed synchronously (in-phase) with respect to applied strain, (2) the Arrhenius plot for the shift factor of L* is composed of two contributions, β (the glass transition) and γ dispersions (local motions related to methylene sequences). These observed dispersions were consistent with the corresponding mechanical dispersions, and (3) the hard segment of SPUU, having a larger soft segment molecular weight (TM-3), has a higher capability of orientation in response to external strain than that having a smaller soft segment molecular weight (TM-1).

Polyurethane elastomer with PEO-PTMO-PEO soft segment for sustained release of drugs

Blood-compatible segmented polyurethanes and polyurethaneureas were evaluated as drug delivery matrices using crystal violet and benzethonium chloride as model drugs. These polymers were synthesized from ABA-type triblock copolyether as a prepolymer, where A stands for polyethylene oxide) and B for polyftetramethylene oxide). Microphase separation was observed in segmented polyurethaneureas, including drug-doped films. Crystal violet dissolved more in the hard segment domain than in the soft segment matrix, whereas benzethonium chloride was easily dissolved in the soft segment matrix. The drug release behaviours from these films were analysed by the exponent relation M/M∞ = ktn, where k and n are constants and MtM∞ is the fraction of drug released until time, t. The constant k grew with increasing poly(ethylene oxide) content in the prepolymer, i.e. increased swelling. The constant n was found to be close to 0.5 in many samples, which suggests the release of drug from these polymers is explained by the Fickian diffusion model. However, the mechanism became non-Fickian with increased swelling of the devices.

Structure and Properties of Fatigued Segmented Poly(urethaneurea)s III. Quantitative Analyses of Hydrogen Bond

Hydrogen bonds in segmented poly(urethaneurea)s (SPUU) were studied with Fourier transform infrared spectroscopy (FT IR). Absorption curves due to the urethane and urea carbonyl groups were resolved into several peaks by a peak resolving method. Evaluation of individual peak intensity enabled one to estimate the amounts of hydrogen bonds formed with urea and urethane carbonyl groups, referred to as hydrogen bond indices, HUA and HUT, respectively. HUA and HUT were defined as the ratios of absorbances of hydrogen bonded carbonyl groups to free carbonyl groups, respectively for urea (UA) and urethane (UT) carbonyl groups. It was found that the indices of hydrogen bonds of urethane and urea carbonyl groups were the parameters which represent phase mixing, i.e., dispersion of hard segments in the soft segment matrix, and the cohesive force in the hard segment domain. The variation of the indices of hydrogen bonds with increasing elongation and temperature indicated progress of the phase mixing and reduction of the cohesive force of the hard segment domain.

Small angle x‐ray studies of siloxane‐urea segmented copolymers

AbstractNovel segmented copolymers were synthesized using aminopropyl terminated linear poly(dimethylsiloxane) oligomers as the soft component and various diisocyanates as the hard segments. As a result of the large differences in the cohesive energy density (solubility parameter) between the two components, phase separation occurs to form a microdomain structure at relatively low oligomer molecular weights. Since chain extenders were not employed during the synthesis, the “hard” segments are strictly related to the length of the diisocyanate moiety utilized in the reaction, In this paper we utilize these copolymers as reasonable models for investigating the various methods available for determining the interfacial layer thickness between the hard and soft phase. Specifically, in these systems there is no hard segment length distribution as is the usual case for segmented urethanes. Utilizing Porod's law, and appropriate analysis, both positive and negative deviations were found in the systematic series of copolymers. The degree of positive and negative character was found to be dependent upon copolymer composition. Negative deviations were accounted for in terms of a finite interfacial thickness, which turned out to be relatively small as anticipated, while the positive deviations were assigned to isolated hard segments that reside within the soft segment matrix, i.e., concentration fluctuations. In calculating the interfacial thickness, several methods were applied and in general, close agreement was obtained. Finally, correlation function analysis in conjunction with determination of the coherent Porod lengths, etc. were determined and discussed accordingly. Cautionary comments are also provided for researchers who apply less complete small angle x‐ray scattering (SAXS) analysis to related block or segmented copolymers with regard to phase separation behavior.

