Synthesis and characterization of polyamides and poly(amide-imide)s based on ether-sulfone-diamines

A series of polyamides and poly(amide-imide)s were prepared by the direct polycondensation of 4,4′-[sulfonylbis(1,4-phenyleneoxy)]dianiline or 4,4′-[sulfonylbis(2,6-dimethyl-1,4-phenyleneoxy)]dianiline with aromatic dicarboxylic acids and phthalimide unit-bearing dicarboxylic acids in a N-methyl-2-pyrrolidone (NMP) solution containing dissolved calcium chloride using triphenyl phosphite and pyridine as condensing agents. The inherent viscosities of the resulting polymers were above 0.45 dL/g and up to 1.70 dL/g. Except for the polyamides derived from terephthalic acid and 4,4′-biphenyldicarboxylic acid, all the other polyamides and all poly(amide-imide)s were readily soluble in polar organic solvents such as NMP, N, N-dimethylacetamide (DMAc), N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), and m-cresol, and afforded transparent and tough films by solution-casting. Most of the polymers showed distinct glass transition on their differential scanning calorimetry (DSC) traces and their glass transition temperatures (T_g) stayed between 140–264 °C. The methyl-substituted polymers showed higher T_gs than the corresponding unsubstituted counterparts. The results of the thermogravimetry analysis (TGA) revealed that all the methyl-substituted polymers showed lower initial decomposition temperatures than the unsubstituted ones.     

Synthesis and properties of amphotropic hydrogen bonded liquid crystalline (LC) poly(ester amide)s (PEA): effect of aromatic moieties on LC behavior

Twelve hydrogen bonded aromatic-aliphatic poly(ester amide)s differing in the structures of their aromatic moieties (isophthalic, terephthalic, 2,6-naphthyl and 4,4′-biphenyl moieties of the dicarboxylic acid and phenylene and xylylene moieties of the amido diol part) were prepared by the polycondensation of amido diols with acid chlorides of isophthalic acid, terephthalic acid, 2,6-naphthalic dicarboxylic acid and 4,4′-biphenyl dicarboxylic acid, respectively. The amido diols were prepared by the aminolysis of γ-butyrolactone with hexamethylene diamine, para phenylene diamine and para xylylenene diamine, respectively. The PEAs were characterised for elemental analysis, FTIR, ¹³C NMR, TGA, DSC, POM, isothermal viscosity measurements and WAXD. Here we are presenting the effect of aromatic moieties on the thermotropic and lyotropic (amphotropic) properties of PEAs. These PEAs are essentially constituted of six types of structural entities, i.e. isophthalic, terephthalic, 2,6-naphthalic and 4,4′-biphenyl moieties containing dicarboxylic acid and the aliphatic, aromatic (phenylene and xylylene moieties) of the di-amide linkage of the amido diol part. The structure of the polymers even in the mesophase is dominated by hydrogen bond interaction between the adjacent chains and also inter plane mesogenic interaction between the rigid aromatic group. It was observed morphologically that the formation of different forms of nematic/smectic/columnar/spherullitic phases in PEAs are due to the delicate balance of self assembling through hetero intermolecular hydrogen bonded amide-amide and amide-ester net works and also inter-plane mesogenic interactions.     

Poly(ethylene terephthalate‐co‐isophthalate) copolyesters obtained from ethylene terephthalate and isophthalate oligomers

A series of poly(ethylene terephthalate‐co‐isophthalate) copolyesters containing upto 50%‐mole of isophthalic units were prepared by polycondensation from ethylene terephthalate and ethylene isophthalate fractions of linear oligomers containing from 5 to 6 repeating units in average. The polyesters were obtained in good yields and with high‐molecular‐weights. The microstructure of the copolyesters was studied as a function of reaction time by ¹³C‐NMR showing that a random distribution of the comonomers was achieved since the earlier stages of polycondensation. The melting temperature and enthalpy of the copolyesters decreased with the content of isophthalic units so that copolyesters containing more than 25% of these units were amorphous. Isothermal crystallization studies made on crystalline copolyesters revealed that the crystallization rate of copolyesters decreased with the content in isophthalic units. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Synthesis and characterization of new optically active and photolable poly (amide-imide)s from N,N ′-(3,3′,4,4′-benzophenonetetracarboxylic)-3,3′,4,4′-diimido-di-L-methionine and different diamines

