Synthesis and Characterization of Nonlinear PETs Produced via a Balance of Branching and End-Capping

Abstract

PET-type polymers have been prepared in the presence of a variety of potential branching agents, such as trimesic acid, and with the control of branching using an end-capping agent, benzyl alcohol. The polymers synthesized have been characterized by dilute solution viscometry, end group analysis, light scattering (M̄w), DSC analysis, and melt rheology. One group of polyesters synthesized with increasing levels of brancher has absolute M̄w values which increase from ∼10K to 350K Da, and yet despite this, all of the macromolecules display roughly the same limiting viscosity number. Furthermore, though the corresponding zero-shear rate melt viscosity increases with M̄w, the values are far below those expected for analogous linear polymers of comparable M̄w. A second group of polyesters synthesized with a fixed level of brancher and increasing levels of end-capper has a much narrower range of M̄w values, ∼30K−100K Da, i.e. ∼3−15 times larger than that of a model linear PET. Despite this, these polymers have melt viscosities below that of the linear model. The results are discussed in light of other data in the literature and confirm that branched analogues of linear PET have both lower solution and melt viscosities. While these materials offer the prospect of more facile processing, their solid-state properties may prove to be limited relative to linear polymers, and they may prove more useful as additives rather than stand-alone materials.