5-Methylene-1,3-dioxane-2-one (exTMC), a six-membered ring cyclic carbonate bearing an exocyclic methylene group, has been investigated as comonomer for trimethylene carbonate (TMC) with the aim to prepare functionalized polycarbonates. Using methane sulfonic acid (MSA) as an organocatalyst, exTMC and TMC copolymerize in a controlled manner to lead to copolymers of adjusted composition and high randomness (the corresponding reactivity ratios have been determined by the Beckingham−Sanoja−Lynd (BSL) method as 0.93−0.95 and 1.04−1.07 for exTMC and TMC, respectively). Subsequent thiol-ene reaction on the exomethylene group with thioglycolic acid or thioglycerol provides aliphatic polycarbonates with adjustable amounts of COOH or OH groups randomly distributed along the polymer chains.
To enhance the pH-responsiveness of poly(lactic acid) (PLA) particles, desired vanillin acetal-based initiators were synthesized and functional PLA was initiated at the chain end. PLLA-V6-OEG 3 particles were prepared using polymers with various M n values of 2400−4800 g/mol. PLLA-V6-OEG 3 was appropriated to achieve a pH-responsive behavior under physiological conditions within 3 min via the six-membered ring diol− ketone acetal. Moreover, it was found that the polymer chain length (M n ) influenced the aggregation rate. TiO 2 was selected as the blending agent to improve the aggregation rate. The PLLA-V6-OEG 3 blended with TiO 2 was found to accelerate the aggregation rate compared with that without TiO 2 , and the best ratio of polymer/TiO 2 was 1:1. To study the effect of the chain end for stereocomplex polylactide (SC-PLA) particles, PLLA-V6-OEG 4 and PDLA-V6-OEG 4 were successfully synthesized. The obtained results of SC-PLA particle aggregation implied that the types of chain end and the molecular weight of polymer could influence the aggregation rate. The SC-V6-OEG 4 blended with TiO 2 could not make our target to aggregate under physiological conditions within 3 min. This study motivated us to control the particle aggregation rate under physiological conditions for applying as a target drug carrier which is significantly influenced by not only the molecular weight but also the hydrophilicity of the chain-end as well as the number of acetal bonds.
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