Liquid crystalline polyurethane. Polyurethanes containing bis-(p-oxymethylphenyl) terephthalate

Several polyurethanes based on bis-(p-oxymethylphenyl) terephthalate (BOPT) were synthesized and studied with respect to some of their thermal properties. BOPT exhibits a mesomorphic phase at 252–264°C. Polymerization was carried out by equimolar reaction with hexamethyl-ene diisocyanate (HDI), 4,4-dicyclohexylmethane diisocyanate (H₁₂MDI) α,α'-diisocyanate-1,3-dimethylcyclohexane (H6 XDI), 4,4′-diphenylmeth-ane diisocyanate (MDI), 2,4-tolylene diisocyanate (TDI), and phenylene diisocyanate (PDI). It became clear that polyurethanes obtained from BOPT with HDI, H₁₂MDI, H₆XDI, and TDI have mesomorphic phases at 243–291, 214–250, 172–229, and 180–234°C, respectively, as determined by DSC and polarized microscopy, and that all polyurethanes are crystalline as evidenced by x-ray diffraction.     

Small-angle X-ray scattering studies of microdomain structure in segmented polyurethane elastomers

The small-angle x-ray scattering (SAXS) technique has been used to characterize the detailed microphase structure of two crosslinked segmented polyurethane elastomers. Both copolymers contain trifunctional polypropylene ether triols in the rubbery elastomeric block, but are synthesized with different hard segments: a symmetric 4,4′-diphenylmethane diisocyanate (MDI) chain extended with butanediol (BD); and an 80/20 mixture of asymmetric 2,4-toluene diisocyanate (TDI) and symmetric 2,6-toluene diisocyanate (TDI) chain extended with ethylene glycol (EG). Calculations of SAXS invariants and determinations of deviations from Porod's law are used to examine the degree of phase segregation of the hard- and soft-segment domains. Results show that the overall degree of phase separation is poorer in the asymmetric TDI/EG-based copolymer than in the symmetric MDI/BD-based copolymer. Determination of diffuse phase boundary thicknesses, however, reveals that the domain boundaries are sharper in the asymmetric TDI/EG system. The contrasting morphologies found in the two systems are interpreted in terms of differences in hard-soft segment compatibility, diisocyanate symmetry, and diisocyanate length. Coupled with conformational considerations, this information is used to construct a new model for polyurethane hard-segment microdomain structure. Important features of the model are that it takes into account the effects of hard-segment sequence length distribution and allows for folding of the longer hard-segment sequences back into the hard-segment domain.     

Polyurethane cationomers. I. Structure-property relationships

Polyether polyurethane cationomers are prepared using poly (tetramethylene oxide) of molecular weight 2000 as soft segments, N-methyl-diethanolamine as chain extender, glycolic acid as quaternization agent, methyl ethyl ketone as solvent, and three different diisocyanates. The three diisocyanates are 4,4′-diphenylenemethylene diisocyanate (MDI), hexamethylene diisocyanate (HDI), and toluene diisocyanate (TDI). Properties of the films cast from solutions of the three series of ionomers are studied by infrared spectroscopy, dynamic mechanical analysis, thermogravimetric analysis, differential scanning calorimetry, wide angle x-ray diffraction, and tensile elongation testing. In the un-ionized and ionized systems, the hard segments exhibit disordered and ordered arrangements, respectively. Ionization disrupts the order and produces increased cohesion in the hard domains, which have opposing effects on the tensile elongation properties. In the MDI and TDI systems, cohesion is predominant, leading to an increased tensile strength and modulus and decreased elongation at break. But in the HDI system, the disruption of the order is predominant, leading to decreased tensile strength and only insignificant reduction in the elongation at break. In the TDI system, the tensile strength is rather low, which is attributed to the poor order in the hard domains resulting from the high content of the asymmetric 2,4-isomer of the urethane.     

