Liquid crystal polymers. VIII. Liquid crystalline polyesters of trans-4,4′-stilbenedicarboxylic acid and 1,3-propanediol

In our recent overview of liquid crystalline polyesters of trans-4,4′-stilbenedicarboxylic acid (SDA) and aliphatic glycols,¹ we reported that “… the 1,3-propanediol polyester did not exhibit thermotropic liquid crystallinity (no stir opalescence or DSC endotherm above T_m), perhaps because of the relatively high T_m (303°C) for a polymer of a glycol having an odd number of carbon atoms.” We now have studied the melting characteristics of another sample of this polymer more carefully and have concluded that it does exhibit a liquid crystalline mesophase over a very narrow temperature range. In this Note we give the thermal properties of this polymer and the thermal and mechanical properties of an SDA/1,3-propanediol copolyester which we also injection molded. These properties are compared and contrasted with those of the similar polyester and copolyester prepared with 1,4-butanediol instead of 1,3-propanediol.     

Effect of structure on the thermal degradation and flame retardancy of hexolic anhydride based polyesters

Based on the anhydrides like hexolic (5,6,7,8,10,10-hexachloro -3a,4,4a,5,8,8a,9,9a-octahydro-5,8-methanonaphtho-[2,3-c]-furan-1,3-dione), maleic and phthalic and diols like 1,4-butanediol, cis-2-butene-1,4-diol and 2,3-dichloro-2-butene-1,4-diol, a family of polyesters has been synthesized using azeotropic condensation technique. The structural characterizations of the polyesters have been carried out using infra-red, 1^H - and ¹³C- nuclear magnetic resonance spectroscopic methods. The thermal properties of the polyesters have been studied using thermogravimetric technique. The off-line pyrolysis of these materials was done. The qualitative and semi-quantitative analyses of the volatiles as well as the heavy mass fractions of the degradation products were carried out using a gas chromatograph coupled to a mass selective detector (GC-MSD). Thermogravimetric data indicate that the thermal stability and the char residue of the polyester resins decrease in the order 1,4-butanediol based>cis-2-butene-1,4-diol based>2,3-dichloro-2-butene-1,4-diol based polyesters. The GC-MSD data indicate that the amount of flame cooling agents (hexa-, isomeric penta-, tetra- and isomeric tri-chlorocyclopentadienes) produced during the pyrolysis of the polyesters increases in the order 2,3-dichloro-2-butene-1,4-diol based<cis-2-butene-1,4-diol based<1,4-butanediol based polyesters. The trends observed in these two parameters which are contributing factors to the flame retardancy of the polyester materials were suitably explained on the basis of the effect of the structural changes in the diol part of the polyesters on the primary degradation mechanism, the β-chain scission process.     

Photolysis of aroyl azides in 2,3-dimethyl-2-butene 2,2,3,3-tetramethyl-1-aroylaziridines and 4,4,5,5-tetramethyl-2-aryl-2-oxazolines

Irradiation of solutions of 2,3-dimethyl-2-butene and substituted aroyl azides in methylene chloride with UV light gave 2,2,3,3-tetramethyl-1-aroylaziridines, which are converted to 4,4,5,5-tetramethyl-2-aryl-2-oxazolines in the presence of sulfuric acid.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 464–466, April, 1977.     

Preparation and characterization of fibres from a thermotropic liquid crystal polyester with non-coplanar biphenylene units

Abstract

Fibres were prepared from the nematic melt of poly(2,2′-dimethyl-4,4′-biphenylene phenylterephthalate). The phenyl substitution in the terephthalic acid moiety in combination with the non-coplanar biphenyl moiety prevent crystallization of this thermotropic polyester. Oriented fibres were prepared by two different methods. Similarly to other thermotropic liquid crystal polymer fibres, chain orientation can be achieved by an elongational flow in a down draw process. This polyester also allows tensile deformation of the spun fibres around the glass transition temperature. In both routes similar degrees of orientation and mechanical properties were obtained. Tensile moduli in the order of 40–45 GPa and tensile strengths up to 550–650 MPa were obtained. The orientation function values were determined to be in the order of 0·8–0·9. A comparison with other unsubstituted thermotropic liquid crystal polyesters at the same level of orientation revealed that the moduli are the same, although the substituents increase the chain diameter. This result may be attributed to an increase of the apparent shear modulus due to an interlocking mechanism of the rigid lateral substituents.     

