Two- and Three-Component Post-Polymerization Modifications Based on Meldrum’s Acid

Circular Design and Functionalized Upcycling of Waste Commodity Polystyrene via C-H Activation Using Microwave-Assisted Multicomponent Synthesis

The inefficient reuse and recycling of plastics-and the current surge of medical and take-out food packaging use during the pandemic-have exacerbated the environmental burden. This impels the development of alternative recycling/upcycling methods to pivot toward circularity. We report the use of the Mannich three-component coupling reaction for the modification of polystyrene (PS) recovered with a 99.1% yield from waste food containers to form functionalized nitrogen and oxygen-rich PS derivatives. A series of functionalized PS with increasing moles of formaldehyde (F) and morpholine (M) (0.5 × 10^-2, 1.0 × 10^-2, and 2.0 × 10^-2 mol) was achieved using a sol-gel-derived Fe-TiO₂ catalyst in a solvent-free, microwave-assisted synthesis. Modified polymers were characterized with viscometry, ¹H NMR, ¹³CNMR (DEPT) FTIR, XPS, UV, and TGA. Functionalization scaled with an increasing ratio, validating the 3CR approach. Further functionalization was constrained by a competing oxidative degradation; however, the varying hydrogen bond density due to nitrogen and oxygen-rich species at higher ratios was shown to compensate for molecular weight loss. The integration of the N-cyclic quaternary ammonium cations exhibited the potential of functionalized polymers for ion-exchange membrane applications.

Facile Multicomponent Polymerization and Postpolymerization Modification via an Effective Meldrum's Acid-Based Three-Component Reaction

Providing access to highly diverse polymer structures by multicomponent reactions is highly desirable; efficient Meldrum's acid-based multicomponent reactions, however, have been rarely highlighted in polymer chemistry. Here, the three-component reaction of Meldrum's acid, indole, and aldehyde is introduced into polymer synthesis. Direct multicomponent polymerization of Meldrum's acid, dialdehyde, and diindole can perform under mild conditions, resulting in complex Meldrum's acid-containing polymers with well-defined structures, and high molecular weights. Additionally, nearly quantitative postpolymerization modification can also perform via this Meldrum's acid-based multicomponent reaction. These results indicate that Meldrum's acid-based multicomponent reaction will be a potential tool to prepare novel polymers.

Post-Polymerization Modification of Ring Opening Metathesis Polymerization (ROMP)-Derived Materials Using Wittig Reactions

This communication describes our recent efforts to utilize Wittig olefination reactions for the post-polymerization modification of polynorbornene derivatives prepared through ring opening metathesis polymerization (ROMP). Polymerizing α-bromo ester-containing norbornenes provides polymers that can undergo facile substitution with triphenylphosphine. The resulting polymeric phosphonium salt is then deprotonated to form an ylide that undergoes reaction with various aryl aldehydes in a one-pot fashion to yield the respective cinnamates. These materials can undergo further modification through photo-induced [2 + 2] cycloaddition cross-linking reactions.