Synthesis,characterization, and solution properties of 5-ethyl-substituted poly(L-prolines). Synthesis of cis- and trans-5-ethyl-L-proline and optically active poly(cis-5-ethyl-D-proline)

This article reports a continuation of our work on the substituent effects on the preferred helical conformations and the mutarotation of substituted poly(L -prolines). The size of the substituent has been increased from a methyl group to an ethyl group in the 5 position. The purpose is twofold: (i) according to our theoretical conformational energy calculations, an ethyl group in the 5 position can exert a greater steric effect than can a methyl group; and (ii) the rotation-isomerization of the ethyl group introduces a new intriguing fact to the problem. The cis isomer of 5-ethylproline was synthesized by catalytic hydrogenation of Δ′-2-ethylpyrroline-5-carboxylic acid, whereas for trans-5-ethylproline, a chemical separation method involving p-toluenesulfonyl chloride was used. The resolution of cis-5-ethylproline and the assignment of absolute configurations have been carried out by fractional crystallization and circular dichroism spectroscopic techniques, respectively. Poly(cis-5-ethyl-D -proline) was obtained from its corresponding N-carboxyanhydrides via a ring opening polymerization.     

Synthesis,separation, and resolution of cis- and trans-3-ethylproline

The synthesis, separation, and optical resolution of cis- and trans-3-ethylproline are described. Two different approaches were employed: (1) The Michael addition reaction of 2-pentenal with diethyl-N-carbobenzyloxyaminomalonate gave the intermediate 3-ethyl-5-hydroxy-N-benzyloxypyrrolidine. Hydrogenolysis of this intermediate followed by acid hydrolysis gave a mixture of cis- and trans-3-ethylproline. Separation of the isomers was accomplished by selective saponification of N-(p-toluenesulfonyl)-cis- and trans-3-ethylproline methyl esters using 0.25N methanolic sodium hydroxide. (2) The Michael condensation of diethyl acetamidomalonate with 2-pentenoic acid ethyl ether produced the intermediate 5,5-bis(ethoxycarbonyl)-4-ethylpyrrolidine. Partial saponification followed by decarboxylation afforded a mixture of cis- and trans-isomers of ethyl-3-ethylpyroglutamate. The diastereoisomers were separated using low temperature fractional crystallization. Reduction of these isomers and tosylation in situ afforded the corresponding N-(p-toluenesulfonyl)-cis- and trans-3-ethylprolinols. Chromic acid oxidation gave N-(p-toluenesulfonyl)-cis- and trans-3-ethylproline. Reaction of these tosylates with 30% hydrogen bromide in acetic acid gave cis- and trans-3-ethylproline. Both optically active isomers of D(+)-and L(-)-trans-3-ethylproline were successfully resolved using (+)-dibenzoyl-D -tartaric acid and (-)-dibenzoyl-L -tartaric acid as resolving agents. The absolute configurations of the optically active isomers were determined by circular dichroism spectroscopy.     

Synthesis and solution properties of comblike poly(mono-n-alkyl itaconates). I. Poly(monodecyl itaconate)

The monoester of itaconic acid with n-decyl alcohol was prepared and polymerized. The polymer was fractionated and characterized by viscometry, size-exclusion chromatography (SEC) and light scattering. Some of the common semiempirical relations for flexible and rigid polymers were used in order to obtain the unperturbed dimensions and the conformational parameters. Thermodynamic and dimensional parameters were determined and calculated. The results are compared with those reported previously for similar compounds.     

Synthesis and solution properties of poly(diphenyl itaconate)

Solid diphenyl itaconate monomer was obtained by esterification in the presence of diphosphorus pentoxide and polymerized in bulk with AIBN as initiator. The non-film forming polymer powder was characterized by fractionation, viscosity measurements, light scattering and other techniques. The relation [n] = 3·6 × 10^?3$\text{M}$^0·70_w, obtained for toluene at 25° was extrapolated to θ-conditions by various procedures: the σ-value of 2·60 for unperturbed dimensions indicates a less pronounced influence of phenyl compared with other C₆ hydrocarbon substitutes.     

