Phase separation and crystallization in double crystalline symmetric binary polymer blends

Blending of two or more pure polymers is an effective way to produce composites with tunable properties. In this paper, we report dynamic Monte Carlo simulation results on the crystallization of crystalline/crystalline (A/B) symmetric binary polymer blend, wherein the melting temperature of A-polymer is higher than B-polymer. We study the effect of segregation strength (arises from the immiscibility between A- and B-polymers) on crystallization and morphological development. Crystallization of A-polymer precedes the crystallization of B-polymer upon cooling from a homogeneous melt. Simulation results reveal that the morphological development is controlled by the interplay between crystallization driving force (viz., attractive interaction) and de-mixing energy (viz., repulsive interaction between two polymers). With increasing segregation strength, the interface becomes more rigid and restricts the development of crystalline structures. Mean square radius of gyration shows a decreasing trend with increasing segregation strength, reflecting the increased repulsive interaction between A- and B-polymers. As a consequence, a large number of smaller size crystals form with lesser crystallinity. Isothermal crystallization reveals that the transition pathways strongly depend on segregation strength. We also observe a path-dependent crystallization behavior in isothermal crystallization: two-step (sequential) isothermal crystallization yields superior crystalline structure in both A- and B-polymers than one-step (coincident) crystallization.     

Transition between crystallization and microphase separation in PS-b-PEO thin film Influenced by solvent vapor selectivity

In this paper, the effect of solvent selectivity on the transition between crystallization and microphase separation of the semicrystalline diblock copolymer polystyrene-b-poly(ethylene oxide) (PS-b-PEO) thin films was investigated. Square-shaped crystals formed due to lower barrier of crystalline nucleation in both poor and good solvent vapor for PEO. However, in poor solvent (cyclohexane) vapor for PEO, crystalline structure changed to microphase separated structure in the square platelets due to the high mobility of PS blocks. Then breakout crystals dominated the morphology of the film. While, in good solvent (water) vapor for PEO, competition between nucleation and dissolution of crystallization caused the formation of imperfect crystals. Then imperfect crystals dissolved due to the high mobility of PEO blocks, and microphase separation dominated the morphology of the film. The gain of free volume of soluble block and the low swelling of crystalline block are keys for microphase separation and crystallization, respectively.     

Synthesis and bulk properties of poly(tetrahydrofuran)-poly(2-methyl-2-oxazoline) ABA triblock copolymers

A series of linear triblock-copolymers of the ABA type in which the central B-block is poly(tetrahydrofuran) (polyTHF) and the A-segments are poly(2-methyl-2-oxazoline) (polyMeOX) were synthesized by a one-pot sequential monomer addition copolymerization, utilizing the living nature of the cationic ring-opening polymerization of both monomers. Films of the copolymers, casted from chloroform solutions, exhibit excellent mechanical properties in comparison with the homopolymers with comparable molecular weights, which was ascribed to the phase separation occurring between the two copolymer segments. Materials, in which the polyTHF B-segment have a molecular weight 13 000 g/mol or higher and each polyMeOX A-block a molecular weight 1500 g/mol, kept elastomeric properties up to 130 °C notwithstanding the fact that this temperature is considerably higher than the melting point of polyTHF and the glass transition temperature of polyMeOX. It was found that these triblock-copolymer materials show a shape memory effect. These observations are attributed to the high degree of phase separation between the two blocks and the strong polar interactions between the polyMeOX segments. Received: 20 March 1997/Revised: 5 September 1997/Accepted: 8 September 1997     

Effect of temperature and water on microphase separation of PCL–PEO–PCL triblock copolymers

Microphase separation of poly(ε-caprolactone-ethylene oxide-ε-caprolactone) (PCL–PEO–PCL), with block number-average molecular weights of 9,100–30,400–9,100 g/mol, was studied. Cylindrical morphology was observed in a solvent-cast sample. When the as-cast sample was heated above the melting points of both PEO and PCL blocks, a change in morphology was observed by Small Angle X-ray Scattering (SAXS). When this sample was cooled to room temperature in the ambient atmosphere, another morphology (lamellae) was observed with SAXS and Atomic Force Microscopy (AFM). This asymmetric change in morphology suggests a role of kinetics (microphase separation and crystallization) in determining the observed microstructures. Addition of water at room temperature also affected microphase separation of the block copolymer due to hydrophilicity of PEO. As the polymer concentration decreases from 100 to 60%, the morphology changes from cylinders to lamellae. Differential Scanning Calorimetry (DSC) data show that water addition decreases PEO crystallinity but PCL crystallinity remains.     

