Reactive modification of polyethylene terephthalate with polyepoxides

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Abstract
In attempts to produce modified poldified polyethlene terephthalate (PET) ressins with improved rheology for applications requiring high viscosity and elasticity (e.g., lowdensity extrusion foaming, extrusion blow molding), a novel dimidodiepoxide of low molecular weight was evaluated aschain extender/branching ageent. Its reactivity was compared with that of an ethylene/glycidy1 methacrylate copolymer. The diepoxide showed higher reactivity than the copolymer and could be used at muchlower concentrations. The complex chain extension/degradation reactions occurring in the melt were followed in a batch mixer by torque changes, and by analyzing the prouducts for residual carboxy1 and hydroxy1 content, intrinsic viscosity, insoluble content and melt viscoelastic properties. The perliminary results of this work indicated an overall decrease in carboxy1 content, increase in hydroxy1 content, increase in intrinsic viscosity ans melt viscosity and storage modulus values depending on mixing time and the type and concentration of the additive. It is shown that under certain conditions. reaction of PET with less than 1 wt% diimidodiepoxide may produce materials with rheological characteristics similar to thouse of PET grades that are extrusion foamable by gas injection to low densities.