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.     

Preparation and properties of transparent thermoplastic segmented polyurethanes derived from different polyols

Various segmented polyurethanes of different soft segment structure with hard segment content of about 50 wt% were prepared from 4,4′‐diphenylmethane diisocyanate (MDI), 1,4‐butanediol and different polyols with a M_n of 2000 by a one‐shot, hand‐cast bulk polymerization method. The polyols used were a poly(tetramethylene ether)glycol, a poly(tetramethylene adipate)glycol, a polycaprolactonediol and two polycarbonatediols. The segmented polyurethanes were characterized by gel permeation chromatography (GPC), UV‐visible spectrometry, differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), X‐ray diffraction, and their tensile properties and Shore A hardness were determined. The DSC and DMA data indicate that the miscibility between the soft segments and the hard segments of the segmented polyurethanes is dependent on the type of the soft segment, and follows the order: polycarbonate segments > polyester segments > polyether segments. The miscibility between the soft segments and the hard segments plays an important role in determining the transparency of the segmented polyurethanes. As the miscibility increases, the transparency of the segmented polyurethanes increases accordingly. The segmented polyurethanes exhibit high elongation and show ductile behavior. The tensile properties are also affected by the type of the soft segment to some extent. POLYM. ENG. SCI., 47:695–701, 2007. © 2007 Society of Plastics Engineers.     

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     

Exploring long-range connectivity of the hard segment phase in model tri-segment oligomeric polyurethanes via lithium chloride

The influence of the extent of hydrogen bonding in mediating the long-range connectivity and percolation of the hard segment phase in model tri-segment oligomeric polyurethanes (PU) was explored by using LiCl as a molecular probe. A 22 wt% hard segment containing model PU plaque based on a mono-functional oligomeric polyether, 80:20 2,4:2,6 isomeric mixture of toluene diisocyanate, and water as a chain extender was employed. Samples cast from 20 wt% solutions in dimethyl acetamide were utilized. The tapping-mode atomic force microscopy (AFM) phase image of the solution cast film sample (soft segment T_g −63 °C) without LiCl exhibited the presence of long interconnected ribbon-like hard domains. The long-range connectivity and percolation of the hard phase that arose during plaque formation gave rise to a brittle rigid solid. A systematic break-up of the hard domains was also observed by AFM when the concentration of LiCl was increased from 0.1 to 1.5 wt%. DSC analysis indicated that the samples were able, however, to maintain a microphase separated morphology even at the highest LiCl concentration utilized in the study. FT-IR data confirmed that LiCl interacts with the hard domains of the model PU samples by disrupting the hydrogen bonding capability of the urea hard segments. A systematic softening of the samples was observed with increasing LiCl content as confirmed by thermomechanical analysis. Thus, this study indicates that hydrogen bonding plays an important role in assisting the hard segments in PU to develop long-range connectivity and percolation of this phase through the soft matrix.     

Phase separation of diamine chain-extended poly(urethane) copolymers: FTIR spectroscopy and phase transitions

As part of our continuing effort to understand microphase separation of poly(urethane urea) block copolymers, FTIR spectroscopy and thermal techniques (DSC and DMA) were used to investigate the phase behavior of two series of MDI-polytetramethylene oxide soft segment copolymers, chain-extended with ethylene diamine or a diamine mixture. Due to the complex nature and multiple absorbances in the carbonyl and N-H regions of the FTIR spectra, quantitative analysis was not possible. However, qualitative trends could be discerned, and the spectral changes were found to be in excellent agreement with our previous quantitative analysis of the same copolymers using small-angle X-ray scattering. DSC and DMA experiments both indicate that the soft phase T_g decreases with increasing hard segment content. This is contrary to increased hard segment mixing in the soft phase, but can be rationalized by taking into consideration soft segment crystallinity and the concentration of ‘lone’ MDI units in the soft phase.     

