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The porphyrin handbook - Kadish K.M.

Kadish K.M. The porphyrin handbook - Academic press, 2000. - 368 p.
Download (direct link): kadishsmishgulilard2000.djvu
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solution of lc (1 mmol) under dry nitrogen are added 400 equivalents of
epoxyethane (11, R=H) at room temperature ([lc]o = 16.7 mM), whereupon
the polymerization immediately starts with heat evolution and is
42 / Metalloporhpyrins as Catalysts
135

6

X = OAc
a: X = Me : X = Et : X = Cl
d: X = OR e: X = OAr f: X = 02CR
g: X = SR h: X = NR2
7a: R =
H 7b: R = Br X = fert-BuCH2, Me(Me02C)CH
8
X = Me
completed within 4 hours (Figure 2).26 The number-average molecular
weight (Mn) of polymer is increased linearly with monomer conversion,
while the ratio of the weight- to number-average molecular weights
(A/w/Mn) remains almost constant close to unity (Figure 3). The molecular
weight of the polymer can also be controlled over a wide
range by changing the mole ratio of monomer to lc (Figure 4), where Mn is
in excellent agreement with the theoretical value calculated by the
equation
(molecular weight of monomer) x (%-conversion/100)

x ([monomet'lu/linitiator],)) (1)
136
Aida and Inoue
,N 1 N
\l / Al
N N
This means that every molecule of lc produces one polymer molecule, a
phenomenon typical of living polymerization. Likewise, lc can also bring
about living polymerization of substituted epoxides such as 1,2-
epoxypropane (11, R = Me) and 1,2-epoxybutane (11, R = Et) to give
polyethers with narrow MWD.26
Although alkali metal alcoholates are known to initiate living anionic
polymerization of epoxyethane (11, R = H), use of these conventional
initiators for the polymerization of substituted epoxides results in the
concomitant occurrence of side reactions with respect to the
substituents.27 28 With
11 (R = Me) as a monomer, a proton transfer from the methyl group of 11
(R = Me) to the growing alcoholate species occurs, to give a polymer
having a hydroxyl ter-
minal and an allyl alcoholate reactive end which can reinitiate the
polymerization (chain-transfer reaction). In such a case, the polymer MWD
tends to become broader and the molecular weight is lower than that
expected from the monomer-to-initiator mole ratio. In sharp contrast, the
polymerization of 11 (R = Me) with aluminum porphyrins
(1) does not involve any such side reactions.6
By taking advantage of the wide availability of lc, a variety of block
copolyethers of different polyether segments can be synthesized by
sequential polymerization of different epoxides using lc.26-29 For
example, when epoxyethane (11, R = H) is added to a polymerization system
of 1,2,-epoxypropane (11, R = Me) after 100% conversion of
11 (R = Me), the polymerization of 11 (R = H) ensures from the reactive
end of the living polymer to give an amphiphilic block copolyether
containing a water-soluble poly(oxyethy-lene) segment (23).29
For the polymerization of epoxides, various aluminum porphyrins having
alcoholate, phenolate and carboxylate ligands (ld-lf) are usable as
initiators, while the organoa-luminum porphyrins with methyl- or ethyl-
axial ligand (la, lb) are ineffective, even at high temperatures. NMR
studies have shown that the axial ligand of the initiator is transferred
to a monomer at the initiation step, generating an aluminum alcoholate
(24, R = Me) (Scheme 2A), which in turn reacts with the monomer at the
propagation step, and grows into a
Table 1. Monomers for Controlled Polymerization with Metalloporphyrins
(ii) Vinyl Monomers
42/Metalloporhpyrins as Catalysts
137
Scheme 1
R3AI

I
HX
Al-R
(-RH)
I
Al-X

X = NR'2 (- HNRy
R1 R2
I w
>|-0/ R3 (1A)

R = Me(a) Et (b)
X = OR' (d)
OAr (e)
02CR' (f)
SR' (with hv) (g)
NR'2 (with LlNR'2) (h)

I
R'M
Al-Cl
(- MCI)

I
Al-R' (1B)
Table 2. Selected 1H NMR Data for the Axial Ligands of Aluminum
Porphyrins in CDCI3 at Room Temperature
Compound
Chemical shifts in <5 (ppm)
Reference
Aluminum alkyls
i
i
Al-CH3

a b

XAI-CH2CH3
Aluminum alcoholates

i
i
I
1
I
1
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