Interpolymeric complexes of polyoctamethyleneacetamidine with polyethers terminally modifi ed with chromophore groups and their nonlinear optical properties

Article abstract of DOI:10.1134/S1070427212090200

Ionic interpolymeric complexes of polyoctamethyleneacetamidine with polyethers terminally modifi ed with 4-[5-(4-hydroxyphenyl)-3-oxopenta-1,4- dienyl]benzoyl (chromophore) groups were prepared. The complexes exhibit third-order nonlinear optical properti

Full text of DOI:10.1134/S1070427212090200

ISSN 1070-4272, Russian Journal of Applied Chemistry, 2012, Vol. 85, No. 9, pp. 1428−1433. © Pleiades Publishing, Ltd., 2012.
Original Russian Text © A.O. Savitsky, L.V. Vinogradova, A.V. Ten’kovtsev, 2012, published in Zhurnal Prikladnoi Khimii, 2012, Vol. 85, No. 9, pp. 1517−1522.
MACROMOLECULAR COMPOUNDS
AND POLYMERIC MATERIALS
Interpolymeric Complexes of Polyoctamethyleneacetamidine
with Polyethers Terminally Modified with Chromophore
Groups and Their Nonlinear Optical Properties
A. O. Savitsky, L. V. Vinogradova, and A. V. Ten’kovtsev
Institute of Macromolecular Compounds, Russian Academy of Sciences, St. Petersburg, Russia;
e-mail: vinogradovaLV@rambler.ru
Received June 14, 2012
Abstract—Ionic interpolymeric complexes of polyoctamethyleneacetamidine with polyethers terminally modified
with 4-[5-(4-hydroxyphenyl)-3-oxopenta-1,4-dienyl]benzoyl (chromophore) groups were prepared. The complexes
exhibit third-order nonlinear optical properties. Factors affecting the third-harmonic generation efficiency were
revealed.
DOI: 10.1134/S1070427212090200
the polymer are ensured [1–4]. Taking into account the
fact that hydrogen bonding or ionic interactions between
the components strongly affect the enthalpy of mixing,
compatibility, and stability of polymer–chromophore
systems, we suggested in this study a new approach to
preparing NLO-active organic materials, based on forma-
tion of ionic interpolymeric complexes (IPCs) between
two polymers, of which one contains covalently bound
anionic chromophore groups and the other acts as a cat-
ionic matrix.As applied to NLO materials, IPCs were not
considered as promising objects until recently.
The modern nonlinear optics requires new materials
for use in photonic information processing devices and for
the development of optical switches and optical shutters
based on nonlinear adsorption. Among materials with
nonlinear optical (NLO) properties, polymers exhibit
indubitable advantages over inorganic materials. They
are cheap and relatively easy in processing; they have
film-forming and other useful properties. In preparation of
organic NLO materials, it is important to ensure their high
service characteristics and chemical and optical stability.
The development of procedures for preparing polymers
modified with chromophores capable of nonlinear inter-
action with electromagnetic radiation and the search for
ways to stabilize such composite materials without cova-
lent binding of the components remain priority problems
of nonlinear optics. When tackling these problems, it is
important to take into account the chromophore distribu-
tion in the matrix, the nature of intermolecular interac-
tions, and the capability of the chromophore component
for self-organization. These aspects were not given due
attention previously.
To prepare IPCs, we used in this study bifunctional
polyethers containing two terminal anionogenic chromo-
phore 4-[5-(4-hydroxyphenyl)-3-oxopenta-1,4-dienyl]
benzoyl groups, and as cationogenic matrix polymer we
used polyoctamethyleneacetamidine.
EXPERIMENTAL
The polyethers modified with chromophore groups
(anionic NLO-active polymeric components of IPCs)
were prepared by modification of a series of polyethers
(М = 0.6 × 103, 2 × 103, and 4 × 103) containing two
terminal amino groups (Jeffamines®, Huntsman). As
To prevent microphase segregation caused by ther-
modynamic incompatibility of the polymeric matrix and
low-molecular-weight chromophore, covalent binding or
strong noncovalent interactions of the chromophore with
1428

