Prediction of miscibility regions in ternary blends of poly(styrene-stat-acrylonitrile), poly(acrylonitrile-stat-methyl methacrylate), and poly(styrene-stat-methyl methacrylate)

The miscibilities of ternary copolymer blends prepared from poly(styrene-stat-acrylonitrile), poly(styrene-stat-methyl methacrylate), and poly(methyl methacrylate-stat-acrylonitrile) were predicted by calculating the interaction parameter, χ_blend, for various blend combinations, from the corresponding binary segmental interaction parameters estimated from previous work. Binodal and spinodal curves were calculated using the Flory-Huggins theory and it was observed that the most accurate estimate of the boundary between miscible and immiscible blends was given by the spinodal. It has also been demonstrated that in some of the ternary blends with fixed copolymer compositions the miscibility of the blend can be altered by changing the ratio of the three components in the mixture. Conditions for miscibility in this ternary system, and possibly a general feature of all such systems, are (a) that at least two of the binary interaction parameters χ_ij are less than the critical value χ_crit, while the third should not be too much larger, that is, one of the copolymers may act as a compatibilizer for the other two copolymers, (b) that the difference Δχ = /χ₁₂ ? χ₁₃/ is small. © 1992 John Wiley & Sons, Inc.     

Miscibility enhancement in blends of polystyrene and polyisoprene modified with electron donor–electron acceptor groups

The use of electron donor–electron acceptor groups to enhance miscibility in polymer blends has been investigated, using the immiscible binary pair polystyrene and polyisoprene as the basic materials. These polymers have been modified by copolymerization with monomers that are either donor or acceptor groups. The copolymers synthesized were poly(styrene-stat-N-itaconimidyl-3,5-dinitrobenzoate), which contains the electron acceptor, and poly[isoprene-stat-N-(2-hydroxyethyl) carbazole methacrylate], which contains the electron donor. Blends were examined using differential scanning calorimetry and dynamic mechanical thermal analysis. The criterion of miscibility was taken to be the presence of only one glass transition temperature in the binary blend, and it was established that at least 20 mol% of the donor–acceptor units had to be incorporated into each chain before a stable one-phase blend was obtained. Miscible blends were observed to undergo a “decomplexation” reaction above the blend T_g, to form partially phase separated blends, with each phase rich in one component and diluted by the second. The value of the blend T_g was above that expected from a weighted average of those of the components, indicating that specific intermolecular interactions, probably charge-transfer complexes, which led to nonbonding crosslinking were present in the blend and stabilized the one-phase system.     

Cyclizations in hyperbranched aliphatic polyesters and polyamides

Hyperbranched aliphatic polyesters of 2,2′-bis-(hydroxymethyl) propanoic acid and hyperbranched aliphatic polyamides obtained from new carboxy- and amino-functionalized caprolactams were studied by NMR spectroscopy and MALDI-TOF mass spectrometry. Ring-chain equilibria taking place through intramolecular hydroxy-ester, carboxy-amide or amine-amide interchanges and leading to the formation of cyclic branches or end-groups were found to exert a predominant influence on the molar mass of these hyperbranched polymers. A number of intra- or intermolecular side reactions, such as the formation of ethers in polyesters and the formation of anhydrides, imides, amidines and secondary amines in polyamides were also detected and resulted in polymer crosslinking on prolonged heating. The existence of such ring-chain equilibria and side-reactions make the control of hyperbranched polymer structure much more difficult than generally accepted.     

脂肪链在吡咯-咪唑聚酰胺及其结合物与B-DNA键合中的作用

吡咯-咪唑聚酰胺是一类人工合成的能够在B-DNA小沟特异性识别碱基序列的有机小分子,并且能通过细胞膜进入细胞,调控基因的表达。它主要由五元杂环化合物N-甲基吡咯(Py)、N-甲基咪唑(Im)、N-甲基-3-羟基吡咯(Hp)芳香氨基酸及脂肪链氨基酸组成。在这种小分子对生物大分子识别事件中, 脂肪链^作为构建聚酰胺及其结合物的一部分, 在聚酰胺特异性识别DNA、延长DNA识别序列、连接分子荧光标记、对DNA指定位点的烷基化及基因调控等方面都起着非常重要的作用。本文阐述了脂肪链在上述诸方面应用的研究进展,并简要地分析了存在的问题和应用前景。     