Tensile strength of polyurethane and other elastomeric block copolymers

Processes that impart strength and toughness are discussed along with reinforcement by colloidal plastics to indicate that high strength, except under restricted test conditions, necessitates a dispersed phase. Thereafter the dependence of the nominal and true tensile strengths on the type, size, and concentration of polar segments in polyurethane elastomers is considered. Data are first examined on formulations devoid of plastic domains and then on those containing domain-forming segments that result from the reaction of toluene-2,4-diisocyanate (TDI) with either toluene-2,4-diamine or 4,4′-methylene-bis-(2-chloroaniline) and from the reaction of 4,4′-diphenyl methane diisocyanate (MDI) with 1,4-butanediol (BD). Segments from TDI and either diamine give plastic domains that are especially effective for augmenting strength over an extended temperature range. Segments from MDI and BD are comparatively ineffective, although the formulation studied exhibits high strength at and below room temperature owing to strain-induced crystallization. From data on various segmented and triblock elastomers, general conclusions are drawn regarding the dependence of strength on the characteristics of the domains and the matrix. For some six segmented and triblock elastomers, it is found that the true tensile strength is essentially independent of the weight fraction of domains provided it exceeds 0.20 or thereabouts.     

Unsaturated poly(ester-imide)s from hydroxy-terminated polybutadiene, dianhydride and diisocyanate

Hydroxy terminated polybutadiene has been used for the first time in the synthesis of poly(ester-imide)s [P(E-I)s]. Anhydride terminated polyester prepolymers were prepared by the reaction of two different polyols--polytetramethyleneoxide glycol (PTMG) of molecular weight 1000 and hydroxy terminated polybutadiene (HTPB) of molecular weight 2500--and different dianhydrides--pyromellitic dianhydride (PMDA), benzophenonetetracarboxylic dianhydride (BTDA) and 4,4^′-(hexafluoroiso-propylidene)diphthalic anhydride (HFDA). The prepolymers were then reacted with different diisocyanates--80:20 mixture of 2,4- and 2,6-tolylene diisocyanate (TDI), 1,6-hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI) and 4,4^′-methylene bis(phenylisocyanate) (MDI) resulting in P(E-I)s. The P(E-I)s were characterised by FT-IR, FT-NMR, GPC, TGA, DSC and for static and dynamic mechanical properties. The polymers based on PTMG showed two distinct melting points and behave as thermoplastic elastomers. The thermal stability and mechanical properties of P(E-I)s based on HTPB were substantially higher than those based on PTMG.     

PROPERTIES OF POLYURETHANE ELASTOMERS PREPARED FROM 1,1''''-ISO-PROPYLIDENE BIS(p-PHENYLENE-OXY) DI-PROPANOL-2, A POLYETHER (OR POLYESTER). AND 4, 4''''-DIPHENYLMETHANE DIISOCYANATE (MDI) BY ONE-STEP REACTION METHOD

Two new types of block polyurethane elastomers were prepared using two polyols polyethyleneadipate and PTHF respectively, and diisocyanate MDI extended with Dianol-33 (a new extender),by one step reaction and casting method. The properties of these polyurethane were studied by employing Instron infrared spectroscopy,DSC and wide angle X-ray diffraction etc.     

Thermal stability of polyurethane materials based on castor oil as polyol component

Preparation of the series of polyurethane elastomers and its nanocomposites from castor oil (a vegetable triglyceride) and different isocyanates (aromatic: toluene diisocyanate, TDI and aliphatic: isophorone diisocyanate, IPDI) is described. The synthesis was carried out in bulk and without catalyst by a one-step reactive process. Different elastomers were prepared by using several stoichiometric imbalances. For polyurethane nanocomposites based on TDI, titanium(IV) oxide nanoparticles was used. The thermal properties of the materials are discussed on the basis of simultaneous TG-DSC measurements results and TMDSC data. TMDSC results show that T _g increases with increasing r = NCO/OH ratio. Namely, with increasing NCO/OH ratio the cross-linkage density increases and as a consequence, the chain mobility decreases, resulting in a higher T _g. It was estimated that the T _g of the samples decreased as the nanofiller content increased due to the changes in the segmental mobility in polyurethane materials. Thermal data refers to increased stability of nanocomposites compared with that of the unfilled elastomers.     

