Segmented Thermoplastic Polyurethanes Research Articles

Influence of soft segment structure, hydrogen bonding, and diisocyanate symmetry on morphology and properties of segmented thermoplastic polyurethanes and polyureas.

A comprehensive review of the structure-morphology-property relations in segmented thermoplastic polyurethanes and polyureas (TPU) is provided. Special emphasis is given to the influence of the soft segment structure, polarity, and molecular weight, diisocyanate symmetry and the nature, extent, and strength of hydrogen bonding on the morphology and thermal and mechanical properties of TPUs. Experimental results obtained on composition-dependent TPU morphology and properties by various techniques were also compared by the morphology profiles generated by computational methods such as quantum mechanical calculations and molecular dynamics simulations.

Large-scale dispersion of the hierarchical (1D, 2D and 3D) carbonaceous nanofillers in thermoplastic polyurethane through supramolecular self-assembly and extrusion

ABSTRACT The hierarchical carbonaceous nanofillers viz. carboxylated multiwalled carbon nanotube (MWCNT-COOH as 1D), hydroxylated few-layer graphene (FLG-OH as 2D), and hybrid 3D i.e., MWCNT-COOH immobilized into FLG-OH were dispersed into segmented thermoplastic polyurethane (TPU) by twin-screw extrusion (TSE). The concentration of nanofillers was varied as 0.25, 0.5, 1.0, 2.0 and 5 wt%. To increase the level of dispersion, hybrid 3D nanofillers were also incorporated into TPU by producing cellular structures through supramolecular self-assembly route (SSAR). The cellular structure in which the nanofillers were found to be uniformly dispersed was then compounded by TSE technique. The large-scale uniform dispersion was observed at higher loading (2 wt%) by SSAR followed by TSE when compared with direct TSE. Uniform dispersion was found at 1 wt% loading by direct TSE. PU nanocomposite film reinforced with 2 wt% hybrid 3D nanofillers showed good gas barrier property with ~63% reduction of helium gas permeability to 472 cm3/m2/day from 1287 cm3/m2/day of neat PU film.

The Role of Diisocyanate Structure to Modify Properties of Segmented Polyurethanes

Segmented thermoplastic polyurethanes (PU) were synthetized using a polycarbonatediol macrodiol as a flexible or soft segment with a molar mass of 2000 g/mol, and different diisocyanate molecules and 1,4-butanediol as a rigid or hard segment. The diisocyanate molecules employed are 3,3'-Dimethyl-4,4'-biphenyl diisocyanate (TODI), 4,4'-diphenylmethane diisocyanate (MDI), 4,4'-Methylenebis(phenyl isocyanate) 1-isocyanato-4-[(4-phenylisocyanate)methyl]benzene and 1-isocyanate-4-[(2-phenylisocyanate) methyl]benzene (ratio 1:1) (MDIi), isophorone diisocyanate (IPDI), and hexamethylene diisocyanate (HDI). The polyurethanes obtained reveal a wide variation of microphase separation degree that is correlated with mechanical properties. Different techniques, such as DSC, DMA, and FTIR, have been used to determine flexible-rigid segment phase behavior. Mechanical properties, such as tensile properties, Shore D hardness, and "compression set", have been determined. This work reveals that the structure of the hard segment is crucial to determine the degree of phase miscibility which affects the resulting mechanical properties, such as tensile properties, hardness, and "compression set".

Biostable Segmented Thermoplastic Polyurethane Shape Memory Polymers for Smart Biomedical Applications

The exceptional tunability of chemical, mechanical, and shape memory properties of segmented thermoplastic polyurethanes (STPUs) makes them promising materials in a wide range of biomedical applications. STPU-based shape memory polymers (SMPs) that stably maintain their chemical, thermomechanical, and shape memory properties even after implantation could provide a reliable platform for controlled environmental response. For example, materials could be actuated at set time points to deliver bioactive agents, or cleavable compounds could be incorporated into a stable SMP that responds to wound signals for use in diagnosis. To this end, a library of STPUs with varying ratios of hard to soft segments was synthesized and characterized. It was found that using polypropylene glycol as the soft segment and triethylene glycol as the chain extender with hexamethylene diisocyanate induced sufficient phase separation in STPUs to provide a shape memory system. The polymers had more than 90% shape recovery ability and high enough transition temperatures (56–58 °C under dry and 44–51 °C under wet conditions) to enable maintenance of their temporary shape at body temperature. We tuned chemical, mechanical, thermal, and shape memory properties by changing the composition and characterized their stability in degradation media (more than 94% mass remaining at 40 days under accelerated conditions for polymers with higher hard segment ratios). The cytocompatible STPUs were highly stable (>90%) in their primary and secondary geometries in in vitro degradation media, indicating that they would stay intact after implantation. Then, the materials were actuated by heating at user-defined time points, upon which they returned to their primary shapes. As a proof of concept, we incorporated magnetic nanoparticles into this system to provide a magnetically actuated SMP that induced 44% shape recovery only after 5 min of exposure to a magnetic field. This system provides a platform for future generations of STPUs that include other cleavable or environmentally responsive components so that wound or clinician-controlled signals can act as external stimuli to cause shape and morphological changes.

