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

Long-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.

Automated summary

Long-chain branched polylactides with high melt strength were prepared by a melting reaction, and the occurrence of chain scissions, branching reactions, and cross-linking reactions were confirmed. Both the branch-on-branch and cross-linked architectures were observed with an increase in the content of Trigonox301 or DCP. The presence of gel fraction indicated a higher likelihood of cross-linking reactions in PLA-LCBD samples, compared to PLA-LCBT.