Nature and structure of once-folded nylon 6 monodisperse oligoamides in lamellar crystals

Macromolecules

Volumn 33, Issue 11, 2000, Pages 4146-4154

  Jones, Nathan A ^a   Sikorski, Pawel ^a   Atkins, Edward D T ^a   Hill, Mary J ^a  

^a UNIVERSITY OF BRISTOL   (United Kingdom)

Author keywords

[No Author keywords available]

Indexed keywords

CONFORMATIONS; CRYSTAL STRUCTURE; CRYSTALLIZATION; ELECTRON MICROSCOPY; HYDROGEN BONDS; MOLECULES; MORPHOLOGY; VAN DER WAALS FORCES; X RAY DIFFRACTION ANALYSIS;

LAMELLAR STACKING PERIODICITY; SYMMETRIC HAIRPIN CONFORMATION;

NYLON POLYMERS;

EID: 0033738159     PISSN: 00249297     EISSN: None     Source Type: Journal    
DOI: 10.1021/ma9921394     Document Type: Article

References (23)

1. Cooper, S. J.; Atkins, E. D. T.; Hill, M. J. J. Polym. Sci., Part B: Polym. Phys. 1998, 36, 2849.
2. Cooper, S. J.; Atkins, E. D. T.; Hill, M. J. J. Macromolecules 1998, 31, 5032.
3. Cooper, S. J.; Atkins, E. D. T.; Hill, M. J. J. Macromolecules 1998, 31, 8947.
4. The chemical synthesis of these high-pedigree monodisperse oligoamides by Dr. G. Brooke and his colleagues at the Chemistry Department, University of Durham, Durham, U.K., was in response to a request by Professor E. Atkins, at the Physics Department, University of Bristol, for high-fidelity oligo- and polyamides, which were considered essential in the study of fundamental aspects of polymer physics, in this case the subtle interplay among van der Waals interactions, hydrogen bonding, chain-folding, and crystallization. We appreciate the foresight of the Engineering and Physical Sciences Research Council, U.K., in supporting this collaborative venture.
5. Brooke, G. M.; Mohammed, S.; Whiting, M. C. Chem. Commun. 1997, 16, 1511.
6. Brooke, G. M.; Mohammed, S.; Whiting, M. C. J. Chem. Soc., Perkin Trans. 1 1997, 22, 3371.
7. Brooke, G. M.; MacBride, J. A. H.; Mohammed, S.; Whiting, M. C. Polymer, in press.
8. Holmes, D. R.; Bunn, C. W.; Smith, D. J. J. Polym. Sci. 1955, 17, 159.
9. In relation to the once-folded 9-amide oligomer. If the amide unit is not in the fold (see Figure 1b and ref 2), then, because of the unequal lengths of the straight-stem pair, one amide unit is not utilized, not even when these once-folded molecules crystallize into lamellae. Therefore, only eight amide units form intramolecular hydrogen bonds. The lamellae would also have a larger surface energy than if the amide units were in the folds. With the amide unit in the fold (see Figure 1a and ref 2), all eight amide units in the straight-stem pair form intramolecular hydrogen bonds. Furthermore, they also form intermolecular hydrogen bonds on crystallization and create lamellae with lower surface energy. Thus, having amide units in the folds does not reduce stabilization of the crystalline lamellae.
10. Bellinger, M. A.; Waddon, A. J.; Atkins, E. D. T.; MacKnight, W. J. Macromolecules 1994, 27, 2130.
11. Atkins, E. D. T.; Hill, M. J.; Hong, S.; Keller, A.; Organ, S. J. Macromolecules 1992, 25, 917.
12. Hill, M. J.; Atkins, E. D. T. Macromolecules 1995, 28, 604.
13. 8). The shift was crudely estimated from the relative intensity of the 002 diffraction signal. There is no doubt that in the 10-amide nylon 6 lamellar structure there is some central sheet c-axis shift, but not as much as 0.37 nm. We have calculated the relative intensities as a function of c-axis shift and find that a range between 0.2 and 0.3 nm is consistent with the experimental results. We have chosen the value of 0.2 nm as the value that gives the best match with the measured 4.77 nm LSP value (see the end of note 18 also). All structures modeled on a 0.2 nm c-axis shift with minimum LSP greater than 4.77 nm would be even less satisfactory if the c-axis shift were greater.
14. The asymmetrically folded 10-amide oligomer (Figure 1c), with an amide fold, was found to be too long to fit into the lamellar crystal (see the structural modeling section in the Results and Discussion), and so detailed modeling of the fold was not necessary.
15. Jones, N. A. Ph.D. Thesis, University of Bristol, U.K., 1996.
16. Pope, D. P.; Keller, A. J. Mater. Sci. 1975, 10, 747.
17. 8 This is not surprising when the effect of folding is considered (see, for example, Figure 7b). These variations in parameters are all within the perceived definition of a nylon 6 α-structure as determined by Salem, D. R.; Weigmann. H. D. Polym. Commun. 1989, 30, 336.
18. 8 deduced from nylon fibers will be submitted separately.
19. Up and down association between molecules is possible if large c-axis relative displacements between molecules are considered. However, the outer-limit lamellar thickness of these structures is in excess of 5.5 nm, and therefore such models can be dismissed.
20. It is also possible for the polar hydrogen-bonded sheets to stack with alternating polarity but with the chain folds embedded within a lamella. Such a structure is not favored since the calculated LSP value exceeds the measured value. Furthermore, the buried fold creates stereochemical clashes in the direction orthogonal to the ac-planes.
21. 2
22. Magill, J. H.; Girolamo, M.; Keller, A. Polymer 1981, 22, 43.
23. Since the fold distribution is different between hydrogen-bonded sheets of the once-folded nylon 6 oligomers and nylon 6 polymer, the requirements for type 1 folding on both sheet edges also change.