Nonequilibrium liquid-liquid phase separation in crystallizable polymer solutions (original) (raw)
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Angewandte Makromolekulare Chemie, 1999
Polyethers based on bis(2-chloroethyl) ether and various bisphenols were obtained using a phase transfer catalysis technique in a liquid /liquid system. 4, bisphenol A, sulfide were used. Only the polymers with azobenzene and biphenyl units exhibited mesophases, since the others have semi-crystalline or amorphous structures. The polymers were characterized by 1 H NMR, DSC and optical microscopy in polarized light. The molecular weights of the samples were low, situated in the oligomeric domain. The various transfer rates of the bisphenols from the aqueous to the organic phase, in some cases, led to very different copolymerization ratios as compared to the feed ratios. The LC polymers exhibited monotropic mesophases, probably for conformational reasons. A comparison between similar polyether structures containing the diethyletheric spacer and an oxetanic one was effectuated. ZUSAMMENFASSUNG: Polyether aus Bis(2-chlorethyl)ether und verschiedenen Diphenolen wurden durch Phasentransferkatalyse in einem zweiphasigen flüssigen System hergestellt. Als Diphenol-Verbindungen wurden 4,49-Dihydroxyazobenzol, 4,49-Dihydroxybiphenyl, Bisphenol A, 2,7-Dihydroxynaphthalin und 4,49-Dihydroxydiphenylsulfid eingesetzt. Lediglich die Polymeren mit Azobenzol-und Diphenyleinheiten bildeten Mesophasen, wohingegen die anderen Produkte semikristalline oder amorphe Strukturen ausbildeten. Die Polymeren wurden durch 1 H NMR, DSC und Polarisationsmikroskopie charakterisiert. Die Proben besaßen niedrige Molekulargewichte im Bereich von Oligomeren. Die unterschiedlichen Transfergeschwindigeiten der Diphenole von der wäßrigen in die organische Phase führten in einigen Fällen zu vom Ausgangsmonomerverhältnis sehr verschiedenen Copolymerzusammensetzungen. Die flüssigkristallinen Polymeren bildeten, vermutlich aufgrund der Molekülkonformation, monotrope Mesophasen. Die Ergebnisse wurden mit denen von Polyethern ähnlicher Struktur mit Diethylether-und Oxetan-Spacern verglichen.
Liquid crystalline behavior of polymers; fundamentals, synthesis and characterizations
2019
As it is well known that, materials that have liquid crystalline properties are early discovered long time ago. These type of materials can carry both type of different types of matter (conventional liquid and solid crystal). Upon inserting such properly to the backbone of any polymer structure. It can enhance its amazing properties to be considered as one of the most and effective smart materials in the last few decades. The current work presents a short summary about the historical overview and some important basic fundamentals of liquid crystalline materials and its different types of calcifications. In addition, a detailed study about liquid crystalline polymers (LCps) have been described classifications and synthetic method. Both types of these polymers were discussed including main chain or side chain polymers. The effects of mesogenic groups, structural unit, substituents and flexible spacers on the thermotropic properties were also displayed. Finally, a brief overview for th...
Open Journal of Organic Polymer Materials, 2013
A new homologous series of thermotropic liquid crystalline copoly(arylidene-ether)s based on 4-teriary butyl cyclohexanone moiety were synthesized by solution polycondensation of 4,4'-diformyl-α,ω-diphenoxyalkanes, I ad or 4,4'diformyl-2,2'-dimethoxy-α,ω-diphenoxyalkanes II ad with the 4-teriary butyl-cyclohexanone III and cyclopentanone. A model compound IV was synthesized from the monomer III with benzaldehyde and characterized by elemental and spectral analyses. The inherent viscosities of the resulting polymers were in the range 0.22-0.92 dI/g. All the copoly(arylidene-ether)s were insoluble in common organic solvents but dissolved completely in concentrated H 2 SO 4 and formic acid. The mesomorphic properties of these polymers were studied as a function of the diphenoxyalkane space length. Their thermotropic liquid crystalline properties were examined by DSC and optical polarizing microscopy and demonstrated that the resulting polymers form nematic mesophases over wide temperature ranges. The thermogravimetric analyses of those polymers were evaluated by TGA and DSC measurements and correlated to their structural units. X-ray analysis showed that copolymers having some degree of crystallinity in the region 2 = 5°-60°. In addition, the morphological properties of selected examples were tested by Scanning electron microscopy.
