Linear Conformation of Poly(styrene-alt-maleic anhydride) Capable of

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J. Phys. Chem. B 2005, 109, 7022-7032

Linear Conformation of Poly(styrene-alt-maleic anhydride) Capable of Self-Assembly: A Result of Chain Stiffening by Internal Hydrogen Bonds C. Malardier-Jugroot,†,‡ T. G. M. van de Ven,†,‡ and M. A. Whitehead*,† Department of Chemistry, McGill UniVersity, Montreal, Canada, andPulp and Paper Research Centre, McGill UniVersity, Montreal, Canada ReceiVed: October 27, 2004; In Final Form: February 9, 2005

A careful conformational analysis of poly(styrene-alt-maleic anhydride) at different pH values is presented. It is found that a strong internal hydrogen bond is formed at intermediate pH, which induces a change in the conformation of the polymer chain, which becomes linear. This linearity does not depend on the chirality of the polymer. The linearity of the chain occurs only at intermediate pH and can explain the association among the chains observed by dynamic light scattering at pH 7.

The association of block copolymers in solution has been extensively studied; their applications range from foam stability1 to drug delivery and nanotechnology.2 The methods used to investigate the mechanisms of association are macroscopic characterization methods such as dynamic light scattering (DLS), viscosity analysis, etc., to define the size and the macroscopic properties of the association, and more precise micro-level characterization methods such as TEM, AFM, etc., to understand the interaction between the molecules and the shape of the association. Quantum mechanical studies of the interactions between the polymer chains are theoretically more demanding due to the large size of the two blocks (A‚‚‚AB‚‚‚B) and are therefore rare in the literature. In comparison, the association between alternating copolymer chains has not been widely studied. Alternating copolymers are repetitive copolymers, and the global behavior of the association can be modeled using a few repetitive conformational units; therefore, quantum chemistry is an excellent method to study alternating copolymers. The repetitive unit will be defined by studying the conformation of the molecule by adding each group composing the polymer part by part. In this paper, the association mechanism of poly(styrenemaleic anhydride) (SMA) in water was investigated. This polymer was studied by Garnier et al.3 using DLS and was found to associate at intermediate pH, but no association was observed at low or high pH. It was suggested that the interactions between two SMA chains can be described as a “zip” mechanism: in solution, to minimize the interactions between the water and the phenyl group, two chains interact by associating their phenyl groups; at the air/water interface, the hydrophobic phenyl group lies out of the water. This mechanism corresponds to reduced interactions between the phenyl groups and water; therefore, it corresponds to a lower free energy of the SMA chain. A theoretical approach was chosen to investigate and characterize the behavior of SMA chains at different pH values; the three pH values chosen are 3, 7, and 12 representing, respectively, the low, intermediate and high pH behavior observed by DLS. The structure, energy, and chemical properties of molecules are related; therefore, the conformation of the polymer studied * Corresponding author. E-mail: [email protected]. † Department of Chemistry. ‡ Pulp and Paper Research Centre.

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

has to be optimized carefully to understand its behavior. Unique macroscopic properties of polymers such as rubber elasticity, electrical and optical properties, dipole moments, etc., are caused by the conformation variability of the chains.4 Polymers have access to a very large number of conformational arrangements, which represent local and global minima in the available potential energy surface (PES) of the molecule. To optimize SMA at different pH values and to understand the association between the chains as a function of pH, a complete conformational method was chosen. In the present work, precise scans were performed around all the dihedral angles of the molecule and all the possible chiralities of the polymer chain were considered. This method will be explained in detail in the next section. 1. Conformation of the Monomer at pH Values 3, 7, and 12 Poly(styrene-maleic anhydride) is a water-soluble polymer; its structure is pH-dependent because of the maleic anhydride ring. In aqueous solution of SMA at pH 3, the maleic anhydride ring is hydrolyzed to give two acid groups (Figure 1). Adding a stoichiometric amount of NaOH to the solution hydrolyzes one acid group, and the pH of the solution becomes 7 (Figure 1). When the pH of the solution is increased to 12, the second acid group is also hydrolyzed (Figure 1). Differences in pH in

10.1021/jp0450944 CCC: $30.25 © 2005 American Chemical Society Published on Web 03/19/2005

Conformation of Poly(styrene-alt-maleic anhydride)

J. Phys. Chem. B, Vol. 109, No. 15, 2005 7023

Figure 2. Representation of the tree branch method of optimization.