对苯二异氰酸酯基聚氨酯弹性体交联度对其形态与摩擦性能的影响

聚氨酯弹性体的摩擦性能在诸如船舶、汽车、生物医用等领域具有十分重要的意义,而通过化学修饰策略实现该类材料摩擦性能的精细设计,仍具有十分迫切的研究需求和广泛的应用前景。 本工作以对苯二异氰酸酯(PPDI)与聚四氢呋喃醚二醇(PTMG)为原料,通过调节1,4-丁二醇与三羟甲基丙烷两种扩链交联剂的混合比例,采用预聚体法合成了具备不同交联度的PPDI基聚氨酯弹性体。 其中,傅里叶变换衰减全反射光谱(FTIR-ATR)、广角X射线衍射(WAXD)、差示扫描量热仪(DSC)等表征结果表明,聚氨酯弹性体中硬段和软段的结晶度随交联度的提升均呈下降趋势。 同时,力学测试表明,材料的弹性模量随之降低,而PPDI基聚氨酯弹性体摩擦系数则明显增大。 此外,滞后回环曲线表明,交联度的改变影响了PPDI基聚氨酯弹性体的阻尼特性,而聚氨酯弹性体阻尼的差异在其摩擦性能对速率的依赖关系中则有所体现。 本工作由此提出,利用不同交联度下PPDI基聚氨酯中软硬段结晶度的变化,在对材料弹性模量和损耗模量进行可控调节的同时,能够实现对其摩擦性能的改变,为PPDI基聚氨酯弹性体的摩擦性能调控提供了一种简单有效的途径。     

PHYSICO-MECHANICAL,OPTICAL, AND WAXS STUDIES ON CHAIN EXTENDED POLYURETHANE

Thermoset polyurethane (PU) elastomers were prepared using castor oil, 4,4′-methylenebis(phenyl isocyanate) (MDI), and tol-uene-2,4-diisocyanate (TDI). The effect of aromatic diamines on the physico-mechanical and optical properties of chain extended polyurethane prepared using castor oil has been investigated. Tensile strength and percent elongation lies in the range 13–24 MPa and 76–32, respectively. Higher tensile strength was observed for 4,4′-diaminodiphenylsulphone (DDS) than the 4,4′-diaminodiphenylmethane (DDM) chain extender. The properties imparted by the extenders are explained on the basis of the groups present in the diamines. These changes have been interpreted quantitatively in terms of microcrystalline parameters computed using wide-angle X-ray scattering data.     

Polydimethylsiloxane–polyurethane elastomers: Synthesis and properties of segmented copolymers and related zwitterionomers

A series of polyurethane block polymers based on hydroxybutyl-terminated polydimethyl-siloxane soft segments of molecular weight 2000 were synthesized. The hard segments consisted of 4,4′-methylenediphenylene diisocyanate (MDI) which was chain extended with either 1,4-butanediol (BD) or N-methyldiethanolamine (MDEA). The MDEA-extended materials were ionized by using 1,3-propane sultone. The weight fraction of hard segments was in the range 0.13–0.39. The morphology and properties of these polyurethane elastomers were studied by a variety of techniques. All of these short-segment block copolymers showed nearly complete phase separation. The zwitterionomer materials exhibited ionic aggregation within the hard domains. Hard-segment crystallinity or ionic aggregation did not affect the morphology. Hard-domain cohesion was found to be a more important factor than hard-domain volume fraction in determining the tensile and viscoelastic properties of these elastomers.     

环氧液晶弹性体材料的制备与力学性能研究

传统的液晶弹性体材料多采用丙烯酸酯类或聚硅氧烷类分子,通过自由基聚合制备.然而由于自由基聚合易被氧气阻聚,固化过程收缩率高且内应力大,传统液晶弹性体材料的力学性能并不是很优异.为解决这一问题,本文合成了带有环氧基团的液晶单体和交联剂,使用碘鎓盐作为引发剂,通过光引发阳离子反应,用原位聚合交联法制备了环氧液晶弹性体材料.光引发阳离子聚合和传统自由基聚合相比,不受氧气影响且弹性体固化时体积收缩率小.对制备出的液晶弹性体材料的晶相和力学等性能进行探究和表征,发现其比传统的丙烯酸酯类或者聚硅氧烷类液晶弹性体材料具有更优异的力学性能,在清亮点以上,其弹性模量达到了0.92 MPa.     