Roles of phase separation and crystallization in the structure formation of new segmented polyurethane ureas and their nanocomposites with single-walled carbon nanotubes

Crystal structure and supramolecular organization of new segmented thermoplastic polyurethane ureas and their nanocomposites with ultra-small additives (less than 0.1 wt.%) of single-walled carbon nanotubes (SWCNTs) have been been investigated using DSC and X-ray diffraction analysis. Taking into account the Avrami model, effects of physical aging and thermal history of the samples on the crystallization rate was described. It was demonstrated that the introduction of ultra small amounts of SWCNTs does not decrease the crystallinity, but decreases the crystallization rate.

Linear segmented polyurethanes. III. Mathematical model for a two‐steps polymerization

AbstractIn the first article of this sequel (J. Appl. Polym. Sci., 2018, 135, 45747), an experimental and theoretical investigation was developed on the two‐steps synthesis of linear segmented thermoplastic polyurethanes. The reactions were carried out at 60°C, with methylene diphenyl diisocyanate (MDI), two poly(tetramethylene oxide) macrodiols, and 1,4‐butanediol (BD) as chain extender. In our second article (J. Appl. Polym. Sci., 2019, 136, 46946), a mathematical model for the prepolymerization was developed, that involved integrating a differential equation for each generated polymer species. The present article extends such model, and predicts the molecular structure along the finishing stage. In each stage, the new model first solves the molar balances at polymer topologies level (i.e.,: Disregarding the molar mass distribution [MMD] of the reacted macrodiol chains), and then calculates the MMD of the evolving polymer and its main subsets through an algebraic convolution procedure. The model reproduces the prepolymerization predictions of our previous article, but is three orders of magnitude faster. In the finishing stage, up to 156,000 polymer topologies and 4.53 × 108 polymer species were calculated; and the rate constant was readjusted to (k2 = 0.00129 L mol−1 s−1), in order to fit the measured MMDs.

High modulus thermoplastic segmented polyurethane/poly(L‐lactide) blends as potential candidates for structural implantable drug delivery systems: I. Structure‐properties relationship study

AbstractStructural polymers with a high modulus of elasticity have the necessary properties for drug eluting implants which are continuously subjected to long‐term loading. The range of polymers that can be used for this purpose is severely limited by the demanding requirements, such as biocompatibility, specific mechanical properties and the capability to control the release rate of incorporated drugs. A new series of blend compositions was developed for these applications, based on a combination of a high modulus thermoplastic segmented polyurethane (TSPU) (shore D hardness) and poly(L‐lactide) (PLLA). The microstructures and properties of these blends were characterized by DSC, tensile tester, FTIR, SEM, WAXD, transmitted light microscopy and elastic recovery testing. The two polymers were found to be immiscible, irrespective of the weight ratio between them, but still compatible, although the compatibility was reduced in blends with equal weight ratios or thereabouts. The dispersed phase in any case spontaneously organized into microspheres embedded within the continuous phase. PLLA could recrystallize as both the dispersed and the continuous phases. The ultimate mechanical properties and the elastic load‐recovery of the blends were largely dependent on the ratio between the polymers. The ability of these blends to create self‐assembled microspheres and the fact that they did not require a compatibilizer or plasticizer point to the potential of these systems to be used for structural implantable drug delivery systems.

Tunable Structure and Properties of Segmented Thermoplastic Polyurethanes as a Function of Flexible Segment.

