Polyesters linear

The free radicals first react with the chemical inhibitor which has previously been added to the resin, since the inhibitor material must be chemically dissipated before any reaction between free radicals and the C=C double bonds can proceed [5]. Apparently, the free radicals serve to open the double bonds in the polyester linear chain to set in motion that portion of the polymerization process designated as initiation. Either the opened double bonds react with the vinyl groups of the monomer, or the free radicals serve to also open (add to) these latter unsaturated C=C bonds, permitting them to perform their cross-linking function, uniting the polyester chains into a three-dimensional network. There is further evidence that free radicals may also, to some degree, react with the unsaturated monomer to form various products of decomposition [5]. 

CLASS Polyesters linear and flexible aromatic polyesters thermoplastics... 

CLASS Polyesters linear aliphatic flexible polyesters thermoplastics STRUCTURE O... 

Polyester, linear, high m.w. See Polyethylene terephthalate Polyester polyol... 

Aminoethylaminopropylmethylsiloxane/dimeth yisiloxane copolymer Dimethicone PEG-20 castor oil PEG-2 laurate SE lubricant, polyamide Glyceryl montanate lubricant, polyester textiles PEG-4 dioctanoate lubricant, polyesters, linear Glyceryl montanate lubricant, polymer processing CIO-12 alcohols C10-14 alcohols C12-14 alcohols C12-18 alcohols C14-16 alcohols C14-18 alcohols Lauryl alcohol lubricant, polymerization Sorbitan sesquioleate... 

Linear Aliphatic Polyesters. Linear ahphatic polyesters are the most frequently used synthetic biodegradable polymers in tissue engineering and many other biomedical applications (26-28). These polymers degrade through hydrolysis of the ester bonds in the polymer backbone. The degradation rates and profiles differ between these polymers owing to their compositional, structural, and molecular weight differences. 

A large number of polyesters is commercially available. These polymers are conveniently classified into the following types - linear unsaturated polyesters linear saturated polyesters of low molecular weight linear saturated polyesters of high molecular weight network polyesters poly(allyl ester)s and polycarbonates. Each of these groups is considered separately in this chapter. 

Just as it is not necessary for polymer chains to be linear, it is also not necessary for all repeat units to be the same. We have already mentioned molecules like proteins where a wide variety of different repeat units are present. Among synthetic polymers, those in which a single kind of repeat unit are involved are called homopolymers, and those containing more than one kind of repeat unit are copolymers. Note that these definitions are based on the repeat unit, not the monomer. An ordinary polyester is not a copolymer, even though two different monomers, acids and alcohols, are its monomers. By contrast, copolymers result when different monomers bond together in the same way to produce a chain in which each kind of monomer retains its respective substituents in the polymer molecule. The unmodified term copolymer is generally used to designate the case where two different repeat units are involved. Where three kinds of repeat units are present, the system is called a terpolymer where there are more than three, the system is called a multicomponent copolymer. The copolymers we discuss in this book will be primarily two-component molecules. We shall discuss copolymers in Chap. 7, so the present remarks are simply for purposes of orientation. 

Resin and Polymer Solvent. Dimethylacetamide is an exceUent solvent for synthetic and natural resins. It readily dissolves vinyl polymers, acrylates, ceUulose derivatives, styrene polymers, and linear polyesters. Because of its high polarity, DMAC has been found particularly useful as a solvent for polyacrylonitrile, its copolymers, and interpolymers. Copolymers containing at least 85% acrylonitrile dissolve ia DMAC to form solutions suitable for the production of films and yams (9). DMAC is reportedly an exceUent solvent for the copolymers of acrylonitrile and vinyl formate (10), vinylpyridine (11), or aUyl glycidyl ether (12). 

Polyesters were initially discovered and evaluated ia 1929 by W. H. Carothers, who used linear aliphatic polyester materials to develop the fundamental understanding of condensation polymerisation, study the reaction kinetics, and demonstrate that high molecular weight materials were obtainable and could be melt-spun iato fibers (1 5). 