Figure 3. Representation of the series of scans in energy method of optimization. When the starting point of the scan does not correspond to the lowest minimum, then the next scan will use the lowest minimum as a starting point.

a SMA solution will give rise to different structures for the polymer through the different degrees of ionization of the molecule. The calculations performed in this study are gas-phase calculations, and the differences in pH will be modeled using the different degrees of ionization of the polymer in solution (Figure 1). The conformation of the monomer was obtained using two methods: (i) the tree branch method,5 and (ii) a series of scans in energy.6,7 The first method adds part by part the groups making the molecule starting with a known structure, for instance ethane (Figure 2). Ethane in its staggered conformation was the starting structure, then the styrene group was added by replacing one hydrogen atom, without any configuration preference, because all the hydrogen atoms of ethane are equivalent (Figure 2 (1)). Then a second group (CH3) is added by replacing another H atom and all the possible positions are optimized

(Figure 2 (2)-(4)); the most stable structure is chosen and used to add the next group of the molecule. The groups are added one by one; therefore, all the possible stable chiralities of the monomer are known and their energies optimized by this sequence. The second method uses precise series of scans in energy to find the most stable molecule for each dihedral angle in the molecule.8-11 In this method, the scans are performed one by one by 4-degrees increase of the dihedral angle, and the most stable structure obtained within one scan is used as a starting structure for the next scan (Figure 3). The main advantage of this technique is that the energy of the different conformations of a molecule can be obtained for one chirality.5 These two methods are complementary and allow a complete description of the possible conformations of the monomers at

7024 J. Phys. Chem. B, Vol. 109, No. 15, 2005

Figure 4. Two conformations of the monomer SMA at pH 7 corresponding to the two hydrolysis sites of the acid groups (white ) H, gray ) C, black ) O, and dark gray ) Na).

pH 3, 7, and 12. The two stable structures obtained with both methods were then compared: they were identical. The conformational search of the monomers was performed at the PM3 level of theory,12,13 the minima were then reoptimized at the RHF/6-31G** and DFT-B3LYP/6-31G** levels of theory. The parameters used for the optimization at pH 7 and 12 for sodium using PM3 are the parameters developed by Brothers and Merz.14 The calculations were performed using Gaussian15 and HyperChem.16 At pH 7, two conformations can be obtained corresponding to the hydrolysis site of the two acid groups. The two structures have very similar energies; therefore, both structures were kept for the study of the dimer at this pH (Figure 4). The difference in enthalpy between the two conformations is 7 kJ/mol, the monomer obtained with the second acid group hydrolyzed being the most stable. The structures optimized at three different pH values are shown in Figure 5. The main difference between the structures obtained for different pH values occurs at pH 7 where the presence of a hydrogen bond changes the geometry of the ground state. This hydrogen bond is very strong (1.68 Å) compared to a typical hydrogen bond found between two water molecules (1.80 Å).17 The hydrogen bond is stabilized by the presence of the sodium counterion close to the COO- group. Indeed, when the calcula-

Malardier-Jugroot et al. tion is performed without the sodium ion, the length of the hydrogen bond increases to 1.82 Å. This hydrogen bond is also stable in an aqueous environment.17 The hydrogen bond was also characterized by orbital analysis (Figure 6). These figures show the delocalized molecular orbitals n° 22 and 24 covering the oxygen atom of the hydrolyzed acid group and the hydrogen atom of the second acid group. It is interesting to note that these orbitals have a pinch between the hydrogen and the oxygen of the hydrogen bond, which is characteristic of the presence of a hydrogen bond.18 The orbitals are very localized on the hydrogen bond of the monomer and only delocalized on the neighboring hydrophilic groups of the hydrogen and the oxygen. Orbital 24 shows a node between the hydrogen-bonded atoms and the neighboring hydrophilic groups. This structural difference of the monomer at different pH values is crucial for the conformation of the polymer. Indeed, the two hydrogen atoms labeled (a) and (b) in Figure 5 are the binding sites for another monomer to be bound to the first monomer in order to form a dimer. The directions of these sites, in the structures at pH 3 and 12 are very similar, but the directions of the binding sites at pH 7 are very different and form an angle of 90° with the sites at pH 3 and 12 (Figure 5). This difference in conformation, between pH 3 and 7, is responsible for a major change in the conformation of the polymer and, as we will show below, explains the different behavior of SMA at different pH values. The conformer at pH 3 with an internal hydrogen bond was also minimized at the RHF/6-31G** level in order to compare it to the structure obtained at pH 7. The minimum obtained is a local minimum, and the difference in energy with the global minimum, shown in Figure 5, is 18 kJ/mol. In addition, the bond length of this internal hydrogen bond is 1.87 Å compared to 1.67 Å for the internal hydrogen bond of the monomer at pH 7. Due to the strong interactions between the water molecules of the first shell of solvation and the hydrophilic part of SMA,17 this less stable structure should not be present in solution. 2. Conformation of the Dimer at pH 3, 7, and 12 2.1. Conformation of the Dimer at pH 3. The dimer structure of SMA possesses four chiral centers: one at each junction between the styrene and the maleic anhydride groups and two at the junction between the two monomers. As the first group of chiral centers does not affect the conformation of the