Effects of nucleating agent and processing conditions on the mechanical,thermal, and optical properties of biaxially oriented polypropylene films

The effects of nucleating agent, temperature of crystallization, and degree of machine direction (MD) orientation on the mechanical, optical, and thermal properties of biaxially oriented polypropylene (BOPP) films were investigated. Addition of nucleating agent improved only the initial tear resistance in the MD; however, the other mechanical and optical properties did not change appreciably. In the set of experiments in which the crystallization temperature was increased, the degree of crystallinity also increased. Thus, Young's modulus, yield stress, and tensile strength increased in both directions with higher degree of crystallinity. The yield strain did not change significantly, but the strain at break was higher. Although the initial tear resistance was smaller in both directions with increasing crystallization temperature, the tear propagation resistance did not change. In this case, haze and diffuse transmittance were slightly higher, but the total transmittance was constant. In the set of experiments in which the machine direction orientation was increased, the degree of crystallinity also became higher. Owing to the effects of higher crystallinity and higher MD orientation, the modulus, yield stress, and tensile strength increased, but the yield strain and tear propagation resistance did not significantly change in both directions.     

Morphologies and structures in poly(<Emphasis Type="SmallCaps">l</Emphasis>-lactide-<Emphasis Type="Italic">b</Emphasis>-ethylene oxide) copolymers determined by crystallization,microphase separation,and vitrification

Morphologies and structures determined by crystallization of the blocks, microphase separation of the copolymers, and vitrification of PLLA block in poly(l-lactide-b-ethylene oxide) (PLLA-b-PEO) copolymers were investigated using microscopic techniques and synchrotron small angle X-ray scattering. The PLLA-b-PEO copolymer films were crystallized from two different annealing processes: melt crystallization (process A) or crystallized from glass state of PLLA block after quenching from melt state (process B). The relationship between the crystalline morphology and microstructure of the copolymers were explored using SAXS. The morphology and phase structure are predominated by crystallization of PLLA block, and greatly influenced by microphase separation of the copolymers. In process B, lozenge-shape and truncated lozenge-shaped PLLA crystals of nanometer scale can be observed. The crystalline morphology is markedly affected by the microstructure formed during the annealing process. Star-shaped morphologies stacked with PLLA single crystals were observed.     

羧酸型聚氨酯脲乳液的微相分离结构研究

利用ＤＳＣ,ＳＥＭ,ＷＡＸＤ对羧酸型聚氨酯脲乳液的微相分离结构进行了研究。结果表明,离子基团的引入,有利于软段和硬段的微相分离,随着离子基团含量的增加,微相分离程度增大。同时,适当增加硬段含量,硬段微区的有序性提高,结晶熔融温度升高。加入少量刚性物质ＭＯＣＡ,能够促进软段和硬段的微相分离。     

Phase behavior and structure formation for diblock copolymers composed of side-chain liquid crystalline and glassy amorphous components

Phase behavior and structure formation in liquid crystallization of a side-chain liquid crystalline (LC) block copolymers composed of poly[11-(4′-cyanophenyl-4″-phenoxy)undecyl acrylate] (PA₁₁OCB) and polystyrene (PSt) were investigated by using a time-resolved small-angle X-ray scattering technique (SAXS), differential scanning calorimetry and polarizing optical microscopy. PA₁₁OCB homopolymer formed smectic (Sm) liquid crystal. Liquid crystallization behavior of the block copolymers depended on the molecular weight and the block composition. When molecular weight was relatively low, order-disorder transition (ODT) was observed. In cooling of such block copolymers, liquid crystallization seemed to wait for the formation of LC-rich microphase by ODT. For the block copolymers with relatively high molecular weight, liquid crystallization slightly enlarged the domain spacing without changing the microphase separation structure in the melt. The order of the LC phase was lowered with decreasing dimensionality of the LC microdomains, that is, the LC blocks formed smectic liquid crystal in the matrix or lamellar microphase while liquid crystallization in the cylindrical microdomains did not show smectic but maybe nematic liquid crystal. Moreover, the LC blocks within the spherical microdomains did not liquid crystallize. From the 2-D SAXS with applying shear flow, the Sm layers were orientated perpendicularly to the interface of the microphase separation. The relation between the layer thickness of the LC phase and the molecular weight suggested that the main chain was extended normally to the interface of the microphase separation.     

