Rapid synthesis of polyamide dendrimers from unprotected AB2 building blocks

A rapid synthetic method for the preparation of polyamide dendrimer without protection and deprotection steps has been developed. A symmetrically branched third-generation polyamide dendrimer was prepared by a convergent method involving activation of focal point with a condensing agent, diphenyl (2,3-dihydro-2-thioxo-3-benzoxazolyl)phosphonate (DBOP), followed by condensation of the active amide with the diaminocarboxylic acid 3,5-bis(4-aminophenoxy)benzoic acid as an AB2 building block.     

Facile synthesis of polyamide dendrimers from unprotected AB2 building blocks

[structure: see text]. A fast, inexpensive, and highly efficient synthesis of aromatic polyamide dendrimers without the need for protection and deprotection steps has been developed. Dendrons and third-generation polyamide dendrimers were easily prepared by a convergent approach involving activation of a focal point with thionyl chloride, followed by condensation with unprotected AB2 building blocks.     

A green and efficient protocol for large‐scale production of glycyrrhizic acid from licorice roots by combination of polyamide and macroporous resin adsorbent chromatography

A green and efficient method for large‐scale preparation of glycyrrhizic acid from licorice roots was developed by combination of polyamide and macroporous resin. The entire preparation procedure consisted of two simple separation steps. The first step is to use polyamide resin to remove licorice flavoniods from the licorice crude extract. Subsequently, various macroporous resins were tried to purify glycyrrhizic acid, and HPD‐400 showed the most suitable adsorption and desorption properties. Under the optimized conditions, a large‐scale preparation of glycyrrhizic acid from licorice roots was carried out. A 20 kg raw material produced 0.43 kg of glycyrrhizic acid using green aqueous ethanol as the solvent. The purity of glycyrrhizic acid was increased from 11.40 to 88.95% with a recovery of 76.53%. The proposed method may be also extended to produce large‐scale other triterpenoid saponins from herbal materials.     

Study on hypochlorite degradation of aromatic polyamide reverse osmosis membrane

A serious limitation of most commercial polyamide reverse osmosis (RO) membranes is their sensitivity to chlorine attack. By studying the hypochlorite degradation of aromatic polyamide RO membrane, this work was to get some understandings in the prevention of membrane depreciation and develop membranes with improved chlorine resistance. Membrane performances, including water flux and salt rejection, were evaluated before and after hypochlorite exposure under different pH and concentration conditions. The results showed that chlorination destroyed hydrogen bonds in polyamide chains, causing a notable decline of membrane flux especially in acid environment; however, membrane performance was slightly improved after the treatment of alkaline hypochlorite solution for a certain time, which was probably due to the effect of amine groups in barrier layer. Based on the attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) characterizations and performance measurements, the results indicated that N-chlorination reaction of aromatic polyamide was also reversible, in other words, the N-chlorinated intermediate could be regenerated to initial amide with the alkaline treatment before ring-chlorination reaction. This conclusion provided several relative suggestions for membrane cleaning procedures. Finally, a method adopting surface coating was proposed to develop membranes with good chlorine resistance, and the preliminary results showed its potential for applications.     

Compatibilization of PA6/rubber blends by using an oxazoline functionalized rubber

The compatibilization of blends of polyamide 6 with a nitrile butadiene rubber has been investigated. The procedure consists of two steps: modification of the nitrile groups of the rubber into oxazoline in the melt through condensation of ethanolamine with formation of a molecule of ammonia, followed by use of the modified rubber as a compatibilizing precursor which is melt mixed with the polyamide to produce the compatibilized blend. The modification reaction has been detected by NMR analysis and a rheological, mechanical and thermomechanical characterization has been carried out on the all the blends. The results indicate that the modification reaction occurs but the conversion of nitrile into oxazoline is relatively low. Use of the modified rubber in the preparation of binary polyamide/rubber blends, leads to an increase in viscosity, which is typical of compatibilized systems, and to enhanced tensile, impact and thermomechanical properties. These phenomena can be explained by the formation of in situ rubber/polyamide copolymers that act as compatibilizers, due to the reaction between oxazoline and the end groups of the polyamide. The presence of residual low molecular compounds, from the modification or from the purification of the rubber worsens all of the properties and inhibits the compatibilizing effect of the modified rubber.     