Morphology and properties of thermoplastic polyurethanes with dangling chains in ricinoleate-based soft segments

In our previous publication on the structure-property behavior of segmented polyurethanes based on castor oil [Petrovi? ZS, Xu Y, Zhang W. Polymer Preprints 2007;48(2):852-3.], the results showed that these materials which possessed a soft segment weight concentration (SSC) of 70% have both low tensile strength and elongation at break. This behavior is distinctly different from segmented polyurethanes of comparable soft segment content obtained from petrochemical polymeric diols that possess terminal hydroxyl groups. The poor elastic properties of these segmented polyurethanes were ascribed to the low molecular weight of the polymers as well as due to the presence of the six-carbon “dangling chain”, which may influence the morphology of the resulting segmented polyurethanes. To further understand this behavior, four segmented polyurethanes with the SSC of 70, 60, 50, and 40%, respectively, were synthesized from a polyricinoleate diol with an M_n of 2580, diphenylmethane diisocyanate (MDI) and butanediol. The objective of this work was to study the effect of SSC on the morphology of the resulting polyurethanes, and to correlate the morphology with the properties of these bio-based segmented polyurethanes. Polymers were characterized by GPC, viscometry and spectroscopic methods. Thermal and mechanical properties of the polymers indicated good microphase separation. Microphase morphology was also noted by SAXS and AFM. Finally, “spherulitic-like” superstructures were noted in the solution cast films that are believed to arise from the nucleation and crystallization of the hard segments.     

Microstructural organization of polydimethylsiloxane soft segment polyurethanes derived from a single macrodiol

Segmented polyurethane (PU) block copolymers were synthesized using 4,4′-methylenediphenyl diisocyanate and 1,4-butanediol as hard segments and oligomeric ethoxypropyl polydimethylsiloxane (PDMS) as the soft segments, with hard segment contents ranging from 26 to 52 wt%. The microphase separated morphology, phase transitions, and degrees of phase separation of these novel copolymers were investigated using a variety of experimental methods. Like similar copolymers with mixed ethoxypropyl PDMS/poly(hexamethylene oxide) soft segments, PU copolymers containing only ethoxypropyl PDMS soft segments were found to consist of three microphases: a PDMS matrix phase, hard domains, and a mixed phase containing ethoxypropyl end group segments and dissolved short hard segments. Analysis of unlike segment demixing using small-angle X-ray scattering demonstrates that degrees of phase separation increase significantly as copolymer hard segment content increases, in keeping with findings from Fourier transform infrared spectroscopy measurements.     

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%.     

The thermal degradation of aqueous polyurethanes with catalysts of different selectivity

The thermal stability of aqueous polyurethanes has been measured by applying the thermogravimetric analysis. The aqueous polyurethanes (aqPUR) with catalysts of different selectivity have been studied by use of the dynamic method. To obtain degradations of 0.025, 0.05 and 0.10, employing the dynamic method, the heating rates of 0.5, 1, 2, 5 and 10 °C min⁻¹ have been used in the range of 30–500 °C. Using the more selective catalysts in the aqueous polyurethanes the total resulting time of the decomposition has increased at all degradation degrees and at all temperatures. This paper shows that the dynamic method based on the thermogravimetric analysis can be used to assess the thermal stability of the aqueous polyurethanes using the catalysts of different selectivity.     

Temperature dependent microphase mixing of model polyurethanes with different intersegment compatibilities

In this paper we explore the temperature dependence of segregation of hard and soft segments of selected segmented polyurethane copolymers using synchrotron small-angle X-ray scattering (SAXS). The copolymers are composed of the same hard segments but three different soft segment chemistries, of particular interest in biomedical device applications. Hard segments are formed from 4,4′-methylenediphenyl diisocyanate and 1,4-butanediol, and soft segments from an aliphatic polycarbonate [poly(1,6-hexyl 1,2-ethyl carbonate)], poly(tetramethylenoxide), or a mixed soft segment synthesized from hydroxyl-terminated poly(dimethylsiloxane) [PDMS] and poly(hexamethylenoxide) macrodiols. The changes in SAXS relative invariants and interdomain spacings are indicative of gradual dissolution of phase separated hard and soft segments with increasing temperature. All copolymers investigated herein, even those containing PDMS soft segments, transform to the single-phase state at a temperature determined by the soft segment chemistry (and hard segment content). The SAXS findings, along with those from parallel temperature-controlled Fourier Transform infrared spectroscopy measurements, also facilitate assignment of the origin of the thermal events observed in the DSC thermograms of these materials.     