Summary N,N^′-(3,3^′,4,4^′-benzophenonetetracarboxylic)-3,3^′,4,4^′-diimido-di-L-methionine (3) was prepared from the reaction of 3,3^′,4,4^′-benzophenonetetracarboxylic-3,3^′,4,4^′-dianhydride (1) with L-methionine (2) in a solution of (glacial acetic acid/pyridine) at refluxing temperature. The phosphorylation polycondensation of the diimide-diacid monomer (3) with 1,3-phenylenediamine (4a), 1,4-phenylenediamine (4b), 2,6-diaminopyridine (4c), 3,5-diaminopyridine (4d), 4,4^′-diaminobiphenyl (4e) and 4,4^′-diaminodiphenylsulfone (4f) was carried out in N-methyl-2-pyrolidone (NMP). The resulting poly (amide-imide)s showed admirable moderate inherent viscosities (0.23–0.48 dl g^-1), good thermal stability and improved optical activity. All of the above compounds were fully characterized by IR spectroscopy, elemental analysis and specific rotation. Some structural characterization and physical properties of these new poly (amide-imide)s are presented.     

A new and efficient synthetic method of a liquid crystalline epoxy resin with biphenol and aromatic ester group

This article describes a high efficient and economical method to synthesize a liquid crystalline epoxy resin (LCER) containing biphenol and aromatic ester group, 3,3′,5,5′-tetramethylbiphenyl-4,4′-diyl bis(4-(oxiran-2-ylmethoxy) benzoate) (4). First, 3,3′,5,5′-tetramethylbiphenyl-4,4′-diyl bis(4-hydroxybenzoate) (3) was prepared by direct esterification of 3,3′,5,5′-tetramethylbiphenyl-4,4′-diol (2) with p-hydroxybenzoic acid (1) in the presence of a certain amount of p-toluene sulfonic acid (p-TSA) as catalyst. And then (4) was synthesized by the reaction of (3) with epichlorohydrin. The chemical structure, melting range, and liquid crystalline phase transition behavior of (4) were characterized by FT-IR, ¹H-NMR, ¹³C-NMR, mass spectroscopy, differential scanning calorimetry (DSC), and polarized optical microscopy (POM).     

Aliphatic-aromatic poly(ester-imide)s from diisocyanates containing ester groups and aromatic dianhydrides

Summary Four new ester group containing diisocyanates, viz., 3,3′-(glutaryldioxy)diphenyl diisocyanate, 4,4′-(glutaryldioxy)diphenyl diisocyanate, 3,3′-(adipoyldioxy)diphenyl diisocyanate, and 4,4′-(adipoyldioxy)diphenyl diisocyanate were synthesized from the corresponding dicarboxylic acids via the Curtius rearrangement reaction. These diisocyanates were polycondensed with pyromellitic dianhydride (PMDA) and benzo-phenonetetracarboxylic dianhydride (BTDA) in dimethylacetamide to yield eight aliphatic-aromatic polyimides containing ester groups in the backbone with inherent viscosities in the range 0.25–0.70 dL/g. These poly(ester-imide)s were semicrystalline in nature and exhibited no weight loss below 300°C in air. N.C. L. Commun. No. 5330     

Synthesis and trans-ureation of N,N’-diphenyl-4,4′-methylenediphenylene biscarbamate with diamines: a non-isocyanate route (NIR) to polyureas

