- Email: [email protected]
Real-time SANS and 1H-NMR studies during “living” anionic polymerization of butadiene in hydrocarbon media
ARTICLE IN PRESS
Physica B 350 (2004) e921–e925
Real-time SANS and 1H-NMR studies during ‘‘living’’ anionic polymerization of butadiene in hydrocarbon media A.Z. Niua,b,*, J. Stellbrinka, J. Allgaiera, L. Willnera, D. Richtera, A. Radulescua, B.W. Koenigc, M. Gondorfd, S. Willboldd, L.J. Fetterse b
a Institut fur Forschungszentrum Julich, D-52425 Julich, Germany . Festkorperforschung, . . . State Key Laboratory of Functional Polymer Materials for Adsorption and Separation, Nankai University, Tianjin, China c IBI 2, Forschungszentrum Julich, D-52425 Julich, und Institut fur . . . Physikalische Biologie, Heinrich-Heine-Univ., D-40225 Dusseldorf, Germany . d ZCH, Forschungszentrum Julich, D-52425 Julich, Germany . . e Department of Chemical Engineering, Cornell University, Ithaca, NY 14584, USA
Abstract Small angle neutron scattering (SANS) and high-resolution proton nuclear magnetic resonance spectra (1H-NMR) studies have been carried out in situ on the organolithium polymerization of butadiene in hydrocarbon media. The time resolved NMR measurements allowed us to evaluate quantitatively the kinetics of the processes involved. The combination of SANS and NMR methods offers a new way to characterize the aggregation behavior of the living chains quantitatively as a function of conversion. The present data show large-scale aggregated species exist during the initiation period. These aggregates of more than 160 living polymer chains diminished as the polymerization progressed. r 2004 Elsevier B.V. All rights reserved. PACS: 82.35.x; 61.12.Ex; 82.56.Dj Keywords: Anionic polymerization; Aggregation; NMR; SANS
1. Introduction ‘‘Living’’ anionic polymerization is a powerful method to produce polymers with controlled, narrow molar mass distribution and well-defined architectures. The anionic polymerization of dienes and styrene in hydrocarbon media based . *Corresponding author. Institut fur . Festkorperforschung, Forschungszentrum Julich . GmbH, 52425 Julich, . Germany. Tel.: +49-2461-616683; fax: +49-2461-612610. Email-addresses: [email protected] (A.Z. Niu), [email protected] (J. Stellbrink).
on organolithium compounds is now recognized to be more complicated than that presented as the ‘‘textbook explanation’’ [1–3]. The polymerization event occurs via an ionic headgroup, e.g., buta+ dienyllithium (R-CH 2 Li ) for the polybutadiene synthesis, which reacts with a monomer, building up the polymeric structure. Under inert conditions such a headgroup may be active for a long period, therefore, this type of polymerization is called ‘‘living’’ polymerization. Since the ionic headgroups cannot be dissolved well in hydrocarbon media, aggregation behavior of the living polymer chains is considered. On the basis of reaction
0921-4526/$ - see front matter r 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.physb.2004.03.238
ARTICLE IN PRESS e922
A.Z. Niu et al. / Physica B 350 (2004) e921–e925
kinetic studies for the polymerization of butadiene a fraction order of 14 process was concluded with respect to headgroup concentration. A text book mechanism evolves, which considers an equilibrium between tetramers and unimers, where only the unimers are the reactive species [4]. In this work, we investigate the polymerization of butadiene with tert-butyllithium in d16-heptane by using the combination of in situ high-resolution proton nuclear magnetic resonance (1H-NMR) and small angle neutron scattering (SANS) techniques, and focus on the aggregates structures during initiation stage. We found that there are large scale three-dimensional aggregates existing in our system, as shown by the power law decay found in the low Q region of our SANS data. A second type of aggregate is found during the polymerization in the mid-Q range. The aggregates were analyzed quantitatively by using polymer volume fraction F(t) and molecular volume of the growing chain Vw(t) obtained from the NMR results. Using this approach the aggregation numbers Nagg as a function of reaction time could be derived.