Macromolecules, 1996
The phase separation and the coarsening process of polymer mixtures with a thermotropic liquid crystalline polymer (LCP) as one component are investigated. The LCP used is a main-chain type copolyester X-7G, comprised of p-hydroxybenzoic acid (60 mol %) and ethylene terephthalate (40 mol %) units. The isotropic, transparent, and homogeneous test specimens of the 50/50 mixtures of X-7G and poly(ethylene terephthalate) (PET) were prepared by a rapid solution-casting with an organic solvent. The specimens were heated rapidly to the test temperature (T jump), and an isothermal phase separation process was investigated at real time and in situ under a polarized light microscope. A rapid phase separation was observed, when the temperature was higher than the melting points of PET and X-7G, allowing us to study the late stage spinodal decomposition into anisotropic and isotropic liquid phases. The following sequences of the decomposition mechanisms were found as time elapses in this stage: (i) the self-similar growth of a percolating network of the anisotropic liquid phase rich in X-7G in the isotropic matrix phase rich in PET, (ii) disruption of the percolating network and shrinkage of the disrupted fragments into the anisotropic droplets, and (iii) diffusion and coalescence of the anisotropic droplets. The two important factors, transesterification and the liquid crystal effect which can affect the phase separation, are also discussed in the text. †
Macromolecules, 1999
A series of liquid crystalline polyethers has been synthesized from 1-(4-hydroxy-4′biphenylyl)-2-(4-hydroxyphenyl)propane and R,ω-dibromoalkanes [TPP(n)]. From the differential scanning calorimetry experiments, the TPP(n)odd)s show multiple phase transitions during cooling and heating. For each TPP(n)odd) the supercooling dependence of these transitions is found to be small. A phase diagram of the transition temperatures and the enthalpy and entropy changes of the transitions with respect to the number of methylene units (n) for TPP(n)odd)s have been obtained. Analyses have been conducted regarding the contributions of both the mesogenic groups and the methylene units to the differently ordered structures. Identification of the ordered structures in each phase has been carried out by combining wide angle X-ray powder and fiber diffraction experiments at different temperatures with polarized light and transmission electron microscopy experiments on the liquid crystal morphology and defects. It is found that for TPP(ne13)s the highest temperature transition is from the isotropic melt to a nematic phase. However, for TPP(ng15)s, the isotropic melt directly converts to a smectic F phase having a monoclinic unit cell (a pseudohexagonal packing tilted toward a side). The WAXD fiber patterns for this phase show that the chain orientation is parallel to the fiber direction. For TPP(ne13)s formation of a smectic F phase with a monoclinic unit cell from the nematic phase can also be determined and the WAXD fiber pattern shows that the chain orientation is at an angle ranging between 0 and 20°w ith respect to the fiber direction. With an increase in the number of methylene units, this angle gradually decreases until n) 15, where this angle becomes zero. Further cooling leads to a smectic crystal G phase for all TPP(n)odd)s, and the different chain orientations with respect to the fiber direction in the WAXD fiber patterns still exist. TPP(ne9)s remain in the smectic crystal G phase down to their glass transition temperatures, while TPP(ng11)s form a smectic crystal H phase (a tilted herringbone, orthorhombic packing tilted toward the b-axis side, and a > b) in a low temperature range.
European Polymer Journal, 2003
The paper presents a study on the relationship between the structure of macromolecular chain and its capacity to generate a mesophase, when mesogens with an azobenzene structure are implied. The polymers have been synthesized by phase transfer catalysis starting from 1,9-dichlorononane and different bisphenols: diphenyl-4,4 0 -bis[(azo-4-)phenol], 4,4 0 -dihydroxyazobenzene, 4,4 0 -dihydroxydiphenyl, bisphenol A and 4,4 0 -dihydroxybenzophenone. The polymers have been characterized by 1 H-NMR spectroscopy, DSC calorimetry, optical microscopy in polarized light and thermogravimetrical analysis. Theoretical conformational studies, using molecular simulations have also been performed. Due to their particular geometry, bis-(azobenzene) units are better mesogenic groups as compared with the azobenzene ones. The highly aromatic structure makes impossible the samples isotropisation, as the degradation processes starting advance. For these polymers, under UV irradiation, due to the presence of two azo groups in each mesogen unit, strong conformational modifications are expected. The replacement of the bis-(azobenzene) moieties with azobenzene ones reduces the transition temperatures, making possible the samples isotropisation.
