Thermoplastic urethane elastomers. I. Effects of soft-segment variations

A series of thermoplastic urethane elastomers with soft segments of varying sequence length was prepared and their dynamic mechanical properties were characterized over a wide temperature range. The polymers were prepared using various molecular weight polycaprolactone diols as the soft segment and 4,4′-diphenylmethane diisocyanate and 1,4-butanediol as the hard segment. The urethane elastomer exhibited soft-segment crystallization when a polycaprolactone diol greater than 3000 M?_n was used. The glass transition temperature of these materials progressively shifted to lower temperatures as the chain length of the soft segment was increased. This dependence was interpreted in terms of a molecular weight relationship similar to that associated with amorphous homopolymers. The dynamic mechanical properties of these polyurethanes appear to be consistent with responses observed for compatible copolymers.     

Effects of rigid segments on structure and properties of unoriented and oriented poly(p-phenylene terephthalamide-co-ethylene terephthalates)

In poly(p-phenylene terephthalamide-co-ethylene terephthalate) the rigid segments of p-phenylene terephthalamide are aggregated as crystalline domains above the weight fraction of the rigid segments, 6 wt%. The rigid segments disturb the crystallization of the flexible segments of poly(ethylene terephthalate) (PET) and are preferentially contained in the amorphous phase of the PET segments. The crystallinity of the PET segments decreased with increasing the content of the rigid segments in the copolymers and the glass transition temperature is decreased by the decrease of the crystallinity below the weight fraction of the rigid segments, 6 wt%, in spite of the depression of micro-Brownian motion of the PET segments due to the rigid segments. The values of Young's modulus E, yield stress σ_y and breaking stress σ_b for the zone-drawn copolymer were conspicuously increased by the rigid segments contained in it, in comparison with those of the zone-drawn PET homopolymer. Such higher values of E, σ_y, and σ_b of the copolymer are originated by greater increases in the orientation of amorphous chains in the copolymer. The rigid segments in the amorphous phase effectively depressed the thermal shrinkage of the zone-drawn and the zone-annealed copolymers.     

Homogeneous nucleation and mesophase formation in glassy isotactic polypropylene

Differential fast scanning chip calorimetry has been employed to study nucleation/ordering during annealing the glass of quenched isotactic polypropylene. Initially non-ordered samples were annealed below the glass transition temperature for different periods of time, and the change of structure during isothermal annealing was then analyzed by monitoring the exchange of latent heat on heating. Primary result of this work is the proof of homogeneous nucleation of ordering and mesophase formation in the glassy state. It is suggested that only local non-cooperative mobility of molecular segments is required to form small, ordered domains, and that the classical nucleation theory, which restricts nucleation of the crystallization/ordering process of polymers to temperatures between the equilibrium melting temperature and the glass transition temperature, needs modification.     

Improved processability of PA66-polyimide copolymers with different polyimide contents

Limitations in the properties of polyamide PA66, such as low glass transition temperature and high water absorptivity, limit its applications. Introduction of amorphous polyimide segments into the PA66 main chain lowers the glass transition temperature and melting temperature and also improves its processability. PA66-polyimide (PA-PI) copolymers with different weight ratios of PI are prepared by high temperature and high-pressure solution polymerization. The degree of crystallization of PA-PI copolymers decreases with increasing PI content. The melting point decreases from 261°C for PA66 to 223°C for PA-PI-4. Dynamic mechanical analysis shows that the T_g increases from 70 to 90°C, and the storage modulus can be well maintained. Rheological studies show that the temperature for processing can reach 70°C. Copolymers with different PI contents show different processing viscosities. In addition, water absorptivity (about 1.8%) and dielectric constant values of PA-PI and PA6/6T are similar.     