Segmented thermoplastic polyurethanes (PUs) were synthetized using macrodiols with different functional groups (carbonate, ester, and /or ether) as a segment with a molar mass of 1000 and 2000 g/mol, and 4,4’-diphenylmethane diisocyanate (MDI) and 1,4-butanediol as a rigid segment. The polyurethanes obtained reveal a wide variation of microphase separation degree that is correlated with mechanical properties and retention of tensile properties under degradation by heat, oil, weather, and water. Different techniques such as differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), Fourier transform infrared (FTIR), and synchrotron small-angle X-ray scattering (SAXS) were used to determine rigid-flexible segments’ phase behaviour. Retention of tensile properties determines the stability of the samples under different external factors. This work reveals that pure polycarbonate-based macrodiols induce the highest degree of phase miscibility, better tensile properties, hardness shore A, and retention of tensile properties under external agents.

The effect of plasticization on the functional properties of thermoplastic polyurethane ureas

Several series of plasticized segmented polyether urethane of linear structure which can be used as the polymer base of thermoplastic materials were synthesized. The possibility of obtaining thermoplastic segmented polyurethane ureas with a softening temperature of 100 ÷120°C when using isophorone diisocyanate as the main element for building polymer chains, and DEHS as a plasticizer was proven. The original method for the purification of aromatic amine 4,4′-methylene-bis(2-chloroaniline) used in the process of synthesizing polyurethane ureas as a chain extender was developed. The polymers obtained have a uniquely low glass transition temperature close to -100°C with a plasticizer concentration of not more than 40%. The strength of these materials is more than 10 MPa at room temperature, and it is more 40 MPa at -70°C.

Tailoring the Shape Memory Properties of Segmented Poly(ester urethanes) via Blending.

Thermoplastic segmented polyurethanes (PUs) can exhibit shape memory behavior, if they feature multiple kinds of physical cross-links that can be dissociated at different temperatures. This is the case if the hydrogen-bonded hard phase is joined with soft segments that can partially crystallize, so that the melting transition acts as the memory switch. For applications in the biomedical field, it is important that the fixation and recovery temperatures can be minutely controlled. We show here that this tailoring can be easily achieved by formulating a commercial PU featuring poly(1,4-butylene adipate) (PBA) as a crystallizable segment (PBA-PU) with either PBA or poly(ε-caprolactone) (PCL) of moderate molecular weight. We show that the nature of the end groups and the processing conditions dictate if there is any reaction between the components or if the product is merely a blend. Interestingly, in either case, the addition of PBA or PCL causes nucleation and thereby a noteworthy increase of the crystallization temperature of the switching element from below to above ambient temperature, so that excellent shape fixity (∼98%) can be achieved at 37 °C. The melting temperature is maintained above 50 °C and significant increases in strength and modulus are achieved. The new materials platform is well suited for applications in which a shape is to be fixed at physiological temperature.

Thermoplastic Polyurethane Elastomers with Aliphatic Hard Segments Based on Plant‐Oil‐Derived Long‐Chain Diisocyanates

AbstractNovel plant‐oil‐derived long‐chain (C19 and C23) α,ω‐diisocyanates, optionally in combination with the corresponding long‐chain diols, provide entirely aliphatic hard segments in segmented thermoplastic polyurethane elastomers (TPUs), with carbohydrate‐based poly(trimethylene glycol) soft segments. Compared to materials based on a mid‐chain monomer analog, phase separation is higher due to an increased flexibility of the aliphatic segments. Although melting points are slightly lower than for HDPE, the long‐chain TPU's solid‐state structure is still dominated by hydrogen‐bonding.

Clarifying the Origin of Multiple Melting of Segmented Thermoplastic Polyurethanes by Fast Scanning Calorimetry

Segmented thermoplastic polyurethanes (TPU) often show multiple endothermic signals during melting in conventional differential scanning calorimetry (DSC). Repeated reorganization during heating and separate crystal melting and phase mixing have been proposed as the origin of this phenomenon. We used fast scanning calorimetry on a series of TPUs with polyether soft segments and hard segments consisting of 4,4′-methylenediphenyl diisocyanate and 1,4-butanediol to differentiate between the two possibilities. Fast heating scans (>500 °C s–1) of isothermally crystallized samples exhibited only a single melting peak, while complementary experiments on quenched, fully amorphous samples showed a single glass transition step indicating a homogeneous mixed phase. These results prove that the multiple melting peaks observed in DSC are related to reorganization during heating, i.e., repeated melting and recrystallization. Phase separation during cooling of such TPUs is induced by crystallization. A comparison with c...

