Aromatic Polyesters synthesis method

The use of silylated monomers is an interesting alternative method of aromatic polyester synthesis since the silylated gaseous by-products cannot participate in the reverse reaction, shifting polyesterification toward polymer formation. Reactions between silyl esters and acetates (Scheme 2.23) and reactions between silyl ethers and acid chlorides (Scheme 2.24) have been applied to the synthesis of linear265-267 and hyperbranched wholly aromatic polyesters202,268 269 (see Section 2.4.5.2.2). 

Throughout this chapter, the examples of polymerizations in compressed CO2 have been primarily for chain growth polymerization processes. However, step-growth methods represent an area of new interest for SCFs. Initial experiments in this area include the synthesis of aromatic polyesters such as poly(ethylene terephthalate) (PET) in SCCO2 as illustrated in Scheme 4.5-9 [144]. An advan-... 

Several synthetic routes are known for the synthesis of aromatic LC polyesters. Melt, solution, and slurry polycondensations are mainly used. Most significant are the polycondensation of terephthalic acid diesters and aromatic diols, the polycondensation of terephthalic acids and acetates of aromatic diols with the addition of transesterification catalysts, and the polycondensation of aromatic diols and aromatic diacid dichlorides [2]. A method successfully utilized for laboratory synhesis is the polycondensation of silated aromatic diols and aromatic diacid dichlorides [3]. Molecular weights depend significantly on the reaction conditions and on the solubility as well as the fusibility of the polyesters, which is relatively poor for para-linked unsubstituted aromatic polyesters. 

The data on aromatic polyesters based on phthalic and -oxybenzoic acid derivatives have been presented and various methods of synthesis of such polyesters developed by scientists from different countries for last 50 years have been reviewed. 

Stabilisers of this type have been claimed as extremely effective UV absorbers for poly(ethylene-co-l,4-cyclohexanedimethylene terephthalate) [98-100], allowing the use of this material in outdoor applications. Developments in novel synthesis methods have improved the inherent stability of this class of additive, paving the way towards their more effective use in aromatic polyesters [101-106]... 

The PTT is aromatic polyester prepared by the melt polycondensation of 1,3-propanediol (1,3-PDO) with either TPA or dimethyl terephthalate (DMT). The PTT is synthesized by the transesterification of propanediol with dimethylene terephthalate or by the esterification of propane diol with TPA. The reaction is carried out in the presence of hot catalyst like titanimn butoxide (Ti(OBu) ) and dibutyl tin oxide (DBTO) at a temperature of 260°C. The important by-products of this reaction include acrolien and allyl alcohol (Chuah, 2001). Direct esterification of propane diol and TPA is considered as the least economic and industrial method. The reaction is carried out in the presence of a heel imder a pressure of 70-150 kPa at a temperature of 260°C. The heel is usually referred to the added PTT oligomers which act as a reaction mediiun and increase the solubility of TPA (Chuah, 2001). Recent studies by different groups show that the selection of the catalyst plays a major role on the reaction rate and PTT properties. Commonly used catalysts like titanium (Doerr et al., 1994), tin (Kurian and Liang, 2001 Fritz et al., 1969) and antimony (Karayannidis et al., 2003 Fitz et al., 2000) compounds have their own limitations. Titanimn-based catalysts are active but the PTT is discolored, antimony-based catalysts are toxic and only active in polycondensation while tin-based compounds have lower catalytic activity. Karayannidis and co-workers (2003) reported the use of stannous oetoate ([CHj(CH2)3CH(C2Hj)COO]jSn) as the catalyst for PTT synthesis but its catalytic activity is poor, resulting in a low molecular weight PTT which was confirmed... 

Production of 1,3-PD in high quality and quantity during the last 15-20years has led to the synthesis of several aliphatic polyesters with biodegradable properties. Poly(propylene alkylanedicarboxylate) polyesters can be prepared by the two-stage melt polycondensation method (esterification and polycondensation) using proper amounts of aliphatic acids and 1,3-PD and a procedure similar to that used for aromatic polyesters. 

Another recent study on polyester synthesis through thiol-ene reactions for preparation of monomers from fatty-acid derivatives was described by Pang and co-workers [16]. Authors adopted the same approach for preparing aliphatic diols and diester from 10-undecen-l-ol, methyl 10-undecenoate and thiols. In parallel, they prepared aromatic diesters from methyl vanillate and a series of thermoplastic polyesters were synthesised by polycondensation of the diols and diesters using conventional transesterification methods. These materials were obtained with Mn values of 12-27 kDa and T values of -13 to 13 °C. 