Modification of the thermal properties and crystallization behaviour of poly(ethylene terephthalate) by copolymerization

Poly(ethylene terephthalate) (PET) is a widely used polyester, which can be crystallized from the melt over a wide range of supercooling conditions or, alternatively, quenched into the amorphous state and, subsequently, crystallized by thermal treatment above the glass‐transition temperature. It is well known that the crystallization of PET can be hindered by means of copolymerization or reactive blending. The incorporation of comonomeric units into the polymer backbone leads to an irregular chain structure and thereby inhibits regular chain packing for crystallization. The crystallization of PET copolyesters is strongly influenced by the chain microstructure regarding comonomer distribution, randomness and length of the crystallizable ethylene terephthalate sequences. This paper is mainly devoted to the thermally induced crystallization behaviour of PET and to reviewing the efforts that have been made in the last decade to modify the glass‐transition and melting temperatures, the crystallinity and the crystallization rate of this polyester. Furthermore, some illustrative experimental data obtained from isothermal and non‐isothermal crystallization of PET are included in this study. © 2003 Society of Chemical Industry     

聚丁二酸丁二醇酯基共聚物及其多嵌段共聚物的合成与性能

采用“一步法”,以丁二酸酐（SAA）和1,4–丁二醇（BDO）为单体、端羟基二元醇为共聚单体合成了聚丁二酸丁二醇酯（PBS）及一系列端羟基二元醇共聚物,同时使酚酞与SAA的缩聚产物参与SAA和BDO的共聚反应,并通过链段调节合成法制备兼具刚性链段和柔性链段的可生物降解三嵌段共聚聚酯热塑性弹性体聚(丁二酸丁二醇酯-共-酚酞丁二酸丁二醇酯)（SAA-PHE-PBS）,研究了PBS及其共聚物的分子量、化学结构组成、热性能和结晶性能,此外,使用南极假丝酵母脂肪酶B测试了PBS及其共聚物的生物降解性能。结果表明,端羟基二元醇共聚物的玻璃化转变温度变化幅度不大,熔融温度无明显改变,结晶度降低,亲水性有所改善,生物降解性能得到大幅度提升;三嵌段热塑性弹性体SAA-PHE-PBS的玻璃化转变温度升高,结晶度与PBS相差不大,疏水性更强,共聚合物的残重率有所增加,生物降解性能有不同程度的降低。     

Practical aspects of physicochemical kinetics using thermal techniques

A number of studies on the kinetics of physicochemical processes are described. The methods used are shown to be potentially useful for making time-temperature predictions and for optimizing process variables. Examples described include (1) the long-term prediction of the performance of a plasticized polyvinyl chloride and doped polyacetylenes; (2) the polymerization of a monomer and the optimization of time, temperature, and initiator concentration variables; (3) analysis of an order/disorder transition in a thermochromic polymer; (4) the crystallization of polymers and the effect of a nucleating agent; and (5) the crystallization of an amorphous metallic glass. The theoretical background, significance, scope, and limitations of these measurements are also discussed.     

Properties of random and block copolymers of butadiene and styrene. I. Dynamic properties and glassy transition temperatures

The effect of monomer sequence on physical properties was investigated for butadienestyrene solution copolymers made by organolithium initiation. The polymers varied from random copolymers of uniform composition along the polymer chain to ideal block polymers of specific block sequence arrangement and included rubbers of intermediate degrees of randomness. Uniform composition random copolymers exhibit a single glass transition temperature and a very narrow dynamic loss peak corresponding to this transition. The glass transition can be predicted from the styrene content and the microstructure of the butadiene portion of the rubber. Random copolymers in which composition varies along the polymer chain, and to some extent between molecules, exhibit a single glass transition, but the dynamic loss peak is broadened. The extent of this broadening is shown to be compatible with the sequence distribution, polymer segments of various compositions losing mobility at different temperatures. This indicates a tendency for association between segments of different temperatures. This indicates a tendency for association between segments of different chains which are similar in composition. Block copolymers display two transitions, corresponding to T_g for each type of block. The position and width of the dynamic loss peaks are related to block length and compositional purity of the blocks.     

