Structural characterization and mass transfer properties of polyurethane block copolymer: influence of mixed soft segment block and crystal melting temperature

An attempt has been made to investigate the influence of mixed soft segment on structure and mass transfer properties of segmented polyurethane (SPU). For this purpose polyurethane block copolymer containing soft segment such as polycaprolactone glycol (number‐average molecular weight 3000, PCL 3000), PCL 3000–polypropylene glycol (number‐average molecular weight 3000, PPG 3000), PCL 3000–polytetramethylene glycol (number‐average molecular weight 2900, PTMG 2900), PPG 3000–PTMG 2900, were synthesized using a two‐step or three‐step synthesis process. All the SPUs were modified with the hydrophilic segment, i.e. diol‐terminated poly(ethylene oxide) (number‐average molecular weight 3400, PEG 3400). Fourier‐transform infrared, wide‐angle X‐ray diffraction, differential scanning calorimetry, and dynamic mechanical thermal analysis were used to characterize the polyurethanes. The mass transfer properties were measured by equilibrium sorption and water vapor permeability measurements. Mixed blocks loosen the inter‐chain interaction due to phase mixing which decreases the crystallization of the soft segment in the resulting SPU. The crystallinity of mixed polyol block SPU increases when both polyols are crystallizable in the pure state. Highest loss tan δ value was observed for the sample containing PTMG 2900–PPG 3000 mixed soft segment due to their flexible and phase mixed structure which increases the chain mobility; this sample performed best among all four SPUs in equilibrium water sorption as well as water vapor permeability owing to their loose and nearly amorphous structure. Soft segment crystal melting further enhances the water vapor permeability significantly, which would make the membrane suitable for breathable textiles, packaging and medical applications. Copyright © 2006 Society of Chemical Industry     

Properties of segmented polyurethanes derived from different diisocyanates

Various segmented polyurethane materials with a polyurethane hard segment (HS) content of 40 wt % were prepared by bulk polymerization of a poly(tetramethylene ether) glycol with M_n of 2000, 1,4‐butanediol, and various diisocyanates. The diisocyanates used were pure 4,4′‐diphenylmethane diisocyanate (MDI), 2,4‐toluene diisocyanate (T100), toluene diisocyanate containing 80% 2,4‐isomer and 20% 2,6‐isomer (T80), isophorone diisocyanate (IPDI), hydrogenated 4,4′‐diphenylmethane diisocyanate (HMDI), and 1,6‐hexane diisocyanate (HDI). The segmented polyurethane materials were characterized by differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), tensile properties, tear strength, and Shore A hardness. The DSC and DMA data show that the thermal transitions are influenced significantly by the diisocyanate structure. In the segmented polyurethane materials with aliphatic HS, the polyether soft segment (SS) is immiscible with the HS. However, in the segmented polyurethane materials with aromatic HS, the SS is partially miscible with the HS. The diisocyanate structure also influences the mechanical properties significantly and is described as the effect of symmetry and chemical structure of the HS. Various solution polymerized polyurethane resins with solid content of 30 wt % were also prepared and their thickness retention, water resistance, and yellowing resistance were determined for the evaluation of their usage as wet process polyurethane leather. The polyurethane resin with aliphatic HS show poorer thickness retention but better yellowing resistance. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 167–174, 2000     

Structural characterization and mass transfer properties of segmented polyurethane: influence of block length of hydrophilic segments

