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Morphology of the poly(styrene-alt-maleic anhydride) micelles obtained

by radiation-induced emulsion polymerization using anionic/nonionic

mixed surfactants templates

Mei Tao a, Zhongqing Hu b,, Zhicheng Zhang b

a Department of Chemistry, Anhui Medical University, 230032 Hefei, Chinab Department of Polymer Science and Engineering, University of Science and Technology of China, 230026 Hefei, China

Received 22 January 2007; accepted 7 June 2007

Available online 12 June 2007

Abstract

Poly(styrene-alt-maleic anhydride) latexes were first obtained by emulsion polymerization induced by gamma ray. FTIR, 1H-NMR and

potentiometric titration methods were used to identify the alternating structure of the product. Then the transmission electron microscopy (TEM)

method was used to observe the morphology of the micelles. As the pH of the latex increases from 3 to 7, the shape of aggregates changes from

short-shuttle to long-rod. When the pH increases to 10, the rod-like aggregates are not found. The result indicates that the linearity of chains

occurring at pH 7 induces the formation of the specific morphology with the cooperation of anionic/nonionic mixed surfactants templates.

2007 Elsevier B.V. All rights reserved.

Keywords: Polymers; Electron microscopy; Poly(styrene-alt-maleic anhydride); Morphology; Surfactant; Template

1. Introduction

One of the most interesting and useful properties of block

copolymers dissolved in a selective solvent is their ability to

spontaneously selfassemble into nano-organized morphologies

(micelles, vesicles, bilayers, etc). [1] These well-organized

nanostructures have received increasing attention in recent

years due to their potential applications range from foam

stability [2] to technological [36] and biomedical [79]. So the

control of the micellar morphology on the nanometer scale is of

great importance to obtain the desired functions and properties.The formation of a specific morphology can be controlled by

various factors, such as the temperature, the copolymer volume

fraction and concentration, the solvent, the presence of

additives, and the sample preparation procedure [1015].

The methods used to investigate the mechanisms of

association are macroscopic characterization methods such as

dynamic light scattering (DLS) [1617], viscosity analysis [17],

small-angle X-ray and neutron scattering (SAXS and SANS)

[1820], etc., to define the size and the macroscopic properties

of the association, and more precise micro-level characteriza-

tion methods such as SEM,TEM [21], AFM [16,2223], etc., to

understand the interaction between the molecules and the shape

of the association.

In comparison, the association between alternating copoly-

merchains has not been widely studied. Alternating copolymers

are repetitive copolymers, and the global behavior of the

association can be modeled using a few repetitive conforma-

tional units. The most familiar of alternating copolymer is poly(styrene-alt-maleic anhydride) (SMA). And it was studied by

Garnier et al. [24] using DLS and was found to associate at

intermediate pH, but no association was observed at low or high

pH. And it was explained by Malardier-Jugroot et al. [25] using

quantum chemistry.

In this work, SMA latexes were first obtained by emulsion

polymerization induced by gamma ray using anionic/nonionic

mixed surfactants templates. FTIR, 1H-NMR and potentiomet-

ric titration methods were used to identify the alternating

structure of the product. TEM was used to observe the

association of SMA formed in the latexes at different pH

Available online at www.sciencedirect.com

Materials Letters 62 (2008) 597599www.elsevier.com/locate/matlet

Corresponding author. Tel.: +86 551 3601586; fax: +86 551 5320512.

E-mail addresses: tm1227@tom.com (M. Tao), zqhu@ustc.edu.cn (Z. Hu),

zczhang@ustc.edu.cn (Z. Zhang).

0167-577X/$ - see front matter 2007 Elsevier B.V. All rights reserved.doi:10.1016/j.matlet.2007.06.011

mailto:tm1227@tom.commailto:zqhu@ustc.edu.cnmailto:zczhang@ustc.edu.cnhttp://dx.doi.org/10.1016/j.matlet.2007.06.011http://dx.doi.org/10.1016/j.matlet.2007.06.011mailto:zczhang@ustc.edu.cnmailto:zqhu@ustc.edu.cnmailto:tm1227@tom.com

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values directly; the three pH values chosen are 3, 7, and 10

representing, respectively, the low, intermediate and high pH

behavior.

2. Experimental

2.1. Materials

MA(99.5%, China National Pharmaceutical Group Corpo-

ration) was recrystallized from chloroform prior to use. St(99%,

Shanghai Linfeng Reagent Company) was distilled from its

commercial material before use. All other reagents were of

analytical grade, and used as received. For the emulsion

polymerizations, deionized water was used.

