嵌段聚酯型聚脲氨酯弹性体的红外光谱研究

用红外光谱法对基于4,4′－二苯基甲烷二异氰酸酯（MDI）、乙二胺（ED）和聚己二酸丁二醇酯（PBA）（分子量分别为1975和1228）的嵌段聚脲氨酸（PUU）弹性体进行了研究。首先归属了PUU的红外吸收谱带,并对前人已经归属过的1600、1317、1520和1230cm^-1谱带提出了新的看法。氚化和变温技术的使用为上述红外谱带的归属和氢键化研究提供了可靠的理论依据。研究结果表明氢键化主要发生在硬段聚集区中,少量的氢键在软、硬段之间的界面上形成,由此推断PUU材料是相分离的。     

Studies on segmented polyurethane—urea elastomers: Structure and properties of segmented polyurethane—ureas having the binary hard segment components

Studies on the structure and properties of segmented polyurethane-ureas having binary hard segment components have been made using infrared dichroism, small-angle x-ray diffraction, and mechanical testing. The results clarify the effect of the domain structure of the hard segments on the mechanical hysteresis behavior of the segmented polyurethane—urea elastomers. Experiments were carried out for film specimens prepared from poly(tetramethylene glycol), 4, 4'-diphenylmethane diisocyanate, and chain extenders such as ethylenediamine and hydrazine. The domain structures of the hard segments were controlled by blending segmented polyurethane-ureas having different chain extenders. The chain-extending reactions were conducted both simultaneously and in a stepwise manner during polymerization using two different chain extenders. The experimental results revealed that the mechanical hysteresis greatly decreased for the specimens of segmented polyurethane-ureas with binary component hard segments which were randomly copolymerized using the mixture of two different chain extenders. It is suggested that the decrease of hysteresis is related to the microdomain structure of segmented polyurethane-ureas composed of small fragments of lamellae. The small lateral size is caused by the restriction of crystal growth in the direction of hydrogen bond formation due to the heterogeneous hard segment components. This hysteresis phenomenon could be verified by the fact that the transverse orientation of the hard segments decreased in the case of the segmented polyurethane-ureas having randomly copolymerized hard segments. To impart the property of ideal rubber elasticity to segmented polyurethane-urea, it is deduced that it is important to control the hard segment domain structure so that it does not form higher-order structures such as lamellae of large lateral size.     

氘化聚酯型聚脲氨酯弹性体的红外光谱研究

用红外光谱法对基于4,4′－二苯基甲烷二异氰酸酯（MDI）、乙二胺（ED）和聚己二酸丁二醇酯（PBA）的嵌段聚酯型聚脲氨酯（PUU）弹性体及其氚化产物进行了研究。结果表明氚化反应对PUU中涉及PUU中涉及氢键化N－H振动红外吸收光谱带的影响较大,受氚化影响较大的那些谱带分别在3332,3190,1600,1539,1317,1257和1230cm^-1附近。另外也发现不同硬段含量和不同聚酯软段分子量的PUU受氚化影响的程度基本相似。     

梯度固化聚氨酯脲中氢键的红外光谱分析

聚氨酯脲弹性体中的氢键可以反映其内部的微相分离状态,并对材料的宏观性能有着比较重要的影响。 通过梯度固化的方法制得了微相分离程度沿厚度方向梯度渐变的聚氨酯脲弹性体。 利用傅里叶变换红外光谱(FTIR)研究了梯度聚氨酯脲弹性体中的氢键,分析了羰基、亚氨基以及醚氧键的氢键,对弹性体的微相分离程度进行了表征。 结果表明,羰基区的氢键化程度随固化温度的升高而升高,表明微相分离程度的逐渐升高。 醚氧键氢键化程度随固化温度改变有差异,亚氨基的氢键化程度在交联较低的试样中随固化温度的升高而升高,在交联程度较高的试样中则相反。 脲羰基形成的三维氢键的强度比醚氧键形成的氢键强。 氢键化醚氧键的振动吸收大约位于1 076 cm-1。     

Dielectric properties of side chain liquid crystalline elastomers: influence of crosslinking on side chain dynamics

Dielectric response, from 1 Hz to 10 MHz, of liquid crystalline side chain elastomers has been compared to the one of analogous uncrosslinked materials. Results are discussed in terms of mobility of the mesogens. Two different systems have been investigated: smectic A elastomers allow to determine the influence of crosslinking on the relaxation (i.e. the reorientation of the whole mesogen around the chain), a S _C ^* elastomer shows the drastic influence of the polymer network on the Goldstone mode. Received 12 October 1998     

FTIR和^1H NMR法研究嵌段聚氨酯的结构

用１，４－丁二醇，乙二胺及二者的混合物为扩链剂，合成了嵌段及嵌段支化型聚氨酯。用ＦＴＩＲ和＾１Ｈ ＮＭＲ法研究了含不同扩链剂的嵌段聚氨酯大分子的支化，并通过积分半定量法考察了配料比与支化率之间的关系。     

Use of combinatorial chemistry to develop photocurable thermoplastic polyurethane elastomers (TPUs)

Combinatorial chemistry was used to develop photocurable thermoplastic polyurethane elastomers through the incorporation of photoreactive diacetylene diols as chain extenders. The methodology applied allowed, in 36 experiments, the choice of the best compromise between mechanical properties and lack of colour. The combinations chosen were scaled up and their properties were evaluated in terms of mechanical properties. The combinatorial approach reduced the estimated time tenfold in developing such type of materials.     