Figure 5. Conformation at pH 3, 7, and 12 of the monomer of SMA at the RHF/ 6-31G** level of theory. The binding sites for another monomer to be bound to the first monomer in order to form a dimer at pH 3 and 12 are identical.


Figure 6. Delocalized molecular orbitals 22 (a) and 24 (b) covering the internal hydrogen bond of the monomer of SMA at pH 7. The bond length is 1.68 Å.

polymer chain, only the dependence on the second group will be presented in this paper. For the dimer conformation, four structures were optimized: the RR, RS, SR, and SS conformations. The structures were optimized at the PM3 level of theory using series of scans in energy because this method gave more stable conformation for the dimers than the tree branch method.

J. Phys. Chem. B, Vol. 109, No. 15, 2005 7025 These structures were re-optimized at the RHF/6-31G** level and are shown in Figure 7. The structures of the dimers obtained at pH 3 show a 90 degree angle between the first monomer and the second (Figure 7). In addition, the orientation of the second monomer compared to the first is dependent on the chirality of the molecule, i.e., the orientation of the second benzene group of the RS dimer is opposed to the orientation of the benzene group of the SS dimer (Figure 7). 2.2. Conformation of the Dimer at pH 7. At pH 7, eight conformations can be obtained corresponding to the hydrolysis site of the two acid groups. The conformational analysis was performed on the eight possible enantiomers using series of scans in energy at the PM3 level of theory. These structures were then re-optimized at the RHF/6-31G** level of theory, and the four most stable structures are shown in Figure 8. The most stable structure obtained for the monomer, with the second acid group hydrolyzed, is now the least stable for the dimer, and the difference in energy is 7 kJ/mol. It is interesting to note that the structures of the dimers obtained with the second acid group hydrolyzed were very close to the structures obtained with the first acid group hydrolyzed. The structures obtained are very linear compared to those at pH 3. The orientations of the benzene groups of all the dimers are very similar (Figure 8). In addition the hydrogen bond

Figure 7. Four different conformations of the dimer of SMA at pH 3 corresponding to the four possible chiralities.


Malardier-Jugroot et al.


Figure 9. Delocalized molecular orbital (DLMO) showing the hydrogen-bond electronic exchange on the first monomer of the SR dimer; similar DLMO is obtained for the second monomer.

Figure 10. Delocalized molecular orbital showing the electronic exchange between the benzene group, the COO- group, and the sodium atom of the SR dimer.

observed in the monomer conformation is still present in the dimer structures (Figure 9). The main change between the conformation of the monomers and dimers at pH 7 is the position of the Na+ counterion which is now located between the COO- group and the benzene ring (see Figures 8 and 10). The orbital analysis shows an electronic exchange between the COO- group, the Na+ counterion, and the benzene ring (Figure 10). The cation-π interactions are well-known stabilization interactions for protein-ligand complexes19-21 and are well described by Hartree-Fock methods with an extended basis set like 6-31G**.22,23 These cation-π interactions are among

the strongest noncovalent interactions20 and have a very important role in self-assembling processes observed in nature. Indeed, these interactions are important for the structural stability of protein structures and protein-ligand interactions, e.g., these cation-π interactions are known to play an important catalytic role in the mechanism by which acetylcholine esterase functions.24 In addition, the cation-π interactions observed in amino acids suggest that the Phe, Tyr, and Trp groups are expected to play a unique role in protein structure and function. These amino acids do not behave as conventional hydrophobic residues as Val, Leu, and Ile.25 In addition, the cation-π interactions




