The effect of peroxides on the structure of high‐melt‐strength polylactide with long‐chain branched architecture or micro‐crosslinking

Abstract

AbstractLong‐chain branched polylactides (PLA‐LCB) with high melt strength were prepared through a melting reaction using Trigonox301 or dicumyl peroxide (DCP). During this reaction, random chain scissions, branching reactions, and cross‐linking reactions took place, as confirmed by the torque‐time rheograms and gel permeation chromatography profiles. It is evident that the random chain scissions are more prominent in PLA‐LCBD compared to PLA‐LCBT. The rheological characterization further elucidated the formation of LCB architecture. With an increase in the content of Trigonox301 or DCP, both branch‐on‐branch architecture and cross‐linked architecture were observed. The preference for branch‐on‐branch architectures was found to be higher in PLA‐LCBT as compared to PLA‐LCBD. Additionally, the presence of gel fraction was more easily detectable in PLA‐LCBD samples, indicating a higher likelihood of cross‐linking reactions in these samples. The emergence of new peaks at the positions of 1.82 and 1.47 ppm establishes a solid theoretical foundation for the potential reaction mechanism. One possible explanation proposed is that the reaction rate of free radicals originating from PLA‐LCBD samples is significantly higher than the diffusion rate of macromolecular free radicals. Consequently, the occurrence of a free radical chain transfer reaction is limited to a very small region, resulting in the formation of a cross‐linked structure. While the free radicals that are produced by the cyclic peroxide actively contribute to the graft reaction, thereby promoting the formation of the LCB structure with a micro‐crosslinking component.