Synthesis and solution properties of poly(2-methylproline)

The resolution of 2-methylproline and the assignment of absolute configuration to the stereoisomer has been carried out. The L-enantiomer was obtained from the fractional crystallization of the quinine salt of (?)-N-carbobenzoxy-2-methylproline and the D-enantiomer from the collected filtrates. The (?)-2-methylproline was assigned the L-configuration by means of the Clough-Lutz-Jirgensons method. Polymers were obtained in bulk from the N-carboxyanhydrides. Although polymers obtained from different solvents exhibited different solubility properties, subsequent spectral studies indicated that this effect was not due to a large conformational change as in the polyproline case. Spectral evidence suggests that poly(2-methylproline) (P2MP) exists as a polyproline type II helix.     

Synthesis and solution properties of poly(ditoluyl itaconates)

The three o-, m- and p- isomers of ditoluyl itaconate were obtained by esterification of cresols and itaconic acid in the presence of diphosphorous pentoxide, and then polymerized in bulk with AlBN as initiator. The polymers were investigated in dilute solution, including $\text{M}{}_{\mathrm{W}}$ determination and precipitation fractionations, and the results compared with those for poly(diphenyl itaconate). The presence and position of -CH, in the aromatic ring influence the initial rates of polymerization, polymer solubilities in organic solvents and $\text{[η]/}\text{M}{}_{\mathrm{W}}$ relations. Unperturbed dimensions, obtained by extrapolating to τ-conditions, vary slightly with the -CH, group position, due to steric and probably other effects.     

Structure and solution properties of radical-initiated poly(vinyl chloride). II. Correlation of solution properties

The results of detailed measurements of osmotic pressure, light scattering, and viscosity of poly(vinyl chloride) solutions are used to establish the molecular weight dependence of [η] and A₂, to estimate the unperturbed dimensions of the poly(vinyl chloride) molecule, and to analyze critically the [η]–M correlations published hitherto.     

Synthesis and properties of poly(5-ethynyluridylic acid)

5-Ethynyluridine 5'-diphosphate has been synthesised from 5-ethynyluridine under carefully controlled conditions to prevent any reaction with the ethynyl group. The compound is a substrate for polynucleotide phosphorylase from Micrococcus luteus and has been polymerised to give poly(5-ethynyluridylic acid). The polymer has a stable secondary structure with a T_m of 76° accompanied by a 16% hyperchromicity in solutions of high ionic strength and forms a 1:1 complex with poly(A) with a T_m of 78°. Thus the presence of the ethynyl group in the pyrimidine ring causes the polymer to have and to form much more stable secondary structures than the corresponding unsubstituted polynucleotide poly(U).     

Synthesis and properties of substituted 2-thioxohexahydropyrimidine-5-carbohydrazides

A regioselective method for the synthesis of substituted (4R*,5S*,6R*)-2-thioxohexahydro-pyrimidine-5-carbohydrazides from the corresponding diastereomers of hexahydro-2H-chromeno[4,3-d]pyrimidines was developed. In acidic medium, the obtained hydrazides are prone to retro reaction to give hexahydro-2H-chromeno[4,3-d]pyrimidines.

     

Synthesis of substituted poly(1-vinylpyrene)s and investigation of their fluorescent properties

A series of functionalized linear poly(1-vinylpyrene) (PVP) polymers bearing substituents such as ? NO₂, ? CHO, ? NH₂, ? Br, and ? CH?C(CN)₂, were prepared by chemical modification of PVP in solution. The degree of substitution in PVP? CH?C(CN)₂ was varied from 40% to nearly 100% by control of the reaction conditions. The other polymers were partially functionalized. The UV-visible and fluorescence spectroscopy of the polymers were studied in solution. The influence of solvent polarity, excitation energy, and degree of substitution on the fluorescence of the polymers were examined. © 1993 John Wiley & Sons, In     

Synthesis and functionalities of poly(N-vinylalkylamide). V. Control of a lower critical solution temperature of poly(N-vinylalkylamide)

