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.     

Phase separation and phase inversion of polyurethane networks

A series of polyurethane networks were prepared from MDI (4,4¹-diphenyl methane diisocyanate), ethylene glycol and a polyoxyethylene-tipped polyoxypropylene triol. The phase separation and phase inversion phenomena of these polyurethane networks were investigated by differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA) and measurement of their tensile properties. The DSC and DMA data indicate that the segmented copolyurethanes possess a two-phase morphology comprising soft and hard segments. It can be found from DSC data that the polyether soft segments exhibit a T_g (glass transition temperature) of –60 °C, and the aromatic hard segments display a T_g of about 128 °C. Two T_gs corresponding to the comprised segments can also be found by DMA for some segmented polyurethanes. Varying the content of aromatic hard segments over the range from 0 to 80 wt% changes the material behavior from a soft rubber through a highly extensible elastomer to a brittle semi-ductile glassy material. Based on the property-composition plots, phase inversion appears to occur at a hard segment content of about 50 wt%.     

Rheological and thermal properties of glycidyl azide polyol‐based energetic thermoplastic polyurethane elastomers

The purpose of this study was to investigate the effects of polyol on glycidyl azide polyol (GAP)‐based energetic thermoplastic polyurethane elastomers (ETPEs). Briefly, a series of GAP/polyol‐based ETPEs (GAP/polyol ETPEs) with different copolyol ratios and hard segment contents were synthesized using GAP‐diol with common polyol and 4,4‐methylenebis(phenylisocyanate)‐extended 1,5‐pentanediol as soft and hard segments, respectively, by solution polymerization in dimethylformamide. The three types of polyols used were poly(tetramethylene ether) glycol (PTMG), polycarbonate‐diol (PCL‐diol) and polycaprolactone‐diol (PCD‐diol). The synthesized GAP/polyol ETPEs were identified and characterized using Fourier transform infrared and ¹H NMR spectroscopy, differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA) and rheometric mechanical spectrometry. For GAP/PCL ETPEs with lower hard segment content, DSC results showed that the GAP segment failed to interact with either the PCL segment or PCL melting. In addition, the results of DMA showed that the presence of PCL segments in ETPEs improved the storage modulus below the melting temperature of the PCL block. Further, the crystalline PCL segments were attributed to reinforcing the ETPEs in a manner similar to that of the hard domain. As the hard segment content increased in the GAP/polyol ETPEs, both GAP/PTMG ETPEs and GAP/PCL ETPEs exhibited microphase separation transitions, while rheological experiments demonstrated a sudden decrease in complex viscosity in neighboring microphase separation transitions. © 2012 Society of Chemical Industry     

Effect of thermal history on properties of block-copolyetheresters with poly(tetramethylene 2,6-naphthalenedicarboxylate) segments

The effect of compression molding on the thermal transitions and crystalline properties of block-copolyetheresters with hard segments of poly(tetramethylene 2,6-naphthalenedicarboxylate) and soft segments of poly(tetramethylene oxide) were investigated by differential scanning calorimetry (DSC), X-ray diffraction, thermal stimulated current (TSC), and dynamic mechanical analysis (DMA). The X-ray diffraction patterns of compression molded samples of the block-copolymers were considerably different from those of the corresponding samples with slow-cooling history. After compression molding, the diffraction peaks were changed completely indicating a different crystalline structure for the polyester segments, and the diffraction peaks became sharper indicating a higher crystallinity. The DSC results also showed that the melting point and crystallinity of the polyester segments were increased after compression molding. The glass transition temperatures of the polyether soft phase and polyester hard phase also were determined by DSC, TSC, and DMA separately with consistent data and were found to be dependent on the content of polyether segments and the molecular weight of the poly(tetramethylene ether)glycol (PTMEG) used. A γ-transition was observed by TSC and DMA and seemed to be independent of the composition and the thermal history. The glass transition temperatures of the polyether soft phase and the polyester hard phase of the block-copolymers derived from PTMEG 650 and PTMEG 1000 shifted to a lower temperature after compression molding possibly because of the partial miscibility between the comprising segments in these two series. The abrupt drop in log G′ in the temperature range of −10–15°C for the block-copolymers derived from PTMEG 2000 was caused by the melting of the polyether segments and indicated that the crystalline properties of the polyether segments could affect their mechanical properties. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 1441–1449, 1999     