A non-isocyanate route (NIR) of making polyureas of high molecular weight has been found through trans-ureation of N,N’-diphenyl-4,4′-methylenediphenylene biscarbamate (4,4′-DP-MDC) with a variety of diamines and mixed diamines. The preparation of 4,4′-DP-MDC was achieved readily by carbonylation of 4,4′-methylenedianiline (4,4′-MDA) with diphenyl carbonate (DPC) using organic acids as catalysts. It was found that the highest yield (99%) of pure 4,4′-DP-MDC can be isolated in a toluene solution under mild conditions co-catalyzed by benzoic acid and tertiary amine. Trans-ureation of 4,4′-DP-MDC with aliphatic amines indicated that the process is a highly solvent dependent process and was found to be extremely facile in dimethyl sulfoxide (DMSO) at 80 °C and in tetramethylene sulfone (TMS) at 140 °C in absence of any catalyst. Particularly, the most effective polymerization process was developed using tetramethylene sulfone (TMS) as the solvent under reduced pressure for concurrently distilling off phenol from the reaction mixture during the polymerization in a shifting equilibrium towards polyurea. However, this solvent-assisted trans-ureation was found to be in-efficient when N,N’-dimethyl-4,4′-methylenediphenylene biscarbamate (4,4′-DM-MDC) was used in a similar condition for comparison. Thus, an efficient green-chemistry process has been developed based on 4,4′-DP-MDC in making urea prepolymers, urea elastomers and urea plastics all in excellent yields without using reactive methylenediphenylene diisocyanate (MDI) or any catalysts in the trans-ureation polymerizations.     

Synthesis and Antioxidancy of Some <Emphasis Type="Italic">n</Emphasis>-Alkyl, <Emphasis Type="Italic">t</Emphasis>-Alkyl,Homologous and Isomeric Lipidic Alkylthiobisphenols

To study the relationship between structure and properties of members of the lipidic thiobis phenol series, as extreme pressure additives in lubricants, a series of homologous compounds has been synthesised by the reaction of alkylphenols with sulphur dichloride. The isomeric n-nonylphenols have been reacted to form the C9 isomeric 2,2′-and 4,4′-thiobisphenols. Longer alkyl side-chains resulted mainly in the formation of 4,4′-thiobisphenols and some of the 2,2′ isomer. With short alkyl, particularly t-alkyl side-chains, steric hindrance resulted in the 2,2′-compound. Additive studies have indicated that the longer chain 4,4′ compounds possessed antioxidant properties comparable and superior to former commercial branched chain 2,2′ compounds produced from petrochemical intermediates. Lipidic alkylthiobisphenols: Long chain phenols, Part 40b (Part 40a, ref 6).     

Effect of chemical structure of aromatic dianhydrides on the thermal, mechanical and electrical properties of their terpolyimides with 4,4′-oxydianiline

Aromatic terpolyimides were synthesized by the reaction of 3,3′,4,4′-oxydiphthalicdianhydride(ODPA), 3,3′,4,4′-biphenyldianhydride(BPDA) and 3,3′,4,4′-benzophenonetetracaboxylicdianhydride(BTDA) with 4,4′-oxydianiline(ODA) via thermal imidization with the view to enhance their tensile properties without compromising thermal properties compared to their homo and copolyimides. Their films were characterized by FTIR, TGA, DSC and XRD. Their FTIR spectra established formation of polyimide by the characteristic vibrations at 1375cm⁻¹(C-N stretch) and 1113 cm⁻¹(imide ring deformation). TGA results showed imidization of residual polyamide acid close to 250 °C and decomposition of polyimides at about 540 °C. XRD results showed amorphous nature for all terpolyimides. Their tensile strength and tensile modulus were higher than either homo or copolyimides. Incorporation of BPDA, without bridging groups between the aromatic rings into the backbone of ODPA/BTDA-ODA is suggested as the cause for such an enhancement. Such terpolyimide can find application as adhesives in making flexible single/multilayer polyimide metal-clad laminates in flexible printed circuits and tape automated bonding applications. In addition, the terpolyimide, BPDA/BTDA/ODPA-ODA (mole ratio 0.5:0.25:0.25:1), showed low dielectric constant (3.52) as BPDA could offer slight rigidity by which the orientation of polar groupings could be reduced.     