Blend formation between homo- and co-polymers at 298.15 k,PMMA-SAN blends

Solution heats in chloroform at 25 °C have been measured experimentally for poly(methylmethacrylate) (PMMA), samples of poly(styrene-co-acrylonitrile) (SAN) containing from 5 to 37 mass% of acrylonitrile, and some PMMA-SAN blends prepared inside the miscibility range. From these data the mixing enthalpies for blend formation were obtained. Use of the mixing heats values in the framework of the Prigogine-Flory-Patterson theory allowed to calculate values of the exchange energy parameters between the components of the blends much more negative than existing literature data. Calculation of binary interaction energy parameters between the single repeat units of the copolymer from the above data, and from model compounds, clearly indicates a strong increase of the intramolecular repulsive energy between nitrile and styrene units of SAN, as compared with the interaction between the corresponding free model molecules. This revised version was published online in July 2006 with corrections to the Cover Date.     

The phase behavior of tetramethyl bisphenol-A polyarylate/aliphatic polyester blends

The phase behavior of blends of tetramethyl bisphenol-A polyarylate (TMPAr) with various linear aliphatic polyesters characterized by the ratio of aliphatic carbons to ester groups in the repeating unit, CH₂/COO = 3 ∼ 9, was examined by differential scanning calorimetry and dynamic mechanical analysis. TMPAr/aliphatic polyester blends prepared by solvent casting were found to be miscible when the CH₂/COO ratio of aliphatic polyesters was larger than 4 and up to 9. The thermodynamic interaction parameter, B for the miscible blends was determined by the analysis of the depression of the melting point of polyester using the Hoffman-Weeks method. From the analysis of the heat of mixing data using a binary interaction model, it was concluded that strong unfavorable intramolecular interaction exists between the  CH₂ and  COO units in aliphatic polyesters and that four substituted methyl groups produces more favorable effects on the miscibility TMPAr with aliphatic polyesters. © 1998 John Wiley & Sons, Inc. J Polym Sci 36 : 201–212, 1998     

Miscibility of poly(ϵ-caprolactone) and of poly(styrene-co-acrylonitrile) with poly(styrene-co-acrylic acid)

The miscibility of poly (?-caprolactone) (PCL) with poly (styrene-co-acrylic acid) (SAA) and of poly (styrene-co-acrylonitrile) (SAN) with SAA was examined as a function of the comonomer composition in the copolymers. For PCL/SAA blends it was found that PCL is miscible with SAA within a specific range of copolymer compositions. Segmental interaction energy densities were evaluated by analysis of the equilibrium melting point depression and application of a binary interaction model. The results suggest that the intramolecular repulsion in SAA copolymer plays an important role in inducing the miscibility. Additionally, the critical AA content in SAA for the blend to be homogeneous was predicted by correlating the segmental interaction energy densities with the binary interaction model. For SAN/SAA blends, it was also found that SAA is miscible with SAN within a specific range of copolymer compositions. From the binary interaction model, segmental interaction energy denisties between different monomer units were estimated from the miscibility map and were found to be positive for all pairs, indicating that the miscibility of the blends is due to the strong repulsion in the SAA copolymers.     

Miscibility of poly(ε-caprolactone), a semicrystalline polymer,with amorphous poly(styrene-4-hydroxystyrene) copolymers

The miscibility of poly(ε caprolactone) (PCL) with poly(styrene-co-4-hydroxystyrene) (PHS) copolymers was investigated as a function of comonomer composition experimentally and with calculations by two models; the binary interaction model and the association model. PCL was found to be completely miscible with PHS copolymers containing 5 or more mole percent of 4-hydroxystyrene (HS) comonomer units for the entire range of blend compositions. Segmental interaction densities, B_ijs, were determined by the analysis of the equilibrium melting point depression and by the application of the binary interaction model. By correlating the segmental interaction energy densities with the binary interaction model, thermodynamic miscibility is for comonomer composition over five mole percent of 4-hydroxystyrene, which is in agreement with the experimental phase behavior. Application of the association model for specific interactions to blends also predicts the experimental miscibility boundary and phase behavior for all the PHS copolymers/PCL blends. © 1995 John Wiley & Sons, Inc.     