X-ray investigations concerning the physical structure of cross-linking in segmented urethane elastomers

In the X-ray diagrams of some segmented urethane elastomers, so-called hard-segment interferences can be observed which indicate a defined geometrical accumulation of the hard segments. These interferences can easily be traced back to a system of hydrogen bridges between the hard segments. They allow an insight into the geometrical structure of the cross-linking as well as into the mechanism of elongation and thermosetting.     

Calorimetric study of the Paranematic-to-Nematic transition of polydomain side-chain liquid-crystalline elastomers with different mesogen composition

The phase transition behaviour of various nematic side-chain liquid-crystalline elastomers with different mesogen composition has been explored by means of high-resolution ac calorimetry. Polydomain samples of the same crosslinking density and different type of mesogens have been investigated. The results show a strong dependence of the phase transition features upon the composition of the mesogen. The distance from the critical point, reflected in the sharpness of the heat capacity anomalies, increases when adding a shorter-length mesogen. The results provide new insight for the impact of mesogens on the thermodynamic behaviour and, thus, on the thermomechanical response of nematic liquid-crystalline elastomers.     

Aminated polyacrylonitrile blends with cellulose acetate

Polyacrylonitriles (PANs) were synthesized and aminated with ethylene diamine (2DA), hexamethylene diamine (6DA), and dodecane diamine (12DA), followed by blending with cellulose acetate (CA). Effects of amination and chain length of diamine on the miscibility of the aminated PAN with CA were studied. Scanning electron microscopy (SEM) micrographs of cryogenically fractured surfaces of the blends showed coarse elliptical dispersions of CA in PAN. The dispersed CA domains decreased in size with an increase in aminated PAN content. The dispersed domain size further decreased with increasing chain length of diamine. and eventually the morphology became almost homogeneous with 12DA-modified PAN blends. With increasing chain length of the diamines, the dynamic loss peak temperature of PAN in blends showed a movement toward that of CA. Fourier transform infrared (FTIR) measurements showed that the specific interaction between the aminated PAN and cellulose acetate is the hydrogen bonding between aprotic hydrogen in aminated PAN and the ester carbonyl of CA, the interactions being increased with increasing chain length of diamine.     

嵌段聚酯型聚脲氨酯硬段微区中氢键化的红外光谱研究

用红外光谱法对基于4,4′二苯基甲烷二异氰酸酯（MDI）、乙二胺（ED）和聚己二酸丁二醇酯（PBA）（分子量分别为1975和1228）的两系列嵌段聚酯型聚脲氨酯（PUU）硬段微区的氢键化进行了研究。发出脲C＝0基随着硬段含量增国出现双峰吸收,提出了PUU不同长度硬段序列中脲C＝0基的两种平面氢键化的模型。认为这些平面氢键可以通过进一步键合来形成硬段微区中的三维氢键。     

Spontaneous thermal expansion of nematic elastomers

We study the monodomain (single-crystal) nematic elastomer materials, all side-chain siloxane polymers with the same mesogenic groups and crosslinking density, but differing in the type of crosslinking. Increasing the proportion of long di-functional segments of main-chain nematic polymer, acting as network crosslinking, results in dramatic changes in the uniaxial equilibrium thermal expansion on cooling from the isotropic phase. At higher concentration of main chains their behaviour dominates the elastomer properties. At low concentration of main-chain material, we detect two distinct transitions at different temperatures, one attributed to the main-chain, the other to the side-chain component. The effective uniaxial anisotropy of nematic rubber, r(T) = / proportional to the effective nematic order parameter Q(T), is given by an average of the two components and thus reflects the two-transition nature of thermal expansion. The experimental data is compared with the theoretical model of ideal nematic elastomers; applications in high-amplitude thermal actuators are discussed in the end. Received 25 June 2001 and Received in final form 29 September 2001     

Surface characteristics of UV-irradiated polyurethane elastomers extended with α, ω-alkane diols