An attempt has been made to investigate the effect of the block length of hydrophilic segments on the structure and mass transfer properties of segmented polyurethane (HSPU). Three different block lengths of hydrophilic poly(ethylene glycol) (PEG) segments were used, namely PEG‐200, PEG‐2000 and PEG‐3400, where the numbers indicate the molecular weight of the PEG in g mol^?1. The HSPU were characterized using Fourier‐transform infrared (FTIR) spectroscopy, wide‐angle X‐ray diffraction (WAXD), differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA) and tensile testing. Mass transfer properties were measured by sorption and water vapour flux (WVF) measurements. The control sample polyurethanes without PEG and a sample with PEG‐200 showed amorphous structure and an unclear phase separation as detected by WAXD, DSC and DMTA. There is evidence that the introduction of PEG blocks into the polyurethane matrix aids soft‐segment crystallization. The percentage crystallinity of soft segments was the highest with PEG‐2000 and an increase of PEG block length to 3400 g mol^?1 resulted in a decrease in crystallinity. Mechanically, polyurethane without PEG is tough while percentage strain at maximum load increased with increasing block length of PEG. In addition, sorption and WVF increased linearly with increasing PEG block length and with temperature. The permeability of such HSPUs is a function of temperature and showed a good fit to an Arrhenius form. Copyright © 2005 Society of Chemical Industry     

Microstructure and water vapor transport properties of functionalized carbon nanotube‐reinforced dense‐segmented polyurethane composite membranes

This work investigates the influence of functionalized multiwall carbon nanotube (MWNT) on microstructure and water vapor transport properties of segmented polyurethane (SPU) membranes. SPUs were reinforced with four different concentration of MWNT viz. 0.25, 0.50, 1.0, and 2.5 wt%. Presence of the microcrystals in all SPU‐MWNT composite membranes was detected by wide angle X‐ray diffraction (WAXD). The percent crystallinity of SPU‐MWNT at 0.25 wt% content of MWNT was increased slightly when compared with the pristine SPU sample. However, further increase of MWNT decreases the order structure. Glass transition temperature was increases with increasing MWNT content in the SPUs, which signifies that MWNT could also affect the amorphous region of SPU. WAXD and transmission electron microscopy (TEM) results evidenced the interaction between SPUs and MWNT. In comparing the water vapor transport properties of MWNT‐SPU composite membranes, it was observed that at 0.25 wt% of MWNT in SPU, water vapor transport property increases slightly at soft segment crystal melting temperature. Further increase of MWNT content has no significant influence on the water vapor transport properties. However, at 2.5 wt% of MWNT in SPU matrix, water vapor transport was decreases due to the increase of stiffness in the polymer chains. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers     

Thermal and mechanical behavior of flexible polyurethane‐molded plastic films and water‐blown foams with epoxidized soybean oil

Water‐blown flexible polyurethane foams and molded plastic films were made by replacing 0 to 50% of Voranol® 4701 in the B‐side of foam and plastic film formulation by epoxidized soybean oil (ESBO). Physical properties of foams including density, 50% compression force deflection (CFD), 50% constant deflection compression (CDC), and resilience were determined. A dynamic mechanical spectrometer (DMS) and a differential scanning calorimeter (DSC) were used to characterize the hard segment (HS) and soft segment (SS) ratio and thermal properties of plastic. Various functional groups in both flexible polyurethane foam and plastic film were characterized using Fourier transform‐infrared spectroscopy with attenuated total reflectance (FTIR‐ATR). When increasing the ESBO content, both density and 50% CFD of water‐blown polyurethane foams decreased first, then increased. On the other hand, the 50% CDC and resilience of foams showed a sharp increase and decrease, respectively. When increasing the ESBO content, the peak of tan δ in DMS analysis and Δc_p in DSC analysis of plastic films both decreased indicating the hard segment increased and the soft segment decreased in plastic film, respectively. The FTIR‐ATR results also show the hydrogen‐bonded urethane group increased in plastic films with increasing ESBO content. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Structure–property relationships of polycarbonate diol‐based polyurethanes as a function of soft segment content and molar mass

Segmented thermoplastic polyurethanes (PUs) have been synthesized with polycarbonate diol as soft segment and 4,4′‐diphenylmethane diisocyanate and butanediol as hard segment. Two different series employing two different soft‐segment molar mass, 1000 and 2000 g/mol, and by changing the hard‐segment content from 32 to 67% have been investigated with the aim to elucidate the effect of the different content variations on the properties. Morphological, thermal, and mechanical properties have been studied by Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), wide angle X‐ray diffraction, atomic force microscopy, tensile and tear strength, hardness, and specific gravity tests. Properties have been explained from the standpoint of miscibility between hard‐ and soft‐segment microdomains of the tailored segmented PUs through an exhaustive analysis. FTIR, DSC, and DMA measurements revealed that miscibility between hard and soft microdomains increases as the molar mass of the macrodiol decreases. An increase in hard‐segment content entailed the formation of larger hard domains with higher crystallinity what results in superior mechanical properties such as higher tensile stress and tear strength, and hardness. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41704.     