Blends of poly(2,6–dimethyl–1,4–phenylene oxide) with styrene copolymers

Binary blends of poly(2,6–dimethyl–1,4–phenylene oxide) (PPE) with various styrene copolymers were investigated. Poly(styrene–co–acrylonitrile) (SAN), poly[styrene–co–(methyl methacrylate)] (SMMA), poly[styrene–co–(acrylic acid)] (SAA) and poly[styrene–co–(maleic anhydride)] (SMA) are only miscible with PPE when the amount of comonomer is rather small. From calculated binary interaction densities it can be concluded that the strong repulsion between PPE and comonomer limits miscibility. In blends of PPE with SAN, as well as with ABS, the inter-facial tension between the blend components is significantly reduced upon addition of polystyrene–block–poly–(methyl methacrylate) diblock copolymers (PS–b–PMMA) and polystyrene–block–poly (ethylene–co–butylene)–block–poly–(methyl methacrylate) triblock copolymers (PS–b–PEB–b–PMMA). They show a profound influence on morphology, phase adhesion and mechanical blend properties.     

Synthesis and liquid-crystalline properties of thermotropic polyamides containing flexible rodlike units and aliphatic spacers

New polyamides with high molecular weights consisting of flexible rod-like mesogenic units (4,4'-diphenyl and 3,4'-diphenyl moieties having bent linkages in the central parts) and aliphatic spacers were synthesized and the thermotropic liquid-crystalline properties were investigated. Differential scanning calorimetry, texture observations by polarizing microscopy, miscibility tests and X-ray analysis suggested that the polymers showed well-defined thermotropic smectic mesophases. The polyamides containing 4,4'-diphenyl moieties had higher transition temperatures and formed more stable liquid-crystalline phases than the polyamide composed of the 3,4'-diphenyl unit with a kinked bond.     

Transition from miscibility to immiscibility in blends of poly(methyl methacrylate) and styrene-acrylonitrile copolymers with varying copolymer composition: a DSC study

The glass transition and the structural relaxation processes have been studied in blends of poly(methyl methacrylate) (PMMA) and styrene-acrylonitrile (SAN) copolymers with different acrylonitrile (AN) contents. The 50/50 wt.% blend of PMMA with the SAN copolymer containing 30 wt.% of AN is immiscible, while blends with copolymers containing between 13 and 26 wt.% of AN are miscible. Thus the upper limit of miscibility is between 26 and 30 wt.% of AN. The temperature dependence of the relaxation times of the conformational rearrangements of polymer chains around the glass transition have been determined in the blends and pure components by modelling DSC thermograms obtained after different thermal histories in each sample. The slope in the Arrhenius diagram logτ vs 1/T around the glass transition temperature is significantly smaller in the blend which is closer to the upper limit of miscibility than in the other miscible blends in which SAN copolymer contains less AN. The change of slope can be ascribed to a distribution in the glass transition temperatures of the different rearranging regions, reflecting the appearance of a microheterogeneity in the blend that cannot be detected as a double glass transition in the blend.     

Miscibility and phase behavior in atactic polystyrene and poly(o-chlorostyrene-co-p-chlorostyrene) blends: Effect of polystyrene molecular weight and copolymer composition

Miscibility in blends of random copolymers of o-chlorostyrene and p-chlorostyrene [P(oClSy-co-pClS_1-y)] with 8 atactic polystyrene (aPS) fractions has been studied at temperatures ranging from 150°C to 300°C. Miscibility windows whose size depends on the molecular weight of the PS and on the copolymer composition, y, were observed for each blend. From these data, the temperature dependence of the three segmental interaction parameters required to describe this system were obtained.     

Biodegradable polycaprolactone–polyanhydrides blends

Biodegradable polymers based on a blend of polycaprolactone (PCL) and aliphatic polyanhydrides with various monomer lengths were prepared to obtain desired polymer blends for use as drug carriers. The physicochemical, mechanical, and drug‐release properties of these blends were investigated by various techniques to evaluate the uniformity degree of the polymer blends to establish their potential applications in drug delivery. The results demonstrated that the heat of fusion (ΔH) of the polyanhydride or the blend is increased in relation to the length of the aliphatic chain. However, the blends had different properties than pure polyanhydride, and the crystallization degree of the blends, as expressed by the ΔH, decreased in relation to the ΔH of the pure polyanhydride. Drug‐release studies from blends of PCL and aliphatic polyanhydrides demonstrated first‐order kinetics of the release rate. Polymer degradation was independent at the polyanhydride monomer length. On the basis of theoretical calculation of the interaction factor, a blend of PCL and poly(dodecanedeoic anhydride) was chosen for further elucidation of its thermal, mechanical, and degradation properties. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3781–3787, 2003     

