When Convergent Syntheses of Graft Block Copolymers Diverge: The Treachery of Chemical Images

A synthetic strategy to produce graft block copolymers (BCPs) with controlled grafting densities using both graftingthrough and grafting-from methods is reported. For graftingthrough, poly(4-methylcaprolactone-block-D, L-lactide) macromonomers were synthesized with a polymerizable maleimide end group. These macromonomers were copolymerized using reversible addition-fragmentation chain-transfer (RAFT) polymerization with styrene and various amounts of N-ethylmaleimide to control grafting density. A kinetic study showed that the macromonomers (> 10 kDa) polymerized at the same rate as N-ethylmaleimide under RAFT conditions, suggesting that uniform grafting density could be achieved. However, incorporating more than 5-10 grafts per chain was found to be challenging and potentially limited by kinetics. A higher number of grafts per chain with controlled densities was achieved using a grafting-fromtechnique. Macroinitiators of styrene, N-ethylmaleimide, and N-(2-hydroxyethyl) maleimide were copolymerized with a fixed density of grafting sites. Subsequently, BCPs were grown off of the macroinitiator using ring-opening transesterification polymerization (ROTEP). (C) 2017 Wiley Periodicals, Inc.