Preparation and properties of segmented thermoplastic polyurethane elastomers with two different soft segments

Thermoplastic polyurethane elastomers were prepared from 4,4‐diphenylmethane diisocyanate (MDI)/1,4‐butanediol (BD)/poly(propylene glycol) (PPG) and MDI/BD/poly(oxytetramethylene glycol) (PTMG). The MDI/BD‐based hard‐segment content of polyurethane prepared in this study was of 39–65 wt %. These polyurethane elastomers had a constant soft‐segment molecular weight (M_n , 2000), but a variable hard‐segment block length (n, 3.0–10.1; M_n , 1020–3434). The effects of the hard‐segment content on the thermal properties and elastic behavior were investigated. These properties of the PPG‐based MPP samples and the PTMG‐based MPT samples were compared. The polyurethane prepared in this study had a hard‐segment crystalline melting temperature in the range of 185.5–236.5°C. With increasing hard‐segment content, the dynamic storage modulus and glass transition temperature increased in both the MPP and MPT samples. The permanent set (%) increased with increasing hard‐segment content and successive maximum elongation. The permanent set (%) of the MPP samples was higher than that of MPT samples at the same hard‐segment content. The value of K (area of the hydrogen‐bonded carbonyl group/area of the free carbonyl group) increased with increasing hard‐segment content in both the MPP and MPT samples, and the K value of the MPT samples was higher than that of the MPP samples at the same hard‐segment content. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 345–352, 1999     

Morphology control of segmented polyurethanes by crystallization of hard and soft segments

Segmented polyurethanes (SPUs) have been designed with controlled hard to soft segment ratios. The confinement effect of the SPU blocks is induced by phase separation of the SPU segments and has been harnessed to selectively control crystallization. Hard segment (HS) concentrations greater than 50 wt.% allowed for the study of morphological changes and mechanical properties associated with confinement of the soft segment (SS). It was observed that crystallization temperature and normalized percent crystallinity were reduced with increasing HS content, creating a largely amorphous PEG SS at ambient temperature. High temperature annealing further confined the SS because the HS had more time to crystallize, which increased confinement. Considerable insight has been gained through the manipulation and characterization of the SS and HS, in an SPU, towards the design of impact absorbing and structural materials.     

Microphase separation and surface properties of segmented polyurethane-Effect of hard segment content

A series of segmented polyurethanes (SPU), based on 4,4′-diphenylmethane diisocyanate and 1,4-butanediol as hard segments (HS) and poly(propylene glycol) (Mn = 1000) as soft segments, were synthesized. Relationships between microphase separation and the surface and adhesive properties were characterized by thermal analysis, X-ray diffraction, contact angle, electron spectroscopy for chemical analysis, T-peel and tensile test measurements. Microphase separation occurred for SPU with an HS content of more than 50 wt% and influenced not only the bulk properties, but also the surface properties. Young's modulus and tensile strength increased abruptly for SPU with an HS content of more than 50wt%. Surface free energy also increased in a stepwise manner at an HS content of about 50wt%. The optimum HS content of SPUs for adhesion, based on T-peel test results, also gave good thermal and mechanical properties.     