Pd immobilized on polyamide based on melamine and terephalic acid as an efficient and recyclable catalyst for Suzuki‐Miyaura coupling reaction

A simple synthetic strategy of polyamide was described from melamine and terephalic acid via one‐step polycondensation. PdCl₂ was then immobilized on the polyamide (denoted as Pd/MPA). Melamine and terephalic acid not only acted as monomers but also provided the ligand sites to help the polyamide to coordinate with Pd(II). The Pd/MPA catalyst was characterized by FT‐IR, TGA, SEM, TEM, XPS, N₂ adsorption‐desorption and atomic absorption spectroscopy. The catalyst was used in Suzuki‐Miyaura coupling reaction of various aryl halides, including less reactive chlorobenzene and benzyl chloride, to give the coupling products in moderate to excellent yields. High turnover frequencies (TOF) up to 29400 h^‐1 can be also obtained. In addition, it behaved truly as a heterogeneous catalyst with high reusability after being recycled 6 times and palladium leaching was negligible during the process. This work provides a practical polyamide support to develop heterogeneous palladium catalysts with simple synthetic procedure and low cost.     

Sequence-selective single-molecule alkylation with a pyrrole-imidazole polyamide visualized in a DNA nanoscaffold

We demonstrate a novel strategy for visualizing sequence-selective alkylation of target double-stranded DNA (dsDNA) using a synthetic pyrrole-imidazole (PI) polyamide in a designed DNA origami scaffold. Doubly functionalized PI polyamide was designed by introduction of an alkylating agent 1-(chloromethyl)-5-hydroxy-1,2-dihydro-3H-benz[e]indole (seco-CBI) and biotin for sequence-selective alkylation at the target sequence and subsequent streptavidin labeling, respectively. Selective alkylation of the target site in the substrate DNA was observed by analysis using sequencing gel electrophoresis. For the single-molecule observation of the alkylation by functionalized PI polyamide using atomic force microscopy (AFM), the target position in the dsDNA (～200 base pairs) was alkylated and then visualized by labeling with streptavidin. Newly designed DNA origami scaffold named "five-well DNA frame" carrying five different dsDNA sequences in its cavities was used for the detailed analysis of the sequence-selectivity and alkylation. The 64-mer dsDNAs were introduced to five individual wells, in which target sequence AGTXCCA/TGGYACT (XY = AT, TA, GC, CG) was employed as fully matched (X = G) and one-base mismatched (X = A, T, C) sequences. The fully matched sequence was alkylated with 88% selectivity over other mismatched sequences. In addition, the PI polyamide failed to attach to the target sequence lacking the alkylation site after washing and streptavidin treatment. Therefore, the PI polyamide discriminated the one mismatched nucleotide at the single-molecule level, and alkylation anchored the PI polyamide to the target dsDNA.     

末端带有溴甲基基团的柱状树枝化聚酰胺的合成与表征

采用大分子单体的方法合成了一种含大量溴甲基官能团端基,主链和侧链均为聚酰胺的功能化柱状树枝化聚酰胺.氯化亚砜的新活化工艺使整个合成过程不需要保护和去保护的步骤且减少了副反应的产生,从而使得合成和纯化更加简单.产物的结构通过红外和核磁得到了证实.由分子量测试知,聚酰胺的重均分子量(Mw)为5.01×104,分子量分布为2.74.由溶解性测试知,该聚合物能溶解于N,N′-二甲基甲酰胺、N,N′-二甲基乙酰胺、二甲亚砜、1-甲基-2-吡咯烷酮和硫酸等溶剂,溶解性能得到了大大的提高,主要是由于侧链树枝化单元和末端溴甲基存在的缘故.由粘度测试知,该聚酰胺的粘度低,主要是由于侧链树枝化单元的屏蔽效应.该聚合物的热性能也由TGA测试得到了表征,结果表明该聚酰胺具有良好的热性能.由于该聚酰胺外端具有大量的溴甲基基团,它可以作为原子转移自由基聚合反应的引发剂来合成大型的梳形聚合物,另外通过把它外围的溴甲基转化为其它的功能化基团,可以使它应用于其它更广的领域.     

