Temperature‐dependent changes in the hydrogen bonded hard segment network and microphase morphology in a model polyurethane: Experimental and simulation studies

Hydrogen bonding between hard segments has a critical effect on the morphology and properties of polyurethanes. Influence of temperature on hydrogen bonded urethane network and melting behavior of a model semicrystalline segmented polyurethane was investigated by experiments and simulations. Polyurethane was synthesized by the stoichiometric reaction between p‐phenylene diisocyanate and poly(tetramethylene oxide) (PTMO) with a molecular weight of 1000 g/mol. Simulations were carried out using dissipative particle dynamics (DPD) and molecular dynamics (MD) approaches. Experimental melting behavior obtained by various techniques was compared with simulations. DPD simulations showed a room temperature microphase morphology consisting of a three‐dimensional hydrogen‐bonded urethane hard segment network in a continuous and amorphous PTMO matrix. The first‐order melting transitions of crystalline urethane hard segments observed during the continuous isobaric heating in DPD and MD simulations (340–360 K) were in reasonably good agreement with those observed experimentally, such as AFM (320–340 K), WAXS (330–360 K), and FTIR (320–350 K) measurements. Quantitative verification of the melting of urethane hard segments was demonstrated by sharp discontinuities in energy versus temperature plots obtained by MD simulations due to substantial decrease in the number of hydrogen bonds above 340 K. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 182–192     

Effect of soft segment component on moisture‐permeable polyurethane films

The effect of soft segment component and molecular weight combination on moisture‐permeable polyurethane films was studied. Moreover, water sorption phenomenon in films was observed with infrared analysis. As for soft segment components, PTMG/PEG and PTMG/PPG were used and molecular weight combinations were changed. Different tendency appeared in the experimental results corresponding to PEG system and PPG system. Moisture permeability P in PEG system increased with increasing PEG content, but P changed little in the case of PPG system. Both hydrogen‐bonded concentration by infrared measurement and the higher order term Δh of Mooney–Rivlin plot by stress–strain relationships indicate the existence of aggregate structure of hard segment. It is considered that ether group in PEG is more active than that in PPG. Therefore, small size of aggregate structure indicated as Δh appears in PEG system owing to inhibition of aggregate structure growth. Whereas, ether group in PPG system does not inhibit hydrogen bond in urethane group and large size of aggregate structure appears. From water affinity relationship analysis, hydrophilicity of samples with PTMG/PEG = 2000/2000 increased with increasing PEG content. Consequently, it is suggested that not only size but also hydrogen‐bonded concentration of urethane group in aggregate structure affects moisture permeability. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 573–583, 2006     

Synthesis,characterization, and physical properties of new copolymers of poly(amino acid)–urethane—copolymers of γ‐methyl‐L‐glutamate‐N‐carboxyanhydride and urethane prepolymer

New copolymers of amino acid and urethane (PAU), in which a polyurethane segment was combined with poly(γ‐methyl‐L‐glutamate) (PMLG) of various contents, were synthesized by the copolymerization of the polyurethane prepolymer (UPP) having isocyanate groups at both terminals of the chain and γ‐methyl‐L ‐glutamate‐N‐carboxyanhydride (NCA) to improve the elastic recovery and adhesion of PMLG for application of PMLG to synthetic leather. The copolymerization of the UPP with NCA was carried out by applying the reactivity of isocyanate and the polymerization mechanism of NCA using the primary amine and tertiary amine as initiators. Infrared (IR) and ¹³C‐NMR spectra of these PAUs as well as the chemical analysis of the PAU intermediates showed that the PAUs would have a multiblock–triblock structure: namely, the PAUs consisted of the block copolymer segments of urethane and a small amount of PMLG at the center of the copolymer chain and most of the PMLG at both terminals of the copolymer chain. The elastic recovery and adhesion of these PAUs were significantly larger than those of the PMLG with the maintenance of a good sense of touch, which was a unique asset of PMLG. Furthermore, it was found that the PAUs had intermediary moisture permeability between that of PMLG and polyurethane. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 383–389, 1999     

Synthesis and thermal behavior of poly(ethylene oxide) poly(N‐substituted urethane)

