Study of poly-ϵ-caprolactone bulk degradation

The thermal stability of poly-?-caprolactone samples obtained by ring-opening polymerization in the presence of different metal alkoxides has been investigated. A significant degradation of the polyesters is observed under isothermal conditions at 120°C. The degradation is related to the nature of the endgroup, the presence of catalyst residues, and the presence of molecular oxygen. The hydroxyl endgroups play a determinant role in the process. They probably give rise, under the influence of catalyst residues, to hydroperoxides which are responsible for the polymer degradation by a radical reaction. It is shown that this is clearly different from the change in molecular weights distribution due to the well-known ester interchange reaction (transesterification equilibrium). Resulting methods for the polymers stabilization are indicated.     

Polyester synthesis in aqueous miniemulsion

Hydrophobic polyesters have been synthesized in miniemulsion in the presence of large amounts of water. The yield of the esterification and the molecular weight of the polyesters have been determined for different reaction conditions. It was found that the dispersion state has no influence on the equilibrium: the yield is the same in 100 nm particles than in very large droplets. However, an important parameter is the water concentration inside the particles, as shown by an increase in the yield with more hydrophobic monomers. Another important parameter is the structure of the alcohol monomer. Alcohol compounds bearing electron-donating groups allow to displace the equilibrium toward ester formation. It is also shown that polyester/polystyrene hybrid particles can be synthesized in a very simple way using a one pot procedure.     

湿固化单组份聚氨酯密封胶的研制

用甲苯二异氰酸酯、聚酯和聚醚通过二步法制备了湿固化单组份聚氨酯密封胶。研究了聚酯和聚醚种类、反应温度和时间、填料和催化剂等对密封胶性能的影响，确定了制备工艺条件和配方。     

Mechanism of the reaction involving the formation of dioxane byproduct during the production of poly(ethylene terephthalate)

The formation of certain low molecular weight by-products during the esterification reaction between ethylene glycol and dimethyl terephthalate was investigated. The result obtained showed that the presence of incorporated diethylene glycol within the polymer led to the formation of low molecular weight side products. An alcoholysis reaction involving the ethylene glycol and the ester was found to show a mechanism that is analogous to that of an ester interchange resulting in the production of the acid and the diethylene glycol precursor of the dioxane by-product.     

Reactions of azelaaldehydic esters

Alkyl azelaaldehydates and their acetals can undergo reactions at either the aldehyde or the ester group to form a variety of novel and reactive monomers and polymers. Pertinent reactions of the aldehyde group (and resultant products) include acetalization with pentaerythritol (diester-acetal), acetalization with glycerol (hydroxy ester-acetal), hydrogenation (hydroxy ester), reductive alkylation of ammonia (amino acid and imino diester), aldolization (dibasic acid) and hydrazone formation (azine dibasic acids). Reactions at the ester group include aminolysis (diacid amides) and hydrazinolysis (hydrazide acetal). These various products can undergo self-condensation or condensation with glycols or diamines to form polyesters, polyamides, poly (ester-acetals) and poly (amideacetals). Polymers with cyclic acetal structures in the polymer backbone have latent crosslinking capabilities. Presented at the AACC-AOCS Joint Meeting, Washington, D.C., April, 1968. No. Utiliz. Res. Dev. Div., ARS, USDA.     

非酸催化合成二元酸酯

利用大孔阳离子交换树脂、改性ＺＳＭ－５分子筛、钛酸酯为催化剂，合成了丁二酸二酯、己二酸二酯。酯收率均在９０％以上。试验了催化剂种类及其用量、反应时间对反应的影响。     

Synthesis and ion binding properties of polyesters and polyamides with diazacrown-ethers

The synthesis of polymers containing a [22] diaza-crown-ether in the backbone is described. These compounds are obtained by polycondensation of N, N′-diethylene amine and N, N′-diethylene alcohol derivatives of the cyclic diamine [23] with various acid dichlorides, leading to polyesters and polyamides. The cation binding properties of these polymers are studied by water-chloroform extraction using picrate salts, and compared with the properties of the analogous monomeric molecules. The binding properties are strongly dependent on the polymeric structure and comparison with the analogue molecules clearly demonstrates that the observed decrease in complex stability is due mainly to the presence near the rings of ester or amide groups. An intramolecular structure is proposed, based on interactions between the nitrogen bridges and the ester or amide groups which lead to the formation of a five-membered ring.     

