X‐ray analysis of the structure of a wholly aromatic polyester with alkoxy sidechains (original) (raw)
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In this study we prepared a series of poly(p-biphenylene terephthalate) with alkoxy side chains attached to terephthalate moiety. The carbon number of alkoxy side chains, n, is ranged from 8 to 18. These polymers exhibited well-defined thermotropic phase behavior with a nematic phase in the higher temperature region and two ordered mesophases in the lower temperature region. One of the lower temperature mesophases was found to be a hexagonal columnar phase in the polymers with smaller values of n (8 to 12), while the other is the layered mesophase preferentially formed from the polymer with n = 18. In the polymers with n = 13, 14, and 16, the columnar and layered mesophases coexist. In these intermediate polymers, the relative amount of the layered phase to the columnar phase increases with the increase of n. Further, it increases when the mesophase temperature decreases, indicating that the layered phase is thermodynamically lower temperature mesophase than the columnar one. While the layered phase is occasionally observed in this kind of polymers with long alkyl side chains, the columnar phase is new and interesting since many chains are included in its hexagonal unit cell. The number of chains increases from 7 to 12 with an increase of n from 8 to 14. To achieve the reasonable packing of the aromatic main chains, we proposed the special hexagonal structure where the fully extended main chains are closely packed with lateral spacing of around 4.5 Å to form a honeycombed network and the molten side chains are accommodated within a resulting cylindrical domain. KEY WORDS Aromatic Polyesters / Alkyl Side Chain / Liquid Crystal / Hexagonal Columnar Phase / Layered Phase /
Macromolecular Chemistry and Physics, 1994
The influence of replacing a methylene group in the middle of the side chain of alkoxy-substituted poly(p-phenylene terephthalate)s by an oxygen atom was investigated by differential scanning calorimetry (DSC), rheological measurements and X-ray diffraction. Due to the presence of the oxygen atom the side chains of the polymer with long side chains (PTA12(O)HQ) lose their ability to crystallize. Except for this difference and a shift of the transition temperatures to lower temperatures, this polymer shows a similar phase behaviour compared to the corresponding alkoxy-substituted polyester PTA12HQ. The polymer with short side chains, PTA6(O)HQ, shows a similar behaviour as the corresponding polymer without an extra oxygen atom, PTA6HQ. Only the transition to the nematic mesophase is shifted to lower temperatures.
Macromolecules, 2013
Phase behavior and crystal structure of a series of poly(2,3-diphenyl-5-alkyl-p-phenylenevinylene) (denoted as DPn-PPV, where n represents the carbon number of the alkyl side-chain, n = 6, 8, 10, 12) were studied using differential scanning calorimetry, one-and two-dimensional (1D and 2D) wide-angle X-ray diffraction (WAXD), and selected area electron diffraction (SAED). The experimental results reveal that DPn-PPV exhibits one crystalline phase at low temperatures. On the basis of 2D WAXD and SAED patterns obtained from the oriented samples, the crystal structures are determined to be orthorhombic for DP6-PPV and monoclinic for DP8-PPV, DP10-PPV, and DP12-PPV. To account for the unusually large unit cell dimensions, we propose that the unit cell of DPn-PPV contains 4 chains (8 chemical repeat units). The complex crystal structure can be attributed to the longitudinal and transverse offsets between the neighboring chains, which shall be mainly due to the requirement of minimizing the steric hindrance caused by the attached pendent groups and maximizing the π−π interaction between the chains. The molecular packing scheme was simulated by using Cerius 2 software, of which the result agrees with the experimental data. The polarized UV−vis absorption and polarized solid-state photoluminescence (PL) property of these polymers was also investigated. The PL spectra indicated that the light emitted from the oriented film was preferentially polarized parallel to the shear direction, implying that DPn-PPV may potentially be useful in linearly polarized luminescence devices.
X-ray Microdiffraction Study of Chain Orientation in Poly(p-phenylene terephthalamide
Macromolecules, 1999
We report the bulk polymerization of ethylglycolide (3,6-diethyl-1,4-dioxane-2,5-dione), isobutylglycolide (3,6-diisobutyl-1,4-dioxane-2,5-dione), and hexylglycolide (3,6-dihexyl-1,4-dioxane-2,5dione) to high molecular weight polymers. The glycolides were prepared by two routes: the reaction of 2-bromoacyl bromides and R-hydroxy acids and the acid-catalyzed oligomerization of 2-hydroxy acids followed by thermal depolymerization of the oligomers in the presence of ZnO. Both methods gave the substituted glycolides as a mixture of diastereomers. The monomers were melt-polymerized using Sn-(2-ethylhexanoate) 2, SnO, SnBr2, SnBr4, PbO, and Ph4Sn with alcohol initiators. The polymerization rates depend on the steric bulk of the monomer, and the kinetic data for polymerizations using Sn(2ethylhexanoate)2 can be fit to an equilibrium model. High molecular weight poly(ethylglycolide), poly-(isobutylglycolide), and poly(hexylglycolide) have Tg's of 12, 22, and -37°C, respectively. These polymers are amorphous and decompose to monomer above 300°C.
