Precision Synthesis and Distinct Assembly of Double-Chain Giant Surfactant Regioisomers

Abstract

The delicate influence of minute structural difference, such as regiochemistry, on self-assembly and phase behaviors has been commonly observed in small molecules but rarely in synthetic polymers. Herein, we report the precision synthesis of a series of double-chain giant surfactant regioisomers and their distinct phase structures and phase behaviors. These giant surfactants possess a hydroxyl-functionalized cubic T8 polyhedral oligomeric silsesquioxane head and two polystyrene tails tethered at para-, meta-, and ortho-configurations and were prepared following the sequential “click” method. As revealed by temperature-dependent small-angle X-ray scattering and bright-field transmission electron microscopy, their order–disorder transition temperatures decrease in the order of ortho-, meta-, and para-isomers, while order–order transitions were observed in the meta-isomer from lamellae to double gyroids and in the ortho-isomer from double gyroids to hexagonal cylinders upon increasing temperature. The mechanisms are elucidated by the influence of the tethering positions on the different free energy contributions, i.e., the interfacial energy, the head-to-head interaction, and the entropic energy of the tails. The distinct assembly behaviors of the three regioisomers are unusual in macromolecules yet resemble small molecules. It opens an avenue to fine-tune the macromolecular assembly at the level of molecular precision.

Regioisomeric Tandem Triblock Shape Amphiphiles Based on Polyhedral Oligomeric Silsesquioxanes

“…It was found that the o-DPOSS-2PS n has the highest order-disorder transitiont emperature among the three isomers. [19] In the current study,a lthough the rigid tBPOSS motif is different from the random-coil-like polystyrenec hains, the physical pictures hould be largely the same. The para-a nd meta-isomers are much lesss table than the ortho-isomerss uch that the ordered structure could either not form or its formation was kinetically prohibited.…”

“…[18] It was found in double-chain giant surfactants that regio-configuration inducesc onsiderable phase boundary shift as well as phase stabilityc hanges. [19] In this contribution, we report the design, synthesis and selfassembly of as eries of tandemt riblock shape amphiphile regioisomersb ased on POSS motifs ( Figure 1). The middle block is the rod-like perfluoroalkyl-POSS( FPOSS)m otif [20] and the two end-blocks are spherical tert-butyl-functionalized POSS (tBPOSS).…”

Macromolecular Isomerism in Giant Molecules

“…The phase diagrams were constructed, which show a systematic phase boundary shift and phase stability variations with changing regio‐configurations (Figure ). With semi‐quantitative calculation, it was inferred that these molecules all adopt “head‐to‐head, tail‐to‐tail” packing models with partial interdigitation . Since the two tails have to bend towards one side, the para ‐isomer would have the largest average interfacial area per molecule with the ortho ‐isomer being the smallest.…”

“…With semi-quantitative calculation, it wasi nferredt hat these mole- Concept cules all adopt "head-to-head, tail-to-tail" packing modelsw ith partial interdigitation. [18] Since the two tails have to bend towards one side, the para-isomer would have the largesta verage interfaciala rea per molecule with the ortho-isomer being the smallest.I th elps to clarify that the stability usuallyi ncreases from para-t oortho-isomers. The observation of order-order and order-disorder transitions was furtherr ationalized by the strong temperature-dependence of collective hydrogen bonding between the heads.…”

The effect of steric repulsion between highly branched hydrophilic blocks on inverse cubic mesophase formation in block copolymers

“…The site-selective functionalization of T8 POSS vertices could lead to the formation of giant amphiphiles capable of selfassembly into complex nanostructures in bulk and in solution. [26][27][28][29] In this work, mono-alcohol heptavinyl POSS was used as a scaffold for the hydrophilic module to host poly(ethylene glycol) (PEG). Seven PEG chains were introduced to all the vertices of POSS with the exception of the alcoholfunctionalized vertex.…”