- Email: [email protected]
Neutron scattering analysis of a block copolymer poly(l,4-phenylene)-block-polystyrene-block-poly( l,4-phenylene)
ELSEVIER
Synthetic Metals 102 (1999) 12461247
Neutron scattering analysis of a block copolymer poly( 1,4-phenylene)-block-polystyrene-black-poly( 1,4-phenylene) E. Mignard, C. Tachon, B. Francois* Laboratoire de Recherche SW les Mate’riaux PolymPres CNRS - UPPA He’lioparc, 2 Av. du PGsident Angot, 64000 Pau, Fr
Abstract Poly( 1,4-phenylene)-block-polystyrene-block-poly( 1,4-phenylene) (PPP-b-PS-b-PPP) blocks copolymers were synthesized by chemical modification of a precursor copolymer. After characterization by Size Exclusion Chromatography (SEC) and UV-Visible spectroscopy, triblock copolymers were studied in CSz solution at room temperature by neutron-scattering analysis. These triblock copolymers are highly aggregated. A ribbon model seems to give the best fit for the PPP core. Keywords:
Other conjugated
and/or conducting polymers, Self-organization
in macromolecules,
set-Bu-,Li+
1. Introduction Poly( 1,4-phenylene) (PPP) receives considerable attention because of its important physical and chemical properties. Nevertheless rigidity and interchain interactions are responsible for its insolubility and unfusibility. That is the reason why among the different ways to solubilise the PPP, we copolymerise it with a block of polystyrene (PS) soluble in usual organic solvent.
Neutron scattering and d@raction
cyclohexane
+ a-methylstyrene
c
FH” ((“-CH2
%+ -,Li
25°C I N,
/ 6
h
= R,Li+ \
-
R-,Li+ cyclohexane,
25°C / N,
PCHD-PS-,Li+
Previous work about PS-b-PPP diblock copolymers [l] has shown the associative behavior of PPP blocks in THF at room temperature. In a first way, these aggregates are considered as starlike polymers. They can lead to particular self-organized thin films with a honeycomb morphology [2] and present interesting photo and electroluminescence properties [3]. Now, we study the physico-chemical properties of the triblock copolymers PPP-b-PS-b-PPP in the same conditions [4]. We want to determine their ability to form a network or not. Thus, we would obtain a new material constituted by conjugated particles organization into insulating matrix. 2. PPP-b-PS-b-PPP
triblock
copolymer
synthesis
The title copolymer is obtained by chemical modification of a precursor: the poly(l,3-cyclohexadiene)-b-polystyrene-b-poly(1,3cyclohexadiene) (PCHD-b-PS-b-PCHD). This precursor is prepared by anionic polymerization of 1,3cyclohexadiene and styrene monomers in a non-polar solvent at room temperature (Fig. 1). The polymerization is started by a coupling product between secondary-butyllithium and CLmethylstyrene. With this weak polarity, we obtain PCHD blocks with a very good 1,4 stereospecificity (up to 99%) necessary to give only poly( 1,4-phenylene). * To whom correspondence should be addressed Telephone: 05 59 72 2121 /Fax: 05 59 80 36 50/e-mail:
[email protected]
2 PCHD-PS-,Li+
c THF-cyclohexane,
tetrachloro-I
PCHD-PS-PCHD
25°C
PCHD-PS-PCHD
N,
,4-benzoquinone
1,2-dichlorobenzene,
130X,
*
PPP-PS-PPP
N,
Fig. 1. Synthesis of PPP-b-PS-b-PPP. We synthesize soluble triblock copolymers with the following sequence molecular weights: 1200-2500- 1200 (copol) and 150027000- 1500 (~0~02). 3. Physico-chemical
characterizations
3.1 Steric Exclusion Chromatography
(S.E.C.)