stabilize the hydrophobic environment of a molecule in aqueous media, and these strong interactions compete with full aqueous solvation of the cation.21 2.3. Conformation of the Dimer at pH 12. The conformational analysis was performed on the four possible enantiomers using series of scans in energy at the PM3 level of theory. These structures were then re-optimized at the RHF/6-31G** level of theory and are shown in Figure 11. The conformations obtained at pH 12 are very similar to the structures obtained at pH 3. As for pH 3, the orientation of the benzene groups is also dependent on the chirality of the dimer (Figure 11). The structures are more rigid than the structure obtained at pH 3 due to the direct interactions between the COO- groups and the Na+ ions. These interactions occur within the same monomer and between the monomers as shown in Figure 11. The orbital analysis of the different isomers shows these interactions (Figure 12). 3. Conformation of the Trimer at pH 3 and 7 The conformations of the trimers at pH 3 and at pH 12 are very similar;26 therefore, only the conformation of the trimer at pH 3 will be presented. An ab initio optimization of the trimer structures would be time-consuming. Therefore this optimization was performed at the semiempirical level of theory. The geometries obtained for the dimers at the semiempirical PM3 level and at the RHF-631G** level, using series of scans, were compared and are very

Figure 12. Delocalized molecular orbital (e ) -1.399 eV) showing the electronic exchange between the COO- groups and the sodium atoms of the RR dimer at pH 12.

similar (Figure 13), both for pH 3 and pH 7. Therefore the optimizations of trimers were performed with the semiempirical PM3 method. The cation-π interactions are also well-described by PM3. Also, the PM3 semiempirical method is consistent and gives values of energy parallel to the experimental results.6 3.1. Conformation of the Trimer at pH 3. The trimer structure of SMA possesses four chiral centers connecting each


Malardier-Jugroot et al. Due to the chirality dependence observed with the dimer conformations, the backbone orientations of the trimers are different. Four conformations are shown in Figure 14 to illustrate the differences between the optimized structures obtained. 3.2. Conformation of the Trimer at pH 7. The conformations of the trimers obtained at pH 7 are very linear. The orientations of the benzene groups of the different trimers at pH 7 are very similar. Four conformations are shown in Figure 15 to illustrate the change in conformation between chains of different chirality. The internal hydrogen bond observed in the monomer and dimer conformations is still present in the conformations obtained for the trimer. The angle between each benzene group of the trimers is about 60° (Figure 16); therefore, the structure should be repetitive after the first trimer, and this was verified with the conformational study of a quadrimer at pH 7. The cation-π interactions observed in the dimer structures are still present in the trimer structures, and these interactions might stabilize the association observed at pH 7. 4. Conformation of the Quadrimer, Pentamer, and Hexamer at pH 3 and 7

Figure 13. Overlay of the SR dimer structure obtained at the PM3 (light blue) and RHF/6-31G** levels of theory (a) at pH 3, and (b) at pH 7.

monomer of the molecule. The different chiralities of the trimer will give 16 possible structures.

4.1. Conformation of the Quadrimer at pH 3. To optimize the quadrimer structure, two methods were used. The first method used energy scans, where all degrees of freedom of the molecule were optimized, and a faster method, which used two trimers to obtain the structure of a quadrimer. The second method (substitution method) uses the fact that the second monomer is constrained by the first monomer and the third monomer, and therefore has the same constraint and interaction as a monomer in the middle of a polymer chain (Figure 17).

Figure 14. Four different conformations of the trimer of SMA at pH 3 among the 16 possible chiralities.



Figure 15. Four different conformations of the trimer of SMA at pH 7 among the 16 possible chiralities.

Figure 16. The angle between each benzene group of the trimer SS SS at pH 7 is ∼60°.

From this observation, the quadrimer conformations can be built directly from two trimer structures and then optimized using PM3 and compared to the same molecule obtained with the scans. Since the molecules obtained were very similar using the two different methods, the substitution method was chosen to build the complete library of structures with different chirality. This method will be very useful to optimize long polymer chains with different chirality.

Figure 17. Schematic representation of the substitution method.