Degradable polymer blends. I. Screening of miscible polymers

Blends of biodegradable polymers having properties distinct from the individual polymer components, and that are suitable for use as carriers of pharmaceutically active agents, were prepared from two or more polyanhydrides, polyesters, and mixtures of polyanhydrides and low molecular weight polyesters. The blends have different properties than the original polymers, providing a mean for altering the characteristics of the polymeric matrix without altering the chemical structure of the component polymers. Aliphatic, aromatic, and copolymers of polyanhydrides were miscible in each other and formed less crystalline compositions with a single melting point which was lower than the melting point of the starting polymers. The polyesters: poly(lactide-glycolide), poly(caprolactone), and poly(hydroxybutyric acid) presented some miscibility in each other. However, the polyanhydrides were immiscible with the polyesters resulting in a complete phase separation both in solution or in melt mixing. Only low molecular weight polyesters (in the range of 2000) of lactide and glycolide, mandelic acid, propylenefumarate, and caprolactone presented some miscibility with polyanhydrides. Similarly, poly(orthoester) and hydroxybutyric acid polymers formed a uniform mixture with the anhydride polymers which had the two melting points of the original polymers. Drug release from polymer blends composed of poly(hydroxybutyric acid) or low molecular weight poly(lactic acid) with poly(sebacic anhydride) (PSA) showed a constant release of drug for periods from 2 weeks to several months as a function of the PSA content in the blend. Increasing the content of PSA, a fast degrading polymer, increases the release rate from the blend. © 1993 John Wiley & Sons, Inc.     

A study of the blending of ethylene–styrene copolymers differing in the copolymer styrene content: Miscibility considerations

Blends of two or more ethylene–styrene (ES) copolymers that differed primarily in the comonomer composition of the copolymers were studied. Available thermodynamic models for copolymer–copolymer blends were utilized to determine the criteria for miscibility between two ES copolymers differing in styrene content and also between ES copolymers and the respective homopolymers, polystyrene and linear polyethylene. Model estimations were compared with experimental observations based primarily on melt‐blended ES/ES systems, particularly via the analysis of the glass‐transition (T_g ) behavior from differential scanning calorimetry (DSC) and solid‐state dynamic mechanical spectroscopy. The critical comonomer difference in the styrene content at which phase separation occurred was estimated to be about 10 wt % for ES copolymers with a molecular weight of about 10⁵ and was in general agreement with the experimental observations. The range of ES copolymers that could be produced by the variation of the comonomer content allowed the study of blends with amorphous and semicrystalline components. Crystallinity differences for the blends, as determined by DSC, appeared to be related to the overlapping of the T_g of the amorphous component with the melting range of the semicrystalline component and/or the reduction in the mobility of the amorphous phase due to the presence of the higher T_g of the amorphous blend component. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2976–2987, 2000     

Novel Methods for Obtaining High Modulus Aliphatic Polyamide Fibers

Super high modulus polyethylene fibers can be created by converting high molecular weight flexible PE chains into highly oriented and extended chain conformations. However, unlike polyethylene, aliphatic polyamides have very high cohesive energy and therefore cannot be easily drawn and highly oriented. This review addresses this fundamental problem by analyzing various novel approaches that can be used to suppress hydrogen bonding in these types of polyamides. Plasticization of such polymers with ammonia, iodine, salts, and Lewis acids, as well as dry spinning, wet spinning, and gel spinning, are discussed. Specialized techniques that involve vibrational zone drawing and annealing as well as laser heating zone drawing and annealing are also reviewed. Some of these methods definitely lead to remarkable improvements in initial modulus and other mechanical properties. The development of recombinant spider silk proteins as well progress in spinning these materials is also reported. The advantages and disadvantages of all of these processes are then summarized.     