Journal of Polymer Science Part A: Polymer Chemistry, 1997
A series of wholly aromatic, thermotropic polyesters, derived from 3,3-bis (phenyl)-4,4-biphenol (DPBP), nonlinear 4,4-benzophenone dicarboxylic acid (4,4-BDA), and various linear comonomers, were prepared by the melt polycondensation reaction and characterized for their thermotropic properties by a variety of experimental techniques. The homopolymer of DPBP with 4,4-BDA had a fusion temperature (T f) at 265ЊC, exhibited a nematic phase, and had a liquid crystalline range of 105ЊC. All of the copolyesters of DPBP with 4,4-BDA and either 30 mol % 4-hydroxybenzoic acid (HBA), 6-hydroxy-2-naphthoic acid (HNA), or 50 mol % terephthalic acid (TA), 2,6-naphthalenedicarboxylic acid (2,6-NDA) had low T f values in the range of 220-285ЊC, exhibited a nematic phase, and had accessible isotropization transitions (T i) in the range of 270-420ЊC, respectively. Their accessible T i values would enable one to observe a biphase structure. Each of the copolymers with HBA or HNA had a much broader range of liquid crystalline phase. In contrast, each of the copolymers with TA or 2,6-NDA had a relatively narrow range of liquid crystalline phase. Each of these polyesters had a glassy, nematic morphology that was confirmed with the DSC, PLM, WAXD, and SEM studies. As expected, they had higher glass transition temperatures (T g) in the range of 161-217ЊC than those of other liquid crystalline polyesters, and excellent thermal stabilities (T d) in the range of 494-517ЊC, respectively. Despite their noncrystallinity, they were not soluble in common organic solvents with the exception that the homopolymer and its copolymer with TA had limited solubility in CHCl 3. However, they were soluble in the usual mixture of p-chlorophenol/1,1,2,2-tetrachloroethane (60/40 by weight) with the exception of the copolymer with 2,6-NDA. ᭧ 1997
Macromolecules, 2007
Isotactic propylene-ethylene (iPPEt) and propylene-butene (iPPBu) copolymers have been prepared with different metallocene catalysts. The different influences of stereodefects (isolated rr triads), ethylene and butene comonomeric units on the crystallization of the R and γ forms of isotactic polypropylene (iPP) have been discriminated. Both iPPEt and iPPBu copolymers crystallize from the melt as mixtures of the R and γ forms. The amount of the γ form increases with increasing crystallization temperature, comonomer concentration, and content of rr stereodefects. In iPPBu copolymers, the amount of the γ form decreases for concentration of butene units higher than 10-14 mol % and is always lower than that crystallized in iPPEt copolymers. Butene units, therefore, favor crystallization of the γ and R forms at low and high concentrations, respectively. These data have indicated that the crystallization of the γ form of iPP is not only related to the value of the average length of the regular propylene sequences 〈L iPP 〉, but is also related to the inclusion of stereodefects and constitutional defects in the crystals of iPP. Very different proportions of ethylene and butene units are included in crystals of the R and γ forms of iPP. Butene units are included indifferently in crystals of the R and γ forms, but probably more easily in the R form at high concentrations. Therefore, at low butene concentration, up to nearly 10 mol %, the effect of shortening of the length of regular isotactic propylene sequences prevails and induces crystallization of the γ form. For butene concentrations higher than 10 mol %, the effect of inclusion of butene units in crystals of the R form prevails, producing a decrease of the amount of the γ form and crystallization of the pure R form for butene contents higher than 30 mol %.
Current Topics in Liquid-Crystalline Polymers
Liquid-Crystalline Polymers, 1990
This chapter provides an overview of current researches on liquid crystalline polymers (LCP's). Topics include syntheses of main-chain and side-chain LCP's, structured characterization of LCP's and LCP networks and rheology and processing. Applications of LCP/polymer blends as self-reinforced polymers and electro-optical meterials are also discussed. Liquid crystal is a term that is now commonly used to describe materials that exhibit partially ordered fluid phases that are intermediate between the three dimensionally ordered crystalline state and the disordered or isotropic fluid state. Phases with positional and/or orientational long-range order in one or two dimensions are termed mesophases. As a consequence of the molecular order, liquid crystal phases are anisotropic, i.e., their properties are a function of direction. Although the technical applications of low molar mass liquid crystals (LC) and liquid crystalline polymers (LCP) are relatively recent developments, liquid crystalline behavior has been known since 1888 when Reinitzer (1) observed that cholesteryl benzoate melted to form a turbid melt that eventually cleared at a higher temperature. The term liquid crystal was coined by Lehmann (2) to describe these materials. The first reference to a polymeric mesophase was in 1937 when Bawden and Pirie (2) observed that above a critical concentration, a solution of tobacco mosaic virus formed two phases, one of which was birefringent. A liquid crystalline phase for a solution of a synthetic polymer, poly(7-benzyl-I^glutamate), was reported by Elliot and Ambrose (4) in 1950. Modern-day interest in LCPs had its origin with the molecular theories of Onsager (5) and Flory (6). They predicted that rod-like molecules would spontaneously order above a critical concentration that depended on the aspect ratio of the molecule. These theories were later expanded to include other effects such as polydispersity (2) and partial rigidity (8).