The effect of fiber coating on the tensile properties of ionomer-based composites

Asbestos fibers, of the chrysotile variety, were coated with a thin polyamide film by an in situ polycondensation technique. Ionomer-based composites were prepared containing the so-modified asbestos fibers in a random in-plane orientation; results of testing the tensile properties of these asbestos/polyamide/ionomer composites are presented. Parameters investigated comprise the asbestos content in the composite and the polyamide content deposited on asbestos. A significant improvement in the tensile performance was established, especially at the intermediate polyamide content of 3.4 phr. The behavior is discussed in terms of possible interactions between the phases present in the composite material.     

Isothermal and nonisothermal crystallization kinetics of novel odd-odd polyamide 9 11

A study on isothermal and nonisothermal crystallization kinetics of odd-odd polyamide 9 11 was carried out by differential scanning calorimetry (DSC). The equilibrium melting temperature of polyamide 9 11 was determined to be 199.1 °C. The Avrami equation was adopted to describe isothermal crystallization of polyamide 9 11. Nonisothermal crystallization was analyzed using both the Avrami relation modified by Jeziorny and the equation suggested by Mo. The isothermal and nonisothermal crystallization activation energies of polyamide 9 11 were determined to be −310.9 and −269.0 kJ/mol using the Arrhenius equation and the Kissinger method, respectively.     

Active polycondensation of diethyl 2,3,4,5-tetrahydroxyadipate with diamines

Polycondensation of diethyl 2,3,4,5-tetrahydroxyadipate with various diamines was carried out in solutions under mild conditions. The polycondensation reaction occurred rapidly even at room temperature in polar solvents such as alcohols, and in aqueous solution a cyclic product was obtained instead of linear polymers although the reaction with diamines was completed within several minutes. Polymers obtained from diethyl 2,3,4,5-tetrahydroxyadipate were a linear polyamide having pendant hydroxyl groups, which decomposed on heating at around 200°C. A solid-phase polycondensation of the precursor polyamide yielded a high molecular weight polyamide.     

A new process for producing polyamide from polyester

A new process for producing polyamide from polyester and diamine was proposed. An attempt was made to produce polyamide 6T from polyethyleneterephthalate or dimethylterephthalate with hexamethylenediamine in water, o‐dichlorobenzene and sulfolane. Characterization of the products by IR, elemental analysis, solution viscosity and GPC were carried out. It became clear that high molecular polyamide 6T could be obtained from polyethyleneterephthalate and hexamethylenediamine in sulfolane. The reaction mechanism was discussed from the viewpoint of the polymer effect and solvent effect. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1413–1423, 1999     

主链含偶氮电活性聚酰胺材料的合成与性质

社会的发展和科技的进步不断对材料提出新的要求,功能材料已经成为新的研究热点,因此设计和研究高分子材料的多功能一体化具有重要的科学和现实意义。作为功能高分子材料的一种,聚苯胺因具有原料廉价、制备简便、环境稳定性好等一系列优点,以及特殊的光学、电学、磁学性质等而成为最具应用潜力的导电高分子材料[1-4]。然而聚苯胺结构上的缺陷和不溶不熔的现象,阻碍了人们对聚苯胺的微观研究和加工应用[5,6]。苯胺齐聚物具有明确的分子结构和良好的溶解性,同时光学和电学性质与聚苯胺十分相似[7,8],基本具备了成为聚苯胺替代者的条件,仅由于缺乏良好的机械性能和环境稳定性而发展受到限制。因此我们从分子设计入手,采用氧化偶联聚合方法,将苯胺齐聚物链段和具有光致异构特性的偶氮苯基团同时引入到具有良好综合性能的聚酰胺主链中,制备出一种兼具光活性和电活性的多功能聚合物材料。     

Synthesis of a Pair of Derivatives of N-Methylpyrrole Polyamide

A pair of derivatives of tetrameric N-methylpyrrole polyamide were synthesized in order to develop a new method for the study of interaction of the polyamide derivatives with DNA. Indole acetic acid and nicotinic acid were introduced to the polyamide in the synthesized compound, which showed an expected red shift in the UV spectrum. These compounds may function as a potential tool in the detection of the polyamide binding to DNA.     