Internal structure and crystallinity investigation of segmented thermoplastic polyurethane elastomer degradation in supercritical methanol

This work is the first to investigate the internal structure and crystallinity variance of segmented thermoplastic polyurethane elastomer (TPU) degradation in supercritical methanol. Molecular weight distribution (MWD) and molecular structure were determined using GPC, FT-IR and NMR. DSC and XRD were employed to explore the thermal behaviour and morphologic change of TPU, respectively. Results indicated that the segmented TPU has unique degradation behavior because of the three kinds of morphology of hard segments. The short range hard segments dissolved in soft blocks were amorphous. The long range hard segments mixed with and separated from soft blocks formed crystallites. These crystallites ruptured from the soft blocks in initial time period and the soft blocks dissolved in methanol, as indicated by the disappearance of the undecomposed TPU peak in MWDs. The remaining residues were hard segments crystallites which had narrow sharp MWDs. The following process was in two phases. In solid phase, hard segments crystalline structures were destroyed gradually, the melting points decreased correspondingly; in liquid phase, soft segments broken from short range hard segments and fractured.

Influence of composition on the isothermal crystallisation of segmented thermoplastic polyurethanes

The crystallisation features of thermoplastic polyurethanes are highly dependent on the thermal treatment applied and on the macromolecular segmental composition.

New thermoplastic poly(carbonate-urethane)s based on chain extenders with sulfur atoms

New thermoplastic segmented polyurethanes were obtained by a one-step melt polyaddition using 40, 50 and 60 mol% poly(hexane-1,6-diyl carbonate) diol of bar{M}_{n} = 860 g mol−1, 1,1′-methanediylbis(4-isocyanatobenzene) and 2,2′-[sulfanediylbis(benzene-1,4-diyloxy)]diethanol, 2,2′-[oxybis(benzene-1,4-diylsulfanediyl)]diethanol or 2,2′-[sulfanediylbis(benzene-1,4-diylsulfanediyl)]diethanol as a chain extender. FTIR, atomic force microscopy, differential scanning calorimetry and thermogravimetry were used to examine the polyurethanes’ structure and thermal properties. Moreover, their Shore A/D hardness, tensile, adhesive and optical attributes were determined. They were transparent high-molar-mass materials showing good tensile strength (up to 51.9 MPa). The polyurethanes exhibited improved adhesion to copper taking into consideration that of conventional ones, and middle or high refractive index values (1.57–1.60), and both these parameters increased with an increase of the content of sulfur atoms in the polyurethane chain. The newly obtained polyurethanes can be considered as materials for numerous medical and optical appliances.

Tailoring the Morphology and Melting Points of Segmented Thermoplastic Polyurethanes by Self-Nucleation

It is demonstrated that the melting behavior and the morphology of three segmented thermoplastic polyurethane elastomers (TPUs) can be tailored by applying self-nucleation (SN) procedures. The self-nucleating temperature ranges for each of the TPU have been first determined by differential scanning calorimetry (DSC), while their morphology was studied by polarized light optical microscopy (PLOM), atomic force microscopy (AFM), and small-angle X-ray scattering (SAXS). When the samples are cooled at slow to moderate rates after SN, the crystallization temperature of the TPUs increases by up to 45 °C, when the samples are ideally self-nucleated. This large reduction in supercooling increases the melting points of the samples by approximately 20 °C. At the same time, SAXS and AFM experiments demonstrate the growth of thicker lamellae under these slow to moderate cooling conditions as compared to untreated samples. When ideally self-nucleated samples are rapidly quenched (e.g., at rates of 100 °C min–1 or larg...

Effect of cooling induced crystallization upon the properties of segmented thermoplastic polyurethanes

Abstract An investigation on the cooling-induced crystallization in three thermoplastic polyurethanes based on MDI, PTMG, and 1.4-BD as chain extender with different hard segment content is reported. Thermal transitions were determined using differential scanning calorimetry (DSC) measurements at different cooling rates, and thermal stability was studied by thermogravimetric analysis. Changes in Raman spectra were useful to correlate the thermal transitions with changes in the morphology of the polymers. The dissimilarity in the composition gave different rheological behavior in the molten state, indicated by the temperature dependence of the viscosity. The mechanical properties and the crystallinity was influenced not only by the cooling rate but also by the hard segment content. Thermoplastic polyurethanes with more hard segment content formed more crystalline hard domains as evidenced by the DSC and atomic force microscopy results.