Crosslinking and grafting ethylene vinyl acetate copolymer with accelerated electrons in the presence of polyfunctional monomers

In this study, we have studied the effects of polyfunctional monomers (PFMs) on physical properties of ethylene vinyl acetate (EVA) copolymer crosslinked with electron beam (EB) or peroxides. The PFMs used were triallylcyanurate, triallylisocyanurate, trimethylolpropane trimethacrylate, zinc diacrylate, and ethylene glycol dimethacrylate. Using PFMs has led to (1) optimum cure time t ₉₀ decrease from 19′25″ to 17′30″–18′45″, (2) scorch time increase from 2′ to maximum 3′45″, (3) increasing the crosslink density of peroxide or EB-cured systems by increasing the efficiency of productive radical reactions. The most efficient PFM for EVA copolymer blends has been triallylisocyanurate. Tensile strength and tear strength of samples crosslinked with EB for all irradiation doses are significantly better than those obtained for samples crosslinked with peroxides (differences up to 190%). The results show that EB irradiation gave the best results     

Zinc(II) Metal–Organic Framework with Nano-Sized Channels Based on Paddle-Wheel Units

A Zn(II) metal–organic framework with nano-sized channels from 4,4′-bipyridine (4,4′-bipy) and 4′-sulfo-biphenyl-4-carboxylate (sbpc²⁻) ligands, {[Zn(μ-4,4′-bipy)_1.5(μ-sbpc)]·5H₂O} _n (1), has been synthesized by the hydrothermal method. Compound 1 was characterized by X-ray powder diffraction, IR spectroscopy, elemental analysis and single-crystal X-ray crystallography. The structural studies show the Zn atoms have a six-coordinate geometry with a distorted octahedral environment constructed of paddle-wheel [Zn₂(OOC)₄] building units with 4,4′-bipy and sbpc²⁻ linkers stacked over each other to generate three-dimensional nano-sized channels occupied by guest H₂O molecules.     

Synthesis and characterization of aromatic polyamides derived from various derivatives of 4,4’-oxydianiline

Three aromatic diamines, 2,2′-diiodo-4,4′-oxydianiline (DI-ODA 2), 2,2′-bis[p-(trifluoromethyl)phenyl]-4,4′-oxydianiline (BTFP-ODA 3) and 2,8-diaminodibenzofuran (DADBF 5) were synthesized by using 4,4-oxydianiline (4,4′-ODA) as the starting material. New aromatic polyamides 6, 7 and 8 were prepared from these three diamines and six commercially available aromatic diacids by direct polycondensation, respectively. Polyamides 6 and 7 contained bulky iodide and p-trifluoromethylphenyl substitutents that would hinder the chain packing and increase the free volume. They exhibited good optical transparency in visible light region and showed excellent solubility in organic solvents such as DMSO, DMAc, DMF and NMP. Polyamides 8 containing planar dibenzofuran moieties had the highest glass transition temperatures and decomposition temperatures among these polyamides. Polyamides 6 had the lowest decomposition temperatures due to the presence of weak carbon–iodine bond. All of these polyamides showed amorphous nature evidenced by wide angle X-ray diffraction. No endothermic peaks were observed from DSC thermograms up to their decomposition temperatures. High optical transparency and excellent solubility combined with good thermal stability make these polyamides attractive for potential soft electronics applications.     