Morphology and water vapor permeability of temperature‐sensitive polyurethanes

A series of segmented polyurethanes (PUs) were prepared, in which five different polyols and hexamethylene diisocyanate were used as soft segments, and 4,4′‐diphenylmethane diisocyanate, hydrophilic segment poly (ethylene glycol) 200 (PEG 200), and chain extender 1,4‐butanediol were used as hard segment. Morphology of the PUs was investigated using differential scanning calorimetry, wide angle X‐ray diffraction, polarizing microscopy, and transmission electron microscopy. Water vapor permeability of the membranes as a function of temperature was tested accordingly. Results show that the presence of PEG200 interferes the crystallization of hard segment in these PUs, and at the same time, increases phase compatibility between soft and hard segment in the PET‐PU. It leads to a lower crystal melting temperature and degree of crystallinity of soft segment in the segmented PU than those of pure polyols, and no crystallization existing in hard segment. A morphological model is proposed, that is, aggregated soft‐segment‐rich domains can be observed clearly in the PUs with high crystallinity in soft segment, while identifiable hard domains are well‐distributed in the soft segment domains in the PU with low crystallinity. Within the temperature range of crystal melting, water vapor permeability of the PU membranes increases significantly with increase of temperature. Such temperature‐sensitive property is triggered by crystal melting of soft segment. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Synthesis and properties of poly(tetramethylene terephthalate-co-ethylene terephthalate)–poly(tetramethylene ether) segmented copolymers

A series of polyether–copolyester segmented copolymers ((PBT–PET)PTMG) based on hard segments of tetramethylene terephthalate–ethylene terephthalate copolyester (PBT–PET) and soft segments of poly(tetramethylene ether)(PTMG) was synthesized. The hard : soft segment weight ratio was 30 : 70 and the mole ratio of PBT : PET was 1 : 10; 1 : 6; 1 : 1; 3 : 1, respectively. Their mechanical properties, morphology, crystallization behavior and optical transparency were investigated and compared with poly(tetramethylene terephthalate)–poly(tetramethylene ether)(PBT–PTMG), as well as with poly(ethylene terephthalate)–poly(tetramethylene ether)(PET–PTMG), consisting of the equivalent composition ratio of hard and soft segments. It was found that the transparency could be improved by introducing a small amount of PBT into PET–PTMG through copolymerization. However, a decrease was observed in the transparency if more PBT was added. This is due to the fact that the copolymerization makes both crystallinity and crystallization rate decrease.     

Segmented polyurethane elastomers by nonisocyanate route

Novel segmented polyurethane elastomers were successfully synthesized by a nonisocyanate route using dicyclic carbonates as precursors for both soft and hard segments. The hard segment was prepared from the dicyclic carbonate of bisphenol A and m‐xylylenediamine as chain extender. The soft segment was poly(tetramethylene ether) glycol of molecular weight 1000. Three polyurethanes with different morphologies were made with soft segment concentration of 70, 50, and 30%. Method of synthesis consisted in preparation of dicyclic carbonate of bisphenol A from a commercial epoxy resin and carbon dioxide, while dicyclic carbonate of poly(tetramethylene ether) glycol (PTMEG) was made from previously prepared diglycidyl ether of PTMEG and carbon dioxide. Polymers were prepared by reacting dicyclic carbonates with m‐xylylenediamine by one‐pot process. The monomers and polymers were characterized by Fourier transform infrared spectroscopy, differential scanning chromatography, thermogravimetric analysis, ¹H NMR, ¹³C NMR, scanning electron microscopy, and mechanical measurements. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42492.     

