Hard Segment Composition Research Articles

Damping properties and transmission loss of polyurethane. I. Effect of soft and hard segment compositions

Damping properties and transmission loss of polyurethane. I. Effect of soft and hard segment compositions

Damping properties and transmission loss of polyurethane. I. Effect of soft and hard segment compositions

A series of polyurethane compositions with soft and hard segments were prepared, and the damping and mechanical properties of these materials were studied. The damping of polyurethane was decreased and shifted to the higher temperature with the content of butanediol (BD) used as a chain extender. The mechanical proper- ties such as tensile strength and hardness (shore A) were increased with increasing BD contents. For application in noise reduction, the transmission loss of the mechanical vibration through solid structure was measured by two methods of extensional and constrained layer configuration. Polyurethane was used as a damping layer. The transmission loss of constrained layer configuration was larger than that of extensional configuration. Although the peak tand value of polyurethane having composition of BD 0.5 was lower than that of BD 0.4, its transmission loss was more effective at higher frequency. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 604 - 611, 2000

Influence of the chemical composition of poly[ester-block-ether]s on the phase structure

The influence of the chemical composition on the phase structure, and from this the structure-property relationships, of poly[ester-block-ether] (PEE) elastomers based on poly(butylene terephthalate) (PBT) hard segments and oligo(α,ω-dihydroxy poly(oxytetraniethylene)) (PTMO) and/or dimer fatty acid (DFA) soft segments was investigated using differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA), and tensile testing. Differences in thermal and mechanical properties with varying hard and soft segment composition are interpreted in terms of the phase miscibility of the various polymers studied.

COMPARATIVE BLOOD COMPATIBILITY OF POLYETHER VERSUS POLYCARBONATE URETHANES IN A EPIFLUORESCENT VIDEO MICROSCOPY

The segmented polyether urethanes (PEUs) have been used in implantable medical devices due to excellent mechanical properties, acceptable blood compatibility, and good biostability. However, recent studies demonstrate that the polyether soft segment of PEU is susceptible to oxidative degradation in vivo due to scission of the polyether group. Recently, polycarbonate urethanes (PCUs) having no ether linkage in the soft segment have been developed, and show improved stability against oxidative degradation over PEUs. The current study evaluates blood compatibility of these PCUs in comparison with PEUs using epifluorescent video microscopy (EVM) combined with a parallel plate flow cell. The authors selected two PCUs, Corethane 80A (Corvita Corporation, Miami, FL) and PCU(1560), and two PEUs, Pellethene 2363-80AE (Dow Chemical Japan, Tokyo, Japan) and Tecoflex EG80A (Thermedics, Inc., Woburn, MA), all of which have similar hard segment compositions (MDI or HMDI:1,4-butanediol(BD)) and the same hardness of 80A. The EVM measured the amount of platelet coverage on the surfaces using human whole blood perfused at a wall shear rate of 100/sec for 20 min. Complement activation (C3a) also was measured. Both PEUs, especially Pellethane, showed significantly higher platelet adhesion than the PCUs (p < 0.05). There were no significant differences in platelet adhesion between the two PCUs. As for C3a measurements, Tecoflex showed higher complement activation than the others. Based on these results, it is recommended that PEUs should be replaced by ether free PCUs for use in implantable blood contacting devices such as artificial hearts and pacemaker lead insulators.

Permeation and sorption of CO2 through amine-contained polyurethane and poly(urea-urethane) membranes

