Reactive modification of polyethylene terephthalate with polyepoxides

In attempts to produce modified polyethylene terephthalate (PET) resins wit h improved rheology for applications requiring high viscosity and elasticit y (e.g., low density extrusion foaming, extrusion blow molding), a novel di imidodiepoxide of low molecular weight was evaluated as chain extender/bran ching agent. Its reactivity was compared with that of an ethylene/glycidyl methacrylate copolymer. The diepoxide showed higher reactivity than the cop olymer and could be used at much lower concentrations. The complex chain ex tension/degradation reactions occurring In the melt were followed in a batc h mixer by torque changes, and by analyzing the products for residual carbo xyl and hydroxyl content, intrinsic viscosity, insoluble content and melt v iscoelastic properties. The preliminary results of this work indicated an o verall decrease in carboxyl content, increase in hydroxyl content, increase in intrinsic viscosity and melt viscosity and storage modulus values depen ding on mixing time and the type and concentration of the additive. It is s hown that under certain conditions, reaction of PET with less than 1 wt% di imidodiepoxide may produce materials with rheological characteristics simil ar to those of PET grades that are extrusion foamable by gas injection to l ow densities.