Effective Guanidine‐Catalyzed Synthesis of Carbonate and Carbamate Derivatives from Propargyl Alcohols in Supercritical Carbon Dioxide

The reactions of propargyl alcohols with carbon dioxide in supercritical carbon dioxide or in acetonitrile with gaseous carbon dioxide in the presence of organic bases as catalysts have been examined. Bicyclic guanidines are effective catalysts for the formation of α‐methylene cyclic carbonates under mild reaction conditions. Oxoalkyl carbonates, oxoalkyl carbamates or α‐methyleneoxazolidinones are obtained in high yields and good selectivities in one‐step starting from propargyl alcohols and an external nucleophile (alcohols or amines) using bicyclic guanidines as catalysts in supercritical carbon dioxide. Propargylic diols under the same reaction conditions underwent a rearrangement process instead of carbon dioxide insertion whereas in the presence of an external nucleophile the formation of oxocarbonates, oxocarbamates or cyclic carbamates was achieved in satisfactory yields.     

Biodegradable poly(ester amide)s – A remarkable opportunity for the biomedical area: Review on the synthesis,characterization and applications

Poly(ester amide)s have emerged in the last years as an important family of biodegradable synthetic polymers. These polymers present both ester and amide linkages in their structure and they gather in the same entity the good degradability of polyesters with the good thermo-mechanical properties of polyamides. Particularly, poly(ester amide)s containing α-amino acids have risen as important materials in the biomedical field. The presence of the α-amino acid contributes to better cell–polymer interactions, allows the introduction of pendant reactive groups, and enhances the overall biodegradability of the polymers.     

The metathesis reaction — a route to the synthesis of elastomeric polymers and a scientific challenge

The metathesis reaction of olefins is generally assumed to proceed via transition metal carbenes and metalla cyclobutane derivatives as key intermediates. Besides the Phillips trisolefin process the reaction has become technically relevant for the synthesis of special polymers such as polynorbornene. Of scientific interest is the mechanism of the reaction. The particular feature of the metathesis of cycloolefins is the formation of a ring chain equilibrium from which not only cyclic oligomers can be isolated and investigated; moreover, the equilibrium concentration of the cyclic oligomers yields valuable conformational information on the respective chain.     

Effect of composition and polyesterification catalysts on the optical properties of cured polyesters

Unsaturated polyesters based on ethylene glycol have been synthesized using a variety of anhydride, saturated and unsaturated dicarboxylic acids and various catalysts. The structure of the polyesters and the effect of the different compositions on the colour of cured polyesters are studied by FTIR, DSC and colorimetry. The structure of cured polyesters greatly depends on the isomerization of maleic acid to fumaric acid during polyesterification. The colour of unsaturated polyesters cured with the most common curing system (MEKP as initiator and CoNp as accelerator) is firstly influenced by the curing accelerator CoNp via the d–d transitions of the transition metal cobalt. Secondly, the composition of the dicarboxylic acids and anhydride used in the polyesterification influences the colour of the polyesters which depends especially on the isomerization of maleic acid. The cured maleate polyesters have more unreacted double bonds and more polar structure because of the presence of carbonyl groups, compared to the corresponding fumarate polyesters, and this structure affects the colour. The residual catalysts from the polyesterification have minor influence on the colour of cured polyesters. Copyright © 2002 Society of Chemical Industry     

The role of flame-retardant chemicals in the thermal degradation of poly(ethylene terephthalate). Studies with the model ester n-propyl pyrene-1-carboxylate

The pyrolysis of n-propyl pyrene-1-carboxylate, a model ester for poly(ethylene terephthalate), has been studied using pyrolysis mass spectrometry. The major mode of decomposition has been identified as the formation of propylene and pyrene-1-carboxylic acid as a result of a cyclic intramolecular rearrangement. When phosphorus or bromine containing compounds are blended with the model ester, no significant changes are observed in the kinetics of the overall pyrolysis, while relatively small changes are observed in the mode of decomposition with the phosphorus compound. The results suggest that the role played by phosphorus and bromine in flame-retarding polyesters is predominately restricted to the gas phase.     

