Chemistry Reference
In-Depth Information
R'''
R''
R'
R''''
N
R
R'
OH
OO
H
H
N
N
HO
OH
Cu
Ph
Ph
O
O
Ph
Ph
R
R'''''
4
5
6
TADDOL
NOBIN
Ph
HO
OH
Ph
OMe
Br
O
O
O
O
O
NH
HN
R
O
N
O
OO
+
Ph
PPh
3
Fig. 10.6
Additional chiral phase
transfer catalysts.
7
8
The phosphonium salt (
8
) reported by Manabe
[243] exhibited moderate enantioselectivity (up
to 50% ee) in the benzylation of alkyl-2-oxo-
cyclopentanecarboxylates.
living condensation polymerisation that they termed
'condensative chain polymerisation'. This novel
concept was based on the assumption that monomer
molecules in the solid phase do not interfere with
each other and that only after transport to the
organic phase, complexed with the phase-transfer
agent, can the activated monomer react with the
polymer end group in this phase (Scheme 10.42).
Using 4-nitrobenzylbromide as initiator (10
mol.%) with an identical amount of crown ether
catalyst, a polymer with
M
w
= 2400 with a narrow
molecular weight distribution (
M
w
/
M
n
= 1.3) was
obtained, characterising a reasonable 'living poly-
merisation' mechanism.
A similar perception was utilised by the same
group in the chain-growth polycondensation of a
phenyl 4-aminobenzoate derivative (Scheme 10.43)
[253]. The monomer was activated by the
crown-CsF complex according to Scheme 10.44.
The highly reactive anilide anion reacted with the
terminal ester function of the growing polymer to
yield a new amide bond. The authors proved that
the reaction of the monomer with itself was much
slower than with the reactive polymer chain. Con-
sequently, a true living polymerisation was apparent
with a polydispersivity as low as
M
w
/
M
n
= 1.1.
Indeed, plotting
M
n
as a function of conversion or as
a function of the monomer/initiator ratio resulted in
6 Phase-transfer Catalysis in
Polymerisation Processes
Phase-transfer catalysis was used widely in macro-
molecular chemistry, particularly in condensation
polymerisation [244]. Several applications in free-
radical-initiated polymerisation by potassium or
sodium peroxydisulfate [245] and in anionic poly-
merisation also are known [246].
Through latter years Tagle's group had continu-
ously developed new novel classes of condensation
polymers prepared via PTC methods. Some recent
products were polycarbonates and thiocarbonates
containing germanium or silicone in the main chain
[247], polyhalodiphenol amides [248] poly(amide)
esters [249] and poly(amide) carbonates [250].
Linear segmented polyesters containing soft per-
fluoropolyether and hard aromatic segments were
prepared by PTC polycondensation of acyl-chloride-
terminated fluorinated prepolymer with various
diphenols [251].
A major breakthrough was made by Yokozawa &
Suzuki [252], who proposed a solid/liquid PTC-based