Effect of low temperature crystallization on 58S bioactive glass sintering and compressive strength

Mesoporous glass 58S (60SiO₂, 36CaO, 4P₂O₅ mol.%) has excellent bioactivity, biocompatibility, and forms strong bonds with bone making it attractive for implants. Mesoporous bioactive glass 58S powder is typically consolidated through sintering in order to produce an implant with sufficient strength to withstand the in vivo loads. However, heating the glass often leads to crystallinity, which is undesirable because it can reduce bioactivity. Hence, there is a trade-off between minimising crystallinity and maximising glass strength. Even at relatively low temperatures, it has been suggested that segregation of calcium and phosphate from silica within the glass can lead to crystallization. In this work, we confirm the occurrence of low temperature segregation in bioactive glass 58S using electron microscopy with elemental mapping. We probe how segregation affects the material properties of post-sintered glasses via comparison to a glass where phase separation is prevented via addition citric acid to the parent sol.     

熔融挤出温度对PA6/CaCl2复合材料结构与性能的影响

采用熔融挤出的方法,制备了PA6/CaCl2复合材料,研究了熔融挤出温度对PA6/CaCl2复合材料的结晶行为和性能的影响。实验结果表明：随熔融挤出温度的提高,CaCl2与PA6的络合反应程度越大,PA6/CaCl2复合材料的结晶度越小,结晶不完善程度越大,复合材料的粘度越大,熔体流动速率越小。随熔融挤出温度的提高,复合材料的拉伸强度先增大后减小,最后近似趋于定值,冲击强度、弯曲强度随熔融挤出温度的提高总体呈增加趋势。     

Synthesis and characterization of LC side chain AB blockcopolymers

Summary The synthesis of liquid crystalline side chain A-B blockcopolymers, prepared by living anionic polymerization in combination with a polymeranalogous reaction is reported. Thereby the A-block was formed from a non mesogenic monomer (styrene, butadiene and n-butylmethacrylate) and the B-block from a monomer with a lateral active group (2-(trimethylsiloxy)-ethylmethacrylate), used for introduction of the side chain mesogens (cholesterylformyl- and 2-(4-[5-hexylpyrimidin-2-yl]-benzoyloxy)-groups). The obtained copolymers show mostly phase separation phenomenons. In dependence of the content of LC side groups a mesomorphic behaviour was observed.     

Vapor‐induced crystallization behavior of bisphenol‐A polycarbonate

The effects of exposure time and vapor pressure on the crystallization behaviors of bisphenol‐A polycarbonate (BAPC) films were investigated at 25°C by using differential scanning calorimetry (DSC). Double melting peaks were observed for various BAPC samples after vapor‐induced crystallization. The low temperature melting peak shifted to higher temperature and became sharper with increasing exposure time, and could be assigned to defective crystals with smaller crystal size. Crystallinity and average crystal dimension normal to (020) were calculated from wide‐angle X‐ray diffraction spectra. A good agreement was obtained between crystallinity values obtained from WAXD and those from DSC. The morphology of crystallized samples after various exposure time periods was examined by means of polarized optical microscopy. Nucleation occurred at the initial stage of vapor‐induced crystallization. Poor crystals become perfect through segment reorganization with increasing exposure time, and spherulites' growth was observed. The average diameter of spherulites increased from 2 μm for 1 h, to 7 and 16 μm after 3 and 56 h, respectively. POLYM. ENG. SCI., 46:729–734, 2006. © 2006 Society of Plastics Engineers     