Poly(N‐substituted urethane)s with an alkyl or ligo(ethylene oxide) monomethyl ether side chain were synthesized by the reaction operating in the following two‐step process: first, by metalation of the starting polymer with potassium tertiary butoxide (t‐BuOK) and then by treatment of the obtained urethane polyanion with tosylate in dimethyl sulfoxide. The thermal properties of poly(ethylene oxide) poly(N‐substituted urethane) (N‐sub PEOPU) were investigated in view of the N‐substitution degree and properties of the substituent. The chemical structures were characterized by Fourier transform infrared, ¹H NMR, and ¹³C NMR spectroscopies. DSC and thermogravimetric analysis (TGA) were used to investigate the thermal properties of N‐sub PEOPUs. As the degree of N‐methylation increased, the glass‐transition temperature (T_g) of the N‐sub PEOPUs linearly decreased from 6 to ?29 °C, and the weight‐loss temperature of 5% (T) from TGA in air increased from 278 to 360 °C. In the fully N‐substituted PEOPUs, the behavior of the thermal decomposition of the PEOPU that was processed in two stages was changed to one‐step decomposition in the temperature range of 360–440 °C. The T_g was shifted to a lower temperature with an increasing length of the substituent in N‐sub PEOPU. Improvement of the thermal stability by N‐substitution was more significant in N‐alkyl PEOPU than in N‐ethoxylate PEOPU. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 4129–4138, 2001     

Synthesis and characterization of poly(dimethylsiloxane‐urethane) elastomers: Effect of hard segments of polyurethane on morphological and mechanical properties

A series of poly(dimethylsiloxane‐urethane) elastomers based on hexamethylenediisocyanate, toluenediisocyanate, or 4,4′‐methylenediphenyldiisocyanate hard segment and polydimethylsiloxane (PDMS) soft segment were synthesized. In this study, a new type of soft‐segmented PDMS crosslinker was synthesized by hydrosilylation reaction of 2‐allyloxyethanol with polyhydromethylsiloxane, using Karstedt's catalyst. The synthesized soft‐segmented crosslinker was characterized by FT‐IR, ¹H, and ¹³C NMR spectroscopic techniques. The mechanical and thermal properties of elastomers were characterized using tensile testing, thermogravimetric analysis, differential scanning calorimetry (DSC), and dynamical mechanical analysis measurements. The molecular structure of poly(dimethylsiloxane‐urethane) membranes was characterized by ATR‐FTIR spectroscopic techniques. Infrared spectra indicated the formation of urethane/urea aggregates and hydrogen bonding between the hard and soft domains. Better mechanical and thermal properties of the elastomers were observed. The restriction of chain mobility has been shown by the formation of hydrogen bonding in the soft and hard segment domains, resulting in the increase in the glass‐transition temperature of soft segments. DSC analysis indicates the phase separation of the hard and soft domains. The storage modulus (E′) of the elastomers was increasing with increase in the number of urethane connections between the hard and soft segments. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2980–2989, 2006     

Calorimetric and Dielectric Study of the Segmented Biodegradable Poly(ester‐urethane)s Based on Bacterial Poly[(R)‐3‐hydroxybutyrate]

Two series of segmented poly(ester‐urethane)s were synthesized from bacterial poly[(R)‐3‐hydroxybutyrate]‐diol (PHB‐diol), as hard segments, and either poly(ε‐caprolactone)‐diol (PCL‐diol) or poly(butylene adipate)‐diol (PBA‐diol), as soft segments, using 1,6‐hexamethylene diisocyanate as a chain extender. The hard‐segment content varied from 0 to 50 wt.‐%. These materials were characterized using ¹H NMR spectroscopy and GPC. The polymers obtained were investigated calorimetrically and dielectrically. DSC showed that the T_g of either the PCL or PBA soft segments are shifted to higher temperatures with increasing PHB hard‐segment content, revealing that either the PCL or PBA are mixed with small amounts of PHB in the amorphous domains. The results also showed that the crystallization of soft or hard segments was physically constrained by the microstructure of the other crystalline phase, which results in a decrease in the degree of crystallinity of either the soft or hard segments upon increase of the other component. The dielectric spectra of poly(ester‐urethane)s, based on PCL and PHB, showed two primary relaxation processes, designated as α_S and α_H, which correspond to glass–rubber transitions of PCL soft and PHB hard segments, respectively. Whereas in the case of other poly(ester‐urethane)s, derived from PBA and PHB, only one relaxation process was observed, which broadens and shifts to higher temperature with increasing PHB hard‐segment content. It was concluded from these results that our investigated materials exhibit micro‐phase separation of the hard and soft segments in the amorphous domains.     

