Polyesterification of dimer

Several papers and patents on polyesterification of dimer acid with various glycols under different experimental conditions appeared in the literature. The dimer acid-based polyesters with a slight variation in composition enjoy a variety of applications. Observations show that a particular property of the product can be enhanced or suppressed by the choice of a proper additive. 

It is quite apparent from the state-of-art of the subject that a variety of dimer acid-based polymeric systems has been investigated from the viewpoint of commercial applications. However, their plasticizing polyester still are known on a limited scaie also, no research in the area of metal containing dimer acid polyesters has been done. The kinetics of the polyesterification of dimer acid with different polyhydroxy compounds was studied by Bajpai and Nivedita [90-94]. 

These results and discussion in favor of the p-toluene sulfonic acid (pTSA) as an effective catalyst for polyesterification of dimer acid and butanediol strongly supports the proton-catalyzed nature of polyesterification. Usually, the proton-catalyzed mechanism for esterification is extrapolated to proton-catalyzed polyesterification [104]. The polyesterification of dimer acid and butanediol involves protonation of the dicarboxylic acid by the reaction of protonated species with the hydroxy group of glycol to yield the polyester. The proton catalyzing the protonation of carboxylic acid is provided by the carboxyl group of the monomer, i.e., dimer acid, and by pTSA in absence and presence of added catalyst, respectively. 

Figure 2. Variation of acid number with time for the polyesterification of dimer acid and butane dio showing effect of catalyst.

A generalized kinetic treatment of the array of processes occurring in condensation polymerization might appear hopelessly complex. In the polyesterification of a hydroxy acid, for example, the first step is intermolecular esterification between two monomers, with the production of a dimer... 

Chemical Reactions. The reactions of dimer acids were reviewed fully in 1975. 1716 most important is polymerization the greatest quantities of dimer acids are incorporated into the non-nylon polyamides, Other reactions of dimer acids that are applied commercially include polyesterification, hydrogenation, esterification, and conversion of the carbuxy groups to various nitrogen-containing functional groups. 

High performance in the synthesis of hydrolytically resistant polyurethanes was obtained by using in the polyesterification reaction, very hydrophobic fatty dimer acids and fatty dimer alcohols, products obtained from vegetable oils (see Chapter 12.5). The use of fatty dimeric acids and fatty dimeric alcohols (obtained by the hydrogenation of dimeric acids or dimeric esters) to build the polyester structure, creates an extremely high hydrophobic environment alongside a low concentration of labile ester bonds. 

The synthesis of dimeric fatty acids is based on the reaction between a fatty acid with one double bond (oleic acid) and a fatty acid with two double bonds (linoleic acid) or three double bonds (linolenic acid), at higher temperatures in the presence of solid acidic catalysts (for example montmorillonite acidic treated clays). Dimerised fatty acids (C36) and trimerised fatty acids (C54) are formed. The dimer acid is separated from the trimeric acid by high vacuum distillation. By using fatty dimeric acids and dimeric alcohols in the synthesis of polyesters and of polyester polyurethanes, products are obtained with an exceptional resistance to hydrolysis, noncrystalline polymers with a very flexible structure and an excellent resistance to heat and oxygen (Chapter 12.5). Utilisation of hydrophobic dicarboxylic acids, such as sebacic acid and azelaic acid in polyesterification reactions leads to hydrolysis resistant polyurethanes. 

Carothers classification (condensation vs. addition) is primarily based on the composition or structure of polymers. The second classification (chainwise vs. stepwise) was proposed by P. J. Floiy, and is based on the kinetic scheme or mechanism governing the polymerization reactions. Step reactions are those in which the chain growth occurs in a slow, stepwise manner. Two monomer molecules react to form a dimer. The dimer can then react with another monomer to form a trimer, or with another dimer to form tetramer. Thus, the average molecular weight of the system increases slowly over a period of time. This is exemplified by the following polyesterification ... 

Huang et al. [51] believed that the ionization proposed by Tang was unlikely under conditions found in polyesterifications, though they supported a 2.5 kinetic order. Their mechanism involved a complex series of interactions between acid dimers. 

Step-growth polymerization occurs when two individual molecules react to form the monomer. Two monomers react to form a dimer. These dimers react to form tetramers, etc. If at each step a byproduct small molecule is excluded, such as water or an alcohol, then we have the so-called condensation polymerization. A scheme describing a polyesterification reaction involving the manufacture of poly ethylene terephtha-late (PET), which is used to produce plastic beverage bottles, is shown below. 

Kinetic considerations are of paramount importance in understanding the mechanism of step-growth polymerization. As stated in Chapter 1, chain-growth polymerizations take place in discrete steps. Each step is a reaction between two functional groups for instance, in a polyesterification reaction it is a reaction between -COOH and -OH. The increase in molecular weight is slow. The first step is a condensation between two monomers to form a dimer ... 

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