Miscibility of segmented polyurethane/poly(vinyl chloride) blends

Miscibilities of segmented polyurethanes (SPUs) and poly(vinyl chloride) (PVC) or functionalized poly(vinyl chloride) (FPVC) were studied with dynamic mechanical analysis, differential scanning calorimetry, and X‐ray diffraction. Mechanical properties of the blends were also studied with tensile measurements. The miscibility of the blends depended greatly on the hard‐segment content of SPU and the existence of the functional groups. The combination of SPU with a low hard‐segment content and PVC with functional groups made the blend system miscible. Moreover, controlling the blend composition of SPU/FPVC allowed us to modify the mechanical properties of SPU, where the elongation at break was multiplied without a significant change in its tensile strength. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 3022–3029, 2001     

Phase separation in segmented polyurethanes derived from mixtures of polyether polyols with different functionality

A series of segmented polyurethanes containing 60 wt° of hard segments (HS) was prepared from MDI (4,4-diphenylmethane diisocyanate) ethylene glycol and mixtures of a polyoxyethylene end-capped polyoxypropylene triol and a polyoxyethylene end-capped polyoxypropylene diol. The effects of the content of polyether diol in polyether polyols on phase separation and properties was investigated by dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC) and investigation of tensile properties. The DSC and DMA results indicate that the polyurethane derived from only polyether triol exhibits obvious phase separation and that the HS is immiscible with the SS, but that the HS is compatible with the HS for the polyurethane derived from polyether diol. As the content of polyether diol increases, the compatibility between HS and SS increases. As the content of polyether diol increases, the tensile strength. elongation. toughness and tear resistance of the polyurethanes increases. but their moduli decrease. The modulus-temperature dependence in the temperature region of –30 to 65 °C increases as the polyether diol content increases.     

Novel poly(methyl methacrylate)‐block‐polyurethane‐block‐poly(methyl methacrylate) tri‐block copolymers through atom transfer radical polymerization

Poly(methyl methacrylate)‐block‐polyurethane‐block‐poly(methyl methacrylate) tri‐block copolymers have been synthesized successfully through atom transfer radical polymerization of methyl methacrylate using telechelic bromo‐terminated polyurethane/CuBr/N,N,N,N″,N″‐pentamethyldiethylenetriamine initiating system. As the time increases, the number‐average molecular weight increases linearly from 6400 to 37,000. This shows that the poly methyl methacrylate blocks were attached to polyurethane block. As the polymerization time increases, both conversion and molecular weight increased and the molecular weight increases linearly with increasing conversion. These results indicate that the formation of the tri‐block copolymers was through atom transfer radical polymerization mechanism. Proton nuclear magnetic resonance spectral results of the triblock copolymers show that the molar ratio between polyurethane and poly (methyl methacrylate) blocks is in the range of 1 : 16.3 to 1 : 449.4. Differential scanning calorimetry results show T_g of the soft segment at ?35°C and T_g of the hard segment at 75°C. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Nuclear magnetic resonance studies of ionomers. 6. Polyurethane-polyphosphonate blends

Blending of a poly(ether urethane) with a polyphosphonate obtained by phase transfer catalyzed polycondensation of 4,4′-biphenol and chloromethylphosphonic dichloride generates a phase-separated material. One phase contains the soft segment of the polyurethane. This has been excluded from a high-T_g phase that contains ionic species formed mainly by proton transfer and elimination reactions between the hard segment of the polyurethane and the polyphosphonate. Two glass transitions appear in the blend: one close to the T_g of the polyphosphonate and one belonging to the excluded soft segment of the polyurethane. The low temperature T_g decreases with the increasing content of the polyphosphonate, whereas the high temperature transition increases slightly, indicating an increasing purity of the soft segment and the presence of ionic interactions in the hard segment. The presence of ionic interactions is confirmed by NMR analysis of the blend. Comparison of the spectra of the blends with those of the pure components, along with two-dimensional experiments, indicate a reaction involving the chloromethyl groups of the polyphosphonate and the nitrogens of the polyurethane.     

