Self-Assembly of Block and Graft Copolymers in Organic Solvents: An Overview of Recent Advances

Abstract

This review is an attempt to update the recent advances in the self-assembly of amphiphilic block and graft copolymers. Their micellization behavior is highlighted for linear AB, ABC triblock terpolymers, and graft structures in non-aqueous selective polar and non-polar solvents, including solvent mixtures and ionic liquids. The micellar characteristics, such as particle size, aggregation number, and morphology, are examined as a function of the copolymers' architecture and molecular characteristics.

Keywords: block copolymers; graft copolymers; micelle; organic solvents; self-assembly; triblock terpolymers.

Figure 1

Basic micellar morphologies for AB copolymers.

Figure 2

Micellization characteristics of PtBMA₃₂₉-b-PVEA₁₄₂ copolymer in methanol as a function of temperature (lower critical solution temperature (LCST) = 53 °C; upper critical solution temperature (UCST) = 32 °C). Adapted from Li et al. [35].

Figure 3

Cryo-TEM images of PB-b-PEO copolymer, with 0.25 mol % PEO, at a concentration of 1 wt % in [BMIM][PF6]. (A) Worm-like micelles with occasional Y-junctions and (B) micellar overlap. “Reprinted with permission from He, Y.; Li, Z.; Simone, P.; Lodge, T.P. Self-assembly of block copolymer micelles in an ionic liquid. J. Am. Chem. Soc. 2006, 128, 2745–2750. Copyright 2017 Americal Chemical Society”.

Figure 4

Schematization of the polyA-polyB diblock copolymer self-assembly process in solvents mixture.

Figure 5

Basic micellar morphologies for linear ABC triblock terpolymers.

Figure 6

Chemical structure of the ABC triblock terpolymer POEGA-PBzA-PFA [85].

Figure 7

Logarithmic variation of the R_h as a function of DP_n total of PB-P2VP-PEO triblock terpolymers in n-heptane [88].

Figure 8

Micellar morphological changes of PS-PB-PMMA triblock terpolymers in acetone/isopropanol mixtures as a function of isopropanol content. “Reprinted with permission from Löbling, T.I.; Ikkala, O.; Gröschel, A.H.; Müller, A.H.E. Controlling multicompartment morphologies using solvent conditions and chemical modification. ACS Macro Lett. 2016, 5, 1044–1048. Copyright 2017 Americal Chemical Society”.

Figure 9

Schematically representation of an AB graft copolymer.

Figure 10

Micellar conformations of PI-g-Pluronic copolymers in hexane (backbone selective solvent) and in ethanol (grafts selective solvent). Adapted from Alexander et al. [116].

Figure 11

Micellar conformation of PGMA-g-(PCEMA-PtBA-MPEG) copolymers in CH₂Cl₂, CH₃OH and H₂O selective solvents, respectively. Adapted from Mo et al. [117].