Phthalocyanine-containing polystyrenes

Article abstract of DOI:10.1039/a900069k

An unsymmetrical phthalocyanine derivative containing a single styrene unit, prepared using a mixed phthalonitrile cyclotetramerisation, can undergo free radical polymerisation to give well-defined polystyrenes in which the macrocyclic components aggregat

Full text of DOI:10.1039/a900069k

Phthalocyanine-containing polystyrenes
Saad Makhseed, Anthony Cook and Neil B. McKeown*†
Department of Chemistry, University of Manchester, Manchester, M13 9PL UK. E-mail: neil.mckeown@man.ac.uk
Received (in Cambridge, UK) 4th January 1999
An unsymmetrical phthalocyanine derivative containing a
single styrene unit, prepared using a mixed phthalonitrile
cyclotetramerisation, can undergo free radical polymer-
isation to give well-defined polystyrenes in which the
macrocyclic components aggregate even in dilute solution.
moiety not only acts as a protecting group during the mixed
cyclotetramerisation reaction between 1 and an excess of
4,5-bis(dodecyloxy)phthalonitrile8 but its relative polarity, as
compared to that of the dodecyloxy side-chains, also facilitates
chromatographic separation of the required unsymmetrical Pc 2
from the Pc by-products.10 Removal of the MEM group
followed by the reaction of the resulting Pc 3 with 1-bromo-
11-(4-vinylphenoxy)undecane11 gives the desired Pc-contain-
ing styrene monomer 4. Spectroscopic and elemental analysis of
4 was consistent with its proposed structure.†
The long alkyl spacing group between the styrene unit and the
Pc ring is designed to minimise any detrimental steric effect on
the polymerisation reaction due to the large macrocycle. Indeed,
free radical polymerisation of 4 can be achieved with high
conversion ( > 85%) to give soluble polymers of reasonable
molar mass (Mn > 40 3 103 amu) and with relatively narrow
polydispersity (Mw/Mn ~ 1.5) as measured by gel permeation
chromatography (GPC) against commercial polystyrene stan-
dards (Table 1). The optimum conditions for polymerisation
proved to be a 0.05 mmol ml21 concentration of monomer 4 in
benzene solution using a 5 mol% concentration of AIBN
relative to 4. Prior complexation of 4 to zinc(ii), to give
monomer 5,† resulted in polymers of higher mass.
Phthalocyanine (Pc) and its derivatives possess interesting
electronic, optical and catalytic behaviour.1 There has been
much interest in the synthesis of phthalocyanine-containing
polymers suitable for the exploitation of Pc functionality.2
Previously, Pc has been incorporated into intractable network
polymers,3 rigid polysiloxanes in which the silicon(iv) ion is
held within the central cavity of the macrocycle,4 main-chain
liquid crystalline polymers,5 polymers formed by the coordina-
tion of bidentate ligands with metal ion containing Pcs,6
dendrimers which comprise a Pc ring at their core,7 and
polymers in which the Pc is a component of a side-chain
attached to the polymer backbone.8 Here we describe the
synthesis of polystyrenes with Pc-containing side-chains. The
widespread use of polystyrene as the substrate for polymer-
supported catalysts, its excellent processability and its optical
clarity make these materials attractive synthetic targets with
numerous potential applications.
The synthetic route to the Pc-containing styrene monomers is
given in Scheme 1. The strategy is to prepare an unsymmetrical
phthalocyanine, which possesses six solubilising alkyl side-
chains and a single reactive hydroxy functionality for the
attachment of the styrene group, via a mixed cyclotetramerisa-
tion of suitable phthalonitrile precursors. In order to protect the
hydroxy group during the base catalysed Pc forming reaction,
4-hydroxyphthalonitrile9 was first reacted with methoxy-
ethoxymethyl chloride (MEM chloride) to give 1. The MEM
It is possible to vary the concentration of Pc functionality
within the resulting materials by preparing random copolymers
from styrene and Pc 4 or 5. Interestingly, the molecular masses
obtained for these copolymers were consistently higher than
those of unsubstituted polystyrene obtained under the same
conditions. This prompted us to perform control experiments in
which styrene was polymerised with or without added un-
reactive metal-free octakis(dodecyloxy)-Pc (ODPc) or its
zinc(ii) derivative (ZnODPc). The polystyrene prepared in the
presence of ODPc or ZnODPc proved to have significantly
higher mass and lower polydispersity than that prepared in its
absence (Table 1). This unexpected result was attributed to the
Pc removing the residual oxygen which remained after
conventional deoxygenation using a repeated freeze–thaw
degassing process. It is well-established from various spectro-
scopic and electronic conductivity studies that Pcs interact
strongly with molecular oxygen. Zinc(ii)-containing Pcs are
particularly efficient at interacting with oxygen and this may
explain why monomer 5 is particularly well-suited to free
radical polymerisation.
UV–VIS absorption spectra of the polymers dissolved in
toluene reveal that there are strong cofacial interactions between
the Pc side-chains. This is apparent from the large bathochromic
shift of the primary Q-band of the Pc from 690 to 620 nm. We
believe that these interactions are primarily intramolecular
because even very dilute solutions show this effect, whereas
solutions of monomer 4 or 5 of similar concentration display an
unperturbed Q-band (Fig. 1). UV–VIS spectra of the copoly-
mers also display the broad absorption band resulting from self-
association. High resolution 1H NMR spectroscopy clearly
shows the presence of the dodecyloxy groups attached to the Pc
side-chains, however the aromatic protons are indicated only by
a single very broad signal centred at d 6.9, presumably due to
intramolecular association of the Pc units. NMR spectra of the
copolymers show clear signals originating from the polystyrene
backbone, however, only broadened resonances from the alkyl
component of the Pc-containing side-chain are apparent. This
CN
CN
i
HO
CN
MEMO
CN
1
ii, iii
R
R
N
N
N
M
N
R
R
N
N
R'
N
N
R
R
2 M = H2, R = OC12H25, R' = OMEM
3 M = H2, R = OC12H25, R' = OH
4 M = H2, R = OC12H25, R' = O(CH2)11
iv
v
O
O
vi
5 M = Zn, R = OC12H25, R' = O(CH2)11
Scheme 1 Reagents and conditions: i, MEMCl, pyridine; ii, 4,5-bis(dodecy-
loxy)phthalonitrile, C5H11OLi, C5H11OH, 135 °C; iii, AcOH; iv, PPTS,
C5H11OH, 135 °C; v, 1-bromo-11-(4A-vinylphenoxy)undecane, K2CO3,
DMF, 50 °C; vi, Zn(OAc)2, C5H11OH, 135 °C.
Chem. Commun., 1999, 419–420
419

