Rheological characterization of long-chain branched poly(lactide) prepared by reactive extrusion in the presence of allylic and acrylic coagents

Reactive extrusion of poly(lactide) (PLA) is implemented to introduce branching, through grafting of multifunctional coagents in the presence of free-radicals. Two types of coagents, allylic and acrylate-based, are compared by analyzing the melt-state linear viscoelastic properties, in combination with triple detection size-exclusion chromatography. The coagent-modified PLA compounds exhibit substantially higher zero shear viscosity, pronounced shear thinning, and higher activation energies for flow when compared to the neat linear PLA. The accompanying increases in the molar mass, broadening of the dispersity, and appearance of high molar mass tails are attributed to the presence of branched architectures. The pronounced deviations from the linear Mark-Houwink plot suggest that long-chain branched structures are generated through the combination of the trifunctional coagents with the PLA macroradicals. The allylic coagent, triallyl mesate (TAM) is substantially more effective in introducing branched structures at low concentrations. On the other hand, the highly reactive acrylate-based coagents are prone to oligomerization in the presence of peroxide resulting in a separate phase, leading to reduced branch density compared to TAM. (C) 2018 The Society of Rheology.