Photorearrangement of vinylidenecyclopropanes to 1,2,3-butatriene derivatives

[reaction: see text] Photoirradiation of benzene solutions containing 1-diarylvinylidene-2,2,3,3-tetramethylcyclopropanes (2a--d) afforded rearranged products 1,2,3-butatrienes (3a-d) in good to high yields. Photorearrangement from 2,2,3-trimethyl and 2,2- and 2,3-dimethyl derivatives 2e--g also proceeded, but the rates of the rearrangement were lower than those of 2a--d. A singlet mechanism is proposed for this photorearrangement, where alkyl migration occurs from 1,3-biradical intermediates generated via the homolysis of the C1-C2 bond. Generation of diarylvinylidene carbenes from 1,3-biradicals might be competitive with the formation of 3.     

Lithiation-methylation of thiasilinane 1-oxides

Lithiation-methylation of 3,3-dimethyl-1λ⁴,3-thiasilinane 1-oxide and 4,4-dimethyl-1λ⁴,4-thiasilinane 1-oxide under the action of butyllithium or lithium diisopropylamide and methyl iodide was studied. In both cases, monomethylation proceeds selectively α to the sulfoxide group to form 2,3,3-trimethyl-1λ⁴,3-thiasilinane 1-oxide and 2,4,4-trimethyl-1λ⁴,4-thiasilinane 1-oxide, respectively. Subsequently, 2,3,3-trimethyl-1λ⁴,3-thiasilinane 1-oxide undergoes monomethylation into the same α position to give 2,2,3,3-tetramethyl-1λ⁴,3-thiasilinane 1-oxide, while 4,4-dimethyl-1λ⁴,4-thiasilinane 1-oxide is dimethylated into the neighboring α’ position to form two stereoisomers of 2,4,4,6-tetramethyl-1λ⁴,4-thiasilinane 1-oxide with axial-equatorial or equatorial-equatorial methyl groups in the 2 and 6 positions.     

Preparation and properties of polyesters from diphenylmethane-4,4′-di(methylthiopropionic acid) and aliphatic diols

The new linear polyesters containing sulfur in the main chain were obtained by melt polycondensation of diphenylmethane-4,4′-di(methylthiopropionic acid) with ethanediol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,2-propanediol, 1,3-butanediol, and 2,2′-oxydiethanol. Low-molecular weights, low-softening temperatures and, very good solubility in organic solvents are their characteristics. The structure of all polyesters was determined by elemental analysis, FT-IR and ¹H-NMR spectroscopy, and x-ray diffraction analysis. The thermal behavior of these polymers was examined by differential thermal analysis (DTA), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). The kinetics of polyesters formation by uncatalyzed melt polycondensation was studied in a model system: diphenylmethane-4,4′-di(methylthiopropionic acid) and 1,4-butanediol or 2,2′-oxydiethanol at 150, 160, and 170°C. Reaction rate constants (k₃) and activation parameters (ΔG^≠, ΔH^≠, ΔS^≠) from carboxyl group loss were determined using classical kinetic methods. © 1997 John Wiley & Sons, Inc.     

A monotropic liquid crystal polyester with a biphasic nematic-smectic phase

The polyesters made from the condensation of isophthalic acid (IA) or terephthalic acid (TA) with the mesogenic diol 4,4′-bis (6-hydroxy hexoxy)biphenyl (BHHBP) are both reported to show a smectic mesophase. However, in our previous work, we found evidence for a mesophase in the polyester containing BHHBP and IA, but not in the one with BHHBP and TA. For the BHHBP-IA polyester, we thought the phase sequence on cooling was I → S_A → K, while on heating the situation was unresolved; there was some indication that on heating, a K → I transition occurs without any intervening mesophase. In other words, it was suspected that the mesophase in the IA polyester was monotropic. In this work, we have now obtained firm evidence that the mesophase behavior of the BHHBP-IA polyester is indeed monotropic. Further, an additional complexity has been found: on cooling, there is in fact a nematic phase, besides a smectic A, and a crystal phase. However, the mesophase appears to be complex. As the nematic and smectic textures occurred simultaneously, it seems that the mesophase is a nematic-smectic biphase. © 1996 John Wiley & Sons, Inc.     

生物可降解聚丁二酸/甲基丁二酸丁二酯系列共聚物的合成和表征

摘要合成了一系列聚丁二酸/甲基丁二酸丁二醇共聚酯(PBSM), 利用DSC, ¹H NMR和X射线衍射等方法对共聚物组成、 热学性能、 结晶性能、 等温结晶行为进行了研究. 结果表明, 引入甲基丁二酸共聚单元较为显著地改变了聚丁二酸丁二酯(PBS)的热学性能, 利用Hoffman\|Weeks方程得到的共聚物平衡熔点随共聚物的组分含量增加而降低, 玻璃化转变温度亦有所降低, 熔点则符合无规共聚物的Flory方程. 此外, 利用Avrami方程分别研究了均聚物PBS及共聚物PBSM-20的等温结晶行为, 结果表明, 在所研究的温度范围内, 聚酯结晶速率随温度升高而降低, PBS和PBSM\-20的Avrami指数分别介于2.8~3.0和2.7~3.0之间, 结晶方式为三维生长异相成核, 而X射线衍射测试结果表明晶体结构几乎不变.     

