Lewis Adduct-Induced Phase Transitions in Polymer/Solvent Mixtures

Abstract

Functionalization-induced phase transitions in polymer systems in which a postpolymerization reaction drives polymers to organize into colloidal aggregates are a versatile method to create nanoscale structures with applications related to biomedicine and nanoreactors. Current functionalization methods to stimulate polymer self-assembly are based on covalent bond formation. Therefore, there is a need to explore alternative reactions that result in noncovalent bond formation. Here, we demonstrate that when the Lewis acid, tris­(pentafluorophenyl) borane (BCF), is added to a solution containing poly­(4-diphenylphosphino styrene) (PDPPS), the system will either macrophase-separate or form micelles if PDPPS is a homopolymer or a block in a copolymer, respectively. The Lewis adduct-induced phase transition is hypothesized to result from the favorable interaction between the PDPPS and BCF, which results in a negative interaction parameter (χ). A modified Flory–Huggins model was used to determine the predicted phase behavior for a ternary system composed of a polymer, a solvent, and a small molecule. The model indicates that there is a demixing region (i.e., macrophase separation) when the polymer and small molecule have favorable interactions (e.g., χ < 0) and that the phase separation region coincides well with the experimentally determined two-phase region for mixtures containing PDPPS, BCF, and toluene. The work presented here highlights that Lewis adduct-induced phase separation is a new approach to functionalization-induced self-assembly (FISA) and that ternary mixtures will undergo phase separation if two of the components exhibit a sufficiently negative χ.

Controlling Polymer Material Structure during Reaction-Induced Phase Transitions

“…The Lewis adduct-induced macrophase separation is predicted to result from the strong B–P bond, which is described by a negative interaction parameter (χ). The experimental results were further supported by establishing a predicted phase diagram using a modified Flory–Huggins model for a ternary mixture containing PDPPS, BCF, and toluene . There is excellent agreement between the experimental results and the predicted ternary phase diagram, indicating that strong intermolecular interactions have the potential to drive phase changes.…”

“…The large colloidal aggregates transition to isolated micelles and PS-PDPPS diblock copolymer chains. Reproduced with permission from ref . Copyright 2022 The Authors.…”

“…Recently, our group revealed that Lewis acid/base adduct formation between a poly(Lewis base) and a Lewis acid will induce either macrophase or nanoscale phase transitions (Figure 7). 23 In the case of macrophase separation, when poly-(diphenylphosphinostyrene) (PDPPS) in toluene is mixed with tris(pentafluorophenyl)borane (BCF) that is also initially dissolved in toluene, the solution will macrophase separate when the boron to phosphorus mole ratio (B/P) is greater than 0.2 (Figure 7a). The Lewis adduct-induced macrophase separation is predicted to result from the strong B−P bond, which is described by a negative interaction parameter (χ).…”

“…RIPT examples beyond polymerization include functionalization, deprotection, conjugation, and chain-scission . Many RIPT examples include polymerizations such as polymerization-induced self-assembly (PISA) , or polymerization-induced microphase separation (PIMS) , (Figure f–h), but there are numerous examples including binding-induced liquid–liquid phase separation in biological systems, degradation/functionalization-driven changes in synthetic macromolecular systems, , or Lewis adduct-induced phase transitions . The phase behavior fundamentals (e.g., macrophase and microphase separation) that control polymer material structure during processing of already synthesized polymers is applicable to chemical reactions, but there is one major difference, the chemical species formed during a reaction are not static and evolve over time.…”

Oxidation-responsive polymer vesicles with order–disorder–order multiple-phase transitions

“…[7][8][9][10][11][12][13][14] Compared with the traditional self-assembly methods, PISA enables the synthesis and self-assembly of the block copolymers in one pot at a high solids content (10-50 wt%). Besides PISA, a variety of RIPT techniques have also been exploited, including RIPT based on functionalization, [15][16][17][18][19][20][21][22] deprotection, [23][24][25][26][27] conjugation, 28 and chain-scission. [29][30][31] For example, He et al synthesized a hydrophilic poly(ethylene glycol)-b-poly(styrene diazonium) and converted the diazonium group into azobenzene via azo coupling reaction in water at high polymer concentration.…”