As an absorbent of CO2, tetraethylenepentamine (TEPA) and/or N-methyldiethanolamine (MDEA) was introduced into the hard segment as chain extenders of the series urethane polymer (PU), urea–urethane polymer (PUU), and segmented urethane/urea–urethane copolymer (SPU) based on 4,4′-diphenylmethane diisocyanate (MDI) and either poly(ethylene glycol (PEG)-400 or -600. The obtained polymers thus contained a nearly equal weight composition of both soft and hard segments and were prepared as polymer membranes for permeation and sorption of CO2. The properties of the polymer membranes were characterized using a Fourier transform IR spectrophotometer, thermal gravimetric analysis, and rheometric measurement. The permeation and sorption isotherms as a function of temperature and pressure as well as the activation energy of permeability and diffusivity and the enthalpy change of the solution were measured. The test temperatures were carried out above and below the Tgs of soft-segment domains or the Tgh of hard-segment domains. The steady-state permeability (P) and diffusion coefficients (D) obtained ranged from 1.01 to 12.9 barrer and 1.04 to 4.04 cm2/s, respectively, and the solubility coefficients (S), from 0.529 to 3.43 cm3(STP)/cm3 polymer-atm at 10 atm and 35°C. The TEPA-containing polymer membranes showed a smaller P and D but a larger S than did MDEA-containing ones. The membranes comprising PEG-600 exhibit the values of P, D, and S at about 11.5-, 2.5-, and 4.5-fold the PEG-400 ones, respectively. For SPU membranes, above Tgs or Tgs, the pressure dependencies of P followed the modified free-volume model. On the other hand, below Tgs, they exhibited a minimum permeability at a certain pressure caused by the plasticization action of sorbed CO2. The sorption isotherms of CO2 indicated that the membranes comprising PEG-400 can be described by a dual-mode sorption model below Tgs. Also, the SPU polymer membranes obied the Henry's law above Tgs as well as Tgh. The characteristic constants of the sorption model were also determined and are discussed. © 1996 John Wiley & Sons, Inc.

Application of enzyme immunoassays for testing haemocompatibility of biomedical polymers

In this study enzyme immunoassays are presented for the assessment of platelet adhesion/activation and fibrinogen adsorption/conformation. The estimation of platelet adhesion and activation was performed with two enzyme immunoassays (EIAs) using monoclonal antibodies directed against CD42b (GP Ib) and CD 62 (GMP 140 or P-Selectin). The applicability of EIA was first demonstrated in microtitre plates coated with fibrinogen. The thrombogenic substrate showed that platelet adhesion and activation reached a plateau level within 30 min. The use of EIA for testing biomaterials was demonstrated with polymeric reference materials where a differentiation of materials with respect to adhesion and activation was achieved. To validate the EIA scanning electron microscopy was applied and confirmed the different extent of adhesion and activation of platelets on reference materials. In addition, polyurethaneureas, based on 4,4′-diphenylmethane diisocyanate and polytetramethylene glycols, with different hard segment content and composition were investigated. It was found that both adhesion and activation were not simply dependent on the hard segment content but also on the hard segment composition. To get more insight into the mechanism of this process, two EIAs for the binding of fibrinogen using polyclonal and monoclonal antibodies were developed. There it was shown that the adhesion and activation of platelets on polyurethaneureas was not simply dependent on the total amount of adsorbed fibrinogen but rather on its conformation, indicated by the binding of the monoclonal antibody directed vs the γ-chain of fibrinogen.

Effect of Hard Segments on Morphology and Properties of Thermoplastic Polyurethanes

A series of thermoplastic polyurethanes was synthesized with varying hard segment composition or content and the effect of the hard segments on morphology and properties was studied by differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), thermal mechanical analysis (TMA), Fourier transform infrared analysis (FTIR) and tensile testing. The diisocyanates included 4,4' -diphenylmethane diisocyanate (MDI) and 4,4' -dicyclohexylmethane diisocyanates (H,2MDI). The chain extenders 1,4-butanediol, 1,5-pentanediol and 1,3-butanediol were used. The soft segment material was poly(oxytetramethylene) glycol of molecular weight 2000. It was found that the interchain attractive forces between hard segments affect physical properties and morphologies. The degree of phase mixing, hardness and strength increased with increasing hard segment content and with decreasing degree of hard segment crystallinity (packing arrangements) at the same hard segment content.