Die Kristallisation von Mehrkomponentensystemen aus hochpolymeren Stoffen

The differences in the crystallization behaviour between a single component system and a multicomponent system are discussed. Examples for multicomponent systems are homopolymers with a broad distribution in molecular weight, mixtures of different homopolymers, swollen polymers, block copolymers, and statistical copolymers. A distribution in molecular weights manifests itself mainly in extended chain crystallization experiments in that way that a fractionation with respect to the chain length takes place. It causes also a broadening of the melting range. The presence of a second noncrystallizable homopolymer which is miscible with the crystallizable homopolymer leads to a reduction of the melting point and a change in the glass transition temperature. The crystallization remains spherulitic. The noncrystallizable component is expelled from the crystals. If the diffusion rate of this component is large, it is also expelled from the spherulites, otherwise it is incorporated into the spherulites. When the noncrystallizable component is expelled from the spherulites, the growth rate of the spherulites decreases during growth. The temperature range in which crystallization takes place is limited by the melting point of the crystallizable component and by the glass transition temperature of the two-component system. If the crystallizable component is not dissolved completely in the noncrystallizable component, this part which is not dissolved crystallizes much more rapidly than the part which is dissolved. Below the glass transition temperature only the part which is not dissolved crystallizes. This gives a possibility to determine the solubility above the melting point. By swelling, the glass transition temperature and therewith the crystallization temperatures are decreased. When, during swelling of an amorphous sample, the glass transition temperature is decreased below the temperature where swelling is performed one observes a front of spherulites penetrating into the sample simultaneously with the swelling agent. On the other hand, when the glass transition temperature remains above the swelling temperature, one can crystallize the sample after swelling is completed by raising the temperature. As in a pure polymer, one then observes the growth of spherulites from statistically distributed centers; the growth rate of the spherulites increases however with increasing time. Block copolymers of a crystallizable component and a non-crystallizable component sometimes are not able to crystallize. This is the case, if the chains of the noncrystallizable component have a cross section which is larger than that of the chains of the crystallizable component and if, in addition, the latter chains are not so long that they can fold several times in order to compensate the difference in the cross sections. When crystallization takes place, spherulites are formed only if the amount of the crystallizable component exceeds a well defined limit. Otherwise only a diffuse birefringence is developed. In this case a much larger supercooling is necessary to crystallize the sample than in the case of spherulitic crystallization. From long period measurements one can conclude how many times each noncrystallizable chain is folded. From the melting and swelling behaviour one learns whether the noncrystallizable chains form loops or tie molecules. With statistical copolymers consisting of crystallizable units and noncrystallizable units the melting point, the rate of crystallization, the degree of crystallization at the end of the process, and the melting point decrease with increasing amount of noncrystallizable units. The noncrystallizable units are incorporated partly also into the crystals.     

Thermal properties and crystallization behavior of dendritic polyetheramides

The semi-crystalline dendritic polymers were prepared from the dendritic polyetheramide with hydroxyl end-groups by being grafted with myristoyl chloride, palmitoyl chloride, and octadecyl isocyanate in different substitution degrees, respectively. The thermal properties and the crystallization behavior of the resulted samples were studied by differential scanning calorimetry and optical microscopy, respectively. The experimental results have shown that the length of the alkyl chain attached and substitution degree have apparent influences on the glass transition temperature, melting enthalpy and the size of crystallite.     

Polyätherester-Block-Copolymere – Eine Gruppe neuartiger thermoplastischer Elastomerer

High melting polyether esters can be prepared by ester interchange from readily available starting materials such as dimethyl terephthalate, polyalkylene ether glycols and linear short chain diols. The resulting block copolymers exhibit a continuous two-phase domain structure consisting of amorphous polyether ester soft segments and crystalline short chain polyester hard segments. By proper selection of the relative amounts of polyether and polyester segments, polymers ranging from fairly soft elastomers to impact resistant elastoplastics may be obtained. The preparation, morphology and physical characterization of polyether esters as well as the effect of the structures of the soft and hard segments on polymer properties are described. Polytetramethylene terephthalate based on polyether esters are particularly suited as thermoprocessable high performance elastomers offering an unusual combination of physical and chemical properties characterized by high abrasion, tear and solvent resistance as well as excellent low and high temperature properties. Because of their good melt stability, low melt viscosity and high crystallization rates, these polymers can be processed within a wide temperature range by all methods commonly used in the plastics industry.     