Anionic ring‐opening polymerization of a five‐membered cyclic urethane derived from d‐glucosamine

The anionic ring‐opening polymerization of a five‐membered cyclic urethane, 2‐amino‐4,6‐O‐benzylidene‐2‐N,3‐O‐carbonyl‐2‐deoxy‐α,d ‐glucopyranoside (MBUG), which was prepared from naturally abundant d ‐glucosamine, was examined. Potassium tert‐butoxide (t‐BuOK) was the most effective initiator among the evaluated bases and produced polyurethane with the Mn of 7800 without any elimination of CO₂. The equimolar reaction of MBUG and t‐BuOK in the presence of CH₃I produced N‐methylated MBUG and suggested that the initiation reaction involves proton abstraction from the NH group. This N‐methylated compound did not undergo the polymerization. Therefore, the mechanism of propagation in the ROP of MBUG should involve the proton abstraction and nucleophilic substitution of the resulting amide anion. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 2491–2497     

Structure and properties of segmented poly(urethaneurea)s with relatively short hard‐segment chains

We report the structure and properties of segmented poly(urethaneurea) (SPUU) with relatively short hard‐segment chains. The SPUU samples comprised poly(tetramethylene glycol) prepolymer as a soft segment and 4,4′‐diphenylmethane diisocyanate (MDI) units as a hard segment that were extended with ethylenediamine. To discuss quantitatively the conformation of the soft‐segment chain in the microphase‐separated domain space, we used SPUU samples for which the molecular weights of the hard‐ and soft‐segment chains are well characterized. The effects of the cohesive force in the hard‐segment chains on the structure and properties of SPUU were also studied with samples of different chain lengths of the hard segment, although the window of x_H, the average number of MDI units in a hard‐segment chain, was narrow (2.38 ≤ x_H ≤ 2.77). There were urethane groups in the soft segments and urea groups in the hard segments. Because of a strong cohesive force between the urea groups, we could control the overall cohesive force in the hard‐segment chains by controlling the chain lengths of the hard segment. First of all, microphase separation was found to be better developed in the samples with longer hard‐segment chains because of an increase of the cohesive force. It was also found that the interfacial thickness became thinner. The long spacing for the one‐dimensionally repeating hard‐ and soft‐segment domains could be well correlated with the molecular characteristics when the assumption of Gaussian conformation was employed for the soft‐segment chains. This is unusual for strongly segregated block copolymers and might be characteristic of multiblock copolymers containing rod–coil chains. The tensile moduli and thermal stability temperature, T_H, increased with an increase of the cohesive force, whereas the glass‐transition temperature, the melting temperature, and the degree of crystallinity of the soft‐segment chains decreased. The increase in T_H especially was appreciable, although the variation in the chain length of the hard segment was not profound. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1716–1728, 2000     

HTPB‐based polyurethanes. II. SINs with PMMA

Simultaneous interpenetrating networks from poly(methyl methacrylate‐co‐ethyleneglycol dimethacrylate) (PA) and a hydroxyl‐terminated polybutadiene‐based polyurethane (PU) were prepared with various hard‐segment contents (X) in the PU and different ratios (PU/PA) between the components. The level of the reinforcement, the mechanism of molecular failure, and the phase inversion depended strongly on X. Dynamic mechanical results indicated that the interpenetration occurred in the rigid blocks of the PU. The improved thermal and mechanical properties observed with higher values of X were interpreted in terms of the molecular weight and polydispersity of the hard blocks in the PU. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2861–2872, 2000     

Conclusive chemical deciphering of the consistently occurring double‐peak carbonyl‐stretching FTIR absorbance in polyurethanes

Polyurethanes include an extremely vast and varied family of polymers, exhibiting a vast range of properties and applications. Although the urethane chemical structure consists of a single carbonyl group, the vast majority of polyurethane Fourier transform infrared spectroscopy (FTIR) spectra exhibit two distinct adjacent carbonyl‐stretching absorbances. It was the purpose of the present research to investigate and determine the reason of occurrence of this consistently observed phenomenon. A polyurethane, designed and synthesized here as linear and containing only urethane and methylene groups, strongly exhibited two very distinct carbonyl‐stretching FTIR absorbances. A new polyurethane, exhibiting an extremely high degree of trifunctional crosslinking, was hereby designed and synthesized to sterically inhibit diisocyanate access to already established urethanes and thus inhibit the allophanate and further tertiary oligo‐uret forming side‐reactions. The resulting polymer dramatically exhibited only a single, strong and sharp, carbonyl‐stretching FTIR absorbance belonging only to the urethane group. Synthesis of a polymer exhibiting a lower degree of crosslinking led to the reappearance of the split double carbonyl‐stretching FTIR absorbance. Solid‐state ¹³C NMR measurement results of the same polymers were highly consistent with the FTIR spectroscopy results. The experimental results of the present research conclusively prove and determine the exclusive side‐reaction‐related double carbonyl‐stretching absorbance in the FTIR analysis of polyurethanes. These research results conclusively reveal that, in fact, the so‐called linear polyurethanes synthesized from diisocyanates and diols are branched or even loosely crosslinked.     