Polyurethane elastomers (PUEs) based on 4,4′-diphenylmethane diisocyanate (MDI), poly (?-caprolactone) (PCL) and extended with series of chain extender (CE) were synthesized via two step polymerization technique. The synthesized samples were irradiated for 50, 100 and 200 h in an UV exposure unit as such the spectral distribution of the light is good match for terrestrial solar radiation. The modifications in the chemical structures of the PU before and after irradiation were characterized using Fourier transform infrared (FT-IR) technique. The effect of irradiation time and chain extenders length on surface properties were studied and investigated. Photo-oxidation of PU surface leads to fast increase in surface free energy and its polar component. Simultaneously, the work of water adhesion to polymer increases significantly during UV-irradiation. The higher changes in surface properties, observed by water absorption (%), equilibrium degree of swelling, as well as monitored by ATR-FT-IR and contact angle measurement, were found for the PU samples extended with higher number of methylene unit and irradiation time.     

Analytic instanton solutions in two-dimensional field models

Two-dimensional scalar field models with nontrivial potential determined in bounded spatial regions are considered. Exact analytic instanton solutions for these models and soliton solutions for similar three-dimensional systems are obtained.     

Suppress polystyrene thin film dewetting by modifying substrate surface with aminopropyltriethoxysilane

Aminofunctional organosilanes, such as 3-aminopropyltriethoxysilane (APTES), have been widely utilized as adhesion promoters, and have also been found to have the ability to prevent dewetting of polymer thin films from substrates. The APTES molecule contains an active terminal amino group that can hydrogen bond with the multiple hydroxylated head groups in itself and hydroxyl groups on a substrate, thus forming cyclic structures and a complex loose network at ambient conditions. Upon heating, the hydrogen bond can be broken, allowing more silanol groups to condense with each other and form siloxane linkages, hence tightening the three-dimensional network. When a polymer thin film is in contact with the APTES layer during the thermal process, the polymer chains can diffuse/penetrate into the APTES network while the network is being tightened by the additional crosslinking. The penetrated and subsequently anchored chains could help to stabilize the thin film on the substrate. This hypothesis was verified by dewetting studies of thin films of polystyrene (PS), having molecular weights above and below the entanglement molecular weight (M_e), from APTES and control surfaces when the systems were subjected to various treatments. Dewetting suppression was observed for PS/APTES that was thermally treated at ∼80 °C or 120 °C prior to the annealing of the thin film at higher temperatures. Much stronger suppression was noticed for PS having a molecular weight higher than M_e. When PS thin films were deposited onto a precured APTES network, no dewetting suppression was observed.     

Disorder by random crosslinking in smectic elastomers

We present a high-resolution x-ray study of the effects of disorder due to random crosslinking on the one-dimensional translational ordering in smectic elastomers. At a small crosslink density of about 5%, the elastomer network stabilizes the smectic structure against layer-displacement fluctuations, and the algebraically decaying layer ordering extends up to several micrometers. With increasing concentration of crosslinks, the finite size of these domains is strongly reduced, indicating that disordering takes over. Finally, at a crosslink concentration of 20%, the structure factor can be described by a Lorentzian, which signals extended short-range correlations. The findings are discussed in terms of recent theories of randomly quenched disorder.     

Physics of the evolution of structure and elastic stresses in Pd-Mo alloys saturated with hydrogen

Specific features in the structural evolution of a Pd-Mo alloy after its electrolytic saturation with hydrogen are studied by x-ray diffraction. It is revealed that these features depend on the concentration of absorbed hydrogen, the initial defect structure, and the character of its transformation upon hydrogen saturation. The factors responsible for the structural evolution depend on the concentration of alloy components and the difference between the hydrogen affinities, Debye temperatures, and elastic constants of the components. A model proposed for the evolution of the structure and elastic stresses in palladium-metal-hydrogen systems accounts for the above factors.     

Diagrammatic decompositions on lattice for correlation functions of Ising spin models by iterative method

In the present paper the iterative method enables us to calculate correlation functions of Ising spin models by two approximate ways. The equations resulting from two models A and B, based on different physical considerations concerning correlations in surroundings of the reference spin, are solved for one, two, and three-dimensional Ising models with nearest neighbour interactions. Except of anomalies occuring in low-dimensional systems the model A leads to the critical pointA _c=0.191 for the three-dimensional cubic Ising model.     

Ab initio study of the structure,cooperativity, and vibrational properties of HNC ternary complexes with two HF molecules

MP2/aug-cc-pVDZ calculations have been used to provide information on the three ternary systems comprising one HNC and two HF molecules. The binding distances, frequency shifts, and interaction energies in these systems have been analysed to study the cooperativity of hydrogen bond in these systems. The cooperativity of hydrogen bond in HNC–HF–HF trimer is larger than that in HF–HF–HNC trimer. The result indicates that the proton acceptor HNC plays a more important role in enhancing the cooperativity of hydrogen bond. Many-body interaction analyses have also been performed for these ternary systems.