Atom transfer radical polymerization of a semifluorinated triblock copolymer of poly(methyl methacrylate)-b-polypentafluorostyrene-b-poly(methyl methacrylate)

Abstract

Controlled radical polymerization (CRP) technique has attracted recent scientific and industrial attention in the field of polymer chemistry. It can be achieved by rapid propagation and reversible termination or transfer reaction that are much faster than the irreversible termination reaction which enables polymer chains to grow more slowly and continuously with conversion. There are largely three systems in CRP such as nitroxide mediated polymerization (NMP), atom transfer radical polymerization (ATRP), and reversible addition fragmentation chain transfer (RAFT). Especially in ATRP, a radical can be formed reversibly polymeric materials by transfer of a halogen from an alkyl halide to a transition metal complex. The reversible formation of active radicals from dormant alkyl halides determines the concentration of radicals and the deactivation process to form the alkyl halides was usually dominant in ATRP to maintain the low radical concentration. Therefore, in ATRP, molecular weights, polydispersity, compositions and architecture can be easily controlled with conversion. Block copolymers have received much scientific and technological attention due to their ability to self-assemble into a series of periodic ordered micro-structures via microphase separation between the constituent block segments. There are a number of applications by using their phase-separated morphology both in the solid state and in solutions. To synthesize these block copolymers with predetermined molecular weights and low polydispersity, anionic polymerization is usually employed. However, its use is highly limited due to the strict reaction conditions such as extremely low temperature, exclusion of moisture and impurity, and stringent drying. Recently, ATRP has been used in such a manner to build block copolymers of radically polymerizable monomers. In this process, active halogens are incorporated at the chain ends of polymers to form macroinitiators. In addition, the ATRP process produces an end-functional polymer that can be used as a macroinitiator for further polymerization with additional monomers, resulting in a multicomponent block copolymer. In the present study, we synthesized a well-defined, semi-fluorinated triblock copolymer of poly(methyl methacrylate)-b-polypentafluorostyrene-b-poly(methyl methacrylate) (PMMA-b-PPFS-bPMMA) by ATRP technique. It has been known that fluorinated chains are less miscible than the corresponding hydrogenated chains due to their extremely low surface energy, and the large size of fluorine atoms of the pentafluorostyrene units of PMMA-b-PPFS-b-PMMA prevents the rotation around the polymer backbones, possibly making the molecules rigid. By analogy with low molar mass compounds, we expect that the suitable composition of the pentafluorostyrene units of PMMA-b-PPFS-b-PMMA easily produces a selfassembled, ordered morphology through the microphase separation between component block segments. The nonpolar nature of pentafluorostyrene units based on the weak intermolecular forces due to a symmetric distribution of most C-F bonds of the pentafluorostyrene units of PMMA-bPPFS-b-PMMA may lead to a well-defined thin film morphology through different wettability of component building blocks on the substrate, which will be also discussed in the present study.