膜分离法精制低不饱和度聚醚多元醇

采用聚醚砜超滤膜对ZSN-330低不饱和度聚醚多元醇进行精制,粗聚醚多元醇由正己烷1∶1体积比稀释,精制效果很好,大部分检测时间下锌、钴离子截留率高达90%以上,含量低于1 mg/g。采用红外分析并验证了截留物中含有双金属氰化络合物催化剂（DMC）成分。考察了膜截留分子量、料液黏度、操作压力、料液流速等对膜通量的影响,确定了较佳的超滤条件为膜截留分子量为150 kDa、由正己烷1∶1稀释、操作压力0.5 MPa、料液流速40 L/h。分别采用去离子水、2‰氢氧化钠溶液、正己烷溶剂超声清洗污染的膜,2‰氢氧化钠溶液的清洗效果较好,膜通量恢复率达66.4%。     

渗透汽化技术在液体分离中的研究新进展

渗透汽化是近年膜科学研究中最活跃的领域之一,在分离液体混合物,尤其是痕量、微量物质的移除,近、共沸物质的分离等方面有独特优势。简要介绍了渗透汽化技术的历史及发展过程,着重介绍了近几年渗透汽化技术在液体分离方面的研究进展。从研究结果来看,从水溶液中分离有机物研究主要集中在醇、酯的分离。在有机物脱水方面,开发出了选择性更好、渗透量更高的膜,乙醇脱水也有不少新的研究成果。特别是在有机混合物分离方面,取得了长足的进展,可以分离更多的有机物。     

New thermoplastic segmented polyurethanes with hard segments derived from 4,4′‐diphenylmethane diisocyanate and methylenebis(1,4‐phenylenemethylenethio)dialcanols

New thermoplastic poly(ether–urethane)s and poly(carbonate–urethane)s were synthesized by a one‐step melt polymerization from poly(oxytetramethylene) diol (PTMO) and poly(hexane‐1,6‐diyl carbonate) diol (PHCD) as soft segments, 4,4′‐diphenylmethane diisocyanate, and 2,2′‐[methylenebis(1,4‐phenylenemethylenethio)]diethanol, 3,3′‐[methylenebis(1,4‐phenylenemethylenethio)]dipropan‐1‐ol or 6,6′‐[methylenebis(1,4‐phenylenemethylenethio)]dihexan‐1‐ol as unconventional chain extenders. The effects of the kind and amount of the polymer diol and chain extender used on the structure and properties of the polymers were studied. The polymers were examined by Fourier transform infrared (FTIR) spectroscopy, X‐ray diffraction analysis, atomic force microscopy, differential scanning calorimetry, thermogravimetric analysis (TGA), TGA coupled with FTIR spectroscopy, and Shore hardness and tensile testing. The obtained high‐molecular‐weight polymers showed elastomeric or plastic properties. Generally, the PTMO‐based polymers exhibited significantly lower glass‐transition temperatures (up to ?48.1 vs ?1.4°C), a higher degree of microphase separation, and ordering in hard‐segment domains in comparison with the corresponding PHCD‐based ones. Moreover, it was observed that the polymers with the PTMO soft segments showed poorer tensile strengths (up to 36.5 vs 59.6 MPa) but higher elongations at break. All of the polymers exhibited a relatively good thermal stability. Their temperatures of 1% mass loss were in the range 270–320°C. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Molecular mobility and hydration properties of segmented polyurethanes with varying structure of soft‐ and hard‐chain segments

The molecular mobility and hydration properties of model segmented polyurethanes from either poly(propylene glycol) (PPG) or poly(butylene adipate) (PBAD), both of molecular weight 2000 (soft segments), and three different diisocyanates (all‐trans 4,4′‐dicyclohexylmethane diisocyanate, 100% t,t HMDI; HMDI with 20% of trans isomers, 20% t,t HMDI; and 4,4′‐diphenylmethane diisocyanate, MDI) (hard segments) were investigated using differential scanning calorimetry (DSC), thermally stimulated depolarization currents (TSDC) measurements, ac dielectric relaxation spectroscopy (ac DRS), equilibrium water‐sorption isotherms (ESI), and dynamic water‐sorption isotherms (DSI). No effects of the structure and of the amount of the soft segments on the overall degree of microphase separation (DMS) into microphases rich in soft and hard segments, respectively, were observed. On the contrary, DMS depends on the composition of the diisocyanates used and systematically increases in the order MDI, 20% t,t HMDI, 100% t,t HMDI as indicated by DSC, TSDC, and ac DRS. The PPG‐based polyurethanes are characterized by larger values of water content at saturation, h, and smaller values of the diffusion coefficient of water, D. h increases with temperature, indicating that the sorption process is endothermic. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 1209–1221, 1999     