Table 1 Characterization of terminated chains Mn (g/mol)
Mw (g/mol)
Mw/Mn
32.0 Ka 31.5 Kb
33.0 Ka 31.3 Kc
1.034a
( Rg (A)
A2 (cm3 mol/g2)
85.3a 89c
3.13(70.03) 104 c
a
GPC. NMR. c SANS. b
1.4 103 mol/l and the monomer concentration was 0.7 mol/l for the polymerization system. The removal of these SANS cells and NMR tubes containing monomer/initiator/solvent solution was operated by heat sealing at 78 C. The prepared SANS and NMR samples were frozen in liquid nitrogen until the measurements commenced. The remaining reactor content was polymerized at 20 C for 3 days, then terminated in a glove box by degassed d-methanol. The terminated solution was filtered to remove the lithium methoxide and finally the solvent was distilled out. The product—polybutadiene was dried on the vacuum line and characterized by GPC, NMR and SANS (Table 1).
2. Experiments 2.2. Sans measurements 2.1. Sample preparation and characterization The basic procedures used for the purification of solvent and monomer are described elsewhere [5]. The polymerization solvent was d16-heptane while the initiator was tert-butyllithium and the monomer was butadiene. The polymerization started with the addition of the initiator solution to the reactor followed by the removal of the hydrogenous solvent via distillation, then the d16heptane was added. A portion of this solution was then captured in a quartz SANS cell and the reactor and cell reservoir cooled to about 78 C, the SANS cell unit removed from the reactor via heat sealing at the constriction. The reactor was then returned to the vacuum line. The required amount of monomer was then distilled into the reactor, which was then removed from the vacuum line by heat sealing at the constriction below the stopcock. The concentration of initiator was
The SANS measurements were done on the KWS-2 instrument at Forschungszentrum Juelich, Germany. A detector setting of 8 m was used with ( The scattering cross a neutron wavelength l=7 A. section dS/dO from polymers in dilute solution is given by dS Dr2 Fð1 FÞ : ¼ dO Na 1=Vw PðQÞ þ 2A2 F
ð1Þ
Here, polymer concentration is given in terms of F which denotes the polymer volume fraction, P(Q) the form factor of the polymer or the polymer aggregates, Vw the corresponding weight average polymer volume, A2 the second virial coefficient, Na the Avogadro number and Eq. (2) defines the scattering contrast Sbs Sbmon Dr ¼ : ð2Þ Vs Vmon
ARTICLE IN PRESS A.Z. Niu et al. / Physica B 350 (2004) e921–e925
The ratio Sbs/Vs is the scattering length density of the solvent while bs denotes the scattering lengths of the atoms forming the solvent molecule and Vs is the corresponding volume. Sbmon/Vmon is the corresponding quantity for the repeat unit. Contributions due to incoherent background and solvent scattering were subtracted from all data sets.
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polymerization in a sealed sample tube. Signal intensities at different reaction times were compared quantitatively via comparison with the residual proton signal of the solvent d16-heptane signal at 0.88 ppm. The initiator (tert-butyllithium) signal is a sharp peak located at 1.07 ppm before polymerization and it shifts to 0.91 and 0.96 ppm after initiated. The fraction of reacted tertbutyllithium at time t was calculated from the signal intensities at 1.07 ppm of the initial spectrum (I1.07 ppm,t=0) and the spectrum at time t (I1.07 ppm,t). Conversion rates Conv(t) were calculated from the signal intensities of the monomer signal at B6.3 ppm (I6.3 ppm,t) and the polymer signals at B2.1 ppm (I2.1 ppm,t, 1,4 structure) and B1.5 ppm (I1.5 ppm,t, 1,2 structure) at time t, e.g.:
2.3. Nuclear magnetic resonance spectra The 1H-NMR spectra were recorded on a Bruker DMX600 spectrometer at 600.14 MHz at 8 C. A long pre-scan delay of 300 s was found to be necessary to ensure complete T1-Relaxation of all signals, a strict requirement for quantitative interpretation of integral peak intensity.
