Diepoxide chain

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). 

These materials differ from the previous class of resin in that the basic structure of these molecules consists of long chains whereas the cyclic aliphatics contain ring structures. Three subgroups may be distinguished, epoxidised diene polymers, epoxidised oils, and polyglycol diepoxides. 

A terminal 1,13 diene with interstitial deka(difluoromethylene) chain is converted to the corresponding diepoxide by repeated reacUon with a very large excess of hypofluorous acid-acetonitrile complex [22](equation 14)... 

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. 

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)...

Haralabakopoulos, A. A., Tsiourvas, D. and Paleos C. M., Chain extension of polyethylene terephthalate) by reactive blending using diepoxides, J. Appl. Polym. Sci., 71, 2121 (1999). 

Effects of Curing Agent Type. Epoxide-Cured Propellant. Carboxyl-terminated polybutadiene is a linear, difunctional molecule that requires the use of a polyfunctional crosslinker to achieve a gel. The crosslinkers used in most epoxide-cured propellants are summarized in Table IV and consist of Epon X-801, ERLA-0510, or Epotuf. DER-332, a high-purity diepoxide that exhibits a minimum of side reactions in the presence of the ammonium perchlorate oxidizer, can be used to provide chain extension for further modification of the mechanical properties. A typical study to adjust and optimize the crosslinker level and compensate for side reactions and achieve the best balance of uniaxial tensile properties for a CTPB propellant is shown in Table V. These results are characteristic of epoxide-cured propellants at this solids level and show the effects of curing agent type and plasticizer level on the mechanical properties of propellants. 

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. 

To further test the functional purity of hydroxyl polymers prepared by the protected initiator and polymer route, two stage chain extensions of two polystyrene diols were carried out. The first stage involved conversion of the diols to acids with succinic anhydride the second stage involved chain extension with a diepoxide (Table III). If one assumes an overall conversion of 97-98%, a UP of 19 requires a functionality 1.93-1.95 based upon step-growth polymeri-... 

The reactivity of a terminal 1,13-diene with an interstitial deca(difluoromethylene) chain 1 is lower towards expoxidation with hypofluorous acid/acetonitrile complex21 due to the electron-withdrawing effect of the perfluoroalkyl chain attached directly to the C = C bond. The diepoxide 2 is obtained by repeated reaction with a very large excess of the oxidizing agent.21... 

Finally, aromatic diols are also forerunners of diepoxides [88-90]. In this latter patent, we can mention the twinned use of both a perfluorinated chained-monoepoxide with these diepoxides. 

Several methods of condensation were used and each of them consisted of binding the perfluorinated chain to a molecule which exhibited two hydroxy groups or a forerunner of the diol (e.g. epoxide-alcohol or diepoxide). 

As an additional component, various thermoplastic polymers can be used. As a binder for copper clad laminates, a solution of solid epoxide resin (Epikote 1001), BPA/DC prepolymer, Zn acetate and poly(phenylene sulfide) was used [83], Other binders for reinforced plastics contain polysulfone. Such compositions consist of liquid BPA/ECH epoxide resin, BPA/DC prepolymer, polysulfone and bis(4-hydro-xyphenyl)sulfone [85]. Bis(4-aminophenyl)sulfone can be also added [86]. In such systems the bisphenol reacts with the epoxide resin as a chain extension agent, whereas the diamine crosslinks the diepoxide. The Tg values are close to 200 °C. They can be increased a little, if the BPA/ECH epoxide resin is replaced by the tetra-epoxide A,A,A, A -tetrakis(2,3-epoxypropyl)diaminodiphenylmethane [87]. 

---