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     

Effect of the hard‐segment structure on the dielectric relaxation of crosslinked polyurethanes

Two series of crosslinked polyurethanes based on poly(tetramethylene ether) glycol soft segments and hexamethylene diisocyanate/1,4‐butane diol and glycerin or castor oil as a hard segments were synthesized, and their dielectric properties were examined. We examined the influence of the structural heterogeneity of the copolymers (as a function of the quantity and structure of the hard segments and crosslinking density, as measured by comonomer composition), frequency, and temperature as experimental variables by observing changes in the dielectric behavior. Two relaxation peaks were observed in the temperature range of −30 to 40°C for polyurethanes with various hard‐segment contents. The dangling chains of the castor oil presented a plasticizing effect that was exerted during the relaxation processes, an effect that was studied. It was found that both the amount and the structure of the hard segment strongly affected the dielectric behavior. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

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.     

Effects of catalyst on sequence distribution and transparency of poly(tetramethylene terephthalate)–poly(tetramethylene ether) segmented copolymers

Polyether-polyester segmented copolymer based on hard segments of tetramethylene terephthalate (PBT) and soft segments of poly(tetramethylene ether glycol) (PTMG) was synthesized by four kinds of catalyst: tetrabutyl titanate and magnesium acetate (Ti-Mg); tetrabutyl titanate and triethanolamine; tetra(isopropyl) titanate; and isopropoxy(triethanolaminato) titanate, respectively. Their segment sequence distributions were analyzed by ¹³C-NMR, based on different chemical shifts of aromatic quaternary carbons in the three different triad sequences. The effects of catalyst on sequence distribution and transparency were investigated. It was found that the copolymer has lower probability of B-T-B when Ti-Mg was used as catalysts, and results in higher transparency. © 1995 John Wiley & Sons, Inc.     

Effect of the degree of soft and hard segment ordering on the morphology and mechanical behavior of semicrystalline segmented polyurethanes

The hierarchical microstructure responsible for the unique energy-absorbing properties of natural materials, like native spider silk and wood, motivated the development of segmented polyurethanes with soft segments containing multiple levels of order. As a first step in correlating the effects of crystallinity in the soft segment phase to the hard segment phase, we chose to examine the morphology and mechanical behavior of polyurethanes containing polyether soft blocks with varying tendencies to crystallize and phase segregate and the evolution of the microstructure with deformation. A series of high molecular weight polyurethanes containing poly(ethylene oxide) (PEO) (1000 and 4600 g/mol) and poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) (1900 g/mol) soft segments with varying hard segment content were synthesized using a two-step solution polymerization method. The presence of soft segment crystallinity (PEO 1000 g/mol) was shown to improve the storage modulus of the segmented polyurethanes below the T_m of the soft block and to enhance toughness compared to the PEO-PPO-PEO soft segment polyurethanes. We postulate that this enhancement in mechanical behavior is the result of crystalline soft regions that serve as an additional load-bearing component during deformation. Morphological characterization also revealed that the microstructure of the segmented polyurethanes shifts from soft segment continuous to interconnected and/or hard domain continuous with increasing hard segment size, resulting in diminished ultimate elongation, but enhanced initial moduli and tensile strengths. Tuning the soft segment phase crystallinity may ultimately lead to tougher polyurethane fibers.     

Mixed macrodiol‐based siloxane polyurethanes: Effect of the comacrodiol structure on properties and morphology