INTERPOLYMERIC COMPLEXES OF POLYOCTAMETHYLENEACETAMIDINE
1429
scribed previously [8, 9]:
starting chromophore for the polyether modification we
used 4-[5-(4-hydroxyphenyl)-3-oxopenta-1,4-dienyl]
benzoic acid:
H
N
N
O
n
Film samples were prepared by casting from solutions
of the components in a common solvent (ethanol) onto
glass supports [cover glass, 18 × 18, GOST (State
Standard) 6672–75], followed by solvent evaporation.
Prior to measurements, the films were dried in a vacuum
(5 mm Hg) to constant weight to remove residual solvent.
The third-order nonlinear optical coefficients χ(3) were
estimated by the method of third-harmonic generation
(THG) [10, 11]. The harmonic was excited in the samples
with a YAG : Nd3+ pulse laser with the emission wave-
length λ = 1064 nm.
HO
COOH
The chromophore was synthesized by two-step aldol
condensation. First, by the reaction of 4-hydroxybenzal-
dehyde with acetone we prepared 4-(4-hydroxyphenyl)-
but-3-en-2-one [5], which was treated in the second step
with the excess of 4-carboxybenzaldehyde to obtain the
chromophore [6].
The chromophore linking via terminal amino groups
of the polyether was performed after preliminary acetyl
protection of the hydroxy group of the chromophore, fol-
lowed by activation of the carboxy group [7] (Scheme 1).
Calorimetric studies of the complexes of the modi-
fied polyethers with polyamidine were performed with a
Mettler TA20 scanning calorimeter. Measurements were
made in the course of heating and cooling (four runs) in
The synthesis of the matrix cationogenic polymer,
polyoctamethyleneacetamidine (polyamidine), was de-
Scheme 1.
O
O
Py
+
(CH3CO)2O
HO
COOH
CH3COO
CH3COO
COOH
COCl
O
O
DMF
C6H6
+
SOCl2
CH3COO
COOH
O
NH2
H2N
+
CH3COO
COCl
O
O
NEt3
THF
HN
NH
CH3COO
OOCCH3
O
O
O
O
NaOH
H2O/EtOH
HN
NH
OH
HO
O
O
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 85 No. 9 2012

