Cascade synthesis of chiral block copolymers combining lipase catalyzed ring opening polymerization and atom transfer radical polymerization.
The enantioselective polymerization of methyl-substituted epsilon-caprolactones using Novozym 435 as the catalyst was investigated. All substituted monomers could be polymerized except 6-methyl-epsilon-caprolactone (6-MeCL), which failed to propagate after ring opening. Interestingly, an odd-even effect in the enantiopreference of differently substituted monomers was observed. The combination of 4-methyl-epsilon-caprolactone with Novozym 435 showed good enantioselectivity also in bulk polymerization and resulted in enantiomerically enriched P((S)-4-MeCL) (eep up to 0.88). Subsequently, a novel initiator combining a primary alcohol to initiate the ring opening polymerization and a tertiary bromide to initiate atom transfer controlled radical polymerization (ATRP) was synthesized, and showed high initiator efficiencies (> 90%) in the ring opening polymerization of 4-methyl-epsilon-caprolactone in bulk. In addition, the enantioselectivity was retained (E = 11). By using Ni(PPh3)2Br2 as the ATRP catalyst, Novozym 435 could be effectively inhibited at the desired conversion of 4-methyl-epsilon-caprolactone, thus ensuring a high enantiomeric excess in the polymer backbone. At the same time, Ni(PPh3)2Br2 catalyzed the ATRP of methyl methacrylate resulting in the formation of P((S)-4-MeCL-b-MMA) block copolymers. By this combination of two inherently different polymerization reactions, chiral P((S)-4-MeCL-b-MMA) block copolymers can be conveniently obtained in one pot without intermediate workup.
Peeters
Joris
J
Laboratory of Macromolecular and Organic Chemistry, Eindhoven University of Technology, PO Box 513, 5600 MB, The Netherlands.
Palmans
Anja R A
AR
Veld
Martijn
M
Scheijen
Freek
F
Heise
Andreas
A
Meijer
E W
EW
D002384:Catalysis; D008049:Lipase / Q000138:chemical synthesis* / Q000378:metabolism; D011108:Polymers / Q000138:chemical synthesis* / Q000378:metabolism; D013237:Stereoisomerism
D011108:Polymers; D008049:Lipase