A stereochemical investigation of 2-methyl- and 2,5-dimethyl-3-phenyl-1,3-oxazolidines using NMR

The stereochemical properties of two 2-methyl-3-phenyl-1,3-oxazolidines and two of its 5-methyl substituted and four of its 2,5-dimethyl substituted derivatives have been investigated by pmr and cmr methods. The compounds of 2,5-dimethyl-3-phenyl-1,3-oxazolidines exist in isomeric cis and trans forms at the two methyl groups on the heterocyclic ring.     

Mesophase stability in binary mixtures of monotropic nematogens

Binary phase diagrams were constructed from laterally substituted methyl azo/ester derivatives, namely 4-(4″-substituted phenylazo)-3-methyl phenyl-4″-alkoxy benzoates (In_a–d). In this group of compound the unsubstituted and chloro-substituted derivatives possess the nematic phase monotropically, while the nitro and methyl analogues are enantiotropically nematogenic. The binary phase diagrams constructed were made once from the monotropic nematogens with each other, and another with the enantiotropic nematogens. In both the cases enantiotropic nematic phase was observed that covers a wide range of composition. The mesophase behaviour of all binary mixtures was investigated by differential scanning calorimetry (DSC) and polarised light microscopy (PLM). The nematic phase was exhibited in all binary mixtures. Independent of the alkoxy chain length, the entropy change, ΔS_N–I of the N–I transition of pure components was found to vary irregularly with the anisotropy of polarisability (?α_X) of the polar substituent, X.     

Preparation and characterization of fibres from a thermotropic liquid crystal polyester with non-coplanar biphenylene units

Fibres were prepared from the nematic melt of poly(2,2'-dimethyl-4,4'-biphenylene phenylterephthalate). The phenyl substitution in the terephthalic acid moiety in combination with the non-coplanar biphenyl moiety prevent crystallization of this thermotropic polyester. Oriented fibres were prepared by two different methods. Similarly to other thermotropic liquid crystal polymer fibres, chain orientation can be achieved by an elongational flow in a down draw process. This polyester also allows tensile deformation of the spun fibres around the glass transition temperature. In both routes similar degrees of orientation and mechanical properties were obtained. Tensile moduli in the order of 40-45 GPa and tensile strengths up to 550-650 MPa were obtained. The orientation function values were determined to be in the order of 0·8-0·9. A comparison with other unsubstituted thermotropic liquid crystal polyesters at the same level of orientation revealed that the moduli are the same, although the substituents increase the chain diameter. This result may be attributed to an increase of the apparent shear modulus due to an interlocking mechanism of the rigid lateral substituents.     

Synthesis of quinoxaline 1,4-dioxides from 4,5(6,7)-dimethylbenzofuroxan

In this study, novel substituted quinoxaline 1,4-dioxides were synthesized from novel substituted benzofuroxan. 4,5(6,7)-Dimethylbenzofuroxan 3 was prepared by the thermal decomposition of 2,3-dimethyl-6-nitrophenylazide 2 . Novel quinoxaline 1,4-dioxides derivatives were obtained using compound 3 and the enolic form of 1,3-diketones 4 catalyzed by silica gel or molecular sieves. These reactions gave isomeric quinoxaline 1,4-dioxides 5 and 6 . These reactions of compound 3 may involve tautomers 4,5-dimethylbenzofuroxan 3a , 6,7-dimethylbenzofuroxan 3b on the surface of a solid catalyst.     

Effects of geminal methyl groups on the tunnelling rates in the ring opening of cyclopropylcarbinyl radical at cryogenic temperature

CVT + SCT calculations on the rate of tunnelling at 20 K in the ring opening of cyclopropylcarbinyl radical, substituted with geminal methyl groups at a ring carbon (1b), have been performed. The calculations predict that, contrary to expectations based on the effect of mass on the rate of tunnelling, the geminal methyl substituents in 1b should make the rate of ring opening to 1,1-dimethyl-3-butenyl radical (2b) 10(4) times faster than the rate of ring opening of unsubstituted cyclopropylcarbinyl radical (1a) to 3-butenyl radical (2a) and almost 10(6) times faster than the rate of ring opening of 1b to 2,2-dimethyl-3-butenyl radical (2c). The reasons for these unexpected findings are discussed.     

