Linear amphiphilic diblock copolymers of lactide and 2-dimethylaminoethyl methacrylate using bifunctional-initiator and one-pot approaches

Linear amphiphilic diblock copolymers of polylactide (PLA) and poly(2-dimethylaminoethyl methacrylate) (PDMAEMA) were synthesized by atom transfer radical polymerization (ATRP) of DMAEMA followed by ring-opening polymerization (ROP) of LLA using the bifunctional initiator, 2′-hydroxyethyl 2-bromoisobutyrate. NMR showed that the resulting PLA block was racemic and a quaternization/precipitation technique showed that there were significant amounts of racemic PLA homopolymer. In addition, simultaneous ATRP of DMAEMA and ROP of l-lactide by tin octoate were conducted at varied temperatures, indicating 90 °C as a suitable compromise temperature; this one-pot process also led to racemization and P(L)LA homopolymer. The racemization was attributed to reversible deprotonation of LLA by the N(CH₃)₂ moiety of (P)DMAEMA and the PLA homopolymer impurity was related to in situ formation of lactoyl lactate (LA–LA) due to nucleophilic ring opening of lactide by the amino moieties of (P)DMAEMA. The methods presented can be useful for the preparation of PDMAEMA–b–PLA/PLA composites in a two-step process or in a single step, one-pot process.