Graft‐interpenetrating polymer networks of epoxy with polyurethanes derived from poly(ethyleneterephthalate) waste

Polyester polyurethanes derived from poly(ethyleneterephthalate) (PET) glycolysates were blended with epoxy to form graft‐interpenetrating networks (IPNs) with improved mechanical properties. Microwave‐assisted glycolytic depolymerization of PET was performed in the presence of polyethylene glycols of different molecular weights (600–1500). The resultant hydroxyl terminated polyester was used for synthesis of polyurethane prepolymer which was subsequently reacted with epoxy resin to generate grafted structures. The epoxy‐polyurethane blend was cured with triethylene tetramine under ambient conditions to result in graft IPNs. Blending resulted in an improvement in the mechanical properties, the extent of which was found to be dependant both on the amount as well as molecular weight of PET‐based polyurethane employed. Maximum improvement was observed in epoxy blends prepared with polyurethane (PU1000) at a loading of 10% w/w which resulted in 61% increase in tensile strength and 212% increase in impact strength. The extent of toughening was quantified by flexural studies under single edge notch bending (SENB) mode. In comparison to the unmodified epoxy, the Mode I fracture toughness (K_IC) and fracture energy (G_IC) increased by ～45% and ～184%, respectively. The underlying toughening mechanisms were identified by fractographic analysis, which generated evidence of rubber cavitation, microcracking, and crack path deflection. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40490.     

Phase separation kinetics and morphology in a polymer blend with diblock copolymer additive

The phase diagram for a low molecular weight blend of deuterated polystyrene (PSD) and polybutadiene (PB) was determined by temperature jump light scattering (TJLS) measurements and phase contrast optical microscopy (PCOM). The PSD/PB blend exhibited upper critical solution temperature behavior, and the critical temperatures measured by these two techniques were consistent. Upon addition of 0 to 0.12 mass fraction of a comparable molecular weight PSD-PB symmetric diblock copolymer, a linear decrease in the phase transition temperature was observed with increasing diblock copolymer content. At a constant, shallow quench depth, the kinetics of phase separation via spinodal decomposition as measured by TJLS were greatly retarded by the presence of the copolymer. Additionally, the time dependence of the concentration fluctuation growth did not seem to follow a universal functional form anywhere in the accessible q range when the diblock was present. The results of morphology study of the blends in the late stage of phase separation by PCOM also indicated that the phase separated domain sizes did not grow to the same size for a given annealing time as diblock content increased.     

Phase separation of the liquid crystal in the cholesterin phase

In the ethyl-cyanoethyl cellulose [(E-CE)C]/acrylic acid [AA]/4-cyano-4'-n-heptyl biphenyl (TCB) solutions, 7CB acted as a diluting reagent when it was added into the (E-CE)C/AA cholesteric liquid crystalline solutions. The dispersed phase with 250–300nm in size appeared after the AA in the isotropic (E-CE)C/AA/7CB solutions with the 7CB concentration (C_7CB) between 27.4 – 41.2wt% was polymerized at 24°C. There was the dispersed phase rich with 7CB in the (E-CE)C/AA/7CB cholesteric liquid crystalline solutions when C_7CB was 43.0wt% at 24°C. The temperature at which the anisotropic phase in the dispersed phase transformed to the isotropic phase in the solutions was increased after the polymerization of the AA, but the transition temperature of the dispersed phase in both the solutions and the films was lower than that of the pure 7CB. Received: 6 October 2000/Revised version: 18 December 2000/Accepted: 28 December 2000     

Phase diagram of different epoxy-amine precursors modified with a thermoplastic: Effect of structure of epoxy-amine system on miscibility