Polyurethane elastomers based on molecular weight advanced poly(ethylene ether carbonate) diols. II. Effects of variations in hard segment concentration

AbstractA series of polyurethane elastomers were studied in which the soft segment composition was a molecular weight advanced poly(ethylene ether carbonate)diol (2025 mol wt) and the hard segment composition was based on MDI/1,4‐butanediol. These polyurethane elastomers had a constant soft segment composition and block length, a constant hard segment composition, but a variable hard segment block length and concentration (31.9–65.2 wt % hard segment). Properties such as rubbery plateau modulus, solvent resistance, melting point, hardness, tensile strength, and hard segment run length all improve with increasing hard segment concentration. DMA and DSC data indicate a partially phase mixed morphology. However, phase mixing must occur at domain boundaries since the soft segment Tg is nearly invariant with hard segment concentration. Annealing studies indicate that the optimum post‐cure temperature, for 1 h, is about 175°C.

Structure-property relationships and moisture sensitivity of PDMS/PTMO mixed soft segment urethane elastomers

Abstract The structure-property relationships of polyurethane elastomers based on 4,4′-diphenylmethane diisocyanate (MDI) and 4,4′-dicyclohexylmethane diisocyanate (HMDI) with PTMO, PDMS, and mixed PTMO/PDMS soft segments were investigated using DSC, dynamic mechanical spectroscopy, tensile testing, and SAXS. Changes in water absorption and moisture sensitivity with compositional changes were investigated through water absorption and physical property measurements. Differences in tensile properties and moisture sensitivity with varying hard and soft segment composition are interpreted in terms of the phase mixing characteristics of the various polymers studied.

Solid state extrusion of thermoplastic elastomers 4

A solid state extrusion technique is applied as to produce oriented block copoly(ether ester) under various physical conditions. The morphology of the extruded samples is characterized in relation to the extrusion parameters and hard segment compositions of the polymer, using thermal analysis and X-ray methods. The lateral dimensions of the crystalline domains are found to be approximately 150 A depending on the extrusion conditions. The statistics of the long range periodicity of the structure along the extrusion direction is in agreement with a one-dimensional two phase model, the crystalline portion of which does not vary much in thickness (35 – 45 A). The unexpected increase in the long period and the thermal shrinkage suggest the existence of strained interlamellar amorphous chains (tie molecules). The observed variations in tensile properties are interpreted under the assumption that both the number of such tie molecules and their fully extended lengths are determined by the hard segment composition and the extrusion conditions. It is also argued that the increase in the glass transition temperature is not only a function of the composition of hard segments in the amorphous phase but also of the number of strained tie molecules.

Structure and morphology of segmented polyurethanes: 2. Influence of reactant incompatibility

By following the copolymerization of a model polyurethane system, HTPBD/2,6 (or 2,4)-TDI/BDO, by optical microscopy, it was found that initial reactant incompatibility was the key factor in determining the final morphology of bulk sample. Based on this finding and the esults from the previous paper, models are proposed to describe the morphology during polymerization of this particular polyurethane system for several hard segment compositions where both macro-phase separation and micro-phase separation of reactants can occur during polymerization. The copolymerization of one seemingly compatible system, PPO-EO/MDI/BDO, which has been previously studied and commercially produced, was also followed by optical microscopy. In the size range which can be detected with an optical microscope using conventional optics, no heterogeneities were observable at the beginning of this reaction but phase separation was evident later in the reaction and can be xplained by the presence of micro-phase separation of reactants. Globule and spherulite formation and the presence of multiple T g's and T m's observed by previous workers can be explained by the two levels of heterogenities present during polymerization.

Diffusion of gases through polyurethane block polymers

AbstractThe diffusivities of simple gases through a series of polyurethane block copolymers of differing aromatic urethane content and type of soft segment were measured using a quadrapole mass spectrometer as a detecting device. Although an Arrhenius expression generally described the temperature dependence of diffusion in this system, a discontinuity was observed in the Arrhenius plots for some materials, and the discontinuity was found to be related to the onset of the glass transition in the hard domains. Increasing the hard segment content of the materials decreased the diffusivity due to the increase in the activation energy of diffusion. Increasing the soft segment length brought about a decrease in the activation energy with an increase in diffusivity. Polyster urethanes had lower activation energies for diffusion than polyether urethanes of similar hard segment composition. Finally, as the penetrant diameter was increased, a decrease in the diffusivity and an increase in the activation energy was noted.