均相玻璃态高分子中溶剂扩散系数的数学模型

以自由体积理论为基础 ,提出改良的玻璃态高分子中溶剂扩散系数的数学模型 .模型推导过程中考虑了溶剂可塑化效应对高分子凝聚态的影响 ,并以明确的物理概念计算玻璃态聚合物的自由体积 .对橡胶态适用的自由体积参数在此模型中保持有效 ,所引入的表达溶剂可塑化效应的唯一参数 β可以通过计算玻璃化温度来确定 .所以 ,本模型中无可调节参数存在 ,具有完全可预测性 .以芳香族溶剂苯、甲苯、乙苯在玻璃态聚苯乙烯和聚甲基丙烯酸甲酯中的扩散系数为例对模型进行验证 ,理论计算结果和实验值取得良好一致     

Synthesis and characterization of block copolyetheresters with poly(tetramethylene 2,6-naphthalenedicarboxylate) segments

The block copolyetheresters with hard segments of poly(tetramethylene 2,6-naphthalenedicarboxylate) and soft segments of poly(tetramethylene oxide) were prepared by melt polycondensation of dimethyl 2,6-naphthalenedicarboxylate, 1,4-butanediol, and poly(tetramethylene ether) glycol (PTMEG) with molecular weights of 650, 1000, and 2000. The block copolymers were characterized by Fourier transform infrared and ¹H-NMR spectroscopy, differential scanning calorimetry, thermogravimetric analysis (TGA), and X-ray diffraction. The block copolymer compositions were governed by the charge molar ratio (x) of PTMEG to dimethyl 2,6-naphthalenedicarboxylate. It was found that the thermal transitions were dependent on the compositions. As x increases, T_m and ΔH_m of the polyester segments decrease due to the decrease in the sequence length. The X-ray diffraction data also indicate that the crystallinity of the polyester segments decreased as x increased. The molecular weight of the PTMEG used has a significant influence on the glass transition temperature (T_g) and the crystallizability of the polyether segments. The polyether segments of block copolymers derived from PTMEG 2000 could crystallize after cooling and showed a T_g of about −67°C, independent of x. However, the polyether segments of copolymers derived from PTMEG 1000 and PTMEG 650 could not crystallize, and the T_g of the polyether segments decreased as x increased. This is described as the difference in the miscibility between amorphous parts of the polyether segments and those of the polyester segments. The TGA results indicate that the composition had little effect on the nonisothermal thermal degradation under nitrogen. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 1411–1418, 1997     

On the glassy state of multiphase and pure polymer materials

In this work we formulate a new glass theory and investigate its suitability for describing the mechanical response of thermoplastic elastomers composed of styrenic-block copolymers. These materials are composed of glassy domains of polystyrene, which physically link soft rubbery chain segments made of either polybutadiene or polyisoprene. We demonstrate that the crossover in the shift factors, observed experimentally to change from Williams-Landel-Ferry to Arrhenius behavior passing through a characteristic crossover temperature T^∗ from below, coincides with the crossover from power-law to stretched-exponential behavior of the stress relaxation found in recent tensile experiments. Moreover, we show that the characteristic crossover temperature T^∗ is identical with the underlying true equilibrium second-order phase transition temperature T₂ of the polystyrene crosslinks, predicted by the thermodynamic theory of Gibbs and Di Marzio for pure glassy polystyrene in the infinite-time limit. By combining the recently introduced theory of Di Marzio and Yang with the significant-structure theory of Eyring and Ree, we develop a new glass theory, which is capable of explaining the mechanical response of multiphase as well as pure glassy materials. Moreover, we show a clear evidence for the existence of T₂ postulated in 1950s for pure glasses and hotly debated since then.     