聚酯型聚氨酯乳液的合成及性能

以异佛尔酮二异氰酸酯（ IPDI）、六亚甲基二异氰酸酯（HDI）和聚己二酸 1,4-丁二醇酯二醇（ PBA）为主要原料制备系列水性聚氨酯乳液（ WPU）。采用红外光谱仪、差式扫描量热仪、 X-射线衍射仪、电子拉力机等对 WPU进行结构表征;为了从聚集状态上对聚氨酯结晶性有更深层次的探究,对 WPU进行了定伸情况下的测试。结果显示：随着硬段含量的增加,硬段 -软段间的氢键相互作用减小,微相分离程度增加,结晶性能降低;随着伸长率的增加,氢键相互作用和结晶性能都表现出先减小后增大的趋势。当硬段含量为 14. 73%时,聚氨酯胶膜拉伸强度达到 40. 11 MPa,剥离强度为 93. 7 N/（25 mm）。     

Processing temperature dependent mechanical response of a thermoplastic elastomer with low hard segment

The mechanical responses including monotonic and cyclic tensile responses have been investigated on a microphase-separated poly (styrene-isoprene-styrene) triblock copolymer (SIS). The specimens were injection-molded by using different melt temperatures to acquire different microphase structures. As a result of temperature-dependent segregation driving force, the specimens with reduced microphase separation can be obtained by increasing processing melt temperature from 180 °C to 240 °C. On the basis of stress-strain behavior, Young's modulus was found to increase with increasing PS domain continuity in the order of disorder state to disordered spheres to body-cubic-centered (BCC) spheres to oriented cylinders morphology. Meanwhile, cyclic hysteresis decreases with reduced microphase separation and with decreasing the applied predetermined maximum tensile strain. In addition, the Mooney–Rivlin phenomenological approach was used to evaluate and explore the relationship between the polymer topological networks and the rubber elasticity of thermoplastic elastomers.     

硬段对聚酯型聚氨酯弹性体微相分离的影响

以聚己二酸-1,4-丁二醇酯二醇(PBA)、4,4′-二苯基甲烷二异氰酸酯(MDI)、乙二醇(EG)、1,4-丁二醇(BDO)和1,6-己二醇(HD)等为主要原料,采用预聚体法制备了一系列热塑性聚氨酯弹性体(TPU)。通过对TPU流变性能、结晶性能、硬度与力学性能的研究,考察了不同扩链剂及不同硬段含量对TPU体系内部微相分离的影响。结果表明,HD-TPU与BDO-TPU微相分离情况相当,均大于EGTPU,且HD-TPU具有较好的结晶性能、拉伸强度及断裂伸长率;随TPU体系硬段含量增加,硬度和拉伸强度增加,断裂伸长率减小,相分离发生越早越快,结晶熔融温度越高,但相分离程度并不高。     

The effect of phase separation on crystal nucleation density and lamella growth in near-critical polyolefin blends

We have studied the effect of liquid-liquid phase separation on crystallization in near-critical blends of poly(ethylene-co-hexene)/poly(ethylene-co-octene) and poly(ethylene-co-hexene)/poly(ethylene-co-butene) using optical microscopy and simultaneous small and wide angle X-ray scattering. Two quenching schemes were used in this study: (1) single-quench, a homogeneous melt quickly cooled to the crystallization temperature, and (2) double-quench, a homogeneous melt quickly cooled to an intermediate temperature, which allows for occurring phase separation but not crystallization, then to the crystallization temperature. We could found more crystalline nuclei in case of single-quench than of double-quench. The long spacing of lamellar crystals is approximately 20 Å larger in single-quench than in double-quench, due primarily to the inclusion of more non-crystallizable components in the amorphous layers of lamellar stacks in the former. The degree of crystallinity is about three times higher in single-quench.     

