Processing, thermoplastics condensation polymerization

Set, V—To convert an adhesive into a fixed or hardened state by chemical or physical action, such as condensation, polymerization, oxidation, vulcanization, gelation, hydration, or evaporation of volatile constituents. The term is most commonly used with thermoplastic adhesives, unless a chemical process, such as polymerization, is involved. 

PGA, is another biodegradable polymer with applicability in bionanocomposites [372] and, like PVA and PVAc, PGA is readily soluble in water and can be processed by extrusion, injection, and compression molding similarly to other thermoplastics. Murugan et al. [373] produced bionanocomposites of PGA and clay by polymerizing glycolic acid under vacuum in the presence and absence of nanoday which act as a catalyst to the condensation polymerization of PGA. They found that addition of clay improved flame retardancy. 

Very highly branched polymers, like polyethylene made by free-radical, high-pressure processes, will have Mw/Mn ratios of 20 and more. Most polymers made by free-radical or coordination polymerization of vinyl monomers have ratios of from 2 to about 10. The M /M ratios of condensation polymers like nylons and thermoplastic polyesters tend to be about 2, and this is generally about the narrowest distribution found in commercial thermoplastics. 

Polymers can be classified in many ways, such as by source, method of synthesis, structural shape, thermal processing behavior, and end use of polymers. Some of these classifications have already been considered in earlier sections. Thus, polymers have been classified as natural and synthetic according to source, as condensation and addition (or step and chain) according to the method of synthesis or polymerization mechanism, and as linear, branched, and network according to the structural shape of polymer molecules. According to the thermal processing behavior, polymers are classified as thermoplastics and thermosets, while according to the end use it is convenient to classify polymers as plastics, fibers, and elastomers (Rudin, 1982). 

Pri ce. The price of a thermoplastic resin is basically determined by the cost of preparation, which in turn strongly depends on the cost of reagents (monomers, catalysts, etc), the complexity of the manufacturing process, and the dimension of production plants. Aliphatic polyketones, for instance, are made from very cheap raw molecules as ethylene, propylene, and CO their cost is determined by the need for expensive catalysts, based on Pd complexes, and the relatively complex production plant. On the other hand, PEN, which can easily be prepared in the same reactors used for PET, suffers from the difficult availability of its basic monomer dimethyl 2,6-naphthalene dicarboxylate. Most engineering polymers contain aromatic monomers, which are difficult to synthesize and polymerize, with slow and sophisticated mechanisms (condensation, substitution, oxidative coupling). 

Reaction polymerization reactions of isocyanates with suitable monomers can he performed in an extruder or in a RIM machine. In the latter reaction thermosets (cross-hnked polymers) are produced. In an extruder usually linear polymers are manufactured. For example from methylene di-p-phenylene isocyanate (MDI), with some macroglycols and 1,4-hutanediol as extenders, segmented polyurethane elastomers are produced in an extruder (6). However, linear condensation polymers are also produced in a vented extruder. For example from MDI, with macrodicarboxylic acids and dicarboxyhc acids as extenders thermoplastic block copolyamide elastomers are produced. The by-product of the condensation reaction, carbon dioxide, is removed in the vented extruder. The polycondensation process can also be performed in solution. For example, MDI can be added to a solution of dicarboxyhc acids in tetramethylene sulfone, with simultaneous removal of the carbon dioxide. Tetramethylene sulfone is the solvent of choice for solution polymerization of isocyanates (7). In addition to dicarboxyhc acids trimellitic acid anhydride and benzophenonetetracarboxylic acid dianhydride (BTDA) are utilized as monomers for condensation polymers. With these monomers poly(amide imides) and poly(imides) are produced. The diisocyanate-derived commercial polycondensation products are listed in Table 1. 

Poly(ethylene terephthalate) (abbreviated PET or PETE) is a semi-aromatic thermoplastic polyester obtained by condensation reaction of difunctional reactants and well-known for more than 60 years. PET is commonly produced by esterification reaction between terephthalic acid and ethylene glycol with water as a byproduct or by transesterification reaction between ethylene glycol and dimethyl terephthalate with methanol as a byproduct. In order to obtain high molar masses polymers, solid-state polymerization is carried out. PET is one of the most important industrial polymers because of its excellent properties as tensile impact strength, chemical resistance, processability, clarity, thermal stability and others. The main applications of PET are fibers for textiles, films and bottles. Annual world PET production is around 60 millions tons. PET materials were manufactured using extrusion, injection molding and blow molding techniques. 

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