A structural study of poly(p-phenylene vinylene)
Polymer, 1992
X-ray diffraction profiles of highly oriented poly (p-phenylene vinylene) (PPV) samples have been acquired at temperatures ranging from 20 to 700 K. The resulting equatorial data have been analysed using a linked-atom-least-square structure factor refinement algorithm that allows for a more complete characterization of the polymer structure and of its temperature-dependent evolution. The resulting analysis identifies strong librational motions of the phenyl rings, a finding in agreement with recent n.m.r, studies. In additon, thin films of PPV are found to possess measurable equatorial anisotropy with [200-1 and [ 110-1 lattice planes preferentially oriented parallel to the film surface.
Journal of Polymer Science Part B: Polymer Physics, 1995
The polymorphic behavior of a polyester consisting of an aromatic triad mesogen and a flexible spacer has been investigated. The effect of thermal and mechanical treatment on the appearance of two crystalline phases stable at room temperature is discussed. The molecular packing (triclinic cell, space group Pi) and the morphological parameters of the crystalline phase stabilized by drawing process are evaluated and refined. The whole-pattern method, based on the analysis of the whole x-ray diffraction pattern from fiber samples of polymer, has been employed. The molecular packing resembles very much that of polyethylene terephthalate.
Macromolecules, 1996
Nine polyesters were synthesized by polycondensation of silylated hydroquinone with substituted terephthaloyl chlorides. Three mono(alkylthio), three bis(alkylthio), and three tetra(alkylthio)terephthaloyl chlorides were used as reaction partners. The length of the alkyl side chains was varied among 8, 12, and 16 carbons. WAXS powder patterns indicate that these polyesters form three different types of sanidic layer structures in the solid state depending on the number of side chains per repeating unit. All three layer structures have an interdigitating of the alkyl side chains in common. As evidenced by 13 C NMR CP/MAS spectroscopy and DSC measurements, the longer side chains form crystalline paraffin domains between the stacks of the main chains. The monosubstituted polyesters form two different LC phases, a biaxial nematic phase with layer structure and at higher temperatures a normal nematic phase. The disubstituted polyesters exclusively form a biaxial nematic melt. Increasing length and number of the side chains reduce the isotropization temperature of all polyesters, and the tetrasubstituted polyesters form an isotropic melt directly upon melting of the crystallized side chains. This result demonstrates that rigid rod polymers are not necessarily mesogenic. The failure to form a LC phase and the good solubility in many common solvents is attributed to poor attractive electronic interactions between the main chains. A more detailed interpretation was achieved by computer modeling.
Synthesis and characterization of new aromatic polyesters containing biphenyl side groups
Journal of Applied Polymer Science, 2007
Aromatic polyesters containing biphenyl side groups were synthesized by phase-transfer catalyzed interfacial polycondensation of 1-(4-biphenylyl)-1,1-bis(4-hydroxyphenyl) ethane (BBHPE) with terephthaloyl chloride (TPC), isophthaloyl chloride (IPC), and a mixture of TPC/IPC (50 : 50 mol ratio). Copolyesters were synthesized by utilizing different molar proportions of BBHPE and 4,4′-isopropylidenediphenol (BPA) with IPC and TPC. The inherent viscosities of polyesters were in the range 0.44–1.26 dL/g. All the polyesters were soluble in organic solvents such as dichloromethane, chloroform, tetrahydrofuran, meta-cresol, pyridine, N,N-dimethylformamide, N,N-dimethylacetamide, and 1-methyl-2-pyrrolidinone. Tough, transparent, and flexible films could be cast from chloroform solutions of these polyesters. WAXD measurements indicated that all the polyesters and copolyesters were amorphous in nature. Glass transition temperature of polyesters were in the range 198–256°C, while the initial de...
Structure of crystalline polymers with unbranched long side chains
1971
The structure and thermodynamic properties of atactic and isotactic acrylic and methacrylic polymers containing 16-18 carbon atoms in the n-aliphatic side chains, and of ccpolymers of hexadecyl acrylate with isopropyl acrylate were studied by means of x-ray and differential thermal analysis. The crystallization of branched acrylic and methacrylic polymers and of acrylic copolymers proceeds in the form of a hexagonal crystal, regardless of the configuration of the backbone chain. Methods of ordering branched macromolecules are proposed, and the melting points, heats and entropies of fusion determined. The role of flexibility of the backbone chains in ordering and the crystallization processes was determined. I n the case of poly(n-alkyl acrylates) the backbone chain is involved in the crystalline lattice; this is not the case in methacrylates and copolymers of hexadecyl acrylate with isopropyl acrylate. Some similarity war assumed between the structure of biopolymers and synt.hetic branched polymers.