ConvðtÞ ¼ ½PðtÞ =ð½MðtÞ þ ½PðtÞ Þ ¼ ðI2:1 ppm;t =4: þ I1:5 ppm;t Þ=ðI6:3 ppm;t =2 þ I2:1 ppm;t =4: þ I1:5 ppm;t Þ: ð3Þ
3. Results Fig. 1 shows the 1H-NMR spectra before and after polymerization, respectively. The molarity of the solvent protons does not change during the
Here, [P(t)] is the polymer concentration at time t and [M(t)] is monomer concentration at time t. Polymerization degree Dp(t) was calculated from before polymerization
CH2=CH-CH=CH2
a b
Solvent Solvent
a
b
Initiator
(a)
6.5
6.0
5.5
5.0
2.5
c, d
e
CH2
CH
2.0
1.5
1.0
a a b -CH2-CH=CH-CH2-
b
CH CH2
f 6.5 (b)
6.0
5.5
after polymerization
f g
g 5.0
e 2.5
2.0
cd 1.5
Chemical shift / ppm
Fig. 1. 1H-NMR spectra of before and after polymerization.
1.0
ARTICLE IN PRESS A.Z. Niu et al. / Physica B 350 (2004) e921–e925
e924
the signal intensities of the polymer signals at B2.1, B1.5 ppm and the signals at 1.07 ppm as
150
¼ ðI2:1 ppm;t =4: þ I1:5 ppm;t Þ= ððI1:07
ppm;t¼0
I1:07
ppm;t Þ=9Þ:
ð4Þ
(dΣ /dΩ )[cm-1]
Here, [Ini(t)] is the initiator concentration at time t and [Ini(t=0)] is initial initiator concentration. Microstructures were calculated from the signal intensities of the polymer signals at B2.1 and B1.5 ppm. In all cases the number of protons correlated with the different signals was taken into account. Fig. 2 shows SANS results on living anionic polymerization at the initiation stage. A strong increase of the scattering intensity towards low Q is observed, indicating the existence of large-scale aggregates. The inset is the reaction time dependence of polymerization degree Dp from the results of 1H-NMR measurement. We calculated F(t) and Vw(t) assuming a time dependent polydispersity (Mw/Mn)=(1+1/Dp). From experimental data we obtained the following power law between Mw and the radius of gyration Rg of polybutadiene in ( Assuming that the heptane: Rg=0.288M0.554 [A]. w growing chain forms star-like aggregates, the calculation of the radius of gyration of the aggregates can be calculated by the following relation qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi Rg;agg ¼ ð3Nagg 2Þ=Nagg Rg;arm : ð5Þ
10
10
2
DP
0
135 min 330 min 500 min 660 min
10
2
10
3
10
50 0
200
400
600
Time [min] Fig. 3. Reaction time dependence of aggregation number of living polymer chains during initiation stage.
Here, Nagg is the aggregation number of living polymer chains. The scattering intensity as function of reaction time t and scattering vector Q was fitted by a simple Guinier approach: IðQ; tÞ ¼ IðQ ¼ 0; tÞ expðQ2 Rg ðtÞ2 =3Þ ¼ FðtÞNagg ðtÞVw ðtÞ expðQ2 Rg ðtÞ2 =3Þ:
ð6Þ
Vw(t) is the molecular volume of the growing chain per head group in cm3/mol, Fig. 3 shows the time dependence of aggregation number fitted from the mid-Q range SANS data during initiation stage. It clearly indicates that the aggregation state of the living polymer chains changes with reaction time during the initiation stage. The aggregation number decreased from B160 to B8 during the polymerization time of 135–660 min [6]1 because the growth of the chain may cause a concurrent decrease in aggregate functionality.