Behaviour of stereoblock poly(<Emphasis Type="Italic">N</Emphasis>-isopropyl acrylamide) in acetone–water mixtures

The purpose of this study was to investigate the usability of poly(N-isopropyl acrylamide) (PNIPAM) as an additive for crystallization of a model drug, nitrofurantoin (NF), and utilizing the thermoresponsivity of the polymer to enable control of the viscosity during the crystallization process. Crystallization of NF in the presence of PNIPAM resulted in dendritic crystal growth and the originally observed growth of needle-shaped crystals was prohibited. The effect of acetone, a cosolvent used for the crystallization, on thermosensitivity of PNIPAM was studied and the properties of atactic PNIPAM and triblock PNIPAM polymers containing atactic and isotactic rich blocks were compared. The investigated PNIPAMs were all soluble in the acetone–water mixtures leading to phase separation at lower temperatures with increasing acetone content, up to approximately 50 vol% (0.20 mol fraction). At higher acetone contents no phase separation was observed on heating. The presence of acetone altered the viscosity of the solutions prior to the phase separation depending on the polymer architecture. The PNIPAM polymers induced smaller and potentially more easily processable crystals, however, the viscosity increase in the presence of acetone occurred only 1–3 °C prior to phase separation complicating the practical use of this approach.     

Influence of heat treatment on the properties of shape memory fibers. I. Crystallinity,hydrogen bonding,and shape memory effect

Shape memory fibers (SMFs) were prepared via melt spinning. The fibers underwent different heat treatments to eliminate internal stress and structure deficiency caused during melt spinning. The influences of heat treatments on the SMF crystallinity, molecular orientation, hydrogen bonding, and shape memory behavior were studied. It was found with increasing heat‐treatment temperature, the soft segment crystallinity, crystallite dimension, and microphase separation increased, and the hydrogen bonding in the hard segment phase increased. Low temperature heat treatments decreased the shape recovery ratios while increasing the shape fixity ratios as a result of internal stress releasing and molecules disorientation. High temperature heat treatments increased the hard segment stability. Increasing heat‐treatment temperature resulted in the improvement of both the shape recovery and fixity, because it promoted the phase separation. The results from DSC, DMA, XRD, and FTIR were used to illustrate the mechanism governing these properties difference. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Structure development during crystallization and solid‐state processing of poly(glycolic acid)

DSC and time‐resolved WAXS and SAXS are used to study the structure development during isothermal crystallization of poly(glycolic acid) (PGA) in the temperature range 180–195°C. It is shown that the crystallization rate increases with degree of supercooling in the temperature range of consideration. WAXS and DSC crystallinity measurements agree well and a final crystallinity of 50% is found independently of the crystallization temperature. In‐situ SAXS measurements indicate that for PGA the final crystal thickness approaches a limiting value of 70 Å independent of the crystallization temperature in the range 195–180°C. The material develops a well‐defined lamellar structure during crystallization at the highest crystallization temperature under study (195°C). We show that by increasing the degree of supercooling it is possible to hinder the formation of the lamellar structure and crystals, resulting in a less ordered structure. We report that PGA fibers with elastic modulus in the range 20–25 GPa can be prepared by adequate control of the structure before solid‐state plastic deformation. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Characterization of eva-based adhesives containing different amounts of rosin ester or polyterpene tackifier

Different amounts (50-170 php--parts per hundred parts of EVA, 33-63 wt%) of two tackifiers (hydrogenated rosin ester, polyterpene resin) were added to an ethylene vinyl acetate (EVA) copolymer containing 28 wt% vinyl acetate. The EVA and the tackifier were characterized using infrared (IR) spectroscopy, DSC measurements, and stress-controlled plate-plate rheology. The properties and compatibility of the EVA-tackifier mixtures were studied using DSC, DMTA, and stress-controlled plate-plate rheology. Immediate adhesion was measured as a quantification of tack, and the T-peel strength of roughened styrene-butadiene rubber/EVA-tackifier adhesive joints was also obtained. The increase in the amount of tackifier noticeably changed the crystallinity of polyethylene blocks in the EVA, and the temperature at the cross-over between the curves of the storage and loss moduli as a function of the temperature was displaced to a lower value. Whereas the hydrogenated rosin ester was compatible with the amorphous ethylene vinyl acetate copolymer regions of the EVA (Tg value increased) reducing its crystallinity, the polyterpene resin was compatible with the polyethylene blocks of the EVA (T g value was not modified), increasing its crystallinity. Immediate adhesion of the EVA-tackifier mixtures was improved by adding both hydrogenated rosin ester and polyterpene tackifiers. On the other hand, there was an optimum tackifier content at which the maximum T-peel strength value was obtained.