N-vinyl-n-butyramide (NVBA), N-vinylisovaleramide (NVIVA), and N-vinyl-n-valeramide (NVVA), which are N-vinylalkylamides with different alkyl groups were synthesized and their solution behavior in a polymeric form was examined. Copolymers of N-vinylisobutyramide (NVIBA) with N-vinylacetamide (NVA), NVIBA with NVVA, and NVVA with NVA were prepared by the solution polymerization to control the LCSTs. The resultant polyNVBA showed a lower critical solution temperature (LCST) sharply at 32°C, but polyN-vinylisovaleramide (polyNVIVA) and polyN-vinyl-n-valeramide(polyNVVA) that have n-butyl and isobutyl groups, respectively, on their side chains were insoluble even in cold water. The water solubility of the resulting polymers was found to vary, depending on the molecular shapes as well as the side chain length of the alkyl groups in question. The copolymers consisting of NVVA, NVIBA, and NVA in water showed LCSTs sharply between 10 and 90°C, depending on changes in their comonomer content. It was found that the changes in LCST that are caused by the incorporation of comonomers are due to changes in the overall hydrophilicity of the polymer. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 3087–3094, 1997     

Synthesis and gas permeation properties of poly(diarylacetylene)s having substituted and twisted biphenyl moieties

Diarylacetylene monomers containing substituted biphenyl ( 1a – f ) and anthryl ( 1g ) groups were synthesized and then polymerized with TaCl₅‐n‐Bu₄Sn catalyst to produce the corresponding poly(diarylacetylene)s ( 2a – g ). Polymers 2a – f were soluble in common organic solvents such as cyclohexane, toluene, and chloroform. According to thermogravimetric analysis, the onset temperatures of weight loss of the polymers were over 400 °C in air, indicating considerably high thermal stability. Free‐standing membranes 2a and 2c – e were prepared by the solution casting method. Desilylation of Si‐containing membrane 2c was carried out with trifluoroacetic acid to afford 3c . All the polymer membranes, especially those having twisted biphenyl groups, exhibited high gas permeability; for example, their oxygen permeability (PO ₂) values ranged from 130 to 1400 barrers. Membrane 2d having two chlorine atoms in the biphenyl group showed the highest gas permeability (PO ₂ = 1400 barrers) among the present polymers. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 861–868, 2010     

反-1,2-双[2-(5-取代苯基恶唑基)]环丙烷的合成与光性能的研究

合成了8个反 -1,2-双[2-(5-取代苯基恶唑基)]环丙烷和2个1,2-双[2-取代苯基恶唑基)]乙烷,其中9个为新化合物.讨论了化合物的结构与其电子光谱及荧光量子产率间的关系.发现恶唑环与三元环间存在一定程度的共轭,并解释了上述化合物荧光量子产率较低的现象.     

Synthesis and functionalities of poly(N-vinylalkylamide). VI. A novel thermosensitive hydrogel crosslinked poly(N-vinylisobutyramide)

A novel thermosensitive poly(N-vinylisobutyramide)(polyNVIBA) hydrogel was prepared by the copolymerization of N-vinylisobutyramide (NVIBA) with butylene-bis-NVA(B-BNVA) as a crosslinker in a high yield. The swelling transition behavior was examined in comparison with poly(N-isopropylacrylamide)(polyNIPAAm) hydrogel. The resulting polyNVIBA hydrogel clearly showed a swelling transion in water at ca. 41°C. To control the transition temperature (T_t) of the gel, crosslinked copolymers of NVIBA and N-vinylacetamide (NVA) were prepared and compared with copolymers of N-isopropylacrylamide(NIPAAm) and NVA. The incorporation of NVA led to a higher swelling transition temperature. T_t of poly(NVIBA-co-NVA) gels was almost the same as those in water-soluble poly(NVIBA-co-NVA). The responses for a swelling transition of polyNVIBA and poly(NVIBA-co-NVA) gels were sharp in comparison to polyNIPAAm gels. PolyNVIBA and poly(NVIBA-co-NVA) gels desorbed 98% of water above T_t. The characteristic and the mechanism of the phase transition on the hydrogels were discussed. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 3377–3384, 1997     

Synthesis and properties of poly(aniline-co-azidoaniline)

Copolymers of polyaniline and o-azidoaniline were synthesized by chemical oxidative polymerization. The copolymers were characterized by powder X-ray diffraction (XRD) and UV/Vis and FT-IR spectroscopy. Thermal activation of the azido chromophore in the copolymer caused it to react and cross-link into adjacent polymer chains. The cross-linking of the copolymers was indicated by the depletion of the azido band in the FT-IR spectrum. The effects of the cross-linking were studied by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and four-probe conductivity. The TGA showed that the thermal stability of the copolymers is improved due to cross-linking. However, the increased thermal stability is accompanied by a decrease in electrical conductivity due to the loss of conjugation detected by UV/Vis spectroscopy and a loss of crystallinity due to the azido substituents, which was demonstrated by XRD.     