The chromatograms of PPP-b-PS-b-PPP copolymers were carried out on THF at 35°C at lml.min~’ with UV-Visible detection. An example is given in Fig. 2 for ~0~02. It shows free chains, with approximately the same retention volume than the precursor, and aggregates with very important molecular weight (molecular weight in linear PS equivalent). Some pure oligophenylene and diblock PPP-b-PS (-9%) are also detected because of transfer and ending reactions during polymerization.
0379-6779/99/$ - see front matter 0 1999 Elsevier Science S.A. All rights reserved. PII: SO379-6779(98)01376-9
E. Mignard -
et al. I Synthetic
102 (1999)
12461247
1247
Table 1 Results for PPP core.
PPP-b-PS-b-PPP 0
Metals
PCHD-b-PS-b-PCHD
Rg, 6)
AZ (m&s)
cop01
M, VP) 332000
154
3.5
cop02
980000
202
1.46 lO-4
0,099
m
(g/ml)
1o-5
2 Max. Abs. = 333.4 nm
-0,001
15
10
Volume
(ml)
25
2o
Fig. 2. S.E.C. chromatograms extracted at 254 nm. The existence of PPP blocks is demonstrated by spectra extracted at each fraction of the chromatograms The max. wavelength absorption increases from the free chain to the aggregates. The conjugated units number determined from the W. Khun relationship [5] gives 11 for aggregates and 6 for free chains.
A very high degree of association (276 for cop01 and 650 for ~0~02) and a small positive second virial coefficient are measured for these triblock copolymers. Considering the scattering in the range of high scattering vector Q, one observes a Porod’s law behavior: the plot Q4G(Q) = f(Q) gives a plateau indicating the presence of sharp interface between the PPP cores and the PS and solvent. The value of this plateau is equal to 271 SN (S and V respectively Surface and Volume of the particle). 0.30 -
3.2 Neutron scattering These experiments were carried out at the I.L.L. (Grenoble). In order to determine the size and shape of PPP core of these aggregates the copolymers have been studied by neutron scattering in CS2 solution. CS2 matches the polystyrene scattering so the measured scattering is basically due to PPP. The scattering function of cop01 is shown in Fig. 3. No welldefined peak, showing a particle organization, is visible. 0
0.04
0.08 Q (A-l)
0.12
0.16
Fig. 5. Porod’s law behavior for copol. 57 d lE+4
s
lE+2
I
I 0,001
0,oi
The results in Fig. 5 (copol) show that the ratio S/V does not change with the concentration between 2 and 16%. Its value is 0.035. This value is compatible with a ribbon model with a 59 A thickness. This is close to the value for the extended PPP chains (length: 69A).
1
O,l
4. Conclusions
Q (A-l)
Fig. 3. Scattering function of copol.
New soluble PPP-b-PS-b-PPP copolymers have been synthesized with up to 50% PPP. They are highly aggregated in solution. A ribbon structure seems to be the most probable. 5. Acknowledgments
1 E-5
We thank Dr. M. Rawiso for his help for neutron scattering measurements. This work was partly supported by the European “SELOA” TRM program. OE+O
1 0
6
/
0,0004 Q2 + 0.01
0,0008 c
Fig. 4. Neutron scattering Zimm plot for copol. The Fig. 4 shows a classical Zimm plot for 4 solutions (concentration: 1, 2, 5, 8.10“ g/ml). It allows the determination of PPP core molecular weight (Mw), radius of gyration (Rg) and second virial coefficient (Ar). Results are given in the Table 1.
6. References [l] B. FranGois, G. Widawski, M. Rawiso, B. Cesar, Synth. Met. 69 (1995) 463. [2] G. Widwaski, M. Rawiso, B. FranGois, Nature 369 (1994) 387. [3] D. B. Romero, M. Schaer, J. L. Staehli, L. Zuppiroli, G. Widawski, M. Rawiso and B. Francois, Solid. state comm. 953 (1995) 185189. [4] E. Mignard, C. Tachon, B. Fran9ois, J. Chim. Phys. 95 (1998) 1221. [5] W. Khun, Helv. Chim. Acta. 31-6 (1948) 1780.