1430
SAVITSKY et al.
the interval from room temperature to 180°С at a scan-
ning rate of 5 deg min–1.
The optical properties of the films are largely deter-
mined by complexation and formation of supramolecular
structures on mixing the solutions of the starting com-
ponents. Therefore, we paid particular attention to these
processes.As we showed in the previous studies [12–14],
the chromophore tends to aggregation owing to formation
of a hydrogen bond system and to intermolecular π–π
interactions. According to [13, 15], the chromophore in
methanol solutions is associated to form structures with
the hydrodynamic radius Rh > 450 nm. Upon complex-
ation, these structures undergo partial deaggregation with
the formation of smaller particles.
λ, nm
Fig. 1. Change in the UV spectrum of the solution of the
chromophore-modified polyether (М = 4 × 103, с = 4 × 10–5 mM)
in the course of titration with a polyamidine solution. (D)
Optical density and (λ) wavelength. Form: (1) neutral and (2)
anionic.
Terminal chromophore groups of the modified poly-
ethers are also capable of aggregation. For example,
a study of the interaction of polyamidine with the
chromophore and chromophore-containing polyethers
in methanol by static and dynamic light scattering [13]
showed that the formation of ionically bonded complexes
in solutions leads to the formation of supramolecular
polymer–chromophore structures of colloidal size (hy-
drodynamic radius Rh ~ 200 nm). The chromophore
components in such structures are in the aggregated state.
On adding the polyamidine to solutions of the modified
polyethers or initial chromophore, the intensity of the
absorption band of the protonated form at λ = 350 nm
decreases and that of the deprotonated form at λ = 450 nm
increases. Analysis of the spectra allows these bands to
be assigned to the phenolic moiety of the chromophore
fragment [16]. In the UV spectra of the complexes in
the solid phase (films), the longer-wave absorption band
undergoes bathochromic shift to λ = 460 nm.
Mixing of alcoholic solutions of the polyamidine and
of the polyethers modified with chromophore groups leads
to a sharp change in the solution color from yellow to red,
suggesting fast proton transfer from the phenol group of
the chromophore to amidine fragments (deprotonation)
(Scheme 2).
By measuring the optical density D of the deproton-
ated form at λ = 450 nm, we obtained the titration curves
of the chromophore-containing components with the
polyamidine (Fig. 2). As can be seen, full deprotonation
of the shortest-chain polyether (М = 0.6 × 103) requires
the largest excess of the polyamidine. For the polyethers
in which the length of the polyether spacer chain between
The spectral changes observed in solutions of the
modified polyether and chromophore itself on interac-
tion with the polyimidine are essentially similar (Fig. 1).
Scheme 2.
(CH2)8
N
(CH2)8
H
H
O
O
N
H
HN
H3C
NH
CH3
O
O
O
O
N
N
H
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INTERPOLYMERIC COMPLEXES OF POLYOCTAMETHYLENEACETAMIDINE
1431
the chromophore groups is the largest (М = 4 × 103),
the required amount of the polyamidine appeared to be
practically the same as for the deprotonation of the free
chromophore. This is due to the fact that, with an increase
in the length of the polyether spacer chain, the chromo-
phore groups become more labile and more accessible
to the polyamidine.
For studying the NLO properties by the THG method,
we used thin films (0.5–5 μm) prepared from solutions
of the complexes of the modified polyethers with poly-
amidine in ethanol. By varying the concentration of the
chromophore component and the film thickness, we ob-
tained samples with the same optical density D ~0.5 at
λ = 460 nm, corresponding to the absorption maximum
of the ionic form of the chromophore in the solid state.
For the films studied, the Beer law is observed:
Fig. 2. Titration curves of solutions of (1, 3, 4) modified poly-
ether and (2) chromophore with a solution of polyamidine in
ethanol. (D) Optical density at λ = 450 nm. Here and in Fig. 4,
α = n/2m, where n is the number of polyamidine amino groups,
and 2m is the number of chromophore groups of the polyethers
(the coefficient 2 takes into account the presence of two chro-
mophore groups per polyether molecule). M: (1) 4 × 103, (3)
2 × 103, and (4) 0.6 × 103.
D = kcl = knl/V,
where k is the absorption coefficient of the NLO com-
ponent, с is the NLO component concentration, l is the
film thickness, n is the number of particles, and V is the
volume.
of interpolymeric complexes, we additionally prepared
films with a fixed content of the NLO-active component
in the solid phase (~14 wt %).As follows from our results
(Fig. 3), the THG efficiency χ(3) for films of polyether/
For comparison, using the similar method, we studied
films of complexes of the initial chromophore with the
polyamidine. The third-order nonlinear optical suscepti-
bility coefficients χ(3) of the complexes were measured
in the presence of excess polyamidine to shift the equi-
librium toward full deprotonation of the chromophore
component (see table). Because of the difference in the
molecular weights of the modified polyethers, such films
were characterized by different content of the NLO-active
component. The polyether/polyamidine films with the
longest-chain polyether (М = 4 × 103) had the lowest
content of the chromophore component and, therefore,
the lowest values of χ(3).
Third harmonic generation in films of interpolymeric complexes
Molar ratio of
χ(3) × 1014,
ionogenic groups CGS units
Complex
Polyamidine : chromophore
1 : 0.17
1 : 0.26
1 : 0.51
133
430
720
Polyamidine : polyether:
M = 0.6 × 103
1 : 0.12
1 : 0.28
1 : 0.53
1 : 0.16
1 : 0.25
1 : 0.47
1 : 0.13
1 : 0.28
82
295
293
It is known that the microstructure of films formed
in the course of solution evaporation depends on the
state of the components in the starting solution [17]. The
common feature of complexation processes in solutions
is partial deaggregation of the chromophore component
and formation of perplexed ionically bonded polymeric
structures within which the chromophore component
forms small aggregates [13]. We expected that, in going
to a solid system (film), the particle aggregation will be
enhanced, but certain features characteristic of solutions
will be preserved. Therefore, to determine how the poly-
ether chain length affects the nonlinear optical properties
M = 2 × 103
M = 4 × 103
14.0
21.1
25.9
5.8
4.6
1 : 0.51
4.3
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 85 No. 9 2012