Thermostable foam organoplastics made from polyimide binders and polyimide felt

A series of composite materials of a new type — foam organoplastics — was obtained from foamed polyimide binders reinforced with Arimid T polyimide felt, and commercially available aromatic monomers were used. Use ofDPO (3,3′,4,4′-diphenyloxidetetracarboxyic acid) dianhydride in the H-complex allows obtaining a melt of lower viscosity (300 Pa-sec), and the viscosity almost does not change at 95°C for 20 min. The viscosity of melts of the H-complexes based on BZP (3,3′, 4,4′-benzophenonetetracarboxylic acid) tends to increase rapidly to the level of 10⁵ Pa·sec, probably due to further “crosslinking” of the H-complex in the conditions of the melt. Replacing the carcinogenic 4,4′-diaminodiphenylmethane (DADPM) diamine by commercially available 4,4′-diaminodiphenyl ether (DADPE) does not significantly alter the rheological behavior of the H-complex melt at 95°C and does not decrease the mechanical characteristics of the foam composites. The mechanical characteristics (bending strength, compressive and shear moduli) of the foam composites based on H-complexes with DPO dianhydride are 1.5 times higher than for the same foam composites using BZP dianhydride. The foam composites based on DPO do not undergo brittle failure but simply bend in bending tests, which can be used to obtain new elastic foam materials. The effect ofnanoparticles on the properties of the foam composites was established. It is expedient to use montmorillonite nanoparticles, which increases the modulus of elasticity and rigidity of the material. __________ Translated from Khimicheskie Volokna, No. 5, pp. 66–70, September–October, 2006.     

Polyimides based on furanic diamines and aromatic dianhydrides: synthesis,characterization and properties

Novel polyimides containing furan moieties were prepared from the resulting furanic diamine monomers with various aromatic dianhydrides including 1,2,4,5-benzene-tetracarboxylic dianhydride, 3,3′,4,4′-biphenyltetracarboxylic dianhydride, 4,4′-oxydiphthalic anhydride, and hexafluoroisopropylidene 2,2-bis(phthalic anhydride), via a two-step process. The resulting polyimides were characterized by solubility tests, viscosity measurements, FTIR, ¹H NMR spectroscopy, differential scanning calorimetric (DSC), and thermogravimetric analysis (TGA) analysis. The polyimides with inherent viscosities in the range of 0.048–0.095 L/g showed excellent solubility in aprotic amide and organic solvents, such as N,N-dimethylacetamide, N-methyl-2-pyrrolidinone, dimethylformamide and acetone, chloroform, etc. DSC showed glass transition temperatures (T _g) in the range of 116–143 °C. These polymers showed excellent thermal stability up to 390 °C.     

Heat stable and organosoluble polyimides containing laterally-attached phenoxy phenylene groups

In this research a diamine monomer containing two phenoxy phenylene lateral groups, 2,2′-bis[(p-phenoxy phenyl)]-4,4′-diaminodiphenyl ether (PPAPE) was used to prepare novel wholly aromatic polyimides by thermal or chemical two-step polycondensation reactions. Comonomers including pyromellitic dianhydride (PMDA), 4,4′-oxydiphthalic anhydride (ODPA), and 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (BTDA) were used for the polyimidization reactions. A reference polyimide was also prepared by the reaction of 4,4′-diaminodiphenyl ether (DADPE) with pyromellitic dianhydride (PMDA). The limited viscosity numbers as well as [`(M)]<sub>n</sub> \overline{M}_n and [`(M)]_w \overline{M}_w values of the resulting polymers were determined. All PPAPE-resulted polyimides had excellent organosolubility in common polar solvents. A low crystallinity extent was only observed using their wide-angle X-ray diffractograms (WAXD). The prepared hinged polyimides could also be cast into transparent and flexible films. The glass transition temperatures of the resulting polyimides were determined by differential scanning calorimetry (DSC) analyses. The thermograms obtained from thermogravimetric analyses (TGA) showed that the phenoxy phenylene lateral groups attached to the macromolecular backbones had no substantial diminishing effect on the thermal stability of these structurally-modified polyimides.     