Two series of polyurethanes were prepared to investigate the effect of comacrodiol structure on properties and morphology of polyurethanes based on the siloxane macrodiol, α,ω‐bis(6‐hydroxyethoxypropyl) polydimethylsiloxane (PDMS). All polyurethanes contained a 40 wt % hard segment derived from 4,4′‐methylenediphenyl diisocyanate (MDI) and 1,4‐butanediol (BDO), and were prepared by a two‐step, uncatalyzed bulk polymerization. The soft segments were based on an 80/20 mixture of PDMS (MW 967) and a comacrodiol (MW 700), selected from a series of polyethers and polycarbonates. The polyether series included poly(ethylene oxide) (PEO), poly(propylene oxide) (PPO), poly(tetramethylene oxide) (PTMO), poly(hexamethylene oxide), and poly(decamethylene oxide) (PDMO), whereas the polycarbonate series included poly (hexamethylene carbonate) diol (PHCD), poly [bis(4‐hydroxybutyl)‐tetramethyldisiloxy carbonate] diol (PSCD), and poly [hexamethylene‐co‐bis(4‐hydroxybutyl)‐tetramethyldisiloxy carbonate] diol (COPD). Polyurethanes were characterized by size exclusion chromatography, tensile testing, differential scanning calorimetry (DSC), and dynamic mechanical thermal analysis (DMTA). The results clearly demonstrated that the structure of the comacrodiol influenced the properties and morphology of siloxane‐based polyurethanes. All comacrodiols, except PEO, improved the UTS of the polyurethane; PHMO and PTMO were the best polyether comacrodiols, while PSCD was the best polycarbonate comacrodiol. Incorporation of the comacrodiol made polyurethanes more elastomeric with low modulus, but the effect was less significant with polycarbonate comacrodiols. DSC and DMTA results strongly supported that the major morphological change associated with incorporation of a comacrodiol was the significant increase in the interfacial regions, largely through the compatibilization with the hard segment. The extent of compatibilization varied with the comacrodiol structure; hydrophilic polyethers such as PEO were the most compatible, and consequently, had poor mechanical strength. Among the polyethers, PHMO was the best, having an appropriate level of compatibility with the hard segment for substantial improvement in mechanical properties. Siloxy carbonate comacrodiol PSCD was the best among the polycarbonates. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 1071–1082, 2000     

Morphology and conductivity changes in a thermoplastic polyurethane‐based copolymer consisting of different soft segments

Three different segmented thermoplastic polyurethanes (TPUs) were synthesized with 4,4′‐methylenebis(phenyl isocyanate) as a hard segment and poly(ethylene glycol) (PEG) or poly(propylene glycol) (PPG) or an equal mixture of PEG and PPG with molecular 2000 as soft segments. The soft‐segment component of TPU was changed to monitor modifications in chemical and physical properties among the three TPUs. Differential scanning calorimetry (DSC) and thermogravimetric analysis were used to monitor changes in thermal characteristics. Fourier transform infrared spectroscopy (FTIR) was employed to predict the interaction between the lithium cation and the hard or soft segment in the presence of added LiClO₄. The deconvolution results of spectral bands associated with the N? H groups of these TPUs were used to obtain such information. Impedance spectroscopy was used to inspect the changes in the bulk conductivity of these TPUs caused by alteration of the soft‐segment component. The conductivity changes were explained through combined DSC and FTIR results. The electrochemical stability of the TPU systems was studied by linear sweep voltammetry. The results showed that the copolymer system had better thermal and electrochemical stability than the other systems. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 1462–1473, 2001     

Synthesis of poly(lactic acid)‐based polyurethanes

Poly(lactic acid) (PLA) is a biodegradable aliphatic polyester, but its brittleness makes it unsuitable for many packaging and appliance applications. The goal of the work reported was to create novel poly(ester urethane)s that incorporate biodegradable poly(lactic acid) diols (PLA‐OHs) and good mechanical properties of increased molecular weight via crosslinked network formation for engineering plastics applications. Three kinds of polyols (PLA‐OHs, PLA‐OHs/poly(tetramethylene ether) glycol or PLA‐OHs/poly(butylene adipate) glycol (PBA)) and two kinds of diisocyanates (4,4‐diphenylmethane diisocyanate (MDI) or toluene 2,4‐diisocyanate (TDI)) were chosen for the soft and hard segments to compare their mechanical properties. In addition, 1,4‐butanediol and trimethylolpropane were each used as chain extender agents. Results showed the PLA/PBA‐polyurethanes (PLA/PBA‐PUs) of the MDI series and the PLA/PBA‐PUs of the TDI series had improved thermal stability and enhanced mechanical properties. Degradation behavior showed the PLA‐based polyurethanes could be degraded in phosphate‐buffered saline solution and enzyme solution. © 2012 Society of Chemical Industry     