Influence of lateral substituents on thermal behavior and solubility of aromatic LC-polyesters

Structure - property relations of substituted para-linked aromatic homopolyesters are reported. Thermotropic liquid-crystalline substituted poly (1,4-phenylene terephthalate)s with phase transition temperatures less than 230 °C and good solubility in common organic solvents have been synthesized. If a noncoplanar 2,2′-disubstituted biphenylene moietyis combined with a monosubstituted phenylene moiety with sufficient bulky substituent, polyester with similar properties were obtained. Although these polyesters are soluble up to high concentrations, no lyotropic liquid-crystalline behavior was observable.     

Thermotropic homopolyesters. IV. Study of fiber formation

We report a melt spinning and viscosity study of two semiflexible homopolyesters containing both rigid and flexible segments in the repeating unit. Single filaments of the polyesters formed from 4,4′-diacetoxybiphenyl and azelaic acid (PB7) and sebacic acid (PB8), and from 4′-hydroxyphenyl-4-hydroxycinnamate and azelaic acid (C7), were spun at temperatures between 205 and 255°C. The temperature dependence of the Newtonian melt viscosity of PB7 and C7 was investigated, and a range of molecular weights was studied for PB7. The spinning parameters, fiber characteristics, and viscosity-temperature behavior are related to the type of mesophase formed. The mechanical properties of fibers spun from both the nematic and smectic phases of these semiflexible chain polymers were poor. Increasing the polymer molecular weight or extrusion rate only afforded a modest improvement in fiber properties. Most polymers could not be spun at temperatures corresponding to the existence of the single mesophase. Hence the low viscosity typical of the nematic mesophase is not necessarily an advantage in fiber formation from the melt. It appears from these results that this type of polyester does not possess adequate chain extension to develop ultrahigh-modulus properties. The director, which describes the local orientation of molecules within the mesophase, may undergo more frequent variations than is the case for rigid chain polyesters. Mechanisms relevant to flexible polymers may contribute to the development of orientation for this class of nematogenic melts.     

X-ray structural studies of several novel nitrocyclopropanes

The x-ray crystal structures forcis,cis- andtrans,trans- 2,3-dimethyl-1-nitrocyclopropanecarboxylic acid, 2,2,3,3-tetramethyl-1-nitrocyclopro-panecarbonitrile, 2,2,3,3-tetramethyl-1-nitrocyclo-propanecarboxamide, andtrans,trans,trans,trans-2,2,3,3-tetramethyl-1,1-dinitrobicyclopropyl are reported. Contrary to expectations, -accepting groups that are syn to dimethyl substituents prefer a conformation perpendicular to the three-membered ring when there is an sp² electron-withdrawing substituent also bonded to the same carbon atom. Ab initio calculations are reported for model compounds and these results are compared with the experimentally determined ones.     

Fischer indolisation of 2,6-dialkyl and 2,4,6-trialkylphenylhydrazones of diketones and ketoesters

Unlike the migration of a methyl group observed in the ZnCl₂ or acetic acid-catalysed indolisation of phenylhydrazones, dry ethanolic HCl catalysed indolisation of 2,6-dimethyl- and 2,4,6-trimethylphenylhydrazones of various substituted butane-2,3-diones and ethyl pyruvates yields 7-methyl- and 5,7-dimethyl-3-substituted indoles indicating elimination of an ortho-methyl group during indolisation.     

Reaction of dichlorocarbene with 2,3-dihydro-5,6-dimethyl-1,4-oxathiin and 2,3-dihydro-5,6-dimethyl-1,4-dithiin

Dichlorocarbene, generated from ethyl trichloroacetate and sodium ethoxide, reacts with 2,3-dimethyl-5,6-dihydro-1,4-oxathiin to give 7,7-dichloro-1,6-dimethyl-2-oxa-5-thiabicyclo[4,1,0]heptane, and with 2,3-dimethyl-5,6-dihydro-1,4-dithiin to give 6-chloro-2,3-dihydro-7-methyl 5-methylene-5(H)-1,4-dithiepin. Both products were oxidised to the corresponding sulfone.     

SYNTHESIS OF NEW BENZOSULFOXIDE MACROCYCLIC COMPOUNDS

Bis(dibenzosulfoxo)-27,30,35,38-tetramethyl-24-crown-6, bis(dibenzosulfoxo)-21,24,29,32-tetramethyl-18-crown-4, dibenzosulfoxo-15,18-dimethyl-12-crown-3 and dibenzosulfoxo-12,15-dimethyl-9-crown-2 macrocycles are synthesized by the reaction of 2,2′-sulfinyl-bis(4-methyl phenol)and 1,2-dibromoethane and diethyleneglycol di-p-toluenesulfonate.