Self-Recognition of 3D Porous Frameworks: Fourfold Diamondoid or Threefold Cuboidal Interpenetrating Nets Formed by Varying Pillar Motifs

Compound [Ni(2,6-ndc)(bpe)(H₂O)] _n (1) was prepared by the hydrothermal reaction of 2,6-naphthalenedicarboxylic acid (2,6-H₂ndc) and trans-1,2-bis(4-pyridyl)ethylene (bpe) with Ni(NO₃)₂·6H₂O under alkaline (NaOH) conditions. Treatment of 2,6-H₂ndc, 4,4′-bipyridine (4,4′-bpy) with M(NO₃)₂·6H₂O (M = Ni or Co) under similar conditions afforded compounds [Ni₂(2,6-ndc)₂(4,4′-bpy)] _n (2) and [Co₂(2,6-ndc)₂(4,4′-bpy)] _n (3), respectively. A single-crystal X-ray diffraction study revealed that compound 1 adopts a 3D fourfold interpenetrating diamondoid network stabilized by inter-net OH···O hydrogen bonds. The anionic 2,6-ndc ligand presents two different bonding characteristics, bis(monodentate) and bis(chelating bidentate) modes. A solid-state structural analysis revealed that compounds 2 and 3 are isomorphous and isostructural. Both present a 3D threefold interpenetrating cuboidal framework, consisting of a 2D (4,4)-net of interconnected [M ₂(O₂C)₄] (M = Ni, Co) paddle-wheel dinuclear units, and pillared by 4,4′-bpy ligands. The degree of interpenetration of these compounds could be adjusted successfully by varying only the organic pillar motifs.     

Shape-selective alkylation of biphenyl catalyzed by H-Mordenites

Liquid phase alkylation of biphenyl was studied over large pore zeolites. Selective formation of the narrowest products, 4,4′’-diisopropylbiphenyl (4,4′’-DIPB), occurred only over HM among the zeolites with twelvemembered pore openings. These shape-selective catalyses are ascribed to steric restriction of transition state and to entrance of bulky substrates into the pores. The dealumination of HM enhanced catalytic activity and the selectivity of 4,4′’-DIPB because of the decrease of coke-deposition, while the activity and the selectivity were low over HM with the low SiO₂/Al₂O₃ ratio. Non-regioselective catalysis occurs on external acid sites because severe cokedeposition deactivates the acid sites inside the pores by blocking pore openings. The selectivity of DIPB isomers was changed with propylene pressure and/or with reaction temperature. 4,4′’-DIPB yielded selectively under high propylene pressure (<0.3 MPa) at 250 °C, while the selectivity of 4,4′’-DIPB decreased under such low propylene pressure as 0.2MPa. Selective formation of 4,4′’-DIPB was observed at moderate temperature such as 250 °C, whereas the decrease of the selectivity of 4,4′’-DIPB occurred at higher temperature as 300 °C. However, 4,4′’-DIPB was almost exclusively isomer in the encapsulated DIPB isomers inside the pores under every pressure and temperature. These decreases of the selectivity of 4,4′’-DIPB are due to the isomerization of 4,4′’-DIPB on the external acid sites. The deactivation of external acid sites of HM was examined to reduce non-regioselective alkylation and isomerization. External acid sites were deactivated by calcination after impregnation of cerium on HM without the decrease in pore radii. Selectivities of 4,4′’-DIPB were improved even at high temperatures in the isopropylation of biphenyl because of the suppression of non-regioselective alkylation and isomerization at the external acid sites. The selectivity of 4,4′’-diethylbiphenyl (4,4′’-DEBP) in the ethylation of biphenyl was much lower than that in the isopropylation. Among the DEBP isomers, 4,4′’-DEBP has the highest reactivity for the ethylation to polyethylbiphenyls inside the pores, whereas the isopropylation of 4,4′’-DIPB was negligibly low inside the pores. These differences are ascribed to the difference in steric restriction at the transition state composed of substrate, alkylating agent, and acid sites inside the pores.     

