Hydrolases in Polymer Chemistry: Chemoenzymatic Approaches to Polymeric Materials - Enzymatic Polymerisation - page 87

O

100

HO

Br

Novozym 435
caprolactone

80

60

Novozym 435
Caprolactone
ATRP catalyst
MMA

O

PCL

Br

40

20

ATRP catalyst
MMA

0

PCL PMMA

0 30 60

Reaction time [min]

90 120

Fig. 6 Left : Strategy for consecutive chemoenzymatic and simultaneous one-pot block copolymer
synthesis combining enzymatic ROP and ATRP. Right : Influence of ATRP-catalyst system on the
conversion of CL in the enzymatic ROP of MMA at 60 ◦ C using ATRP-3 as initiator: filled squares
reaction in absence of ATRP-catalyst; open circles CuBr/PMDETA (1:1:1 ratio with respect to
initiator); filled triangles CuBr/dNbpy (1:2.1:1 ratio with respect to initiator); open inverted trian-
gles CuBr (1:1 ratio with respect to initiator); filled diamonds CuBr 2 (1:1 ratio to initiator). CL
conversion was determined with 1 H-NMR [ 26 ]

like nickel have a strong inhibiting effect on the enzyme, whereas typical ATRP
copper catalysts were tolerated by the enzyme (Fig. 6 ) . The chemoenzymatic cas-
cade reaction was most successful when the ATRP components were added after
the enzymatic process. High block copolymer yields were obtained in that approach,
whereas homopolymer impurities were observed when all components were present
from the beginning.
By taking advantage of the simultaneous enzyme inhibition by nickel, the nickel-
catalyzed ATRP, and the stereoselectivity of the enzyme, Peters et al. obtained chiral
block copolymers by this method from 4-methyl- -caprolactone (4-MeCL) by [ 27 ] .

The polymerization of racemic 4-MeCL showed good enantioselectivity and pro-
duced a chiral macroinitiator with ATRP endgroup by selectively polymerizing only
the ( S

ε

-4-MeCL. Macroinitiation was then started by adding the nickel catalyst and
methyl methacrylate (MMA) to the reaction mixture, which simultaneously inhib-
ited the enzyme and activated the ATRP process. Chiral poly[MMA- b -( S

)

) -4-MeCL]

was successfully obtained in this synthesis.
Howdle and coworkers reported that a one-pot, simultaneous synthesis of block
copolymers by enzymatic ROP and ATRP employing initiator ATRP-3, CL, and
MMA is possible in supercritical CO 2 (

[ 28 ] . The authors could show that
theCLactsasascCO 2 cosolvent and was crucial for the radical polymerization
to remain homogeneous and controlled. The unique ability of scCO 2 to solubilize
highly fluorinated species was utilized by extending this methodology to the synthe-
sis of novel copolymers consisting of a semifluorinated block of poly(1 H ,1 H ,2 H ,
2 H -perfluorooctyl methacrylate) (PFOMA) and PCL [ 29 ] . Block copolymers were
successfully synthesized by a two-step process based on the sequential monomer

scCO 2 )