Synthesis and characterization of bismaleimides derived from polyurethanes

A series of novel bismaleimides (BMIs) were prepared from maleic anhydride and polyurethane prepolymers based on MDI (4,4′-diphenylmethane diisocyanate) and polyether and polyester diols with various chain lengths. All the BMIs were characterized by IR, ¹H-NMR, and elemental analysis. DSC studies indicated that the thermal polymerization of the BMIs could be carried out in the temperature range of 102–245°C, and that curing behavior was significantly affected by the molecular weight of the BMIs. The crosslinked BMI elastomers showed good mechanical properties and much better thermal stability than that of the traditional polyurethane elastomers. The glass transition temperatures, mechanical, and dynamic mechanical properties were dependent on the types of polyols used and the resultant crosslink densities due to various chain lengths of the BMIs. © 1994 John Wiley & Sons, Inc.     

Synthesis and properties of isocyanate curable millable polyurethane elastomers based on castor oil as a renewable resource polyol

Millable polyurethane elastomers based on difunctional castor oil and poly(propylene glycol), 2,4-toluene diisocyanate and 1,4-butane diol were prepared and cured using toluene diisocyanate dimer as crosslinking agent. All elastomers were characterized by conventional methods. Physical, thermal and mechanical properties of elastomers were studied. Investigation of these properties showed that the elastomers could be tailor made in order to fulfill industrial needs.     

Thermal stability and combustibility of butyl and halogenated butyl rubbers

The effects of flame retardants such as hydrated aluminium oxide, antimony trioxide and chloroparaffin on the thermal properties and flammability of sulphur vulcanizates of butyl and halogenated butyl elastomers were studied. The thermoanalytical curves of the elastomers were interpreted. Greater tendencies to thermal degradation were observed for halogenated butyl elastomers than for the original butyl rubber elastomer. This was confirmed by elastomer combustibility studies. The use of these flame retardants allowed the formation of self-extinguishing vulcanizates of the investigated elastomers.     

牛血清白蛋白在医用聚氨酯弹性体表面的吸附

制备了具有较好机械性能的异佛尔酮二异氰酸酯(IPDI)型聚氨酯弹性体胶片, 并进行表面肝素化处理, 得到抗凝血医用导管材料. 将聚氨酯胶片浸泡在牛血清白蛋白(BSA)水溶液中, 利用稀溶液黏度法研究了牛血清白蛋白在聚氨酯胶片表面的动态吸附情况, 并采用界面校正黏度方程计算溶液浓度变化. 研究发现, 牛血清白蛋白分子能迅速吸附到聚氨酯胶片表面, 但达到吸附平衡需要较长时间. 牛血清白蛋白在聚氨酯表面吸附后的溶液中分子构象发生变化.     

Synthesis, characterization and properties of a novel fluorinated polyurethane

A novel fluorinated polyurethane (FPU) was prepared by fluorinated polyether glycol (PTMG-g-HFP) as a soft segment, 1,6-hexamethylene diisocyanate (HDI) or toluene diisocyanate (TDI) as a hard segment and 1,4-butanodiol (BDO) as a chain extender. Fourier transform infrared spectroscopy (FTIR), ¹H NMR, ¹³C NMR and gel permeation chromatography (GPC) were used to characterize the structure of the fluorinated polyurethane. The thermal stabilities of the fluorinated polyurethane and the corresponding hydrogenated polyurethane were studied by thermogravimetric analysis (TGA). X-ray photoelectron spectroscopy (XPS) analysis at two different sampling depths for the fluorinated polyurethane was used to investigate the surface compositions of FPU. And the mechanical properties of the fluorinated polyurethane and the corresponding hydrogenated polyurethane were also measured. Chemical resistance of polyurethane films was estimated through spot tests with different solvents. The results showed that FPU had high thermal stability, strain-hardening property and good chemical resistance. The XPS measurements showed the fluorine enrichment on the surface of FPU.     

