Synthesis of supramolecular polymers by grafting of Thy and DAT stickers on telechelic PPO chains

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Differences with other types of self-assembly

Supramolecular polymers are closely related to other types of self-assembly, such as crystals, bolaamphiphiles, block copolymers and other so-called polymerization of molecules in biology. This part aims at clarifying the distinctions between supramolecular polymers and these other self-assembled structures.

Differences with crystals: dynamic

Crystals are also reversibly self-assembled molecules by noncovalent interactions, but unlike supramolecular polymers, the dynamic is frozen in crystals. As a result, crystals form brittle solids.

Differences with block copolymers: directionality and size

As mentioned before, block copolymers can self-assemble into various morphologies.121,122 However, unlike supramolecular polymers, block copolymers selfassembly is mostly induced by non-directional interactions (van der Waals, electrostatic, hydrophobic and entropic interactions), although directional interactions such as hydrogen bonding can also control the self-assembly.
Moreover, block copolymers are usually much bigger molecules than supramolecular polymers units. Nevertheless, miniature block copolymers where the blocks are oligomers rather than polymers can also self-assemble. For instance, Stupp and his coworkers reported  on the self-assembled nanostructures of miniaturized triblock copolymers consisting of a nine units polystyrene block, a nine units polyisoprene block and a three biphenyl ester units rigid block.124 Furthermore, Matsushita and his coworkers observed that their triblock copolymers composed of a central polystyrene block (of 11 000 g/mol) and outer oligonucleotide blocks of only five thymidine phosphate units microphase-separated in a cylindrical morphology.
However, the same compound with only one thymidine unit was disordered and not microphase-separated.125 In fact, the tendency to microphase-separate of their triblock copolymer series seems to increase with the number of thymidine phosphate units.

Differences with supramolecular block copolymers: one spacer

The concept of supramolecular block copolymers,126,127 also called pseudo block copolymers,128 is closely related to that of main-chain supramolecular polymers, except that several types of oligomeric spacers, instead of just one, are used (Figure I.30). The block copolymer aspect allows these materials to microphase-separate while the supramolecular aspect brings responsiveness and reversibility.129 The simplest form of supramolecular block copolymers results from the self-assembly of two one-end-functionalized polymers into diblock supramolecules (Figure I.31).

Differences with bolaamphiphiles, HEUR and ionomers: directionality

Bolaamphiphiles are composed of a central hydrophobic core capped on both ends with a hydrophilic group.133 Therefore, bolaamphiphiles are basically triblock copolymers where the two end-blocks are comprised of only one monomer. They self-assemble in various supramolecular morphologies (micelles, cylinders, …) because of the incompatibility between the hydrophilic and hydrophobic parts. 133,134 Therefore, unlike the supramolecular polymer concept, the self-assembly of bolaamphiphiles is induced by less specific solvent-surfactants interactions and non-directional interactions, although in some bolaamphiphiles directional ydrogen bonding associations play an important role. It should be noted that the term bolaamphiphile is almost always used in the context of aqueous solutions.
Hydrophobically end-capped polymers (such as hydrophobic ethoxylated urethane: HEUR) and ionomers form reversible networks by clustering of the end groups, through hydrophobic and dispersion interactions for HEUR,135 and through coulomb forces for ionomers.136 Therefore, unlike the supramolecular polymer concept, the end groups are associated through non-directional interactions.

A primary amine end-functionality to connect the stickers

The spacers must be connected to the stickers, so they need to be at least bifunctional, and preferably with highly reactive functions. That is why we have chosen commercial PPO end-functionalized by primary amine groups, Jeffamine ®, and more specifically Jeffamines ® D Series (bifunctional) and T Series (3-armed branched trifunctional) (Chart II.1, Jeffamines ® M Series [monofunctional] were also used as a control). In this chapter we will  focus on the functionalization of Jeffamines ® D Series.
Halogen functionalized stickers can then easily be grafted by nucleophilic substitution, while carboxylic acid functionalized stickers can easily be grafted by amidation.

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Number average molecular weight Mn estimated from 1H NMR

1H NMR of commercial Jeffamine ® D-230, D-400 and D-2000, diamine telechelic poly(propylene oxide) (denoted as NH2-PPO-X-NH2, where X is the molecular weight in g/mol), allows the determination of its number average molecular weight (Mn). Indeed, the CH3 protons in 􀁄-position of the amine end-groups (b, see Chart II.2) are shifted upfield  compared to the CH3 protons in the middle of the chain (a), as illustrated on the abscissa of signals (equations 1 and 2, with Ia and Ib the integral of the a and b signals, respectively). Mn and x values obtained in this fashion are gathered in Table II.1. The values are close to the values from Huntsman technical bulletins. Given the values of Mn determined by integrating the a and b 1H NMR signals, Jeffamine D230 will now be denoted as NH2-PPO-250-NH2 1c, Jeffamine D400 as NH2-PPO- 460-NH2 1b, and Jeffamine D2000 as NH2-PPO-2200-NH2 1a.

Polydispersity index Ip estimated from GC-MS and GPC

Gas Chromatography coupled to Mass Spectrometry (GC-MS) was performed on NH2-PPO-X-NH2 1b-c. Chromatograms reveal NH2-PPO-250-NH2 1c is constituted of oligomers bearing 2, 3 and 4 repetition units, while NH2-PPO-460-NH2 1b contains oligomers with 2 to 9 repetition units. Indeed, each oligomer size appears on the GC chromatogram as a distinct peak with tailing characteristic of primary amines (Figure II.2). Peaks were easily attributed thanks to their associated MS spectrum. Indeed, the MS spectra almost all contain the M-1 peak characteristic of primary amines.

Table of contents :

Acronyms and Abbreviations
Chapter I. From polymers and supramolecular chemistry to supramolecular polymers
1. Polymers
2. Supramolecular chemistry
3. Supramolecular polymers
Chapter II. Synthesis of supramolecular polymers by grafting of Thy and DAT stickers on telechelic PPO chains
1. Telechelic PPO chains as spacers between the stickers
2. Grafting DAT sticker
3. Grafting Thy sticker
4. Blending Thy-PPO-X-Thy with DAT-PPO-X-DAT
5. Heteroditopic grafting of Thy and DAT (grafting Thy on one side and DAT on the other side)
Chapter III. Supramolecular polymers in solution: solvent dependent behavior
1. Supramolecular polymers in solution
2. Supramolecular polymers act as bolaamphiphiles in a dissociative solvent
3. Supramolecular polymers are associated in a non-dissociative solvent
4. Conclusions and perspectives
Chapter IV. Order and disorder in bulk supramolecular polymers.
1. Order-disorder transition in supramolecular polymers
2. Disorder in supramolecular polymers
3. Suppression of mesoscopic order by complementary interactions in supramolecular polymers
Chapter V. Glass transition of supramolecular polymers in the bulk
General Conclusion
Appendix I. Material and methods
Appendix II. Synthesis and characterization
Appendix III. Résumé en français


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