Going beyond the classical amphiphilicity paradigm: the self-assembly of completely hydrophobic polymers into free-standing sheets and hollow nanostructures in solvents of variable quality

Abstract

Self-assembly is well-known to occur in amphiphiles, and the totally hydrophobic ones are never reported to self-assemble. In this work we report for the first time that the latter can self-assemble into free-standing sheets and hollow spheres in toluene/methanol mixed solvents by modulating the solvent quality. The homopolymers studied in this work are polystyrene (PS), polyphenylacetylene (PPA), and poly(3-hexyl thiophene) (P3HT), representing polymers with different rigidity. All the three form a homogenous solution in toluene, but self-assembly occurs in the toluene/methanol mixed solvents. Micrometer sized free-standing sheets were formed for PS, PPA, and P3HT at methanol volume fractions being 43%, 50%, and 67%, respectively, and hollow spheres were observed for PPA at higher methanol fractions of 75 and 90%. Under the latter solvent conditions, PS forms solid spheres, yet ill-defined aggregates and free-standing sheets coexist in the case of P3HT. This non-solvent induced self-assembly was explained by a delicate balance of two "opposing forces": van der Waals attractive and entropic repulsive forces generated between the segments of these homopolymers within a single chain, between two chains, and among more chains in the solvents of worsened quality.

Cu-Catalyzed Azide-Pt-Acetylide Cycloaddition: Progress toward a Conjugated Metallopolymer via iClick

“…Saturated polymers with aliphatic repeat units are more flexible than unsaturated polymers with alternating single and multiple bonds. − The rigidity/flexibility determines the morphology of the polymer in the solid state and available conformations in solution. , A polymer with conjugated alternating single and multiple bonds permits the tuning of the HOMO–LUMO gap (where HOMO denotes the highest occupied molecular orbital and LUMO represents the lowest unoccupied molecular orbital) to within the visible light spectrum, , whereas the lack of conjugation in aliphatic polymers leads to a large gap typically accessed by ultraviolet (UV) light. , A small HOMO–LUMO gap allows conjugated polymers to be used in photovoltaics, − in nonlinear optics, − as antimicrobial agents, − and as chemical sensors. − Polytriazoles (PTA) are a class of polymers that contain alternating single and multiple bonds. , Electron transfer through 1,2,3-triazoles was studied previously − and can offer some unique advantages in nonlinear optics , and photovoltaic applications. , van Maarseveen, Reek, and co-workers prepared the first conjugated polytriazole via copper-catalyzed azide alkyne cycloaddition (CuACC) − between diazide and diyne monomers according to the general reaction in Figure A. Since then, expansion of this method led to the synthesis of PTAs that combine the azide and alkyne into a single monomer, thus alleviating the stoichiometric challenge inherent to step-growth polymerizations. − Coordination of triazoles to metal ions can alter their ability to facilitate electron transfer. , We recently combined PTA synthesis concepts and iClick …”

“…1−4 The rigidity/flexibility determines the morphology of the polymer in the solid state 3 and available conformations in solution. 5,6 A polymer with conjugated alternating single and multiple bonds permits the tuning of the HOMO−LUMO gap (where HOMO denotes the highest occupied molecular orbital and LUMO represents the lowest unoccupied molecular orbital) to within the visible light spectrum, 1,7 whereas the lack of conjugation in aliphatic polymers leads to a large gap typically accessed by ultraviolet (UV) light. 1,7 A small HOMO−LUMO gap allows conjugated polymers to be used in photovoltaics, 8−14 in nonlinear optics, 15−19 as antimicrobial agents, 20−22 and as chemical sensors.…”

Thiophene α-Chain-End-Functionalized Oligo(2-methyl-2-oxazoline) as Precursor Amphiphilic Macromonomer for Grafted Conjugated Oligomers/Polymers and as a Multifunctional Material with Relevant Properties for Biomedical Applications

“…These end-groups not only allowed the induction of properties that these flexible, commodity polymers never had [ 8 , 42 ] but greatly impacted the class of CPs, enabling the synthesis of grafted CPs (g-CPs) having well-defined oligomeric/polymeric side chains. Thus, the appearance of electroactive macromonomers afforded the movement of the so-called “solvent skin” concept of CP side groups beyond the solubility paradigm [ 43 ], while changing the classical amphiphilicity paradigm [ 44 , 45 ].…”