Diepoxide chain extenders

PET chain-extended with a diepoxide as chain extender can exhibit varying degrees of branching and cross-linking depending on the level of chain extender used [13, 14], The branched and cross-linked PETs exhibit significant improvement in tensile properties. 

Bikiaris and Karayannidis [5] have investigated the use of diimidodiepoxides as chain extenders for PET resins. Starting with a PET having an IV of 0.60 dL/g and a carboxyl content (CC) of 42 eq/106 g, they obtained PET with an IV of 1.16 dL/g and a CC below 5 eq/106 g. The typical reaction condition for the coupling of PET was heating with the chain extender under an argon atmosphere above its melting temperature (280 °C) for several minutes. 

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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). 

Bikiaris, D. N. and Karayannidis, G. P., Calorimetric study of diepoxide chain-extended poly(ethylene terephthalate), J. Therm. Anal. Calorim., 54, 721 (1998). 

Figure 14.4 Chemical structures of two common epoxy chain extenders for PET (a) a diepoxide, e.g. Shell Epon 828, based on bisphenol A diglycidyl ether (b) a tetraepoxide, e.g. Ciba MY721, based on tetraglycidyl diaminodiphenyl methane (TGDDM)...

Chain Extension of -U-Polystyrene Hiols. A two-stage chain extension of the. -kJ -polystyrene diols was accomplished by carboxylation of the diols with succinic anhydride followed by chain extension with a diepoxide. The succinic anhydride reaction was carried out 120-130°C under nitrogen. The reaction was monitored bj changes in the carbonyl bands at 1715 and 1740 cm in the infrared spectra of the reaction mixtures. The resulting dicarboxylic acid polymers were chain-extended in bulk at 130°C for 9 hours with Sow s HER diepoxide, equivalent weight =171, using bis( 3,5-diisopropylsalicylato)Cr (III) as the catalyst. 

The main aim of this study was to assess the utility of these relatively cheap, readily available diepoxides. Authors admitted that all were less effective chain extenders than custom-made diepoxides and the bisoxazolines. 

In a later study by Dhavalikar and Xanthos [180], the authors investigated di- and tri-functional additives. The diepoxides used were the commercially oriented additives, diglycidyl ether of bisphenol A with molecular weight of approximately 350 (Epon 828) and N,N -bis[3(carbo-2",3 -epoxypropoxy)phenyl]pyromellitimide. Such additives have long been considered to be suitable chain extenders, with their ability to react with carboxyl and hydroxyl end groups ... 

Tetraalkyl- and 1,2,2,6,6-pentaalkyl piperidine-based HALS which have been claimed specifically as stabilisers for aromatic polyesters include alkylamine derivatives such as pentakis(2,2,6,6-tetramethyl-4-piperidinyl)diethylenetriamine-N,N,Nl N", N -pentaacetate [184] unsymmetrical siloxanes with HALS moieties at one end and a reactive group on the other, e.g., -Si(CH2)30H group capable of reacting with acid chain ends in the polymer [185] and HALS diepoxides, which chain-extend and UV-stabilise polyesters and polyamides [186]. 

Unmodified epoxy resins vary from the viscous liquid diepoxide 0 (molecular weight 340 and with n = 0 in the general formula above) to solid polymers of molecular weights up to 8000 (n = 26). The resins become solid at molecular weights above 700. While a number of standard grades can be purchased, it is more and more usual for resin producers to take the diepoxide 0 resin, and to react this with bisphenol A to form chain extended epoxy resins in their own resin plant. This process is also termed epoxy advancement. An advantage of this process is that the producer may then introduce other diphenols or hydroxy functional materials to modify the properties of the extended epoxy resin. 

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