Synthetic Metals 102 (1999) 12461247
Neutron scattering analysis of a block copolymer poly( 1,4-phenylene)-block-polystyrene-black-poly( 1,4-phenylene) E. Mignard, C. Tachon, B. Francois* Laboratoire de Recherche SW les Mate’riaux PolymPres CNRS - UPPA He’lioparc, 2 Av. du PGsident Angot, 64000 Pau, Fr
Abstract Poly( 1,4-phenylene)-block-polystyrene-block-poly( 1,4-phenylene) (PPP-b-PS-b-PPP) blocks copolymers were synthesized by chemical modification of a precursor copolymer. After characterization by Size Exclusion Chromatography (SEC) and UV-Visible spectroscopy, triblock copolymers were studied in CSz solution at room temperature by neutron-scattering analysis. These triblock copolymers are highly aggregated. A ribbon model seems to give the best fit for the PPP core. Keywords:
Other conjugated
and/or conducting polymers, Self-organization
in macromolecules,
set-Bu-,Li+
1. Introduction Poly( 1,4-phenylene) (PPP) receives considerable attention because of its important physical and chemical properties. Nevertheless rigidity and interchain interactions are responsible for its insolubility and unfusibility. That is the reason why among the different ways to solubilise the PPP, we copolymerise it with a block of polystyrene (PS) soluble in usual organic solvent.
Neutron scattering and d@raction
cyclohexane
+ a-methylstyrene
c
FH” ((“-CH2
%+ -,Li
25°C I N,
/ 6
h
= R,Li+ \
-
R-,Li+ cyclohexane,
25°C / N,
PCHD-PS-,Li+
Previous work about PS-b-PPP diblock copolymers [l] has shown the associative behavior of PPP blocks in THF at room temperature. In a first way, these aggregates are considered as starlike polymers. They can lead to particular self-organized thin films with a honeycomb morphology [2] and present interesting photo and electroluminescence properties [3]. Now, we study the physico-chemical properties of the triblock copolymers PPP-b-PS-b-PPP in the same conditions [4]. We want to determine their ability to form a network or not. Thus, we would obtain a new material constituted by conjugated particles organization into insulating matrix. 2. PPP-b-PS-b-PPP
triblock
copolymer
synthesis
The title copolymer is obtained by chemical modification of a precursor: the poly(l,3-cyclohexadiene)-b-polystyrene-b-poly(1,3cyclohexadiene) (PCHD-b-PS-b-PCHD). This precursor is prepared by anionic polymerization of 1,3cyclohexadiene and styrene monomers in a non-polar solvent at room temperature (Fig. 1). The polymerization is started by a coupling product between secondary-butyllithium and CLmethylstyrene. With this weak polarity, we obtain PCHD blocks with a very good 1,4 stereospecificity (up to 99%) necessary to give only poly( 1,4-phenylene). * To whom correspondence should be addressed Telephone: 05 59 72 2121 /Fax: 05 59 80 36 50/e-mail:
[email protected]
2 PCHD-PS-,Li+
c THF-cyclohexane,
tetrachloro-I
PCHD-PS-PCHD
25°C
PCHD-PS-PCHD
N,
,4-benzoquinone
1,2-dichlorobenzene,
130X,
*
PPP-PS-PPP
N,
Fig. 1. Synthesis of PPP-b-PS-b-PPP. We synthesize soluble triblock copolymers with the following sequence molecular weights: 1200-2500- 1200 (copol) and 150027000- 1500 (~0~02). 3. Physico-chemical
characterizations
3.1 Steric Exclusion Chromatography
(S.E.C.)
The chromatograms of PPP-b-PS-b-PPP copolymers were carried out on THF at 35°C at lml.min~’ with UV-Visible detection. An example is given in Fig. 2 for ~0~02. It shows free chains, with approximately the same retention volume than the precursor, and aggregates with very important molecular weight (molecular weight in linear PS equivalent). Some pure oligophenylene and diblock PPP-b-PS (-9%) are also detected because of transfer and ending reactions during polymerization.
