Thermoplastic condensation polymers

Because commercial synthetic thermoplastic polymers are either addition polymers or condensation polymers, depolymerization occurs by different routes. Addition polymers, for which the synthesis reactions are essentially not reversible, depolymerize by pyrolysis or such severe chemical attack that few useful monomers can be practically recovered. With pyrolysis, a wide spectrum of species are created, which offers little in the way of valuable reaction products without costly separation processes. The overall yield to desired products can be unattractively low. 

Further classification of polymers in the groups of additional polymers and condensation polymers has been on monomer composition, because this provides an orderly approach, whereas classification based on polymer uses, such as plastics, elastomers, fibers, coatings, etc. would result in too much overlap. For example, polyamides are used not only as synthetic fibers but also as thermoplastics molding compounds and polypropylene, which is used as a thermoplastic molding compound has also found uses as a fiber-forming material. 

Many of these linear chain polymers have the advantage for characterization that they are soluble in organie solvents. This has aided greatly, as will be shown later, in the analysis of chain structures and reaction mechanisms and the determination of molecular weight. Most linear polymers, both condensation and addition, also reversibly soften and flow on heating and conversely harden and become rigid on cooling. These materials are sometimes called thermoplastics because they flow... 

Uses. The largest uses of butanediol are internal consumption in manufacture of tetrahydrofuran and butyrolactone (145). The largest merchant uses are for poly(butylene terephthalate) resins (see Polyesters,thermoplastic) and in polyurethanes, both as a chain extender and as an ingredient in a hydroxyl-terminated polyester used as a macroglycol. Butanediol is also used as a solvent, as a monomer for vadous condensation polymers, and as an intermediate in the manufacture of other chemicals. 

A series of compounded flame retardants, based on finely divided insoluble ammonium polyphosphate together with char-forming nitrogenous resins, has been developed for thermoplastics (52—58). These compounds are particularly useful as iatumescent flame-retardant additives for polyolefins, ethylene—vinyl acetate, and urethane elastomers (qv). The char-forming resin can be, for example, an ethyleneurea—formaldehyde condensation polymer, a hydroxyethylisocyanurate, or a piperazine—triazine resin. 

The packaging (qv) requirements for shipping and storage of thermoplastic resins depend on the moisture that can be absorbed by the resin and its effect when the material is heated to processing temperatures. Excess moisture may result in undesirable degradation during melt processing and inferior properties. Condensation polymers such as nylons and polyesters need to be specially predried to very low moisture levels (3,4), ie, less than 0.2% for nylon-6,6 and as low as 0.005% for poly(ethylene terephthalate) which hydrolyzes faster. 

Aniline—formaldehyde resins were once quite important because of their excellent electrical properties, but their markets have been taken over by newer thermoplastic materials. Nevertheless, some aniline resins are stiU. used as modifiers for other resins. Acrylamide (qv) occupies a unique position in the amino resins field since it not only contains a formaldehyde reactive site, but also a polymerizable double bond. Thus it forms a bridge between the formaldehyde condensation polymers and the versatile vinyl polymers and copolymers. 

Braided Synthetic Nonabsorbable Sutures. Braided synthetic nonabsorbable sutures are made by melt-spinning thermoplastic polymers into fine filaments (yams), and braiding them, with or without a core, to form multifilament sutures in a range of sizes. Nylon-6,6 [32131 -17-2] (7) is a polyamide produced by the condensation polymerization of adipic acid and 1,6-hexanediamine. 

Nylon resins are important engineering thermoplastics. Nylons are produced by a condensation reaction of amino acids, a diacid and a diammine, or by ring opening lactams such as caprolactam. The polymers, however, are more important for producing synthetic fibers (discussed later in this chapter). 

Polycarbonates (PC) are another group of condensation thermoplastics used mainly for special engineering purposes. These polymers are considered polyesters of carbonic acid. They are produced by the condensation of the sodium salt of bisphenol A with phosgene in the presence of an organic solvent. Sodium chloride is precipitated, and the solvent is removed by distillation ... 

Combined liquid crystalline polymers, 49 Combustion testing, 245 Composites, thermoplastic, 32 Compression force deflection (CPD), 244 Compression tests, 242 Condensation... 

Self-condensation of the potassium salt of 2-hydroxy-8-bromodibenzo-thiophene 5,5-dioxide in dimethyl sulfone gives a thermoplastic polymer of unit structure 150. ... 

Baekeland recognized that the trifunctional phenol would produce network polymers and therefore used difunctional ortho- or para-substituted phenols to produce linear paint resins. Linear thermoplastic products are formed by alkaline or acid condensation of formaldehyde with phenol derivatives such as /r-cresol (structure 4.81). 

Highly cross-linked condensation materials form the basis for a number of important adhesives and bulk materials, especially phenolic and amino plastics. Most of these products have formaldehyde as one of their starting reactants. These materials are thermosets that decompose prior to melting, and are therefore more difficult to recycle than most condensation polymers that are thermoplastics and do melt prior to decomposition. 

The polymers can be categorised as formaldehyde containing and formaldehyde free and as thermoset or thermoplastic resins. Typical formaldehyde containing resins are melamine formaldehyde sulfonamide resins, where the sulfonamide is ortho and para toluenesulfonamide. The sulfonamide, which is a solvent for the dye, undergoes a condensation polymerisation with formaldehyde and melamine, the latter acting as a cross-linking agent. Non-formaldehyde, thermoplastic resins are usually polyamides and polyesters. 

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