(226h) Synthesis of Well-Defined Poly (Styrene-block-Methyl methacrylate) Copolymers By Classical Anionic and Controlled Radical Polymerization (CRP) Methods

Block copolymers constitute a fascinating group of polymeric materials belonging to the “soft matter” family. These materials are formed by blocks of polymeric chains from different monomers. In most cases, these blocks are thermodynamically incompatible, but the covalent bonds between them impose specific arrangements, generating particular morphologies both in bulk and in solution.

In the particular case of block copolymer films over specific substrates, much work has focused on manipulating the film thickness, the surface energies of each block, and the interfacial interactions of each block with the substrate to generate useful, perpendicularly (vertically) oriented morphologies with high degrees of long-range lateral order. (Widin, Kim et al. 2013)

In the present work, two different synthetic methods were used to produce well-defined diblock copolymers based on styrene and methylmethacrylate (PS-b-PMMA): classical anionic polymerization (high vacuum techniques), and controlled radical polymerization (CRP). The aim of this work is not only to obtain well-defined PS-b-PMMA but also to prove that the copolymers obtained by CRP exhibits the same behavior as those obtained by the classical anionic polymerization (Soeriyadi, Boyer et al. 2011; Gao, Zhang et al. 2011).

Anionic and controlled radical polymerization (CRP) techniques have allowed the routine preparation of block copolymers with two or three different monomer blocks. However, anionic polymerization must be performed under a rigorous set of polymerization conditions. For CRP, after each block addition, the copolymer requires purification to eliminate unreacted monomers prior to the next chain-extension step with another monomer.

The copolymers obtained were chemically characterized by nuclear magnetic resonance (¹H-NMR), Fourier transform infrared spectroscopy (FTIR), size-exclusion chromatography (SEC), and the morphological characterization was determinate by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). From this analysis, the main features of the block copolymers (such as their chemical composition or morphologies and scattering size domains developed on thermal treatment) are discussed, consequently studied how the composition and the morphology of the copolymers relate with the final properties. Different morphologies can result when they are solution cast from different solvents.

Gao, J., Z. Zhang, et al. (2011). "Copper(0)-mediated living radical copolymerization of styrene and methyl methacrylate at ambient temperature." Macromolecules 44(9): 3227-3232.

Soeriyadi, A. H., C. Boyer, et al. (2011). "High-order multiblock copolymers via iterative Cu(0)-mediated radical polymerizations (SET-LRP): Toward biological precision." Journal of the American Chemical Society 133(29): 11128-11131.

Widin, J. M., M. Kim, et al. (2013). "Bulk and thin film morphological behavior of broad dispersity poly(styrene-b-methyl methacrylate) diblock copolymers." Macromolecules 46(11): 4472-4480.