0379-6779/99/$ - see front matter 0 1999 Elsevier Science S.A. All rights reserved. PII: SO379-6779(98)01376-9
E. Mignard -
et al. I Synthetic
102 (1999)
12461247
1247
Table 1 Results for PPP core.
PPP-b-PS-b-PPP 0
Metals
PCHD-b-PS-b-PCHD
Rg, 6)
AZ (m&s)
cop01
M, VP) 332000
154
3.5
cop02
980000
202
1.46 lO-4
0,099
m
(g/ml)
1o-5
2 Max. Abs. = 333.4 nm
-0,001
15
10
Volume
(ml)
25
2o
Fig. 2. S.E.C. chromatograms extracted at 254 nm. The existence of PPP blocks is demonstrated by spectra extracted at each fraction of the chromatograms The max. wavelength absorption increases from the free chain to the aggregates. The conjugated units number determined from the W. Khun relationship [5] gives 11 for aggregates and 6 for free chains.
A very high degree of association (276 for cop01 and 650 for ~0~02) and a small positive second virial coefficient are measured for these triblock copolymers. Considering the scattering in the range of high scattering vector Q, one observes a Porod’s law behavior: the plot Q4G(Q) = f(Q) gives a plateau indicating the presence of sharp interface between the PPP cores and the PS and solvent. The value of this plateau is equal to 271 SN (S and V respectively Surface and Volume of the particle). 0.30 -
3.2 Neutron scattering These experiments were carried out at the I.L.L. (Grenoble). In order to determine the size and shape of PPP core of these aggregates the copolymers have been studied by neutron scattering in CS2 solution. CS2 matches the polystyrene scattering so the measured scattering is basically due to PPP. The scattering function of cop01 is shown in Fig. 3. No welldefined peak, showing a particle organization, is visible. 0
0.04
0.08 Q (A-l)
0.12
0.16
Fig. 5. Porod’s law behavior for copol. 57 d lE+4
s
lE+2
I
I 0,001
0,oi
The results in Fig. 5 (copol) show that the ratio S/V does not change with the concentration between 2 and 16%. Its value is 0.035. This value is compatible with a ribbon model with a 59 A thickness. This is close to the value for the extended PPP chains (length: 69A).
1
O,l
4. Conclusions
Q (A-l)
Fig. 3. Scattering function of copol.
New soluble PPP-b-PS-b-PPP copolymers have been synthesized with up to 50% PPP. They are highly aggregated in solution. A ribbon structure seems to be the most probable. 5. Acknowledgments
1 E-5
We thank Dr. M. Rawiso for his help for neutron scattering measurements. This work was partly supported by the European “SELOA” TRM program. OE+O
1 0
6
/
0,0004 Q2 + 0.01
0,0008 c
Fig. 4. Neutron scattering Zimm plot for copol. The Fig. 4 shows a classical Zimm plot for 4 solutions (concentration: 1, 2, 5, 8.10“ g/ml). It allows the determination of PPP core molecular weight (Mw), radius of gyration (Rg) and second virial coefficient (Ar). Results are given in the Table 1.
6. References [l] B. FranGois, G. Widawski, M. Rawiso, B. Cesar, Synth. Met. 69 (1995) 463. [2] G. Widwaski, M. Rawiso, B. FranGois, Nature 369 (1994) 387. [3] D. B. Romero, M. Schaer, J. L. Staehli, L. Zuppiroli, G. Widawski, M. Rawiso and B. Francois, Solid. state comm. 953 (1995) 185189. [4] E. Mignard, C. Tachon, B. Fran9ois, J. Chim. Phys. 95 (1998) 1221. [5] W. Khun, Helv. Chim. Acta. 31-6 (1948) 1780.