Influence of Hard Segment on Thermal Degradation of Thermoplastic Segmented Polyurethane for Textile Coating Application

An attempt has been made to investigate the thermal degradation of thermoplastic segmented polyurethane (TSPU) as a function of hard segment (HS) content. TSPU, and its corresponding hard segment and soft segment, has been studied in air and nitrogen. Comparing the results of solid conversion of polyurethane in different conditions (air and nitrogen), significant differences were observed. Derivative thermogrametry (DTG) analysis revealed that the degradation was a three-step weight loss process in air and two steps in nitrogen. Multiphase degradation occurs in air due to the oxidation reaction of polymer. Therefore, an extra peak appeared in air (in the temperature range between 509 and 583°C). Degradation temperature of 10% (T₁₀) and the temperature of half-decomposition (T_d,1/2) increased with decreasing hard segment content in the TSPU. Thermal stability of polyurethanes decreased after introduction of hydrophilic segment (PEG-200) in the polymer backbone due to the increasing oxygen molecules. The surfaces of the original films, detected by scanning electron microscopy (SEM), were smooth. However, stress cracking was observed for heat-treated deformed TSPU films with higher hard segment content.     

Nonisothermal crystallization kinetics of carbon nanotubes containing segmented polyurethane elastomer

Nanocomposites of the segmented polyurethane (SPU) elastomer with different concentrations of multiwall carbon nanotubes (MWCNTs) have been prepared. Scanning electron microscopy has been used to visualize the surface morphology and distribution of the nanotubes inside the matrix. Differential scanning calorimetry has been utilized to investigate the effects of MWCNTs on the crystallization characteristics of the SPU by collecting data at four cooling rates namely 5, 10, 15, and 20°C/min in the temperature range between 200°C to ambient. The results reveal that MWCNTs act as effective nucleating agent for crystallization of the hard segment of SPU and advance the onset and peak temperatures of crystallization by 38 and 23°C, respectively. The associated enthalpy and extent of crystallization are also increased by 34%. Different crystallization kinetic parameters have been calculated using both modified Avrami and combined Ozawa‐Avrami models to suggest a three dimensional growth of crystallization of SPU and its nanocomposites. The activation energy has been calculated using Kissinger method, which indicates that activation energy decreases with increasing concentration of MWCNTs. The calorimetric results have further been correlated with thermomechanical analysis and glass transition temperature of the nanocomposites corresponding to soft segment is found to increase by 20°C. POLYM. ENG. SCI., 56:1248–1258, 2016. © 2016 Society of Plastics Engineers     

Comparison of properties of thermoplastic polyurethane elastomers with two different soft segments

Two series of thermoplastic polyurethane elastomers [poly(propylene glycol) (PPG) based PP samples and poly(oxytetramethylene)glycol (PTMG) based PT samples] were synthesized from isophorone diisocyanate (IPDI)/1,4-butanediol (BD)/PPG and IPDI/BD/PTMG. The IPDI/BD based hard segments contents of polyurethane prepared in this study were 40–73 wt %. These polyurethane elastomers had a constant soft segment molecular weight (average M_n, 2000) but a variable hard segment block length (n, 3.5–17.5; average M_n, 1318–5544). Studies were made on the effects of the hard segment content on the dynamic mechanical thermal properties and elastic behaviors of polyurethane elastomers. These properties of PPG based PP and PTMG based PT samples were compared. As the hard segment contents of PP and PT samples increased, dynamic tensile modulus and α-type glass transition temperature (T_g) increased; however, the β-type T_g decreased. The permanent set (%) increased with increasing hard segment content and successive maximum elongation. The permanent set of the PT sample was lower than that of the PP sample at the same hard segment content. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 1349–1355, 1998     

Influence of rigid segment content on the piezoresistive behavior of multiwall carbon nanotube/segmented polyurethane composites

Tensile piezoresistive properties of multiwall carbon nanotube (MWCNT)/segmented polyurethane (SPU) composites comprising 15, 30, and 50 wt % rigid segment (RS) contents and 2, 4, and 6 wt % MWCNT contents are investigated. The physicochemical properties of such composites are used to better understand their mechanical and piezoresistive behavior. Infrared spectra shows that for 15 and 30 wt % RS composites the addition of MWCNTs promotes a more structured RS domain which increases the phase separation, while for 50 wt % RS composites the MWCNTs disrupt the RS domains of the polymer with a high phase separation. Overall, MWCNT content has less effect on the phase separation than RS content. The composites with 6 wt % MWCNT content reached electrical conductivities of the order of ～10^?1 S/m using 15 and 50 wt % RS polymers. Upon deformation, composites with 15 wt % RS and 4 wt % MWCNT achieved changes in electrical resistance of the order of 5000 times their unstrained value, which are outstanding values that can be exploited for applications such as human motion detection. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 44448.     

