Chain extenders commercially available

There is a wide range of chain extenders commercially available for PET (Table 14.2). Bifunctional chain extenders promote linear chain extension while tri- and tetra-functional chain extenders promote chain branching. Such reactive compounds are also known as repair additives since they can reverse the molecular weight loss of hydrolytically damaged PET. 

During this reaction, some caprolactam is also liberated. The reaction is largely completed within the processing time (typically 3-5 min). The increase in intrinsic viscosity of PET can be adjusted by the amount of CBC. In practice, about 0.5 wt% of CBC is typically used. CBC is commercially available under the trade-name ALLINCO (DSM, Geleen, The Netherlands). ALLINCO is one of the most effective chain extender systems available for PET [21, 22], CBC is often used in combination with PBO for an enhanced chain extension effect. Typically, the relative viscosity of PET is increased from 1.6 to 2.0 with a stoichiometric amount of CBC + PBO (ca. 1.2 wt%) in a single-screw extruder at 300 °C. 

Figure 14.4(a) shows the structure for a common diepoxide chain extender. Haralabakopoulos et al. [12] have reported that the molecular weight of PET increases via chain extension reactions with commercially available diepoxides. Low concentrations of extender and short reaction times generally favoured chain extension. In addition, purging with nitrogen resulted in chain extended polymers having the highest values of intrinsic viscosity (e.g. 0.82 dL/g). 

The modified cephalosporin ceftobiprole (31-8), yet another compound that contains a double bond at the ring carbon, though in this case with a rather complex extended side chain, has shown activity in the clinic against some strains of multidrug resistant bacteria. The synthesis starts with the weU-precedented acylation of the cephalosporin (31-2), available in several steps from the commercially available 7-acetoxy cephalosporanic acid, with the activated thiadiazole carboxylic acid (31-1). The hydroxyl group in the product (31-3) is then oxidized with manganese dioxide to afford the corresponding aldehyde (31-4). This product is then condensed with the fcw-pyrrolidyl phosphonium salt (31-5), itself protected with the... 

Biomer is a commercially available, medical grade segmented poly(ether urethane urea) (PEUU), which is prepared by treating an isocyanate-capped polyetherurethane with diamine (e.g. ethylenediamine) as chain extender... 

The unique molecular packing of rod-like chains in liquid crystalline polymers (LCP) closely resembles the extended chain structure of highly oriented flexible chain polymers, suggesting that these materials are good candidates for barrier applications. Thermotropic LCP s, first developed in the early 1970 s, have been the object of much interest because of their excellent mechanical properties and ease of product fabrication. Preliminary observations have shown that a commercially available wholly aromatic thermotropic copolyester has gas permeability coefficients that are lower than those of polyacrylonitrile (4.). These results raise some fundamental questions as to the nature of the mechanism for transport of small molecules through a matrix of ordered rigid rod-like chains. 

The principal components of commercially available urethane coatings are di- or polyisocyanates and di- or polyhydroxy compounds. Active hydrogen-containing compounds, especially diols and diamines, as well as alkanolaraines, are also employed as chain extenders. In addition, various cross-linking agents such as neutral or tertiary amine based triols or tetrols are also used. 

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