Synthesis
of polymerizable squaric ester amides. (A) General chemical
structure of synthesized monomers with a pendant squaric ester amide
group. (B) Synthesis route toward the most suitable monomer squaric
ester amide methacrylamide (MA-SQ). (C) Schematic illustrations and
(D) synthesis schemes of RAFT homopolymerization of MA-SQ with a small
molecular trithiocarbonate chain transfer agent (TTC-CTA) (C1 and
D1) and block copolymerization with macro-chain-transfer agent PEG-TTC-CTA
(C2 and D2) (reaction conditions: (i) DMF, 70 °C, 0.2 equiv AIBN
per 1.0 equiv TTC-CTA, and (ii) DMF, 70 °C, 50 equiv AIBN (to
remove the TTC end group)). (E) Molecular weight distributions of
polymers obtained by radical polymerization: (E1) RAFT-derived homopolymer
compared to the homopolymer obtained by FRP; (E2) RAFT-derived block
copolymer compared to PEG-TTC-CTA as macro-chain-transfer agent.