| Supramolecular block copolymers, which are the supramolecular analog of covalently-bonded block copolymers, consist of individual polymer blocks connected by non-covalent bonds. They can be produced by self-assembly of telechelic oligomers or polymers with complementary end-groups, e.g., hydrogen bonding or acid-base interactions, such that a variety of block combinations may be achieved by simple mixing of the appropriate polymers. Supramolecular block copolymers are advantageous for fabricating nanostructured functional materials, since they can exhibit morphologies mimicking conventional covalently-bonded block copolymers and the reversible nature of the supramolecular bonds between blocks allows for unique responses to external stimuli. Various applications of these materials have been explored, such as self-healing, thermally tunable nanostructures, nanoporous materials, and nanostructured assemblies.;In the first part, a supramolecular multiblock copolymer, was synthesized by mixing two telechelic oligomers, alpha,o-sulfonated polystyrene, HO3S-PS-SO3H, derived from a polymer prepared by reversible addition--fragmentation chain-transfer (RAFT) polymerization, and alpha,o-amino-polyisobutylene, H2N-PIB-NH2, prepared by cationic polymerization. During solvent casting, proton transfer from the sulfonic acid to the amine formed ionic bonds that produced a multiblock copolymer that formed free-standing flexible films with a modulus of 90 MPa, a yield point at 4% strain and a strain energy density of 15 MJ/m3. Small angle X-ray scattering characterization showed a lamellar morphology, whose domain spacing was consistent with the formation of a multiblock copolymer based on comparison to the chain dimensions. A reversible order-disorder transition occurred between 190°C and 210°C, but the sulfonic acid and amine functional groups decomposed at those elevated temperatures based on companion optical microscopy and spectroscopy measurements. For high non-linear strains, the dynamic modulus, G', decreased by nearly an order of magnitude and the loss modulus, G', decreased by a factor of 1.4, but both recovered to their original values once the strain was reduced to within the linear response region.;In the second part, two groups of RAFT agents that contain either quaternary ammonium or quaternary phosphonium groups were prepared. At first, a series of trithiocarbonate RAFT agents containing quaternary ammonium functionality in the "R-group" (RAFT-NR3) were synthesized via a facile and high-yield approach. The synthetic route first involves the optimized synthesis of 4-(bromomethyl)-N,N,N-trialkyl benzyl ammonium bromide compounds, which were subsequently reacted with the alkyl trithiocarbonate anion to directly produce the trithiocarbonate RAFT agent. However, quaternary ammonium group partially degraded when the RAFT agents were used in polymerizations at 120 °C. This issue was overcome by using lower polymerization temperature. On the other hand, quaternary phosphonium-containing, trithiocarbonate RAFT agents (RAFT-PR3) were also synthesized via similar synthetic method. It was found that the thermal stabilities of RAFT-PR3 were enhanced compared to comparable quaternary ammonium-containing RAFT agents, which significantly improved the retention of the cationic end-functionality of the polystyrene obtained at 120 °C. For both classes of RAFT agents, the crude polystyrene can be further purified via column chromatography to afford high purity hemi-telechelic cationomers.;In the third part, matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-ToF MS) was used to quantify the sulfonation level and sulfonation distribution of sulfonated polystyrene ionomers prepared by homogeneous solution sulfonation. The sulfonation levels obtained by MALDI ToF-MS and acid-base titration were compared, and the sulfonate distributions determined by MALDI-ToF MS were compared with theoretical random distributions. The results indicate that the sulfonation reaction used produces a sample with a random sulfonate distribution. |