4
Time [min] -1
10
-2 -2
10
100
1
10
10
NAgg
Dp ðtÞ ¼ ½PðtÞ =ð½Iniðt ¼ 0Þ ½IniðtÞ Þ
-1
Q [Å ]
Fig. 2. SANS data of the living polybutadienyllithium chains during the initiation stage. The solid line is the fitting results of the Guinier method. The inset shows the polymerization degree Dp as a function of reaction time from NMR results.
4. Conclusion By combining time resolved 1H-NMR and SANS experiments we have shown, that there is a complex aggregation behavior in the polymerizing solution. We found two families of aggregated species at the early reaction stages. During the initiation period highly aggregated structures with ( ( NaggE100 and 10 ApR gp100 A are found in the 1 The induction period changed when we investigated the system without void volume; see Ref. [6].
ARTICLE IN PRESS A.Z. Niu et al. / Physica B 350 (2004) e921–e925
( 1oQo3 102 A ( 1) comid-Q range(1 102 A existing with even larger, giant structures in the ( 1). It indicates that lower Q range (Qo1 102 A the viewpoint of kinetic orders of anionic polymerizations are related directly to aggregation states is incorrect, at least in the system of this work.
References [1] R.N. Young, R.P. Quirk, L.J. Fetters, Adv. Polym. Sci. 56 (1984) 1.
e925
[2] L.J. Fetters, N.P. Balsara, J.S. Huang, H.S. Jeon, K. Almdal, M.Y. Lin, Macromolecules 28 (1995) 4996. [3] M. Van Beylen, S. Bywater, G. Smets, M. Szwarc, D. Worsfold, J. Adv. Polym. Sci. 86 (1988) 87. [4] M. Swarz, in: J.E.Mc. Grath (Ed.), Anionic Polymerization Kinetics Mechanisms and Synthesis, Vol. 1, ACS Symposium Series 166, Washington, DC, 1981. [5] M. Morton, L.J. Fetters, Rubber Chem. Technol. 48 (1975) 359. [6] A.Z. Niu, J. Stellbrink, J. Allgaier, L. Willner, D. Richter, B.W. Koenig, M. Gondorf, S. Willbold, L.J. Fetters, R.P. May, Macromolecular Symposia, 2003, in press.
Physica B 350 (2004) e921–e925
Real-time SANS and 1H-NMR studies during ‘‘living’’ anionic polymerization of butadiene in hydrocarbon media A.Z. Niua,b,*, J. Stellbrinka, J. Allgaiera, L. Willnera, D. Richtera, A. Radulescua, B.W. Koenigc, M. Gondorfd, S. Willboldd, L.J. Fetterse b
a Institut fur Forschungszentrum Julich, D-52425 Julich, Germany . Festkorperforschung, . . . State Key Laboratory of Functional Polymer Materials for Adsorption and Separation, Nankai University, Tianjin, China c IBI 2, Forschungszentrum Julich, D-52425 Julich, und Institut fur . . . Physikalische Biologie, Heinrich-Heine-Univ., D-40225 Dusseldorf, Germany . d ZCH, Forschungszentrum Julich, D-52425 Julich, Germany . . e Department of Chemical Engineering, Cornell University, Ithaca, NY 14584, USA
Abstract Small angle neutron scattering (SANS) and high-resolution proton nuclear magnetic resonance spectra (1H-NMR) studies have been carried out in situ on the organolithium polymerization of butadiene in hydrocarbon media. The time resolved NMR measurements allowed us to evaluate quantitatively the kinetics of the processes involved. The combination of SANS and NMR methods offers a new way to characterize the aggregation behavior of the living chains quantitatively as a function of conversion. The present data show large-scale aggregated species exist during the initiation period. These aggregates of more than 160 living polymer chains diminished as the polymerization progressed. r 2004 Elsevier B.V. All rights reserved. PACS: 82.35.x; 61.12.Ex; 82.56.Dj Keywords: Anionic polymerization; Aggregation; NMR; SANS
1. Introduction ‘‘Living’’ anionic polymerization is a powerful method to produce polymers with controlled, narrow molar mass distribution and well-defined architectures. The anionic polymerization of dienes and styrene in hydrocarbon media based . *Corresponding author. Institut fur . Festkorperforschung, Forschungszentrum Julich . GmbH, 52425 Julich, . Germany. Tel.: +49-2461-616683; fax: +49-2461-612610. Email-addresses: [email protected] (A.Z. Niu), [email protected] (J. Stellbrink).