1432
SAVITSKY et al.
T, °C
Polyamidine
+ polyether:
M = 0.6 × 103
Polyamidine
+ chromo-
phore
Polyamidine Polyamidine
+ polyether: + polyether:
M = 2 × 103 M = 4 × 103
Fig. 4. Thermograms of polyamidine/polyether complexes
(М = 0.6 × 103). (Т) Temperature. Component molar ratio α:
(1) 2 and (2)10.
Fig. 3. Parameter χ(3) of the films of the complexes as a func-
tion of the polyether chain length. NLO component content
14 wt %.
of incompatible polymers by introducing anionogenic
chromophore groups leads not only to stabilization of
interpolymeric complexes due to ionic interactions, but
also to an increase in the degree of ordering, leading to
enhancement of the heat resistance of the compounds
(upper temperature limit of service properties).
polyamidine complexes decreases with an increase in
the polyether spacer length. Because the films contained
the same amount of the chromophore component, the
observed differences in χ(3) can be attributed to features
of aggregation of the chromophore component. Probably,
with an increase in the polyether chain length, the capa-
bility of the chromophore groups for the intermolecular
interactions and formation of aggregated structures
decreases.
CONCLUSIONS
(1) New interpolymeric complexes of polyoctameth-
yleneacetamidine with polyethers terminally modified
with 4-[5-(4-hydroxyphenyl)-3-oxopenta-1,4-dienyl]-
benzoyl chromophore groups, exhibiting third-order
nonlinear optical properties, were synthesized.
Our previous study of the NLO properties of model
systems, chromophore potassium salt in poly-N-vinylpyr-
rolidone matrix [14], showed that the cubic susceptibility
χ(3) in the films increase with an increase in the size of
the chromophore component aggregates. Apparently, in
polyether/polyamidine films prepared using the polyether
with the larger length of the spacer between the chromo-
phore groups (М = 4 × 103), the aggregates formed by
the NLO-active component are the smallest. These data
convincingly show that specifically the capability for
aggregation and the cooperative effects observed in the
aggregates, and not only the NLO component concentra-
tion, are responsible for the manifestation of the NLO
properties.
(2) A study of how the length of the polymeric spacer
between the terminal chromophore groups of the poly-
ethers affects the nonlinear optical properties of their
interpolymeric complexes with polyoctamethyleneacet-
amidine showed that the efficiency of the third harmonic
generation in the complexes is determined not only by
the concentration of the NLO component, but also by the
capability of the chromophore groups for aggregation and
by the cooperative effects manifested in the aggregates.
(3) Introduction of anionogenic chromophore groups
into the structure of one of the components of blends
of incompatible polymers leads both to stabilization of
interpolymeric complexes via ionic interactions and to an
increase in the degree of ordering, making the compounds
more heat-resistant.
The interpolymeric complexes combine two ther-
modynamically incompatible polymers: polyamidine
and polyether. It is known that blends of these polymers
exhibit two glass transition points corresponding to those
of the individual components [18]. A study of the poly-
ether/polyamidine complexes by differential scanning
calorimetry showed a well-defined peak in the region of
120°С, corresponding to an endothermic phase transi-
tion of first order (melting) (Fig. 4). This fact means
that modification of one of the components of a blend
ACKNOWLEDGMENTS
The authors are grateful to V.A. Lukoshkin and
F Böhme for the assistance in the studies.
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INTERPOLYMERIC COMPLEXES OF POLYOCTAMETHYLENEACETAMIDINE
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