The different conformations obtained for the trimer at pH 3 had a U- or Z-shape structure, depending on the chirality of the oligomer chain. This difference in configuration is also observed with the quadrimer conformation. In Figure 18, two quadrimers with different chirality are shown. The first one is SR-RRSR and the second one is SR-SR-SR; therefore, these two polymers differ only by one junction in the middle of the molecule. This difference causes a rotation around this junction, and the conformation changes from a steplike conformation to a well-like conformation. The change in conformation can be observed in the backbone representation of the quadrimer in Figure 18. During the synthesis of SMA, the chirality of the polymer was not controlled; therefore, the polymer studied will have different chirality between each monomer along the chain. The difference in conformation caused by the change in chirality of the molecule implies that two chains with different chirality will not associate along the polymer chains; only a very weak interaction between two benzene rings will be possible (Figure 19). These results are in agreement with the DLS study where little or no association was observed at low pH. Due to the self-avoidance problem often encountered by nonlinear polymers,27 the structures at pH 3 for oligomers larger than quadrimers are difficult to obtain. Indeed the substitution model will not be applicable when the self-avoidance occurs within a structure, and therefore only a complete optimization using scans would be accurate. This complete optimization would be too time-consuming for molecules larger than


Malardier-Jugroot et al.

Figure 18. Two different conformations of the quadrimers of SMA at pH 3 corresponding to two chiralities (SR RR sr and SR SR SR). The first structure has a steplike conformation and the second a well-like conformation.

Figure 19. Representation of the possible association between two chains of different chirality at pH 3.

quadrimers to obtain the complete library of structures with different chirality. Oligomers larger than quadrimers for structures at pH 3 were not optimized because the chirality dependence of the polymer has already been proved by the study of the different trimers and quadrimers. 4.2. Conformation of the Quadrimer at pH 7. For the optimization of the quadrimer conformations at pH 7, the two methods described in section 4.1 were used and the structures obtained with the two methods were compared. Because the molecules obtained were very similar using the two different methods, the substitution method was chosen to build the complete library of structures with different chirality. Two configurations with different chirality are shown in Figure 20. All the structures obtained were very linear, and the orientations of the benzene groups of the different oligomers obtained are very similar.

In addition, the quadrimer conformations at pH 7 show a repetition of the same monomer orientation from the quadrimer, and therefore the repetitive unit for SMA at pH 7 can be defined as three monomer units. Because the orientations of the benzene groups are very similar along the polymer chain, regardless of the chiralty, two chains can associate by stacking interactions of the benzene rings (Figure 20). We have shown that this stacking leads to the selfassembly of SMA chains into helical nanotubes, in which 8 chains make up one twist of a helix.26,28 4.3. Conformation of the Pentamer and Hexamer at pH 7. The structures obtained at pH 7 are the only structures where a repetitive unit was found. These conformations are the only ones which can associate with strong interactions between the chains. Therefore, the structures of the pentamers and hexamers needed to be optimized for the study of the interactions between the chains. These oligomers were optimized using the substitu-



Figure 20. Two different conformations of the quadrimers of SMA at pH 7 corresponding to two chiralities (SR-RR-SR and SR-SR-SR). The structures are very linear, and the orientations of the benzene groups are similar.

Figure 21. Conformation of the hexamer of chirality SR-SS-RS-RR-SS (a) compared to the conformation of the hexamer of regular chirality SS-SS-SS-SS-SS (b). The red rectangles show the orientation of the 1st and 4th benzene groups of each oligomer, the blue rectangles show the orientation of the 2nd and 5th benzene groups, and the green rectangles show the orientation of the 3rd and 6th benzene groups.

tion method. The association among the SMA chains at pH 7 were also observed experimentally.29 The conformations obtained with different chiralities were very linear, as shown in Figure 21. The structures obtained confirm that the repetitive unit is the trimer. Very similar orientations of the benzene rings were found along the chains of different chirality and therefore confirm the possibility of strong interactions between the chains, regardless of their chirality (Figure 21). 5. Conclusion In this paper, the conformations of oligomers of SMA at different pH values in the gas phase were investigated using theoretical methods to explain the different behavior observed by dynamic light scattering, which showed that the polymer chains associate at intermediate pH, but no association was observed at low or high pH. The numerical conformational analysis of the monomers performed at three pH values (3, 7, and 12) showed a unique

conformation at pH 7, where a strong hydrogen bond induces a change in the orientation of the binding sites compared to the conformation at pH 3 and 12. The dimer structure of SMA possesses two chiral centers, and therefore all the structures need to be investigated. For the dimer conformation, four structures were optimized: the RR, the RS, the SR, and the SS conformations. The conformations optimized at pH 3 and 12 are very different from the conformation at pH 7. Indeed, at pH 3 and 12, a 90° angle is observed between the two monomers, whereas at pH 7 a completely linear structure was obtained. The hydrogen bond observed in the conformation of the monomer at pH 7 is also present in the conformation of the different dimers at pH 7. The main difference between the conformations of the chains at pH 3, 7, and 12 is the chirality dependence of the conformation and the 90° angle between the monomers at pH 3 and 12. To associate, the chains at pH 3 and 12 would need a large decrease in entropy, which would destabilize the system. At pH 7 the chains are very close to the optimal structure needed