on organolithium compounds is now recognized to be more complicated than that presented as the ‘‘textbook explanation’’ [1–3]. The polymerization event occurs via an ionic headgroup, e.g., buta+ dienyllithium (R-CH 2 Li ) for the polybutadiene synthesis, which reacts with a monomer, building up the polymeric structure. Under inert conditions such a headgroup may be active for a long period, therefore, this type of polymerization is called ‘‘living’’ polymerization. Since the ionic headgroups cannot be dissolved well in hydrocarbon media, aggregation behavior of the living polymer chains is considered. On the basis of reaction
0921-4526/$ - see front matter r 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.physb.2004.03.238
ARTICLE IN PRESS e922
A.Z. Niu et al. / Physica B 350 (2004) e921–e925
kinetic studies for the polymerization of butadiene a fraction order of 14 process was concluded with respect to headgroup concentration. A text book mechanism evolves, which considers an equilibrium between tetramers and unimers, where only the unimers are the reactive species [4]. In this work, we investigate the polymerization of butadiene with tert-butyllithium in d16-heptane by using the combination of in situ high-resolution proton nuclear magnetic resonance (1H-NMR) and small angle neutron scattering (SANS) techniques, and focus on the aggregates structures during initiation stage. We found that there are large scale three-dimensional aggregates existing in our system, as shown by the power law decay found in the low Q region of our SANS data. A second type of aggregate is found during the polymerization in the mid-Q range. The aggregates were analyzed quantitatively by using polymer volume fraction F(t) and molecular volume of the growing chain Vw(t) obtained from the NMR results. Using this approach the aggregation numbers Nagg as a function of reaction time could be derived.
Table 1 Characterization of terminated chains Mn (g/mol)
Mw (g/mol)
Mw/Mn
32.0 Ka 31.5 Kb
33.0 Ka 31.3 Kc
1.034a
( Rg (A)
A2 (cm3 mol/g2)
85.3a 89c
3.13(70.03) 104 c
a
GPC. NMR. c SANS. b
1.4 103 mol/l and the monomer concentration was 0.7 mol/l for the polymerization system. The removal of these SANS cells and NMR tubes containing monomer/initiator/solvent solution was operated by heat sealing at 78 C. The prepared SANS and NMR samples were frozen in liquid nitrogen until the measurements commenced. The remaining reactor content was polymerized at 20 C for 3 days, then terminated in a glove box by degassed d-methanol. The terminated solution was filtered to remove the lithium methoxide and finally the solvent was distilled out. The product—polybutadiene was dried on the vacuum line and characterized by GPC, NMR and SANS (Table 1).
2. Experiments 2.2. Sans measurements 2.1. Sample preparation and characterization The basic procedures used for the purification of solvent and monomer are described elsewhere [5]. The polymerization solvent was d16-heptane while the initiator was tert-butyllithium and the monomer was butadiene. The polymerization started with the addition of the initiator solution to the reactor followed by the removal of the hydrogenous solvent via distillation, then the d16heptane was added. A portion of this solution was then captured in a quartz SANS cell and the reactor and cell reservoir cooled to about 78 C, the SANS cell unit removed from the reactor via heat sealing at the constriction. The reactor was then returned to the vacuum line. The required amount of monomer was then distilled into the reactor, which was then removed from the vacuum line by heat sealing at the constriction below the stopcock. The concentration of initiator was
The SANS measurements were done on the KWS-2 instrument at Forschungszentrum Juelich, Germany. A detector setting of 8 m was used with ( The scattering cross a neutron wavelength l=7 A. section dS/dO from polymers in dilute solution is given by dS Dr2 Fð1 FÞ : ¼ dO Na 1=Vw PðQÞ þ 2A2 F
ð1Þ
Here, polymer concentration is given in terms of F which denotes the polymer volume fraction, P(Q) the form factor of the polymer or the polymer aggregates, Vw the corresponding weight average polymer volume, A2 the second virial coefficient, Na the Avogadro number and Eq. (2) defines the scattering contrast Sbs Sbmon Dr ¼ : ð2Þ Vs Vmon
ARTICLE IN PRESS A.Z. Niu et al. / Physica B 350 (2004) e921–e925
The ratio Sbs/Vs is the scattering length density of the solvent while bs denotes the scattering lengths of the atoms forming the solvent molecule and Vs is the corresponding volume. Sbmon/Vmon is the corresponding quantity for the repeat unit. Contributions due to incoherent background and solvent scattering were subtracted from all data sets.