超柔软易染新型聚酯的热性能研究

超柔软易染聚酯是一种新型功能性聚酯产品。通过差示扫描量热测试,就其构成成分对玻璃化转变温度、冷结晶温度、熔点、熔融结晶温度的影响进行了研究,为后道加工工艺的选择提供参考依据。     

Phase separation in segmented polyurethanes

Phase separation in a segmented polyurethane has been studied by differential scanning calorimetry. The glass transition temperature of the soft phase decreases logarithmically with time to a limiting value at each annealing temperature. The magnitude of the decrease is larger at low annealing temperatures, but the normalized rate of logarithmic decrease is smaller. At high annealing temperatures, long sequences of hard segments are excluded from the soft phase in which short segments are still soluble. At low temperatures, even short hard segments separate from the soft phase. The exclusion of the hard segments from the soft phase is a relatively fast process, but the development of order in hard domains takes longer time to reach steady state.     

DSC studies on the transitions in poly(vinylidenefluoride) and some related copolymers

Summary The transition properties of poly(vinylidenefluoride) and of some related copolymers, either semicrystalline or amorphous, were studied by differential scanning calorimetry in the temperature range from 200 K to 500 K. The amorphous copolymers exhibit a single glass transition. Melting endotherms and a lower glass transition [Tg(L)] are systematically observed in the semi-crystalline materials as well as an upper glass transition [Tg(U)] for certain thermal and mechanical histories of the samples. Conditions for [Tg(U)] existence are related to solid state morphology of the macromolecules and loop length in the folded chains.     

Block copolyetheresters. V. Low-temperature properties of thermotropic block copolyetheresters

The low-temperature properties of block copolyetheresters with hard segments of poly(alkylene p,p′-bibenzoate) and soft segments of poly(tetramethylene ether) were investigated by differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). In the temperature range of −100 to 60°C, two transition temperatures, a glass transition temperature (T_g) and a melting temperature (T_m), were found by DSC and are attributed to the polyether segments. The T_g monitored by DSC of the polyether segments of the block copolyetheresters is around −68°C and independent of the composition and the type of polyester segment. Thus, the amorphous parts of the polyether segments should be immiscible with the amorphous parts of the polyester segments. The polyether segments of the block copolyetheresters exhibit a lower T_m and a lower crystallinity than those of the poly(tetramethylene ether)glycol due to the presence of the polyester segments. The crystallizability of the polyether segments is dependent on the composition to some extent. The DMA data show that the dynamic modulus drops more abruptly around −10 to 15°C, indicating that the mechanical properties may change significantly due to the melting of the polyether segments. © 1996 John Wiley & Sons, Inc.     

Crystallization phenomena in some polyester — urethanes

A density balance has been used to measure the crystallization isotherms of poly(ethylene adipate) and copolymers which were prepared by extending the polyester with four different diisocyanates. The occurrence of extensive secondary crystallization processes precluded satisfactory interpretation in terms of the Avrami theory and further analysis could only be based on the half-time for crystallization. This parameter has the advantage that it is determined directly and is independent of any theoretical analysis. The presence of very small concentrations of diisocyanate units can have a profound effect on the rate of crystallization if they are very different structurally from the parent polyester, e.g. a molar concentration of about 5% of 2,4-tolylene diisocyanate increases the half-time by a factor of 20 whereas the same concentration of hexamethylene diisocyanate has an insignificant effect. The temperature dependence of the half-times is discussed in relation to several theories of crystallization.     

Thermoplastic urethane elastomers IV. Effects of cycloaliphatic chain extender on dynamic mechanical properties

The dynamic mechanical properties of a series of thermoplastic urethane elastomers have been studied as a function of molecular composition and temperature. Polymers based on polycaprolactone diol, an isomeric mixture of tolylene diisocyanate and hydrogenated Bisphenol-A as the chain extender were prepared at various relative concentrations of hard and soft segments. The glass transition temperatures of these polymers progressively shifted to higher temperatures as the relative hard segment content was increased. This variation was accurately described by the Fox relationship for amorphous copolymers. These results can be interpreted in terms of the relative degree of segregation between the segment of the block copolymers.