Structure of poly(styrene‐b‐ethylene‐alt‐propylene) diblock copolymer micelles in binary solvent mixtures

Abstract

The effect of solvent selectivity on the micelle structure formed by a poly(styrene‐b‐ethylene‐alt‐propylene) diblock copolymer (PS‐PEP, MPS = 42,000 g/mol and MPEP = 62,000 g/mol) in solutions of squalane, a highly selective solvent for the PEP block, and 1‐phenyldodecane, a neutral solvent, is investigated using dynamic light scattering (DLS) and small‐angle X‐ray scattering (SAXS). The results reveal that addition of 1‐phenyldodecane systematically reduces solvent selectivity, leading to decreases in the critical micelle temperature (TCMT) and the average number of chains in a micelle (Nagg), and an increase in the solvent fraction in the core. However, the core blocks have essentially unperturbed dimensions (i.e., Rc ≈ 2 × ⟨Rg⟩o, where ⟨Rg⟩o is unperturbed radius of gyration of the core block), and therefore the micelle core radius (Rc) is nearly independent of solvent selectivity, which has not been anticipated by previous theoretical descriptions. These results demonstrate that under such conditions, excluded volume effects in the corona blocks play the dominant role in determining micelle structure. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 22–31

Effect of Solvent Selectivity on Chain Exchange Kinetics in Block Copolymer Micelles

“…18,19 Recently, Choi et al systematically investigated a series of PS-PEP diblock copolymers in pure squalane and binary solvent mixtures of squalane and 1-phenyldodecane, where 1-phenyldodecane is a less selective solvent than squalane. 20,21 In good agreement with observations by Quintana et al and Bang et al, the authors observed a smaller aggregation number, lower CMT, and higher solvent fraction in the core upon increasing the volume fraction of 1-phenyldodecane in binary solvent mixtures.…”

“…20 Bang et al also showed no solvent in the core of PS-PI micelles in tetradecane at temperatures of 40 °C or more below T CMT . 18 We calculated T g wet assuming that the core composition is the same as the overall solvent composition (see above) using the volume fraction of binary mixed solvent in the core reported by Choi et al 20,21 and listed in Table 3. The estimated T g for the slightly solvated PS core would not change significantly with small variations in solvent composition due to the similar T g values of squalane and 1-phenyldodecane.…”

Spontaneous Self‐Assembly and Micellization of Random Copolymers in Organic Solvents

“…Finally, the nonselective solvent is removed from the solution with methods such as solvent evaporation or dialysis . This creates kinetically frozen micelles in the solution …”

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

“…Choi et al [ 56 ] studied the self-assembly of PS 404 - b -PEP 886 diblock copolymers in a mixture of 1-phenyldodecane (δ = 17.4 MPa 1/2 )/squalane (δ = 16.6 MPa 1/2 ). At 110 °C and a 50/50 ratio of 1-phenyldodecane/squalane, the micellar R h was equal to 280 nm, which is much higher than the value of 40 nm determined by Growney et al [ 41 ] for the PS 315 - b -PEP 1203 micelles in n -heptane, at the same temperature.…”

“…If this requirement is not met, then a partition of the solvents may occur, which leads to a swelling of the micellar core by either one or both solvents in presence. A second possibility to use organic solvent mixtures in the self-assembly process of polyA- b -polyB copolymers was investigated by different authors [ 54 , 55 , 56 ]. Their approach consists in the solubilization of the copolymer in a common solvent S , a “ good ” solvent for both polyA and polyB sequences.…”