Esterification and Transesterification of Renewable Chemicals

An overview is given of newly developed Lewis or Brønsted acid and base catalysts for esterification, transesterification and ester interchange reactions. The most relevant applications of these catalysts and reactions in the domain of renewable resources, in particular, oils and fats, are discussed.     

Transesterifications in a polyblend of poly(butylene terephthalate) and a liquid crystalline polyester

Transesterfication between a liquid crystalline polyster and poly(butylene terephthalate) was followed quantitatively by analyzing ¹³C-NMR spectra of the 50:50 blend after heat treatmetn at 290°C for varying lengths of time. Differential scanning nalysis was employed to follow the interchange reactions. From analysis of triad sequences of the transesterified blends, it was clear that measurable exchange reactions occurred when the blend was kept at 290°C for 20 min. The distribution of sequences tends to approach that of a statistical binary copolymer as the heat treatment period is increased. The results ontained from this investigation show that polyblends between an LC polyesterand conventional polyesters must be handled carefully. Otherwise, ester interchange reactions are inevitable.     

由二氧化碳出发合成有机碳酸酯

对以二氧化碳为原料合成有机碳酸酯的环氧路线、酯交换和直接合成方法作了综合评述 ,认为直接合成是最佳的合成路线。碳酸酯的直接合成可在均相及多相催化体系中进行 ,负载金属、金属甲氧基化合物及碱均可作为催化剂。直接法研究的关键在于高性能催化剂的开发、由二氧化碳对金属 -氧键插入反应导致的催化循环的构筑及耦合反应的应用。     

Synthesis of oligocarbonate diols from ethylene carbonate and aliphatic diols catalyzed by alkali metal salts

The influence of alkali metal salt catalysts and reaction conditions on the oxyethylene units formation in the synthesis of oligocarbonate diols from five-membered cyclic carbonates and aliphatic diols is presented. The reaction mechanism, involving the alkoxide group formation from cyclic carbonate and alkali metal salts has been proposed and discussed. The oligomeric products were analyzed by means of MALDI-TOF mass spectrometry and NMR spectroscopy.     

NiBa catalysts for CO2-reforming of methane

Ni–Ba catalysts supported on γ-Al₂O₃ for the dry reforming of methane were prepared, characterized and studied under reaction conditions. Ba incorporation inhibits the formation of Ni spinel. All the Ni–Ba catalysts studied are highly active for the CO₂-reforming of methane. However, the Ni–Ba catalyst with high Ba and Ni content was the most active and stable catalyst, due to the presence of accessible Ni particles stabilized by the formation of BaAl₂O₄.     

高选择性合成羟基对苯二甲酸单酯的反应规律及其应用

为满足羟基有序改性高聚物的需要,研究了制备AB型新单体所需关键中间体--羟基对苯二甲酸单甲酯的合成方法。探讨了不同位置酯化和双酯单水解的理论和反应规律,建立了一种通用于非对称取代对苯二甲酸单酯的合成和分离纯化技术。结果表明:以羟基对苯二甲酸(HTA)为起始原料,先经氯化亚砜作用下的甲醇双酯化,再经碱性水溶液中的单水解反应,高选择性地合成了2-羟基-4-羧基苯甲酸甲酯(α-MHT),总收率76%以上;而HTA硫酸催化甲醇直接单酯化则制得3-羟基-4-羧基苯甲酸甲酯(β-MHT),收率近70%。 同时在2,6-二羟基对苯二甲酸(DHTA)单酯化合物α-单甲酯(α-MDHT)和β-单甲酯(β-MDHT)的合成中得到应用。     

A mechanism for flame retardation of poly(ethylene terephthalate)

The thermolysis of vinyl methylterephthalate has been studied as a model of poly(ethylene terephthalate) (PET) thermolysis. Based upon this reaction, a potential mechanism for PET flame retardation is proposed. The assumption is made, based upon firm experimental evidence, that the initial step in PET degradation is formation of a vinyl ester and a carboxylic acid. The essentials of the mechanism are that this vinyl ester participates in a vinyl polymerization reaction and produces a linear polymer. This linear polymer then is involved in a chain-stripping reaction with the loss of methylterephthalate and the concomitant formation of a polyene. In the last step, this polyene undergoes a cyclization reaction and yields a crosslinked product. There are two stages at which PET undergoes crosslinking: In the second step the linear vinyl polymer is produced; in the last step ultimate crosslinking with the formation of cyclic structure is observed.