The miscibility of a thermoplastic with the precursors of different epoxy-amine systems was analyzed thermodynamically in which the dependence of interaction parameter on temperature and composition χ (T, ?) and the polydispersity of components were considered. The epoxy-amine precursors were different only in the nature of amino groups, which were provided by a monoamine and a diamine in different proportions. Cloud-point curves were measured for five unreacted modified systems resulting that miscibility of the system increased with the proportion of monoamine. The thermodynamic analysis was realized in two steps: first, the model was applied to each system individually and secondly, a general equation for χ (T, ?) depending on the monoamine-diamine proportion was searched and used to analyze all systems together. Theoretical calculations of cloud-point curves, shadow curves, spinodal curves, critical points, vitrification curves and species distributions were realized and discussed for those systems.     

Shear-induced phase separation and crystallization in semidilute solution of ultrahigh molecular weight polyethylene: Phase diagram in the parameter space of temperature and shear rate

In the previous papers, we elucidated enhancement of concentration fluctuations, phase separation, and crystallization induced by steady state or step-up shear flow, as observed by shear small-angle light scattering, optical microscopy, and birefringence, for a semidilute solution of ultrahigh molecular weight polyethylene in paraffin as an athermal solvent. However the studies were done only at a given temperature of 124 °C, which is higher than the nominal melting temperature of the quiescent solution T_nm (115–119 °C). It is crucial to extend the studies over a wider temperature range in order to generalize shear-induced phase behavior of the solution. Thus in this work we constructed a kind of phase diagram in the parameter space of temperature (T) and shear rate (). The temperature range covered was higher than T_nm, so that the phase diagram is strictly concerned with shear-induced phase behavior (i.e., without shear the solution is homogeneous and in a single-phase state). The diagram identified Regimes I–III in the T– space as will be detailed in the text. In constructing the phase diagram we found the following new points also. (i) The critical shear rate _cx which defines the boundary between Regimes I and II was independent of T. (ii) Regime III identified previously through the dependence of the integrated scattered intensity only at a particular temperature T = 124 °C was further separated into two regimes of III_a and III_b below and above a critical temperature (147 °C), respectively, through the observation of the dependence as a function of T: In Regime III_a, the sheared solution developed the optically anisotropic fibrous structures, indicative of the shear-induced crystallization triggered by the shear-induced concentration fluctuations in Regime II; In Regime III_b, the solution is so stable that it did not show a trend of the shear-induced crystallization even at the highest shear rates accessible in this experiment, but it only showed the shear-induced phase separation. (iii) The critical shear rates _c,streak and _cz, which define respectively the boundary between Regimes II and III_a and that between Regimes II and III_b, are sensitive to temperature.     

Characterization of permeation behaviors of ethanol–water mixtures through sodium alginate membrane with crosslinking gradient during pervaporation separation

Dense sodium alginate (SA) membranes crosslinked with glutaraldehyde were prepared by a new solution technique, which had different extents of crosslinking gradient structures. The SA membranes having a crosslinking gradient structure were fabricated by exposing one side of the membrane to the reaction solution while blocking the other side by a polyester film to prevent the reaction solution from contacting it. The extent of the crosslinking gradient was controlled by the exposing time. When the swelling measurements were performed with uniformly crosslinked membranes in aqueous solutions of 70–90 wt % ethanol contents, it was observed that the crosslinking could reduce both the solubility of water in the membrane and the permselectivity of the membrane toward water. The pervaporation separation of the ethanol–water mixture of 90 wt % ethanol content was carried out with membranes with different extents of crosslinking gradients. As the crosslinking gradient was developed more across the membrane, the resulting flux as well as the separation factor to water was found to decrease while the membrane became stable against water. The pervaporation performances of the membranes with different membrane loadings in a membrane cell were also discussed using the schematic concentration and activity profiles of the permeant developed in them. The pervaporation separations of the ethanol/water mixtures through the membrane with an optimal crosslinking gradient were performed at different feed compositions and temperatures ranging from 40 to 80°C. The change in the membrane performance due to the relaxation process during pervaporation was observed with the operating temperature and feed composition. The relaxational phenomena were also elucidated through an analysis of the experimental data of the membrane performance measured by repeating the operation in a given temperature range. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 1607–1619, 1998