7032 J. Phys. Chem. B, Vol. 109, No. 15, 2005 for association in solution and will be stabilized by the interaction between the benzene rings along the chain; therefore, this association will be favored at pH 7. The linearity of chains occurring at pH 7 explains the association of the polymer in solution at pH 7.26 This careful conformational study of the polymer at different pH values is essential to understand the association mechanism of the polymer chains. Acknowledgment. NSERC(CANADA).

This research was supported by

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Malardier-Jugroot et al. (12) Stewart, J. J. P. Optimization of Parameters for Semiempirical Methods I-Method. J. Comput. Chem. 1989, 10 ( 2), 209. (13) Stewart, J. J. P. Optimization of Parameters for Semiempirical Methods II-Applications. J. Comput. Chem. 1989, 10 (2), 221. (14) Brothers, E.; Merz, K. Sodium Parameters for AM1 and PM3 Optimized Using a Modified Genetic Algorithm. J. Phys. Chem. B 2002, 106, 2779. (15) Frisch M. J.; et al. Gaussian 98W (Revision A.5); Gaussian, Inc.: Pittsburgh, 1998. (16) HyperChem release 5.11, for Windows molecular modelling system, Hypercube Inc., Ont., Canada, 1999. (17) Malardier-Jugroot, C.; van de Ven, T. G. M.; Whitehead, M. A. Study of the water conformation around hydrophilic and hydrophobic parts of styrene-maleic anhydride. J. Mol. Struct. (THEOCHEM) 2004, 679, 171. (18) Gaudreault, R. Mechanism of flocculation with poly(ethylene oxide) and novel cofactors: theory and experiment. Ph.D. Thesis, Department of Chemistry, McGill, Montreal, Canada, 2004. (19) Alkorta, I.; Elguero, J. Aromatic Systems as Charge Insulators: Their Simultaneous Interaction with Anions and Cations. J. Phys. Chem. A 2003, 107, 9428. (20) Ma, J.; Dougherty, D. The Cation-π interaction. Chem. ReV. 1997, 97, 1303. (21) Wintjens, R.; Lievin, J.; Rooman, M.; Buisine, E. Contribution of Cation-π Interactions to the Stability of Protein-DNA Complexes. J. Mol. Biol. 2000, 302, 393. (22) Kumpf, R.; Dougherty, D. A Mechanism for Ion Selectivity in Potassium Channels: Computational Studies of Cation-π Interactions. Science 1993, 261, 1708. (23) Mecozzi, S.; West, A.; Dougherty, D. Cation-π Interactions in Simple Aromatics: Electrostatics Provide a Predictive Tool. J. Am. Chem. Soc. 1996, 118, 2307. (24) Barak, D.; Ordentlich, A.; Segall, Y.; Velan, B.; Benschop, H.; De Jong, L.; Shafferman, A. Carbocation-Mediated Processes in Biocatalysts. Contribution of Aromatic Moieties. J. Am. Chem. Soc. 1997, 119, 3157. (25) Jorgensen, W.; Severance, D. Aromatic-aromatic interactions: free energy profiles for the benzene dimer in water, chloroform, and liquid benzene. J. Am. Chem. Soc. 1990, 112, 4768. (26) Malardier-Jugroot, C. Novel self-assembly of an alternating copolymer into nanotubes: theoretical investigation and experimental characterization. Ph.D. Thesis, Department of Chemistry, McGill, Montreal, Canada, 2004. (27) Gelin, B. Molecular Modeling of Polymer Structures and Properties; Hanser-Garner: Cincinnati, 1994. (28) Malardier-Jugroot, C.; van de Ven, T. G. M.; Whitehead, M. A. Novel self-assembly of an amphiphilic copolymer into nanotubes: theoretical characterisation using molecular orbital theory. Nanotechnology, to be submitted. (29) Malardier-Jugroot, C.; van de Ven, T. G. M.; Whitehead, M. A. Characterization of a novel self-association of an alternating copolymer into nanotubes in solution. Mol. Simul. 2005, 31, 2-3, 173-178.

Linear Conformation of Poly(styrene-alt-maleic anhydride) Capable of

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