Polyphosphonates obtained by vapor-liquid interfacial polycondensation

Summary A series of polyphosphonates were synthesized by base promoted liquid-vapor interfacial polycondensation of various alkyl (aryl) phosphonic dichlorides (methylphosphonic dichloride (MPD), cyclohexylphosphonic dichloride (CPD) and phenylphosphonic dichloride (PPD)) with different bisphenols (hydroquinone (HQ), bisphenol A (BA), 4,4′ - biphenol (BP), 1,5-naphtalenediol (ND) and 4,4′ - sulfonyldiphenol (SD)). The polyphosphonates were characterized by infrared (IR) and proton magnetic resonance (¹H-NMR) spectroscopy. Yields in the range of 20–80% and Mn of ∼ 8500–35000 were obtained. DSC measurements show Tg in the range 95°–148°C. These polymers are soluble in solvents such as N,N-dimethylformamide, tetrahydrofuran and chloroform. Polyphosphonates were stable up 240°–300°C in air atmosphere. Received: 11 March 2002 / Revised version: 29 May 2002 / Accepted: 12 June 2002     

Effect of struture and form on the ability of plant sterols to inhibit cholesterol absorption in hamsters

We investigated the effect of three types of plant sterols (4-desmethylsterols, 4,4′-dimethylsterols, and pentacyclic triterpene alcohols) in three forms (free, esterified with FA, or with phenolic acids) on cholesterol absorption. Plant sterol fractions derived from soybean (99% 4-desmethylsterols), rice bran (70% 4,4′-dimethylsterols), or shea nut (89% pentacyclic triterpene alcohols) were fed to male hamsters (n=20/group) as free sterols or esterified with FA or phenolic acids (cinnamic or ferulic). Cholesterol absorption was measured after 5–8.5 (mean, 7) wk by a dual-isotope technique. Soybean sterol intake significantly reduced cholesterol absorption efficiency (23%) and plasma total cholesterol (11%). Rice bran sterols tended to lower cholesterol absorption efficiency by 7% and plasma total cholesterol by 5%, whereas shea nut sterols had no effect. In hamsters, dietary 4-desmethylsterols were more effective than 4,4′-dimethylsterols in lowering cholesterol absorption and levels of cholesterol in blood. Pentacyclic triterpene alcohols had no effect on the absorption of cholesterol or on its level in blood. Esterification with FA did not impair the ability of 4-desmethylsterols and 4,4′-dimethylsterols to inhibit cholesterol absorption, whereas esterification with phenolic acids reduced this ability. This study supports the use of 4-desmethylsterols, esterified with FA to increase solubility, as the most effective cholesterol-lowering plant sterols in the diet.     

Synthesis and properties of novel aromatic polyamides with non-conjugated bichromophoric units in the main chains

A dicarboxylic acid bearing two cinnamic acids units linked in their para positions by a methylene bridge was synthesized by the reaction of 4,4′-methylene-bis(benzaldehyde) and malonic acid, characterized by spectral and elemental analysis and used to prepare a series of novel photocrosslinkable aromatic polyamides through its reaction with various ether-bridged aromatic diamines. ¹H and ¹³C NMR, IR and UV spectroscopy confirmed the structure of the monomer and photopolymers. The resulting polymers with inherent viscosities of 0.65–1.14 dL/g were soluble in polar aprotic solvents, such as DMF, DMSO, DMAc and NMP, and showed good film-forming properties. Their weight-average and number-average molecular weights, determined by GPC (polystyrene standard), were in the range 57,400–84,300 and 24,000–40,900, respectively. The percent of water absorbed at 65% relative humidity varied between 1.57% and 2.35%. The polyamides exhibited glass transition temperatures between 202 and 239 °C, and they were stable up to a temperature of 350 °C in air. Wide-angle X-ray scattering diagrams did not show any crystalline reflection and no endothermic peak attributable to polymer melting was observed in DSC curves of the polymers. These photosensitive polymers exhibited strong UV absorption maxima both in solution and film state, and displayed three photochemical transformations under the UV exposure, viz. a trans-cis isomerization, favored in the early stage of UV irradiation, a bimolecular cyclodimerization, leading to the generation of a cyclobutane ring, and a photo-Fries rearrangement evidenced only in polymer solutions.