Molecular mixing of incompatible polymers through formation of and coalescence from their common crystalline cyclodextrin inclusion compounds

We describe the successful mixing of polymer pairs and triplets that are normally incompatible to form blends that possess molecular‐level homogeneity. This is achieved by the simultaneous formation of crystalline inclusion compounds (ICs) between host cyclodextrins (CDs) and two or more guest polymers, followed by coalescing the included guest polymers from their common CD–ICs to form blends. Several such CD–IC fabricated blends, including both polymer1/polymer2 binary and polymer1/ polymer2/polymer3 ternary blends, are described and examined by means of X‐ray diffraction, differential scanning calorimetry, thermogravimetric analysis, Fourier transform infrared spectroscopy, and solid‐state NMR to probe their levels of mixing. It is generally observed that homogeneous blends with a molecular‐level mixing of blend components is achieved, even when the blend components are normally immiscible by the usual solution and melt blending techniques. In addition, when block copolymers composed of inherently immiscible blocks are coalesced from their CD–ICs, significant suppression of their normal phase‐segregated morphologies generally occurs. Preliminary observations of the thermal and temporal stabilities of the CD–IC coalesced blends and block copolymers are reported, and CD–IC fabrication of polymer blends and reorganization of block copolymers are suggested as a potentially novel means to achieve a significant expansion of the range of useful polymer materials. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4207–4224, 2004     

Temperature‐dependent polymer–polymer interactions in polystyrene–polyethylene blends

The effect of the temperature on the interaction between the components of an immiscible polystyrene–polyethylene blend has been analyzed with different techniques. Lap‐shear‐strength data and morphological observations indicate an enhanced interaction between the polymeric phases at elevated temperatures, at which dispersive forces are known to predominate. This raises the degree of compatibility of the polymeric components. Rheological measurements also justify the concept of increased adhesion between the components of the blend when it is processed at very high temperatures. Differential scanning calorimetry analysis lends support to an improved homogeneity of the blend at an elevated temperature; this is again consistent with an improved interaction between the blend phases. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2545–2557, 2004     

Polyamide–polyester multiblock copolymers by chain‐coupling reactions of carboxy‐terminated polymers with phenylene and pyridylene bisoxazolines

Polyamide–polyester multiblock copolymers were synthesized through the reaction of α,ω‐dicarboxy polyamides and polyesters with various arylene bis(2‐oxazoline)s. 2,2′‐(2,6‐Pyridylene)bis(2‐oxazoline) was very reactive and yielded multiblock copolymers with number‐average molar masses ranging from 15,000 to 25,000 after 30 min of reaction in the bulk at 200 °C. The molar masses and thermal properties of the resulting random multiblock copolymers (glass‐transition temperature, melting temperature, and melting enthalpy) were close to those of their alternating homologues prepared by conventional polycondensation between diamino polyamides and dicarboxy polyesters. This showed that the presence of coupling agent moieties in the polymer chains did not exert a significant influence on the block copolymer morphology. The chain‐coupling method showed several advantages over conventional polycondensation: a much shorter reaction time, a lower temperature, no byproducts, and easy control of the final copolymer properties through the mass ratio of the starting oligomers. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1331–1341, 2005     

Reactively and physically compatibilized immiscible polymer blends: stability of the copolymer at the interface

This paper reports on the interfacial behaviour of block and graft copolymers used as compatibilizers in immiscible polymer blends. A limited residence time of the copolymer at the interface has been shown in both reactive blending and blend compatibilization by preformed copolymers. Polystyrene (PS)/polyamide6 (PA6), polyphenylene oxide (PPO)/PA6 and polymethylmethacrylate (PMMA)/PA6 blends have been reactively compatibilized by a styrene-maleic anhydride copolymer SMA. The extent of miscibility of SMA with PS, PPO and PMMA is a key criterion for the stability of the graft copolymer at the interface. For the first 10 to 15 minutes of mixing, the in situ formed copolymer is able to decrease the particle size of the dispersed phase and to prevent it from coalescencing. However, upon increasing mixing time, the copolymer leaves the interface which results in phase coalescence. In PS/LDPE blends compatibilized by preformed PS/hydrogenated polybutadiene (hPB) block copolymers, a tapered diblock stabilizes efficiently a co-continuous two-phase morphology, in contrast to a triblock copolymer that was unable to prevent phase coarsening during annealing at 180°C for 150 minutes.