e923
polymerization in a sealed sample tube. Signal intensities at different reaction times were compared quantitatively via comparison with the residual proton signal of the solvent d16-heptane signal at 0.88 ppm. The initiator (tert-butyllithium) signal is a sharp peak located at 1.07 ppm before polymerization and it shifts to 0.91 and 0.96 ppm after initiated. The fraction of reacted tertbutyllithium at time t was calculated from the signal intensities at 1.07 ppm of the initial spectrum (I1.07 ppm,t=0) and the spectrum at time t (I1.07 ppm,t). Conversion rates Conv(t) were calculated from the signal intensities of the monomer signal at B6.3 ppm (I6.3 ppm,t) and the polymer signals at B2.1 ppm (I2.1 ppm,t, 1,4 structure) and B1.5 ppm (I1.5 ppm,t, 1,2 structure) at time t, e.g.:
2.3. Nuclear magnetic resonance spectra The 1H-NMR spectra were recorded on a Bruker DMX600 spectrometer at 600.14 MHz at 8 C. A long pre-scan delay of 300 s was found to be necessary to ensure complete T1-Relaxation of all signals, a strict requirement for quantitative interpretation of integral peak intensity.
ConvðtÞ ¼ ½PðtÞ =ð½MðtÞ þ ½PðtÞ Þ ¼ ðI2:1 ppm;t =4: þ I1:5 ppm;t Þ=ðI6:3 ppm;t =2 þ I2:1 ppm;t =4: þ I1:5 ppm;t Þ: ð3Þ
3. Results Fig. 1 shows the 1H-NMR spectra before and after polymerization, respectively. The molarity of the solvent protons does not change during the
Here, [P(t)] is the polymer concentration at time t and [M(t)] is monomer concentration at time t. Polymerization degree Dp(t) was calculated from before polymerization
CH2=CH-CH=CH2
a b
Solvent Solvent
a
b
Initiator
(a)
6.5
6.0
5.5
5.0
2.5
c, d
e
CH2
CH
2.0
1.5
1.0
a a b -CH2-CH=CH-CH2-
b
CH CH2
f 6.5 (b)
6.0
5.5
after polymerization
f g
g 5.0
e 2.5
2.0
cd 1.5
Chemical shift / ppm
Fig. 1. 1H-NMR spectra of before and after polymerization.
