Molecular weight linear

Homopolymer. Acetal homopolymers are prepared from formaldehyde and consist of high-molecular-weight linear polymers of formaldehyde. 

Some 2,000—3,000 t/yr of these specialty alcohols are produced ia the United States (Exxon) and ia Germany (Henkel) (28). Their high Hquidity because of branching permits use of less volatile, higher molecular weight materials, reported to be less irritating than the lower molecular weight linear alcohol materials, ia a variety of cosmetic products (29). 

Esters. Neopentyl glycol diesters are usually Hquids or low melting soflds. Polyesters of neopentyl glycol, and in particular unsaturated polyesters, are prepared by reaction with polybasic acids at atmospheric pressure. High molecular weight linear polyesters (qv) are prepared by the reaction of neopentyl glycol and the ester (usually the methyl ester) of a dibasic acid through transesterification (37—38). The reaction is usually performed at elevated temperatures, in vacuo, in the presence of a metallic catalyst. 

Oxidative coupling polymerizations represent a general reaction for the preparation of high molecular weight linear polymers from many 2,6-di- and... 

There are two commercial PPS processes being practiced worldwide the Phillips process and the Kureha process. Although these processes contain some common steps, there are distinguishing features, most notably in the reagents used to faciUtate the synthesis of high molecular weight linear PPS. 

The first commercial PPS process by Phillips synthesized a low molecular weight linear PPS that had modest mechanical properties. It was usehil in coatings and as a feedstock for a variety of cured injection-molding resins. The Phillips process for preparing low molecular weight linear PPS consists of a series of nucleophilic displacement reactions that have differing reactivities (26). 

The process implications of equation 3 go beyond the weU-known properties (27—29) of NMP to faciUtate S Ar processes. The function of the aminocarboxylate is also to help solubilize the sulfur source anhydrous sodium sulfide and anhydrous sodium hydrogen sulfide are virtually insoluble in NMP (26). It also provides a necessary proton acceptor to convert thiophenol intermediates into more nucleophilic thiophenoxides. A block diagram for the Phillips low molecular weight linear PPS process is shown in Eigure 1. 

Fiber. High molecular weight linear PPS is weU-suited for fiber applications. The inherent properties of PPS (flame resistance, chemical resistance, and thermal stability) make PPS fiber highly desirable ia textile applications (128). PPS fiber has been designated by the U.S. Federal Trade Commission as a new generic class of materials called sulfar. Typical fiber properties are listed ia Table 7 (see High performance fibers). 

Polystyrene [9003-53-6] (PS), the parent of the styrene plastics family, is a high molecular weight linear polymer which, for commercial uses, consists of - 1000 styrene units. Its chemical formula (1), where n = - 1000, tells htde of its properties. 

Caprolactam is an amide and, therefore, undergoes the reactions of this class of compounds. It can be hydrolyzed, Ai-alkylated, O-alkylated, nitrosated, halogenated, and subjected to many other reactions (3). Caprolactam is readily converted to high molecular weight, linear nylon-6 polymers. Through a complex series of reactions, caprolactam can be converted to the biologically and nutritionally essential amino acid L-lysine (10) (see Amino acids). 

Hexachlorocyclotriphosphazene (cycHc trimer) is a respiratory irritant. Nausea has also been noted on exposure (10). Intravenous and intraperitoneal toxicity measurements were made on mice. The highest nonlethal dose (LDq) was measured as 20 mg/kg (11). Linear chloropolymer is also beUeved to be toxic (10). Upon organic substitution, the high molecular weight linear polymers have been shown to be inert. Rat implants of eight different polyphosphazene homopolymers indicated low levels of tissue toxicity (12). EZ has been found to be reasonably compatible with blood (13), and has lower hpid absorption than fiuorosihcone. 

With one exception no other high molecular weight linear polyesters have achieved any sort of commercial significance for films and fibres. The one exception is the condensation polymer of dimethyl terephthalate and 1,4-cyclo-hexylene glycol (also known as 1,4-cyclohexanedimethanol) (Figure 25.19). 

The flocculation activity of polymers increases with increasing molecular weight. Linear macromolecules are better flocculents than branched ones with the same total molecular weight. In the future the largest growth of polymer applications is expected to be in waste and water treatment, because of ecological problems. 

High molecular weight linear polyethylene was obtained from ethylene polymerization by TiCl2 (146) this polymer contained only vinyl-type double bonds (less than 0.1 per 1000 carbon atoms). 

Chemistry, reaction mechanisms, and properties have been extensively reviewed.4,5,10-20 Hie present chapter deals witii only one type of fully cyclized aromatic heterocyclic polymers die high-molecular-weight linear polymer witii a special emphasis on die synthesis and structure—property relationships for specific applications. 

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