Table 1 Polymerisation data for Pc-containing styrenes prepared using the conditions described in the text. Each figure for conversion and Mn is an average
of several runs.
R
R
N
N
N
M
N
R
R
y
N
N
O
(CH2)11
O
N
N
x
R = OC12H25
R
R
Monomer(s)
x (%)
y (%)
Conversion (%) < Mn > (amu)
< Mw > / < Mn >
4
5
100
100
0.5
20
0.5
0
0
0
99.5
80
99.5
100
100
100
87
90
95
95
94
89
90
88
44 3 103
53 3 103
72 3 103
46 3 103
80 3 103
8 3 103
1.6
1.3
1.7
1.5
1.7
1.7
1.7
2.0
4 + styrene
5 + styrene
5 + styrene
Styrene + ODPc
Styrene + ZnODPc
Styrene
0
0
10 3 103
7 3 103
We thank Kuwait University (S. M.) and the EPSRC (A. C.)
for the provision of studentships.
Notes and references
† Selected data for 4: l(toluene)/nm 700, 664, 646, 398, 342; n (thin film)/
cm21 3422 (NH); dH(benzene-d6, 500 MHz, 60 °C) 23.40 (2H, br s), 0.99
(18H, t), 1.30–1.85 (108H, br m), 2.08–2.24 (12H, br m), 3.78 (2H, t), 4.24
(12H, br s), 4.40 (2H, br s), 5.06 (1H, d), 5.56 (2H, d), 6.64 (1H, dd), 6.85
(2H, d), 7.27 (2H, d), 7.68 (1H, br s), 8.30–8.70 (7H, br m), 9.12 (1H, br s);
m/z (MALDI) 1906 (M+). For 5: l(toluene)/nm 679, 612, 360; dH(benzene-
d6, 500 MHz, 60 °C) 1.01 (18H, t), 1.40–1.70 (96H, br m), 1.72–1.88 (12H,
br m), 2.08–2.24 (12H, br m), 3.80 (2H, t), 4.12–4.26 (12H, br m), 4.36 (2H,
br s), 5.06 (1H, d), 5.56 (2H, d), 6.64 (1H, dd), 6.85 (2H, d), 7.27 (2H, d),
7.65 (1H, br s), 8.15–8.65 (7H, br m), 9.12 (1H, br s); m/z (MALDI) 1971
(M+).
Fig. 1 UV–VIS absorption spectrum for (a) the monomer 5 and (b) the
polystyrene derived from 5 (x = 100%).
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observation reinforces the evidence from UV–VIS spectros-
copy that Pc self-association is a feature of the dilute solution
behaviour of the copolymers even for those which possess only
a small degree of Pc side-chain substitution ( ~ 0.5 mol%
concentration).
Unlike the precursors and monomers 2–5 which form a
columnar mesophase at elevated temperatures, thin films of the
Pc-containing homopolymers are birefringent solids up to their
decomposition temperatures (~ 300 °C). The copolymers are
isotropic glassy solids with well-defined glass transition
temperatures. Thin films of the copolymers, fabricated by spin-
coating or by melt processing, are optically clear and highly
coloured. The non-scattering nature of these films make them
suitable for optical studies.
This work illustrates the compatibility of Pc-containing
styrene monomers with free radical polymerisation to produce
well-defined macromolecules. It allows the design of novel,
readily processed functional materials including polymeric
dyes, polymer supported Pc-catalysts, photobactericidal poly-
mers12 and polymers for various optical applications.
11 A. Cook, S. Greenfield and N. B. McKeown, manuscript in prepara-
tion.
12 R. Bonnett, D. G. Buckley, T. Burrow, A. B. B. Galia, B. Saville and
S. P. Songca, J. Mater. Chem., 1993, 3, 323.
Communication 9/00069K
420
Chem. Commun., 1999, 419–420