Inelastic response of copolyurethane elastomers with varying soft segment molecular weights and preparation procedure

A family of thermoplastic polyurethane elastomers (TPUs) based on the soft segment poly(oxytetramethylene) (PTMO₂₀₀₀ and PTMO₁₀₀₀) were synthesized by the one‐shot and prepolymer methods. Two hard segments were chosen, 4,4′‐methylenebis(phenyl isocyanate) (MDI) (non‐crystallizable) and 4,4′‐dibenzyl diisocyanate (DBDI) (crystallizable). Microphase separation and crystallinity were investigated using small‐angle X‐ray scattering and wide‐angle X‐ray scattering, and dynamic viscoelastic properties were also determined. An increased hard phase degree of crystallinity was primarily achieved by use of DBDI instead of MDI, regardless of the preparation procedure and soft segment molecular weight. An increase of the molecular weight leads to an increase in phase separation and to a decrease in hysteresis. For the DBDI based polymers, a lower soft segment molecular weight resulted in an increase in crystallinity. The DBDI series of TPUs obtained by the one‐shot and prepolymer methods showed higher hysteresis and residual elongations compared with the corresponding materials achieved with MDI. Although the materials varied widely in response to first loading, regardless of the preparation procedure, they displayed remarkable reproducibility and commonality in cyclic responses within the maximum strain envelope. The thermomechanical experiments revealed a better thermal behavior with increase of the soft segment molecular weight from PTMO₁₀₀₀ to PTMO₂₀₀₀.© 2013 Society of Chemical Industry     

Synthesis of oxazolidines as latent curing agents for single‐component polyurethane adhesive and its properties study

Four oxazolidine compounds OX₁–OX₄ were prepared. Their structures were characterized using Fourier transform infrared spectra, ¹H‐NMR, ¹³C‐NMR, and ESI‐MS. The hydrolysis kinetics research of oxazolidines suggested that the hydrolysis of oxazolidine followed the first‐order reaction. The gap of the ground energies between the open‐ and closed‐ring was calculated using Gaussian software, which indicated that the stability of the open‐ring system of OX₁ was the best. Then, the obtained oxazolidines were applied to single‐component polyurethane (SPU) and filler CaCO₃ was added to investigate the effect of the two above on the properties of SPU. The results show that the pore size and the number of bubbles produced in the SPU decreased with the increase of the rate of hydrolysis of the added oxazolidine, and the bondability of the polyurethane was better. With the increase of CaCO₃ content, the polyurethane surface became smoother and the bond strength was stronger. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45722.     

Synthesis and characterization of bis‐triethoxysilane endcapped polyurethane/urea

A type of bistriethoxysilane endcapped polyurethane/ureas (SPU) with well‐defined structure was synthesized from bis(triethoxysiylpropyl) amine and purified prepolymers, which were obtained from the reaction of 2,4‐toluene diisocyanate (TDI) and polyoxyethylene glycol (PEG) with different molecular weight. Then, fourier transform infrared spectroscopy (FTIR), hydrogen nuclearmagnetic resonance (¹H‐NMR) and standard dibutylamine back‐titration method were used to confirm the structures of prepolymers and SPUs. Moreover, the properties of SPU were investigated by wide angle X‐ray diffraction (WAXD), differential scanning calorimetry (DSC), thermogravimetric analyses (TGA), and percentage of water uptake. Results indicated that these polyurethanes were amorphous, and the percentage of water uptake and thermal stability of these polyurethanes went up with the increase of M _n of SPU, accompanying with the glass transition temperature (T_g) values decreased with the increase of M _n. This study provides us with a method to synthesize well‐defined end‐functionalized polyurethane. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011