Nucleation-Elongation Polymerization under Imbalanced Stoichiometry

Journal of the American Chemical Society

Volumn 125, Issue 52, 2003, Pages 16294-16299

  Zhao, Dahui ^a   Moore, Jeffrey S ^a  

^a UNIVERSITY OF ILLINOIS AT URBANA CHAMPAIGN   (United States)

Author keywords

[No Author keywords available]

Indexed keywords

STEP-GROWTH POLYMERIZATION;

ALDEHYDES; AMINES; CONDENSATION; MOLECULAR WEIGHT DISTRIBUTION; MONOMERS; NUCLEATION; OLIGOMERS; REACTION KINETICS; STOICHIOMETRY; THERMODYNAMICS;

POLYMERIZATION;

ALDEHYDE; AMINE; IMINE; OLIGOMER;

ARTICLE; ENERGY; MELTING POINT; MOLECULAR WEIGHT; POLYMERIZATION; PROTEIN FOLDING; PROTEIN STRUCTURE; STOICHIOMETRY; SYNTHESIS;

EID: 0346434111     PISSN: 00027863     EISSN: None     Source Type: Journal    
DOI: 10.1021/ja038252y     Document Type: Article

References (45)

1. Oosawa, F.; Asakura, S. Thermodynamics of the Polymerization of Protein; Academic Press Inc.: New York, 1975.
2. Precedents of synthetic polymerizations with a nucleation process are limited. See: (a) Kern, W.; Jaacks, V. J. Polym. Sci. 1960, 48, 399-404.
3. (b) Leese, L.; Baumber, M. V. Polymer 1965, 6, 269-286.
4. In both of these reactions, crystallization of the polymeric products occurred. Nucleation has thus partially coincided with the formation of crystal nuclei. The supramolecular energy in these polymerizations was mostly derived from polymer crystallization. More recently, a cooperative chain growth has been reported in the supramolecular polymerization of certain urea derivatives through H-bond interactions: (c) Lortie, F.; Boileau, S.; Bouteiller, L. Chem.-Eur. J. 2003, 9, 3008-3014. In this case, the polarization of the urea units resulting from dimerization favors further H-bonding and chain elongation into polymers.
5. (a) Flory, P. J. Principles of Polymer Chemistry; Cornell University Press: Ithaca, 1953; Chapter 3.
6. (b) Odian, G. Principles of Polymerization, 3rd ed.: John Wiley & Sons: New York, 1991; Chapter 2.
7. (a) Seebach, D.; Matthews, J. L. Chem. Commun. 1997, 2015.
8. (b) Gellman, S. H. Acc. Chem. Res. 1998. 31, 173.
9. (c) Kirshenbaum, K.; Zuckermann, R. N.; Dill, K. A. Curr. Opin. Struct. Biol. 1999, 9, 530.
10. (d) Barron, A. E. Curr. Opin. Chem. Biol. 1999, 3, 681.
11. (e) Stigers, K. D.; Soth, M. J.; Nowick, J. S. Curr. Opin. Chem. Biol. 1999, 3, 714.
12. (f) Archer, E. A.; Gong, H. G.; Krische, M. J. Tetrahedron 2001, 57, 1139.
13. (g) Gong, B. Chem.-Eur. J. 2001, 7, 4336.
14. (h) Cubberley M. S.; Iverson, B. L. Curr. Opin. Chem. Biol. 2001, 5, 650.
15. (i) Hill, D. J.; Mio, M. J.; Prince, R. B.; Hughes, T. S.; Moore, J. S. Chem. Rev. 2001, 101, 3893.
16. (j) Schmuck, C. Angew. Chem., Int. Ed. 2003, 42, 2448.
17. (a) Zhao, D.; Moore, J. S. J. Am. Chem. Soc. 2002, 124, 9996-9997.
18. (b) Zhao, D.; Moore, J. S. Macromolecules 2003, 36, 2712-2720.
19. For investigations at folding-driven syntheses of mPE imine oligomers, see: (a) Oh, K.; Jeong, K.-S.; Moore, J. S. Nature 2001, 414, 889-893.
20. (b) Nishinaga, T.; Tanatani, A.; Oh, K.; Moore. J. S. J. Am. Chem. Soc. 2002, 124, 5934-5935.
21. (c) Oh, K.; Jeong, K.-S.; Moore. J. S. J. Org. Chem. 2003, 68, 8397-8403.
22. Additional evidence for the helical structure of the polymers has recently been obtained. The Mark-Houwink coefficient α of ca. 1.6 indicates a highly elongated, rigid rod structure: Flory, P. J. Principles of Polymer Chemistry; Cornell University Press: Ithaca, 1953; Chapter 7.
23. Zhao, D.; Moore, J. S. Org. Biomol. Chem. 2003, 1, 3471-3491.
24. For biological systems, nucleation-elongation polymerization under imbalanced stoichiometry is not easily studied because the monomers (globular proteins) are typically self-complementary (i.e., A-B type) and the stoichiometry is thus intrinsically balanced.
25. A classical example of polymerization under imbalanced stoichiometry is interfacial polymerization: (a) Morgan, P. W.; Kwolek, S. L. J. Chem. Educ. 1959, 36, 182-184.
26. (b) Morgan, P. W.; Kwolek, S. L. J. Polym. Sci. 1959, 40, 299-327.
