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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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active species (1-M- ) (initiation step), followed by repeated additions
of

Copyright 2000 by Academic Press All rights of reproduction in any form
reserved.

ISBN 0-1 2-393200-9/$30.00
133
134
Aida and Inoue
(A) Ideal Case (Living Polymerization)
-* M M M M ' I-M-M-M-M-M-*
-* M M M M I-M-M-M-M-M-*
-* + M M M M > -- I-M-M-M-M-M-*
-* M M M M I-M-M-M-M-M-*
-* M M M M ,
I-*
O-l'
Case
M M M M
M M M M
M M M M
M M M M
M M M M
I-M-M-M-M-M-M-M-M-M-M-*
(Termination)
I-M-M-* ^ I-M-M-* (Dead)
(Chain Transfer) 0-1'
I-M-M-M-M-* =>
l-M-M-M-M-O (Dead) + I -
Figure 1. Schematic representation of addition polymerization. I and :
initiator, M: monomer, terminator, 0-1': chain transfer agent Ik:
active end, and O', inactive end.
M to I-M- at the propagation step to give a higher molecular weight
polymer (I-(M)n-A). If the initiation step is much faster than the
propagation and the propagation proceeds uniformly with respect to all
growing polymer molecules (1-(M)" ). a polymer with uniform
molecular
weight should then be formed. However, even under these conditions, the
MWD is not necessarily narrow, because there are many opportunities for
side reactions which would result in an irreversible deactivation of the
growing species. These side reactions will interfere with the uniform
growth of the polymer chains and a broadening of the polymer MWD will
result.
In 1956, Szwarc and coworkers,4 5 in their basic studies on electron-
transfer processes between organometallic reagents and unsaturated
compounds, discovered the first example of the formation of a
monodisperse polymer. They noticed that the polymer formed from styrene
in the presence of sodium naphthalide under rigorously dry and inert
conditions was of very narrow MWD, as indicated by a ratio of weight- to
number-average molecular weights (Mw/ Mn) which was close to unity.
Addition of a fresh feed of styrene to a completely polymerized system
(the first-stage polymerization) led to the second-stage polymerization,
resulting in further growth of all the growing polymer molecules. Such a
polymerization is named "living polymerization,"4 as the growth pattern
of the macromolecule can be viewed as analogous to the growth of a
biological organism.
A key to achieving living polymerization is to develop well-behaved
initiators, because the initiator affects both the relative rate of
initiation to propagation and the potential for side reactions.6-7 In
this chapter, we focus on the precision synthesis of macromolecules with
metalloporphyrins as initiators. Extensive initial studies by Inoue and
Aida,8-9 and more recent studies by Wayland et al.10 have shown that the
metalloporphyrins which are applicable to controlled macromolecular
synthesis include compounds of aluminum (1-4), zinc (5), manganese (6),
cobalt (7) and rhodium (8). The first two nontransition metal
metalloporphyrins are effective for anionic (nucleophilic) polymerization
while
the latter two transition metal complexes are suitable for radical
polymerization. Under certain conditions, aluminum complexes of Schiff
bases (9) and phthalocyanines (10) are also effective for anionic
polymerization.
II. Metalloporphyrins Containing Nontransition Metals
Aluminum porphyrins are versatile initiators which are applicable to
controlled ring-opening polymerization of various heterocyclic monomers
(Table 1) such as epoxides (ll),11 oxetanes (12)12 lactones with four-,
six-, and seven-membered rings (13 -15),13-17 lactide (16),18 six-
membered cyclic carbonates (17)19 and cyclic siloxanes (19).20 They are
also excellent initiators for the controlled addition polymerization of
unsaturated monomers such as acrylates
(20),21 methacrylates (21)22 and methacrylonitrile (22).23-24
A. RING-OPENING POLYMERIZATION OF HETEROCYCLIC MONOMERS
Aluminum tetraphenylporphyrin with axial bound chloride, (TPP)AICI, lc is
an effective initiator for the anionic ring-opening polymerization of
epoxides (ll).25-26 This complex can be easily synthesized by reacting
free-base tetraphenylporphyrin, (TPP)H2, with chlorodiethylaluminum in
CH2C12 under nitrogen, where the reaction proceeds rapidly and
quantitatively at room temperature with evolution of two equivalents of
ethane with respect to (TPP)H2. According to Scheme 1, a variety of
aluminum porphyrins can be synthesized using some organoaluminum
compounds and they are easily identified by 'H NMR (Table 2).
Here is an example of the polymerization of epoxides: To CH2CU
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