Hydrogen‐bonding,crystallinity, and morphological properties of poly(silicic acid)/waterborne polyurethane nanocomposites

Unique nanocomposites consisting of poly(silicic acid) nanoparticles (PNs) and waterborne polyurethane (WPU) were prepared. The aliphatic WPU prepared in this study was end‐capped with a silanol group, which could react with PNs via a sol–gel process. PNs were modified with phenyltrimethoxysilane (PTMS) and 3‐(trimethoxysilyl)propyl ester (TMPE) and then blended with WPU. The structure–property relationships were examined. Solid‐state ²⁹Si NMR spectra of WPU showed that structures T₁, T₂, and T₃ of WPU decreased and structures Q₃ and Q₄ of PN/WPU nanocomposites increased gradually. When the PN concentration increased to 10 wt %, PN/WPU nanocomposites exhibited the maximum fraction of hydrogen‐bonded carbonyl groups. In the PTMS–PN and TMPE–PN systems, the fraction of hydrogen‐bonded carbonyl groups fluctuated stably when the concentrations of PTMS–PN and TMPS–PN exceeded 5 wt %. The X‐ray diffraction results revealed that α‐form, γ‐form, or triclinic crystallization could be found in the WPU matrix. A differential scanning calorimetry spectrum showed that the crystalline structure of the hard segment of WPU was influenced by the nanoparticle concentration. The degrees of crystallinity were 88% for the PN/WPU nanocomposites, 41% for the PTMS–PN/WPU nanocomposites, and 54% for the TMPE–PN/WPU nanocomposites when the PN, PTMS–PN, and TMPE–PN concentrations were 5 wt %. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1076–1089, 2005     

Morphology of polyurethanes with triol monomer crosslinked on hard segments

Polyester‐based polyurethanes containing ≈60 wt % of polyester were synthesized from low molecular weight polyester (M_n ≈2000) and 4,4′‐methylene bis(phenyl isocyanate) (MDI), with butanediol as a chain extender and glycerol as a crosslinker. The triol crosslinker was used in substitution for the 1,4‐butanediol chain extender; thus, the crosslinker was chemical bonded to the hard segments of polyurethane. The morphologies of these polyurethanes were studied by differential scanning calorimetry (DSC), small‐angle X‐ray scattering (SAXS), TMA (thermal mechanical analysis), and FTIR (Fourier transform infrared spectroscopy). Owing to the highly steric hindrance, the presence of triol crosslinker in the hard segments resulted in a decrease in the aggregation of hard segments through hydrogen bonding. The experimental results revealed that the degree of phase segregation of soft and hard segments decreased with increasing the triol crosslinker content in the hard segments. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2673–2681, 1999     

Polyisobutylene‐based polyurethanes X: PU nanocomposites with s‐containing soft segments

Sulfur‐containing polyisobutylene (PIB)‐based polyurethane nanocomposite (PIB_s‐PU/NC) was synthesized using HO? CH₂CH₂? S? PIB? S? CH₂CH₂? OH for the soft segment, conventional hard segments of MDI and BDO, and organically modified montmorillonite (OmMMT) nanolayers. The properties of PIB_s‐PU/NC containing 72.5% PIB and 0.5% OmMMT were studied and contrasted with unmodified PIB_s‐PU. PIB_s‐PU/NC produces colorless optically clear films exhibiting enhanced tensile strength, elongation, oxidative–hydrolytic stability, and creep resistance relative to that of PIB_s‐PU. FTIR spectroscopy indicates H bonded S atoms between soft and hard segments, and OmMMT nanolayers. DSC and XRD suggest randomly dispersed low‐periodicity crystals and urea groups between galleries. We propose that minute amounts of OmMMT nanolayers become covalently attached to polyurethane chains and beneficially affect properties by acting as co‐chain extender/reinforcing filler. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 2760–2765     