2.2. Synthesis of the SMA latexes

In a typical procedure to prepare the SMA latexes, 1.2 g of

p-Octyl polyethylene glycol phenyl ether (OP-10), 1.0 g of

sodium dodecyl sulfate (SDS) and 4.9 g of maleic anhydride

(MA) was first added to 88.0 g of deionized water. After

completely dissolved, 5.2 g of styrene was added to and mixed

with a stirrer thoroughly. Purified nitrogen was bubbled through

the mixture for about 20 min to get rid of oxygen. After that the

emulsion was directly fed into a sealed glass ampoule and

subjected to the-ray radiation using 60Co source (2.22 1015 Bq)

at room temperature with dose rate 50 Gy min1. 0.5 mol L1

NaOH aqueous solution was used to adjust the pH value.

2.3. Measurement

FTIR spectra were recorded on a VECTOR22 FTIR

spectrometer using a KBr pellet. 1H-NMR spectra(400 MHz)were taken on a Bruker ACF spectrometer using deuterium

acetone as a solvent.

TEM images were obtained using a Hitachi Model H-800

transmission electron microscope with an accelerating voltage

of 200 kV.

Polymerization kinetics was studied by gravimetric method.

3. Results and discussion

FTIR, 1H-NMR and potentiometric titration methods were used to

identify the alternating structure of SMA obtained from the previous

process. FTIR, cm1

: C=O 1850 and 1790, CC (benzyl ring) 1600,1500, 1450 and 700; 1H NMR(500 MHz, acetone-d6), ppm: 1.82.1

(CH2CH(C6H5)), 3.3(anhydride unit), 7.8(benzyl ring); potenti-

ometric titration (acid number): 543 mgKOH/g (meaning MA%mol in

the copolymer to about 50). The resulted nanostructures were

characterized by TEM.

Another evidence of the alternating structure of the product is that

the acid number is nearly changeless to about 543 mgKOH/g (meaning

MA%mol in the copolymer to about 50) with the increase of

conversion.

Scheme 1 indicates that the structure of SMA is pH-dependent from

theory [25]. And Fig. 1 shows the morphology of the SMA micelles at

different pH values.

As the pH of the latex increases from 3 to 7, the shape of aggregates

changes from short-shuttle to long-rod. when the pH increases to 10,the rod-like aggregates are not found. This result confirms the model

brought forward by Malardier-Jugroot et al. [25] using a more directly

method. At pH 3 and 10, the 90 angle between two monomers induces

the interlaced-orthogonal structure of the backbone of SMA. The

shuttle-like association was successfully observed by TEM with the

size about 200400 nm in the latexes. And at pH 7, the chains of SMA

seem to be linear; so the rod-like micelles were obtained with much

long size about several micron.

Another explanation should be the effect of the mixed surfactants

templates. It is well-known that the geometry of the surfactant plays a

Scheme 1. Structure of styrene-maleic anhydride at three different pH values.

Fig. 1. TEM images of the micelles of SMA at different pH values: A. pH=3; B. pH=7; and C. pH=10.

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crucial role on the aggregation of the surfactants in solution.

Israelachvili et al. [26] and Kumar and Mittal [27] defined a packing

parameter (P) to estimate the aggregate structures formed from

surfactant in aqueous solution:

P V

a0lc1

Where a0 is the interfacial area occupied by the surfactant

headgroup; lc and V are the critical chain length and the volume of

the hydrophobic group, respectively. The surfactant is expected to form

spherical micelles forPb1/3, rodlike micelles for 1/3bPb1/2, vesiclesfor 1/2bPb1, or planar bilayers for P= 1.

The lc and Vcan be estimated by the following equations proposed

by Tanford [28]:

V 0:0274 0:0269n nm3

2

lcVl 0:154 0:1265n nm 3

where n is the number of carbon atoms of the alkyl chain, and l is the

fully extended length of the alkyl chain. By assuming that the molecule

is in an all-transconfiguration, the critical chain length lc is equal or

close to l.For a given surfactant molecule, the values of Vand lc are almost

constant, while a0 is not a simple geometrical area, but an equilibrium

parameter derived from thermodynamic considerations. This parameter

can be adjusted by changing the solution conditions. [29,30] Because

the decreases of a0 can result in an increase of V/a0lc, thus, one can

achieve a transition from spherical micelles to rodlike micelles and

possibly to bilayer or vesicle aggregates by modifying solution

conditions.

According to the method proposed by Tanford, [28] the molecular

parameters and the P values of SDS and OP-10 used in the present

study are calculated, and the results are listed in Table 1.

When two surfactants are mixed together, the ideal mixing

surfactants packing parameter can be obtained from the following

equation [32]:

Pmix fAPA fNPN 4

where fA is the mole fraction of the anionic surfactant, fN is the fraction

of nonionic surfactant.

According to Eq. (4), one can see that the value of Pmix should be

among 1/3 and 1/2 as the packing parameters of both two surfactants

were below 1/2 and on 1/3. So the mixed surfactant system could form

rod-like templates.

