Synthesis of well-defined ABC2, AB2C3, (ABC2)4, and (ABC2)6 miktoarm star-branched polymers by combining organocatalyzed group transfer polymerization and ring-opening polymerization using multialdehydes as chain linkers

A series of well-defined ABC2, AB2C3, (ABC2)4, and (ABC2)6 type miktoarm star branched polymers consisting of poly(methyl methacrylate) (PMMA), poly(methyl acrylate) (PMA), and poly(L-lactide) (PLLA) were obtained by the combination of organocatalyzed group transfer polymerization (GTP) and ring-opening polymerization (ROP) using bi and trialdehydic aromatic compounds, 4-(diethoxymethyl)benzaldehyde and benzene-1,3,5-tricarbaldehyde respectively, as the chain end coupling agents. The entire synthetic route includes three main steps. The first one is an arm-first route in which the Mukaiyama aldol-type end coupling reaction between a living PMMA obtained through the t-Bu-P4-catalyzed GTP of MMA and an excess amount of a coupling agent was implemented to afford the aromatic aldehyde-bearing PMMA macroterminator. The second one is still an arm-first route in which a further aldol-type end coupling reaction between the aldehyde group left in the aforementioned PMMA macroterminator and a living PMA obtained by the dimethylphenylsilane-mediated B(C6F5)3-catalyzed GTP of MA to produce the multihydroxyl functionalized PMMA and PMA based copolymers, which were later used as the macroinitiators. Therefore, the third one is the ROP of L-lactide (LLA) using the above macroinitiators to give the final star branched polymers in a core-first way. Interestingly, the PMA and PMMA arms could be readily cleaved from the end-coupling bonds using fluoride anion. The resulting star branched polymers were well characterized by SEC, 1H NMR, MALLS, and TGA measurements.