Structure‐property relationship of L‐tyrosine‐based polyurethanes for biomaterial applications

The structure‐property relationship of L ‐tyrosine‐based polyurethanes was demonstrated by using different polyols and diisocyanates. L ‐tyrosine‐based chain extender, desaminotyrosyl tyrosine hexyl ester (DTH), was used to synthesize a series of polyurethanes. Polyethylene glycol (PEG) or poly caprolactone diol (PCL) was used as the soft segment and hexamethylene diisocyanate (HDI) or dicyclohexylmethane 4,4′‐diisocyanate (HMDI) was used with DTH as the hard segment. The polyurethanes were characterized to investigate the effect of structure on different polyurethane properties. From FTIR and DSC, these polyurethanes exhibit a wide range of morphology from phase‐mixed to phase‐separated structure. The decreasing molecular weight of the PEG soft segment leads to relatively more phase mixed morphology whereas for PCL‐based polyurethanes the extent of phase mixing is less with decreasing PCL molecular weight. Results show that PCL‐based polyurethanes are mechanically stronger than PEG‐based polyurethanes but PCL‐based polyurethanes degrade slower and absorb less water compared with PEG‐based polyurethanes. The HMDI‐based polyurethanes are less crystalline and comparatively more hydrophobic than HDI‐based polyurethanes. The characterization results show that the polyurethane properties are directly related to the structure and can be varied easily for a different set of properties that are pertinent for biomaterial applications. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

The effect of fluorinated side chain attached on hard segment on the phase separation and surface topography of polyurethanes

It has been well established that polyurethanes exhibit a two-phase micro-structure due to the thermodynamic incompatibility between the soft segments and hard segments. In this work, we reported the effect of fluorinated side chain attached on hard segment on the phase separation and surface topography of polyurethanes. Two sets of fluorinated polyurethanes, namely, poly(ether urethane)s and poly(carbonate urethane)s containing various amounts of chain extender of fluorinated side chains, were investigated by DSC, XPS, DMA, AFM and FTIR. It was found that the phase separation in both bulk and surface increases in fluorinated poly(carbonate urethane)s and the phase mixing increases in fluorinated poly(ether urethane)s, with increasing amounts of fluorinated side chain. The increased degree of hydrogen bonding between hard segments and soft segments was observed by FTIR for fluorinated poly(ether urethane), which is believed to result in the enhanced phase mixing, and the enhanced association of domains with long-range order (hydrogen bonding) between hard segments was evident for fluorinated poly(carbonate urethane)s, which may correspond to the enhanced phase separation. The result is new and provides direct connection between surface topography and bulk phase separation of polyurethanes.     

Low‐modulus siloxane‐based polyurethanes. I. Effect of the chain extender 1,3‐bis(4‐hydroxybutyl)1,1,3,3‐tetramethyldisiloxane (BHTD) on properties and morphology

A series of eight polyurethane elastomers was prepared using a two‐step bulk polymerization procedure to investigate the effect of the siloxane chain extender 1,3‐bis(4‐hydroxybutyl)1,1,3,3‐tetramethyldisiloxane (BHTD) on polyurethane properties and morphology. All polyurethanes were based on 40 wt % hard segment derived from 4,4′‐methylenediphenyl diisocyanate (MDI) and a mixture of 1,4‐butanediol (BDO) and BHTD in varying molar ratios. The soft segment was based on an 80 : 20 (w/w) mixture of the macrodiols α,ω‐bis(6‐hydroxyethoxypropyl)polydimethylsiloxane (PDMS, MW 965) and poly(hexamethylene oxide) (PHMO, MW 714). Polyurethanes were characterized by size‐exclusion chromatography, tensile testing, differential scanning calorimetry, dynamic mechanical thermal analysis, and FTIR spectroscopy. Clear and transparent polymers were produced in all cases with number‐average molecular weights in the range of 90,000 to 111,000. The ultimate tensile strength decreased only slightly (15%), but Young's modulus and flexural modulus decreased by 76 and 72%, respectively, compared with that of the pure BDO extended polyurethanes as the amount of BHTD was increased to 40 mol %. This change resulted in “softer” and more elastic polyurethanes. Polyurethanes with BHTD contents above 40 mol % were more elastic but had poor tensile and tear strengths. A 60 : 40 molar ratio of BDO : BHTD produced a “soft” polyurethane, which combined good tensile strength and flexibility. The DSC and DMTA results confirmed that the incorporation of BHTD as part of the hard segment yielded polyurethanes with improved compatibility between hard and soft segments. IR data indicated that the amount of hard segments soluble in the soft‐segment phase increased with increasing BHTD, contributing to the improved phase mixing. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 736–746, 2002     