Transparent thermoplastic polyurethanes based on aliphatic diisocyanates and polycarbonate diol

Segmented thermoplastic polyurethanes (PUs) were synthetized using polycarbonate diol as soft segment with a molar mass of 500 and as a hard segment 1,5-pentanediol with a combination of isophorone diisocyanate (IPDI) and hexamethylene diisocyanate (HDI). Differential scanning calorimetry, differential mechanical analysis, Fourier transform infrared-attenuated total reflection spectroscopy, haze, transmittance, hardness, tensile properties and retention of tensile properties tests were employed to characterize the different PUs. The results of this study show that IPDI/HDI relation has a significant impact on the phase mixing, crystallinity and therefore on the PU’s properties. The variation of diisocyanate type ratio allows obtaining PUs of different nature from a high rubbery material with a high content in IPDI to high crystalline PU increasing the HDI content. Material transparency was also modified by decreasing the amorphous nature of the materials with the increase in the HDI content. The weather resistance of the final PU is related with the different isocyanate relation.

Effect of intersegmental interactions on the morphology of segmented polyurethanes with mixed soft segments: A coarse-grained simulation study

Segmented thermoplastic polyurethanes, polyureas and polyurethaneureas (TPU) based on a given hard segment and two chemically different soft segments display interesting microphase morphologies and thermal, mechanical and surface properties. In these systems the final TPU morphology is mainly controlled by the structure, amount and molecular weight of the soft segment oligomers and the nature and extent of specific intermolecular interactions between the mixed soft segments themselves and with the urethane hard segments. These interactions lead to variable compatibilities between the soft and hard segments resulting in interesting TPU morphologies. The proper choice of the two chemically different soft blocks provides more flexibility in controlling the extent of microphase separation, size and shape of the microphase domains and offers new possibilities for controlling the properties of TPUs. In this study coarse grained computer simulations were carried out to better understand the nature of intermolecular interactions and to elucidate the equilibrium microphase morphologies of TPUs with two different soft segments at 300 K. Model TPU systems investigated are comprised of poly(tetramethylene oxide) (PTMO) or poly(hexylethyl carbonate) (PHEC) and polydimethylsiloxane (PDMS) or polyisobutylene (PIB) soft segments with molecular weights in the range of 500–2500 g/mol. Hard segments consisted, in all cases, of diphenylmethane diisocyanate (MDI) based urethane repeat units and ranged from 25 to 50% by weight. Through coarse grained Dissipative Particle Dynamics (DPD) simulations it was demonstrated that by varying the composition and the chain lengths of the soft and hard blocks, quite different morphologies from homogeneous (or mixed) to gradient and to completely microphase separated structures were attainable. As expected, fairly hydrophobic soft blocks such as PIB and PDMS favored strong microphase separation when compared with relatively hydrophilic PHEC and PTMO segments. For comparison, morphologies of the TPUs based on single soft segments (PTMO, PHEC, PDMS and PEO) with varying molecular weights and hard segment contents were also simulated.

Impact of the poly(propylene oxide)-b-poly(dimethylsiloxane)-b-poly(propylene oxide) macrodiols on the surface related properties of polyurethane copolymers

Segmented thermoplastic polyurethane copolymers (PURs) were synthesized using 4,4'-methylenediphenyl diisocyanate and 1,4-butanediol as the hard segment and ?,?-dihydroxy-poly(propylene oxide)-b-poly(dimethylsiloxane)-b-poly(propylene oxide) (PPO-PDMS) as the soft segment. The content of incorporated soft segments in PURs varied in the range from 40 to 90 wt.%. The structure, molecular weights and crystallinity of obtained copolymers were monitored by FTIR, 1H, 2D NMR spectroscopy, GPC and DSC analysis, respectively. Surface free energy analysis indicates the presence of hydrophobic (siloxane) groups on the surface, giving highly hydrophobic nature to the obtained PURs films. Water absorption measurements showed that the increase of the hydrophobic PPO-PDMS segment content, led to the decrease of percentage of absorbed water in copolymers. SEM and AFM analysis revealed that copolymers with lower content of PPO-PDMS segments have higher microphase separation between segments. The results obtained in this work indicate that synthesized PURs based on PPO-PDMS, demonstrated proper surface and morphological properties with a great potential for variety of applications such as hydrophobic coatings in biomedicine.