Synthesis of POSS–polyurethane hybrids using octakis(m‐isoprenyl‐α,α′‐dimethylbenzylisocyanato dimethylsiloxy) octasilsesquioxane (Q8M8TMI) as a crosslinking agent

A series of polyurethane hybrid networks have been synthesized using octakis(m‐isoprenyl‐α,α′‐dimethylbenzylisocyanato dimethylsiloxy) octasilsesquioxane (Q₈M₈^TMI) as a crosslinking agent. The formation of the urethane linkages within the polyurethane hybrids was confirmed by photoacoustic FTIR spectroscopy. The TGA and DSC studies demonstrated that the incorporation of the POSS crosslinking agents altered the thermal properties of the polyurethanes, and that this was dependent on the length of the polyethylene glycol chain. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 5038–5045     

Syntheses and characterizations of soft‐segment ionic polyurethanes

Novel soft‐segment ionic polyurethane (linear and crosslinking) have been prepared based up on sodium sulfonate–side chains poly(ethylene oxide) (SPEO). SPEO was synthesized by grafting the sodium sulfonate onto the chain of poly(ethylene oxide) with molecular weights of 400, 600, 800, and 1000. The SPEO and the ionic polyurethane were characterized by elemental analysis, ¹H‐NMR, ¹³C‐NMR, gel permeation chromatography, and impedance analysis. The effect of plasticizer on the ionic conductivity of the polyurethane was also investigated. These solid polymer electrolytes possess a higher ionic conductivity (about 10⁻⁶ S/cm at room temperature) than the corresponding sulfonated hard‐segment polyurethane electrolytes. The presence of the hydroxyl group in the electrolyte tends to lower the ionic conductivity. Crosslinking of polyurethane results in the enhancement of the dimensional stability, while maintaining the same level of the ionic conductivity. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 837–845, 1999     

Wide angle X‐ray diffraction and Fourier transform infrared dichroism studies of stretched‐recovery‐restretched process of polyurethane/clay nanocomposite

An intercalated polyurethane (PU) /clay nanocomposite was prepared by in situ intercalative polymerization. The PU/clay nanocomposite pellet or film samples were stretched‐recovery‐restretched, using selfmade microstretching tools. The changes of the basal spacings of clay and the orientation of polymer chain segments during the stretched‐recovery‐restretched process were studied by wide angle X‐ray diffraction (WAXD) and Fourier transform infrared (FTIR) dichoism techniques. The WAXD results show that the basal spacing of clay did not change obviously, indicating that no macromolecular chains entered or moved out of the interlayer space, and the orientations of both hard and soft segments inside the interlayer space did not change obviously, either. The FTIR dichroism tests suggest that outside the interlayer space, the orientation of the hard chain segment increased, decreased, and then increased again during the stretched‐recovery‐restretched process. However, no obvious changes of the degree of orientation of the soft segment were observed during the processes, the slightly orientation might be released during the relaxation process before the measurements. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 654–660, 2007     

Mesogen‐controlled ion channel of star‐shaped hard–soft block copolymers for solid‐state lithium‐ion battery

Novel star‐shaped hard–soft triblock copolymers, 4‐arm poly(styrene)‐block‐poly [poly(ethylene glycol) methyl ethyl methacrylate]‐block‐poly{x‐[(4‐cyano‐4′‐biphenyl) oxy] alkyl methacrylate} (4PS‐PPEGMA‐PMAxLC) (x = 3, 10), with different mesogen spacer length are prepared by atom‐transfer radical polymerization. The star copolymers comprised three different parts: a hard polystyrene (PS) core to ensure the good mechanical property of the solid‐state polymer, and a soft, mobile poly[poly(ethylene glycol) methyl ethyl methacrylate] (PPEGMA) middle sphere responsible for the high ionic conductivity of the solid polyelectrolytes, and a poly{x‐[(4‐cyano‐4′‐biphenyl)oxy]alkyl methacrylate} with a birefringent mesogens at the end of each arm to tuning the electrolytes morphology. The star‐shaped hard–soft block copolymers fusing hard PS core with soft PPEGMA segment can form a flexible and transparent film with dimensional stability. Thermal annealing from the liquid crystalline states allows the cyanobiphenyl mesogens to induce a good assembly of hard and soft blocks, consequently obtaining uniform nanoscale microphase separation morphology, and the longer spacer is more helpful than the shorter one. There the ionic conductivity has been improved greatly by the orderly continuous channel for efficient ion transportation, especially at the elevated temperature. The copolymer 4PS‐PPEGMA‐PMA10LC shows ionic conductivity value of 1.3 × 10^?4 S cm^?1 (25 °C) after annealed from liquid crystal state, which is higher than that of 4PS‐PPEGMA electrolyte without mesogen groups. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 4341–4350     