Synthesis and properties of poly(dimethylxylylenylamides)

Poly(dimethylxylylenylamides) were synthesized from six different diphenylenediamenes and two dimethyl-substituted xylylenyldiacid chlorides by solution polycondensation at low temperature. The model compound 2,5-demethyl1,4-benzediacetanilide was synthesized and characterized by infrared (IR) and nuclear magnetic resonance (NMR) spectroscopy. The polyamides were characterized by IR and viscosity measurements. Some of the polyamides showed crystalline behavior in the x-ray diffractograms. The polyamdes have decomposition temperatures in the range 370–310°C in air and are soluble in all amide solvents. The effects of subsituents on crystallinity, thermal stability, and solubility of the polymides are also discussed.     

Preparation and thermal properties of asymmetrically substituted poly(silylenemethylene)s

Poly(silylenemethylene)s of the types [SiMeRCH₂]_n and [SiHRCH₂]_n were prepared by the ring-opening polymerization (ROP) of 1,3-disilacyclobutanes (DSCBs) containing n-alkyl substituents, such as C₂H₅, n-C₃H₇, n-C₄H₉, n-C₅H₁₁, and n-C₆H₁₃, or a phenyl group on the Si. These new polymers include a monosilicon analog of poly(styrene), [SiHPhCH₂]_n. Improved synthesis routes to the DSCB monomers were developed which proceed through Grignard ring closure reactions on alkoxy-substituted chlorocarbosilanes. All of these asymmetrically substituted polymers were obtained in high molecular weight form, except for [SiHPhCH₂]_n. The configurations of all of the polymers were found to be atactic. The aryl-substituted polymers have higher glass transition temperatures (T_gs) and thermal stability than those of the alkyl-substituted poly(silylenemethylene)s. Unlike the polyolefins of the type [C(H)(R)CH₂]_n, where T_g drops continuously from R = Me to n-Hex, the T_gs of the n-C_nH_2n+1 (n = 2–6)-substituted [SiMeRCH₂]_n PSM's appear to reach a maximum (at −61°C) for the R = n-Pr-substituted polymer. Moreover, where it was possible to make direct comparisons among similarly substituted atactic polymers, all of the poly(silylenemethylene)s were found to have lower T_gs than their all-carbon analogs. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 3193–3205, 1997     

Synthesis of associating poly(acrylic acid) in supercritical carbon dioxide and its solution properties

Hydrophobically associating polymers have been synthesized in supercritical carbon dioxide by copolymerization of acrylic acid with different amounts of acrylate with hydrocarbon or fluorocarbon groups. It was found that conversion of hydrocarbon comonomers was above 95% whereas that for fluorocarbon comonomers was only about 50%. In addition, large amounts of hydrophobic groups could be easily introduced to poly(acrylic acid) by reaction in supercritical carbon dioxide. The solution properties were investigated by rheology. The results indicated that intermolecular association of the copolymer was strong and viscosity was maximum under acidic conditions. In aqueous solutions fluorocarbon hydrophobes associated much more strongly than the hydrocarbon variety, but the viscosifying effect of PAAC-18 series copolymers in 2% (w/w) solution was more pronounced than that of the PAAF series, results which did not agree with the conclusions of Ravey and Stébé. It was also found that the thixotropy behavior of copolymer solution at pH 3.2 was more complex than that at pH 5.0, at which pseudoplasticity only was observed for solutions of all copolymers. Contact angles of copolymer solutions on a glass sheet were measured. The data indicated that contact angles of hydrocarbon-modified polymers were smaller than those of fluorocarbon analogues. As time passed the contact angle became smaller and smaller. Fluorocarbon analogues were better than hydrocarbon analogues, and longer hydrophobic chains were better than shorter chains, at maintaining the hydrophobic character of the surface.