多元醇对对苯二异氰酸酯基聚氨酯微孔弹性体的形态与性能影响

以对苯二异氰酸酯(PPDI)、1,4-丁二醇、水、聚四氢呋喃醚多元醇(PTMEG)和氢化端羟基丁二烯多元醇(HLBH)为原料,采用两步法制备出聚氨酯微孔弹性体样品。通过傅里叶变换衰减全反射红外光谱(FTIR-ATR)、动态机械分析(DMA)、差示扫描量热仪(DSC)、万能材料试验机等技术手段对样品的微相分离、耐低温性能、动态生热进行了系统表征。结果表明,两种多元醇结构对泡孔尺寸影响不大,微孔尺寸在100~300μm之间,其中以150μm尺寸左右的泡孔居多;HLBH制备的聚氨酯微孔弹性体硬段形成的氢键数量多于PTMEG制备的微孔弹性体,具有更好的微相分离;由于较好的微相分离结构,HLBH样品在-30~150℃具有很宽的模量平台区,而PTMEG样品受软段的低温结晶影响,在0℃以下模量急剧上升,HLBH样品低温下的刚度变化优于PTMEG样品;同时HLBH样品的滞后生热亦小于PTMEG样品,具有更好的动态疲劳性能。     

Synthesis and thermo-mechanical characterization of high performance polyurethane elastomers based on heterocyclic and aromatic diamine chain extenders

Two series of 4,4′-diphenylmethane diisocyanate (MDI) and poly(ethylene glycol adipate) (PEGA)-based polyurethane and polyurethaneurea elastomers were synthesized via a one-shot polymerization method and characterized using FTIR, ¹H NMR and ¹³C NMR. The samples in the first series are extended by aliphatic diol chain extenders while in the second series mixtures of aliphatic diols and furanic or aromatic diamine chain extenders are used. TGA experiments revealed that with furanic or aromatic diamine chain extenders the polymer degradation temperature is shifted 90 °C upwards, irrespective of the annealing time at 100 °C according to ASTM 0573-99. The values of Young's modulus and of the tensile strength are higher and the strain at break is lower for the samples in series 2 compared to those in series 1. Increasing the annealing time at 100 °C lowers Young's modulus. Dynamic mechanical thermal analyses points to a progressive microphase separation with annealing time.     

Synthesis and characterization of polydimethylsiloxane polyurea-urethanes and related zwitterionomers

A series of segmented polyurea urethane and polyurea block copolymers based on a hexane diisocyanate (HDI) modified aminopropyl terminated polydimethylsiloxane soft segment was synthesized. The hard segments consisted of 4,4′-methylene diphenylene diisocyanate (MDI) which was chain extended with 1,4-butanediol (BD), N-methyldiethanolamine (MDEA), or ethylene diamine. Zwitterionomers were prepared by quaternizing the tertiary amine of the MDEA extended material with γ-propane sultone. The effect of chemical structure on the extent of phase separation and physical properties was studied using a variety of techniques including thermal analysis, dynamic mechanical spectroscopy, tensile testing, and small-angle x-ray scattering. It was observed that the compatibility between the nonpolar polydimethylsiloxane soft segments and the polar urethane hard segments was improved by inserting HDI linkages into the polydimethylsiloxane soft segments. The aggregation of hard segments was enhanced by increasing hard-segment content or by the introduction of ionic functionality. The tensile strength and modulus of these materials was higher than those of polyurethanes containing soft segments based on polydimethylsiloxane and its derivatives.     

Thermal stability enhancement of polyurethanes by surface treatment

Both oxidation and methoxymethylation of the surfaces of a series of MDI (methylene diphenyl isocyanate) and TDI (toluene diisocyanate) polyether and polyester soft segment 1–4 butanediol polyurethanes result in increased thermal stability as measured by TG. Explosive loss of mass above the hard segment melting temperature suggests that the diffusion of the dissociated diisocyanate moiety is hindered at lower temperatures. Thus suppression of the depolycondensation reaction by chemical blockage of the surface may result in a material with an increased service life at use temperatures as thermal stability of a polyurethane may depend upon the low diffusivity of its diisocyanate comonomer. The effect of vacuum, oxygen and water vapor on the kinetics of mass-loss of several of the polyurethanes is presented. In celebration of the 60^th birthday of Dr. Andrew K. Galwey