4. Conclusions

In summary, as the SMA micelles were prepared by

emulsion polymerization, the different shape and size of

associations were successfully observed by TEM at different

pH values. The result indicates that the linearity of chains

occurring at pH 7 induces the formation of the specificmorphology with the cooperation of anionic/nonionic mixed

surfactants templates.

References

[1] T. Tuzar, P. Kratochvil, in: E. Matijevic (Ed.), In Surface and Colloid

Science, 15, Plenum Press, New York, 1993, p. 1.

[2] F. Calleja, Z. Roslaniec, Block Copolymers, Dekker, New York, 2000.

[3] Zhang, Z-L. Wang, J. Liu, S. Chen, G-Y. Liu, Self-Assembled

Nanostructures, Kluwer Academic/Plenum Publishers, New York, 2003.

[4] S.A. Jenekhe, X.L. Chen, Science 283 (1999) 372.

[5] P.S. Weiss, Nature 413 (2001) 585.

[6] J. Gunther, S.I. Stupp, Langmuir 17 (2001) 6530.

[7] V.P.J. Torchilin, Control. Release 73 (2001) 137.

[8] K. Kataoka, A. Harada, Y. Nagasaki, Adv. Drug Delivery Rev. 47 (2001)

113.

[9] R. Savic, L. Luo, A. Eisenberg, D. Maysinger, Science 300 (2003) 615.

[10] F. Henselwood, G. Liu, Macromolecules 30 (1997) 488.

[11] M. Svensson, P. Alexandridris, P. Linse, Macromolecules 32 (1999) 637.

[12] Y. Yu, L. Zhang, A. Eisenberg, Langmuir 21 (2005) 1180.

[13] B.M. Discher, Y.Y. Won, D.S. Ege, J .C.-M. Lee, F.S. Bates, D.E. Discher,

D.A. Hammer, Science 284 (1999) 1143.

[14] I.W. Hamley, J.S. Pedersen, C. Booth, V.M. Nace, Langmuir 17 (2001)

6386.

[15] L. Zhang, A. Eisenberg, J. Am. Chem. Soc. 118 (1996) 3168.

[16] Ouarti, P. Viville, R. Lazzaroni, E. Minatti, M. Schappacher, A. Deffieux,

R. Borsali, Langmuir 21 (2005) 1180.

[17] G. Mountrichas, M. Mpiri, S. Pispas, Macromolecules 38 (2005) 940.

[18] V. Castelletto, I.W. Hamley, Langmuir 20 (2004) 2992.

[19] C. Sommer, J.S. Pedersen, V.M. Garamus, Langmuir 21 (2005) 2137.

[20] O.V. Borisov, E.B. Zhulina, Macromolecules 36 (2003) 10029.

[21] L.C. Gao, L.Q. Shi, Y.L. An, W.Q. Zhang, X.D. Shen, S.Y. Guo, B.L. He,

Langmuir 20 (2004) 4787.

[22] J.L. Logan, P. Masse, B. Dorvel, A.M. Skolnik, S.S. Sheiko, R. Francis, D.

Taton, Y. Gnanou, R.S. Duran, Langmuir 21 (2005) 3424.

[23] I.M. LaRue, Adam, M. da Silva, S.S. Sheiko, M. Rubinstein,

Macromolecules 37 (2004) 5002.

[24] G. Garnier, M. Duskova-Smrckova, R. Vyhnalkova, T.G.M. van de Ven, J.-F.

Revol, Langmuir 16 (2000) 3757.

[25] C. Malardier-Jugroot, T.G.M. van de Ven, M.A. Whitehead, J. Phys.

Chem. B. 109 (2005) 7022.

[26] J.N. Israelachvili, D.J. Mitchell, B.W. Ninham, J. Chem. Soc. Faraday

Trans. 72 (1976) 1525.

[27] P. Kumar, K.L. Mittal, Handbook of Microemulsion Science and

Technology, Marcel Dekker, New York, 1999.

[28] C. Tanford, The Hydrophobic Effect: Formation of Micelles and

Biological Membranes, Wiley, New York, 1980.

[29] S. Svenson, Curr. Opin. Colloid Interface Sci. 9 (2004) 201.

[30] R. Nagarajan, Langmuir 18 (2002) 31.

[31] G.X. Zhao, B.Y. Zhu, Principle of Surfactant Action, China Light Industry,

Beijing, 2003.

[32] A. Sein, J.B.F.N. Engberts, E. Vanderlinden, J.C. Vandepas, Langmuir 9

(1993) 1714.

Table 1

Values of hydrophobic chain volume, V, critical chain length, lc, optimal

headgroup area, a0, and packing parameter, P, for SDS and OP-10 pure micelles

[31]

Surfactant V(nm3) lc(nm) a0 (nm2)a P

OP-10 0.31 1.48 0.60 0.35

SDS 0.35 1.7 0.50 0.41aDatum at 25 C.

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