27. A more recent example of polymerization under imbalanced stoichiometry: (a) Kimura, K.; Kohama, S., Yamashita, Y. Macromolecules 2003, 36, 5043-5046.
28. (b) Kimura, K.; Kohama, S.; Yamashita, Y. Macromolecules 2002, 35, 7545-7552. In this case, crystallization of the polymer product was responsible for driving the polymer growth by excluding the monofunctional monomer.
29. Very similar distributions were obtained when 1 was in excess. SEC traces of these reactions are shown in the Supporting Information.
30. Sequences containing an even number of repeating units are statistically suppressed under conditions of imbalanced stoichiometry relative to those having an odd number of repeating units.
31. An open-driven system was chosen to obtain a reaction conversion comparable to that achieved in the metathesis polymerization in acetonitrile for a consistent comparison of the product distribution.
32. Prest, P.-J.; Prince, R. B.; Moore, J. S. J. Am. Chem. Soc. 1999, 121, 1, 5933-5939.
33. n′ = 1 + 2/(2 - p - rp) if monomers are not counted. These values tend to 3.0 and 5.0, respectively, when stoichiometry imbalance r = 0.5 and reaction conversion p → 1.
34. 1H NMR spectrum of the product mixture.
35. We note that for isodesmic polymerizations the product distribution should follow statistical predictions throughout the entire course of the reaction, both at equilibrium and at any point prior to that.
36. (a) Nelson, J. C.; Saven, J. G.; Moore, J. S.; Wolynes, P. G. Science 1997, 277, 1793.
37. (b) Prince, R. B.; Saven, J. G.; Wolynes, P. G.; Moore, J. S. J. Am. Chem. Soc. 1999, 121, 3114-3121.
38. Previous models used to describe nucleation-elongation (or more generally, nonisodesmic) polymerizations do not differentiate species bearing different functional groups and are therefore not suitable for nonstoichiometric analyses. Moreover, these models do not consider the small-molecule byproduct that results from metathesis. For examples of equilibrium models of indefinite association, see: Martin, R. B. Chem. Rev. 1996, 96, 3043-3064.
39. Because only the thermodynamic equilibrium state is under investigation here. the equations do not necessarily have to be the kinetically most favorable pathways. As long as the correlations of concentrations with thermodynamic constants are appropriately expressed, the choice of a certain set of expressions over another will not alter the analysis result.
40. The equilibrium model represented by eq 1 should generally be applicable to various polymerizations that have a single nucleation step and form a small-molecule byproduct. See the Supporting Information for details on the specific chemical structure correlation of the model with the mPE metathesis polymerization.
41. The calculations were conducted using Mathematica 4.2. Numerical solutions were acquired as the software failed to generate algebraic solutions.
42. 2 for the results from this model to exactly match those of an isodesmic model derived in ref 3. The reason for this coefficient 4 is currently unclear.
43. n′ = 2([PA] + [PB] + [EgA] + [EgB])/([EgA] + [EgB]).
44. Theoretically, the polymer portion of the product (excluding the monomer) from the nucleation-elongation polymerization should have a polydispersity index of ca. 2.0. However, in the current reactions broader distributions were observed. Moreover, certain specific chain lengths appeared to be more abundant than the others according to SEC analyses. The presence of such potentially stable species is consistently reproducible and seems to be sequence dependent (for another set of starter sequences with a slightly different backbone structure, monomodal SEC traces were recorded, cf. ref 5b). Although a number of possibilities may be proposed (e.g., the existence of higher order structures), unambiguous evidence that can lead to a definitive explanation for this phenomenon is currently unavailable.
45. Although the equilibrium constant used in these calculations may not accurately reflect the values of the real system, it is reasonable to conclude that the mPE starter sequences exhibit the predicted characteristics of a nucleation-elongation polymerization.