Soluble aromatic polyamide bearing ether linkages: synthesis and characterization

Soluble aromatic polyamide chains were prepared by reacting 4–4′-oxydianiline with isophthaloyl chloride in dimethylacetamide. To quench the HCl produced during the polymerization reaction, a stoichiometric amount of triethylamine was added. The precipitates formed were separated leaving behind clear polyamide resin. Thin and transparent film was obtained by evaporating the solvent and was subjected for Fourier transform infrared (IR), nuclear magnetic resonance (NMR), gel permeation chromatography, thermogravimetric analysis, differential scanning calorimetry, water absorption, and mechanical analyses. The transparent film was found to be soluble in dimethylacetamide, dimethyl sulfoxide, and dimethylformamide. IR and NMR spectroscopic analyses confirmed the structure of the polyamide while the gel permeation chromatography revealed the formation of a high-molecular-weight polymer. Thermogravimetry, differential scanning calorimetry, water absorption, and mechanical testing were also performed to further verify its physical properties. A soluble aromatic polyamide was successfully synthesized by solution polymerization and characterized. The polyamide has film-forming property, and the film is transparent, mechanically strong, and thermally stable.     

Morphology and properties of ternary polyamide 6/polyamide 66/elastomer blends

The aim of the work presented is to evaluate the mechanisms and phase interactions in ternary blends based on different polyamides and functionalised elastomers, and to establish a correlation between the morphology controlled by the specific binary interactions, and physical and technological properties, respectively. The properties of the ternary system polyamide 6/polyamide 66/ elastomer depend on the specific blend morphology which is determined mainly by the differences of the surface tension of the components. A phase‐in‐phase structure was observed by microscopic study (AFM) in the ternary polyamide 6/polyamide 66/elastomer blends with maleic anhydride grafted ethene‐octene copolymer, and a “quasi” phase‐in‐phase structure in blends with maleic anhydride grafted ethene‐propene‐diene copolymer as the elastomer phase. An incorporation of polyamide inside of the elastomer particles was observed in the first case due to the difunctionality of polyamide 66. This type of morphology causes an increased elongation at break and toughness of these blends. In comparison to the binary polyamide based blends the ternary blends show an increased elastic modulus, elongation at break and yield stress as well as a high impact strength at low temperatures up to ?20 °C. Copyright © 2003 John Wiley & Sons, Ltd.     

Durable flame‐retardant finishing for polyamide 66 fabrics by surface hydroxymethylation and crosslinking

This paper describes an attempt to develop a durable finishing method in order to improve the fire performance of polyamide 66 fabrics. Hydroxymethylation with a 36% formaldehyde aqueous solution in association with a pad‐curing process to enable the fabric to react with flame‐retardant solutions was used in the finishing process. The fire performance of treated samples was characterized by limiting oxygen index (LOI) and vertical flammability tests, and the results show that the LOI value can increase from 21.6% to 46.2%. The thermal behavior of untreated and treated polyamide 66 fabrics was investigated by using thermogravimetic analysis and differential scanning calorimetry. Furthermore, residual char of treated fabric sample is much higher than that of untreated fabric sample. Fourier transform infrared spectroscopy proves that the substituted hydroxymethyl groups do exist on the molecular chain of polyamide fabric sample after surface modification. The morphology of residue char of polyamide 66 fabric samples was analyzed by scanning electron microscope, and the mechanical properties were also investigated and discussed. Copyright © 2012 John Wiley & Sons, Ltd.     

Thin-layer chromatography of sulphonamides on silica gel G and polyamide layers by means of a polar mobile phase.

A thin-layer chromatographic system based on polyamide or silica gel G layers and an aqueous mobile phase was used for the separation of a series of sulphonamides. A linear relationship between RM values on polyamide layers and the acetone concentration in the mobile phase allowed the calculation of extrapolated RM values. The influence of the nature of the stationary phase on the migration of compounds is discussed.     

Synthesis of polyimides from N,N′-bis(phenylsulfonyl)pyromellitimide and aromatic diamines

A novel and successful synthesis of polyimide has been performed by the two-step polymerization of N,N′-bis(phenylsulfonyl)pyromellitimide (BPSP) and bis(4-aminophenyl) ether (ODA). The ring-opening polyaddition reaction proceeded in N-methyl-2-pyrrolidone at room temperature through the formation of the open-chain polyamide, which was subsequently converted by heating to the polyimide along with the elimination of benzenesulfonamide. The polymerization of BPSP with ODA took place fairly rapidly to give the polyamide having inherent viscosity in the range of 0.6–0.8. The polyamide solution was resistant to hydrolysis, but was somewhat susceptible to imidization reaction. The thermal imidization of the open-chain polyamide occurred far more readily than that of the polyamic acid derived from pyromellitic dianhydride and ODA.