Poly(dimethylsiloxane)/poly(hexamethylene oxide) mixed macrodiol based polyurethane elastomers. I. Synthesis and properties

The compatibilizing effect of poly(hexamethylene oxide) (PHMO) on the synthesis of polyurethanes based on α,ω‐bis(6‐hydroxyethoxypropyl) poly(dimethylsiloxane) (PDMS) was investigated. The hard segments of the polyurethanes were based on 4,4′‐methylenediphenyl diisocyanate (MDI) and 1,4‐butanediol. The effects of the PDMS/PHMO composition, method of polyurethane synthesis, hard segment weight percentage, catalyst, and molecular weight of the PDMS on polyurethane synthesis, properties, and morphology were investigated using size exclusion chromatography, tensile testing, and differential scanning calorimetry (DSC). The large difference in the solubility parameters between PDMS and conventional reagents used in polyurethane synthesis was found to be the main problem associated with preparing PDMS‐based polyurethanes with good mechanical properties. Incorporation of a polyether macrodiol such as PHMO improved the compatibility and yielded polyurethanes with significantly improved mechanical properties and processability. The optimum PDMS/PHMO composition was 80 : 20 (w/w), which yielded a polyurethane with properties comparable to those of the commercial material Pellethane™ 2363‐80A. The one‐step polymerization was sensitive to the hard segment weight percentage of the polyurethane and was limited to materials with about a 40 wt % hard segment; higher concentrations yielded materials with poor mechanical properties. A catalyst was essential for the one‐step process and tetracoordinated tin catalysts (e.g., dibutyltin dilaurate) were the most effective. Two‐step bulk polymerization overcame most of the problems associated with reactant immiscibility by the end capping of the macrodiol and required no catalysts. The DSC results demonstrated that in cases where poor properties were observed, the corresponding polyurethanes were highly phase separated and the hard segments formed were generally longer than the average expected length based on the reactant stoichiometry. Based on these results, we postulated that at low levels (∼ 20 wt %) the soft segment component derived from PHMO macrodiol was concentrated mainly in the interfacial regions, strengthening the adhesion between hard and soft domains of PDMS‐based polyurethanes. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 2026–2040, 2000     

Polyurethane elastomers through multi-hydrogen-bonded association of dendritic structures

A series of hydrogen bonding-rich polyurea/malonamide dendrons have been utilized as building blocks for the synthesis of novel dendritic polyurethane elastomers. Based on the resulting microstructure of soft segments reinforced by the rigid dendritic domains, the hydrogen bonding enforced phase separation of segmented polyurethanes was explored. DSC and FT-IR results indicate that a certain degree of phase separation between dendritic and poly(tetramethylene oxide) (PTMO) domains. The domain size of phase separation are less than 100 nm based on the results obtained from the atomic force microscopy (AFM) and small-angle X-ray scattering (SAXS). The analysis of tensile measurements indicates that the incorporation of various contents of different dendrons as the hard segments allows these polymers to exhibit drastically different mechanical properties. Furthermore, low complex viscosity is observed at medium temperatures (above 130 °C) via the rheological analysis. With good mechanical properties at room temperature and low melt viscosity at medium temperatures, these thermoplastic elastomeric polyurethanes are suitable for applying in hot-melt process.