Structure and morphology of segmented polyurethanes: 3. Electron microscopy and small angle X-ray scattering studies of amorphous random segmented polyurethanes

Transmission electron microscopy and small angle X-ray scattering techniques have been applied to investigate the bulk morphology of compression moulded samples of an amorphous segmented polyurethane system. Samples of different hard segment content, from 13% to 74% by weight, were synthesized by solution polymerization, so that the hard segment sequence length distribution of each sample approximated the most probable distribution. Microscopy results indicate that meandering cylinders of the soft segment phase are present in the 74% sample. An alternating plate-like structure is found in the 52% sample. However, for samples of hard segment content lower than 50%, results from electron microscopy were inconclusive. The Percus-Yevick hard sphere liquid theory taking into account the polydispersity of domain size was applied to calculate the scattering behaviour of these lower hard segment content samples and compared with the experimental data. Modelling results and mechanical behaviour of these samples lead to the conclusion that discrete hard segment domains of anisotropic shape are present in the soft segment matrix. This conclusion is also supported by the results from calculations of specific area of domains. A spectrum of morphologies varying with sample composition is thus obtained for this particular system of polyurethanes.

A matrix shear model to describe the orientation behaviour of segmented, polyurethane elastomers

As a result of infrared dichroism and dynamic mechanical measurements on segmented polyurethane elastomers during orientation, a model is suggested for the orientation behaviour based on shear of the soft segment matrix. The hard segment domains are assumed to behave as indeformable platelets which determine the matrix shear plane in their vicinity. On extension of the elastomer, the platelets rotate into the stretch direction by shear of the matrix. The behaviour of the dynamic compliance on stretching is determined at each stage of the deformation by the platelet orientation corresponding to the superimposed static strain. This model provides a better description of the orientation behaviour than given by a pseudo-affine transformation of domains.

THE MECHANICAL PROPERTIES OF POLYETHER-COPOLYESTER ELASTOMERS

Polyether-copolyester block copolymer (T/i_??_Ph-E1540), in which the aromatic homopolyester (T) usually serves as the hard segment (the crystallizable parts of chains) were replaced by the aromatic copolyester (T/i_??_Ph), were synthesized.In this case, since the replacement of the hard segment depressed the rates of the growth of their crystallites and caused their crystallinity to decrease, the lowering of the fiber-strength was presupposed. It was suggested that this lowering would be compensated by increasing of the quantity of the hard segment.The purpose of this work was to investigate how the above mentioned replacement by the copolyester hard segment and compensation by the increment of the hard segment ratio affected the mechanical properties of block copolymers.The results obtained were as follows:1) As for the melt-spun fibers (T/i_??_Ph-E1540 [50/50]), since the ratio of i_??_Ph increased, their tensile strength and Young's modulus tended to become lower and elasticity greater.2) The melt-spun fibers whose i_??_Ph ratio ranging from 15.0 to 17.5 wt% exhibited the mechanical properties superior to those of T-E1540 [40/60].3) For the X-ray diagrams of the drawn and heat-treated fibers, the apparent degree of crystallinity of the hard segment in T/i_??_Ph (82.5/17.5)-E1540 [50/50] was nearly equal to that of T-E1540 [40/60] when their strengths of the interference spots on the equator of the diagram were compared with one another. The particle sizes of crystallites of the former, calculated from the breadth in radians of the diffraction interference at points of half-maximum intensity, were smaller than those of the latter.4) Further, on the particle sizes, the results observed under the polarizing microscope had the same tendencies as those described in (3), and the uniform dispersion of crystallites of T/i_??_Ph (82.5/17.5)-E1540 [50/50] within the soft segment matrix was also recognized.

Phase separation in urethane elastomers as Judged by low-angle X-Ray scattering. II. Experimental Results

Abstract Supposing complete segregation, volume and density of the hard segment domains in thermoplastic urethane elastomers are easily calculated from the chemical composition of the elastomers. These hypothetical values may be compared with experimental small-angle X-ray findings, resulting in a realistic picture of the actual state of segregation. A similar situation holds true for the specific surface area of the domains. With respect to elastomers of MDI, hydrazine, and a linear polyester or a polyether with a hard segment volume fraction of about 15%, specific surface areas of the domains of about 220 m2/cm3 were found. They are characterized by diffuse transition zones, the width of which was about 20 A. The segregation was further more incomplete due to isolated MDI blocks dissolved in the soft segment matrix as well as to soft segments included in the domains.

Phase separation in urethane elastomers as judged by low-angle X-ray scattering. I. Fundamentals

Abstract In thermoplastic urethane elastomers, phase separation between hard and soft segments resulting in a domain structure is an essential condition for a sufficiently high heat distortion temperature. The state of segregation, i.e., the domain structure, is characterized by the following aspects: 1) the size distribution, i.e., the dispersion level of the domains; 2) the sharpness of diffuseness of the domain boundaries, and 3) hard segments dissolved in the soft segment matrix or soft segments included in the domains. The state of segregation may be evaluated by means of low-angle X-ray scattering. The fundamental theory, based on Porod's theory of low-angle scattering, is given in this paper. Experimental findings will be discussed in a later paper.