This is the preferred method for the synthesis of both, aliphatic and aromatic polyesters derived from CHDM. The reaction is usually accomplished in two steps. The first step is carried out under a pressure which depends on the diacid or the dimethyl ester derivative used for the synthesis. Usually an excess of diols to diacid (1.2-2.2 1) is employed so a mixture of short oligomers is produced. In the second polycondensation step, which is carried out at higher temperatures and under vacuum, the oligomers react to generate the polymer and the excess of diol is removed. If the resulting polyester is crystalline it may be subjected to solid state postpolycondensation (SSP) in order to increase the molecular weight. 

Method for Producing High-Molecular Polyarylenesulfideketone. US Patent 47182122. Ogawa, T., Marvel, C. S. (1985). Polyaromatic Esterketones and Ester-Ketone-Sulfones having Various Hydrophilic Groups. J. Polym. Sci. Polym. Chem. Ed, 25(4), 1231-1241. Percec, V. Nava, H. (1988). Synthesis of Aromatic Polyesters by Scholl Reaction 1, Poly( 1,1-Dinaphthyl Ester Phenyl Ketones)./. Polym. Sci. A, 26(3), 783-805. 

Methods of synthesis of thermotropic polyesters, Poly-p-phenylene terephthalate and poly-p-hydroxybenzoate are the simplest and most accessible representatives of the aromatic polyesters ... 

Hyperbranched polymers are formed by polymerization of AB,-monomers as first theoretically discussed by Flory. A wide variety of hyperbranched polymer structures such as aromatic polyethers and polyesters, aliphatic polyesters. polyphenylenes, and aromatic polyamides have been described in the literature. The structure of hyperbranched polymers allows some defects, i.e. the degree of branching (DB) is less than one. The synthesis of hyperbranched polymers can often be simplified compared to the one of dendrimers since it is not necessary to use protection/deprotection steps. The most common synthetic route follows a one-pot procedure " where AB,-monomers are condensated in the presence of a catalyst. Another method using a core molecule and an AB,-monomer has been described. ... 

Palladium- or nickel-catalysed carbonylation polycondensation of dibromoar-enes with bifunctional nucleophilic monomers such as aromatic diamines and bisphenols in the presence of carbon monoxide appeared to be a new promising method for the synthesis of aromatic polyamides [scheme (15)] and polyesters [scheme (16)] respectively [162-170], The first successful example was the synthesis of high molecular weight polyaramide according to scheme (15) (Ar1 = m-C6H4-, Ar2 = p-C6H4 O C6H4 ) [162],... 

In condensation polymerization, the use of NIR to follow the reactant concentrations at elevated temperatures (200-300 °C) has been applied to the synthesis of aromatic and aliphatic polyesters (Dallin, 1997). This provides an accurate alternative to the routine measurement of acid values, hydroxyl number and viscosity, with the added advantage of providing continuous data throughout the polyesterification, which allows optimum conversion. Related examples of the use of NIR include studies of esterification of low-molar-mass analogues (Blanco and Serrano, 2000) or transesterification of an existing polymer or copolymer (Sasic et al, 2000). The NIR method allowed quantitative determination of rate constants, end points and yield and equilibrium constants as well as mechanistic information, which allowed the esterification to be optimized through the use of higher temperatures and an excess of acetic acid (Blanco and Serrano, 2000). 

This melt phase polycondensation method was also applied for the synthesis of a good number of aliphatic (24,27,28,32) and aromatic (11,46,47,50,55) polyesters and copolyesters derived from 1,4-CHDM. Depending on the polyester to be prepared, small variations in temperature or/and reaction time are introduced, and the catalyst is specifically chosen. The target is in most of cases to minimize undesirable side reactions giving rise to coloration of the final product. 

High-tempoature equilibrium polycondensadon (more precisely, reacyladon) of acetyl derivatives of bisphenols and aromatic dicarboxylic acids is the basic method of synthesis of fibw-forming LC polyesters ... 

A new route to a controlled synthesis of heavily aromatic substituted polyesters has been investigated. The method involves an alternating copolymerisation of an aldehyde and a ketene. PEK and MBA can be copolymerised under /THF/nBuLi/ — 20°C/LiCl/CH3OH/ conditions to obtain an alternating PEK/ MBA copolymer MJM = 1.15, = 5.1 kg/mol). The alternating structure... 

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