However, because of the low melting poiats and poor hydrolytic stabiUty of polyesters from available iatermediates, Carothers shifted his attention to linear ahphatic polyamides and created nylon as the first commercial synthetic fiber. It was nearly 10 years before. R. Whinfield and J. T. Dickson were to discover the merits of poly(ethylene terephthalate) [25038-59-9] (PET) made from aromatic terephthaUc acid [100-21-0] (TA) and ethylene glycol [107-21-1] (2G). 

Staple. PET staple is widely used in 100% polyester or cotton-blend fabrics for apparel. Typical cotton-blend polyester staple fibers have a linear... 

Along with cotton blends, polyester blends with rayon or wool are also important. Wool—polyester blends are widely used in men s suiting materials. For these fabrics, PET staple or tow can be used with a linear density typically about 0.16—0.45 tex per filament (1.5—4 dpf) and a staple length of 50—75 mm (2—3 in.). 

Extmsion of polyethylene and some polypropylenes is usually through a circular die into a tubular form, which is cut and collapsed into flat film. Extmsion through a linear slot onto chilled rollers is called casting and is often used for polypropylene, polyester, and other resins. Cast, as well as some blown, films may be further heated and stretched in the machine or in transverse directions to orient the polymer within the film and improve physical properties such as tensile strength, stiffness, and low temperature resistance. 

The largest commercial use of ethylene glycol is its reaction with dicarboxyUc acids to form linear polyesters. Poly(ethylene terephthalate)... 

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. 

Manufacture. The manufacture of 1,4-cyclohexanedimethanol can be accompHshed by the catalytic reduction under pressure of dimethyl terephthalate ia a methanol solution (47,65). This glycol also may be prepared by the depolymerization and catalytic reduction of linear polyesters that have alkylene terephthalates as primary constituents. Poly(ethylene terephthalate) may be hydrogenated ia the presence of methanol under pressure and heat to give good yields of the glycol (see Polyesters) (66,67). 

Because lactic acid has both hydroxyl and carboxyl functional groups, it undergoes iatramolecular or self-esterificatioa and forms linear polyesters, lactoyUactic acid (4) and higher poly(lactic acid)s, or the cycUc dimer 3,6-dimethyl-/)-dioxane-2,5-dione [95-96-5] (dilactide) (5). Whereas the linear polyesters, lactoyUactic acid and poly(lactic acid)s, are produced under typical condensation conditions such as by removal of water ia the preseace of acidic catalysts, the formation of dilactide with high yield and selectivity requires the use of special catalysts which are primarily weakly basic. The use of tin and ziac oxides and organostaimates and -titanates has been reported (6,21,22). 

Glycols and epoxides react with maleic anhydride to give linear unsaturated polyesters (61,62). Ethylene glycol and maleic anhydride combine to form the following repeating unit. This reaction is the first step in industrially important polyester resin production (see Polyesters, unsaturated). 

Typical textile fibers used, for example, in a needle-punched filter fabric, are a blend of 3.3- and 6.6-dtex (3- and 6-denier) polyester staple. These fibers are - 5 cm long, have diameters ranging from 18 to 25 pm, mass-per-unit-length or linear density values ranging from - 350 to 650 mg per 1000 m, and length-to-width ratios in the order of 1000 to 1. 

The majority of spunbonded fabrics are based on isotactic polypropylene and polyester (Table 1). Small quantities are made from nylon-6,6 and a growing percentage from high density polyethylene. Table 3 illustrates the basic characteristics of fibers made from different base polymers. Although some interest has been seen in the use of linear low density polyethylene (LLDPE) as a base polymer, largely because of potential increases in the softness of the final fabric (9), economic factors continue to favor polypropylene (see OlefinPOLYMERS, POLYPROPYLENE). 

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