Chlorine degradation of polyether-based polyurethane

The tensile properties of polyether-based polyurethane (PU) filaments decrease with increasing chlorine concentrations as well as with treatment times. Fourier transform infrared (FTIR) results show the formation of quinoid, azo, and aldehyde groups in the chlorine-treated PU, and increased hydrogen bonding between the C O C in the soft segment and the N H in the hard segments. A breakdown mechanism involving chain cleavages along the ether linkages in the soft segments as well as at the urethane linkages of the hard–soft segment interfaces is proposed. Chlorine-treated PU showed increased solubility in tetrahydrofuran (THF). The molecular weight data of the THF-soluble portion of treated PU also support the proposed locations of chain scissions. The increased soft segment T_g and T_m with increasing chlorine concentrations are results of increased phase-mixing and hydrogen bonding. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 3263–3273, 1997     

Syntheses and characterization of physically crosslinked hydrogels from dithiocarbamate‐derived polyurethane macroiniferter

A dithiocarbamate (DC)‐based polyurethane macroiniferter (PUMI) was synthesized and used to prepare physically crosslinked polyurethane‐block‐poly (acrylamide) (PU‐b‐PAAm) and polyurethane‐block‐poly(vinyl pyrrolidone) (PU‐b‐PVP) hydrogels. The success of the reactions has been confirmed by FTIR, ¹H‐NMR, and ¹³C‐NMR Spectroscopy analyses. The number average molecular weight of the block copolymers increased linearly with conversion and copolymerization time and thus followed a “living” radical mechanism. The water transport behavior of these polyurethane‐based hydrogels such as water uptake rate, equilibrium water content (EWC), transport number (n), characteristic diffusion rate constant (K), diffusion coefficient (D), and pH effect on EWC has been investigated. The results revealed that PU‐b‐PAAm hydrogels followed Fickian diffusion suggesting diffusion controlled swelling kinetics, whereas the PU‐b‐PVP hydrogels followed non‐Fickian diffusion indicating that both diffusion and structural relaxation controlled the water transport. The PU‐b‐PAAm hydrogels showed higher swelling at both low and high pH than at a neutral pH. This is attributed to protonation of the tertiary amines of N,N′‐diethyl‐N,N′‐bis(2‐hydroxyethyl) thiuram disulfide (DHTD) at low pH and base hydrolysis of amide segments at high pH. In the thermogravimetric analysis; PUMI, PU‐b‐PVP and PU‐b‐PAAm have degraded in three distinct stages related to CS₂ evolution, hard segment degradation, and soft segment degradation. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6272–6284, 2008     

Effects of hard‐segment polymers on CO2/N2 gas‐separation properties of poly(ethylene oxide)‐segmented copolymers

Poly(ethylene oxide)‐segmented polyurethanes (PEO‐PUs) and polyamides (PEO‐PAs) were prepared, and their morphology and CO₂/N₂ separation properties were investigated in comparison with those of PEO‐segmented polyimides (PEO‐PIs). The contents of the hard and soft segments in the soft and hard domains, W_HS and W_SH, respectively, were estimated from glass‐transition temperatures with the Fox equation. The phase separation of the PEO domains depended on the kind of hard‐segment polymer; that is, W_HS was in the order PU > PA ≫ PI for a PEO block length (n) of 45–52. The larger W_HS of PUs and PAs was due to hydrogen bonding between the oxygen of PEO and the NH group of urethane or amide. The CO₂/N₂ separation properties depended on the kind of hard‐segment polymer. Compared with PEO‐PIs, PEO‐PUs and PEO‐PA had much smaller CO₂ permeabilities because of much smaller CO₂ diffusion coefficients and somewhat smaller CO₂ solubilities. PEO‐PUs also had a somewhat smaller permselectivity because of a smaller solubility selectivity. This was due to the larger W_HS of PEO‐PUs and PEO‐PAs, that is, a greater contamination of PEO domains with hard urethane and amide units. For PEO‐PIs, with a decrease in n to 23 and 9, W_HS became large and CO₂ permeability decreased significantly, but the permselectivity was still at a high level of more than 50 at 35 °C. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1707–1715, 2000