1.0
ARTICLE IN PRESS A.Z. Niu et al. / Physica B 350 (2004) e921–e925
e924
the signal intensities of the polymer signals at B2.1, B1.5 ppm and the signals at 1.07 ppm as
150
¼ ðI2:1 ppm;t =4: þ I1:5 ppm;t Þ= ððI1:07
ppm;t¼0
I1:07
ppm;t Þ=9Þ:
ð4Þ
(dΣ /dΩ )[cm-1]
Here, [Ini(t)] is the initiator concentration at time t and [Ini(t=0)] is initial initiator concentration. Microstructures were calculated from the signal intensities of the polymer signals at B2.1 and B1.5 ppm. In all cases the number of protons correlated with the different signals was taken into account. Fig. 2 shows SANS results on living anionic polymerization at the initiation stage. A strong increase of the scattering intensity towards low Q is observed, indicating the existence of large-scale aggregates. The inset is the reaction time dependence of polymerization degree Dp from the results of 1H-NMR measurement. We calculated F(t) and Vw(t) assuming a time dependent polydispersity (Mw/Mn)=(1+1/Dp). From experimental data we obtained the following power law between Mw and the radius of gyration Rg of polybutadiene in ( Assuming that the heptane: Rg=0.288M0.554 [A]. w growing chain forms star-like aggregates, the calculation of the radius of gyration of the aggregates can be calculated by the following relation qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi Rg;agg ¼ ð3Nagg 2Þ=Nagg Rg;arm : ð5Þ
10
10
2
DP
0
135 min 330 min 500 min 660 min
10
2
10
3
10
50 0
200
400
600
Time [min] Fig. 3. Reaction time dependence of aggregation number of living polymer chains during initiation stage.
Here, Nagg is the aggregation number of living polymer chains. The scattering intensity as function of reaction time t and scattering vector Q was fitted by a simple Guinier approach: IðQ; tÞ ¼ IðQ ¼ 0; tÞ expðQ2 Rg ðtÞ2 =3Þ ¼ FðtÞNagg ðtÞVw ðtÞ expðQ2 Rg ðtÞ2 =3Þ:
ð6Þ
Vw(t) is the molecular volume of the growing chain per head group in cm3/mol, Fig. 3 shows the time dependence of aggregation number fitted from the mid-Q range SANS data during initiation stage. It clearly indicates that the aggregation state of the living polymer chains changes with reaction time during the initiation stage. The aggregation number decreased from B160 to B8 during the polymerization time of 135–660 min [6]1 because the growth of the chain may cause a concurrent decrease in aggregate functionality.
4
Time [min] -1
10
-2 -2
10
100
1
10
10
NAgg
Dp ðtÞ ¼ ½PðtÞ =ð½Iniðt ¼ 0Þ ½IniðtÞ Þ
-1
Q [Å ]
Fig. 2. SANS data of the living polybutadienyllithium chains during the initiation stage. The solid line is the fitting results of the Guinier method. The inset shows the polymerization degree Dp as a function of reaction time from NMR results.
4. Conclusion By combining time resolved 1H-NMR and SANS experiments we have shown, that there is a complex aggregation behavior in the polymerizing solution. We found two families of aggregated species at the early reaction stages. During the initiation period highly aggregated structures with ( ( NaggE100 and 10 ApR gp100 A are found in the 1 The induction period changed when we investigated the system without void volume; see Ref. [6].
ARTICLE IN PRESS A.Z. Niu et al. / Physica B 350 (2004) e921–e925
( 1oQo3 102 A ( 1) comid-Q range(1 102 A existing with even larger, giant structures in the ( 1). It indicates that lower Q range (Qo1 102 A the viewpoint of kinetic orders of anionic polymerizations are related directly to aggregation states is incorrect, at least in the system of this work.
References [1] R.N. Young, R.P. Quirk, L.J. Fetters, Adv. Polym. Sci. 56 (1984) 1.
e925
[2] L.J. Fetters, N.P. Balsara, J.S. Huang, H.S. Jeon, K. Almdal, M.Y. Lin, Macromolecules 28 (1995) 4996. [3] M. Van Beylen, S. Bywater, G. Smets, M. Szwarc, D. Worsfold, J. Adv. Polym. Sci. 86 (1988) 87. [4] M. Swarz, in: J.E.Mc. Grath (Ed.), Anionic Polymerization Kinetics Mechanisms and Synthesis, Vol. 1, ACS Symposium Series 166, Washington, DC, 1981. [5] M. Morton, L.J. Fetters, Rubber Chem. Technol. 48 (1975) 359. [6] A.Z. Niu, J. Stellbrink, J. Allgaier, L. Willner, D. Richter, B.W. Koenig, M. Gondorf, S. Willbold, L.J. Fetters, R.P. May, Macromolecular Symposia, 2003, in press.