Molecular Disorder and Mesoscopic Order in Polydisperse Acrylic Block Copolymers Prepared by Controlled Radical Polymerization

Abstract

Self-assembly of high molecular weight polydisperse acrylic block copolymers and their blends is presented under conditions as close as possible to thermodynamic equilibrium. Di- and triblock copolymers comprising a poly(butyl acrylate) (PBA) first or middle block, and poly(methyl methacrylate) (PMMA) second or outer blocks, denoted MBA and MBAM, respectively, are prepared by nitroxide-mediated polymerization (NMP). Their particularity is that the acrylic block is controlled while the methacrylate block is polymerized via an uncontrolled radical process under the synthesis conditions used. Overall composition and molecular weight polydispersities are large. Molecular disorder does not yield macrophase separation, and TEM on solvent cast films reveals lamellar and poorly ordered bicontinuous, cylindrical, or spherical morphologies. Except for the lamellar phase, clear multiple orders of diffraction are not visible in SAXS, and scattering profiles instead indicate a liquidlike order of microdomains. More importantly, morphology boundaries are strongly shifted compared to those commonly accepted for model monodisperse block copolymers. Hence, symmetric copolymers adopt morphologies with highly curved interfaces while lamellae are displaced to PMMA-rich compositions. These results suggest that unbalanced polydispersity between the two blocks can induce interfacial curvature toward to broadest molecular weight distribution, thereby releasing stretching energy of the whole chain. This effect is expected to be encountered in radical or hybrid block copolymer syntheses whenever control cannot be optimized for all blocks.

Synthesis, characterization and properties of amphiphilic block copolymers of 2-hydroxyethyl methacrylate and polydimethylsiloxane prepared by atom transfer radical polymerization

“…This phenomenon was attributed to the high miscibility of pHEMA blocks with shorter PDMS blocks. 34 This observation was in agreement with the SAXS profile of H97S3, which had primary reflection with a very low intensity.…”

Four‐Phase Morphologies in Blends of ABC and BAC Triblock Terpolymers

“…Although long time the idea was set that ordered microphases in block copolymers can be achieved only by a narrow dispersity, [68] some studies have demonstrated their self-assembly into well-ordered structures even presenting a broader molecular weight distribution (MWD). [69][70][71][72][73] Our starting materials for the blends exhibit, with values of 1.16 and 1.19 for neat SIM and ISM, by themselves relatively broad MWDs and as both terpolymers have unequal molecular weights the combination in a blend provides both a polydispersity in molecular weight and composition. The repulsive segmental interactions between the copolymer blocks is the driving force for microphase separation and leads them to stretch in order to adopt a minimum of interfacial contact area.…”

Synthesis of poly(di[methylamine]ethyl methacrylate)‐b‐poly(cyclohexyl methacrylate)‐b‐poly(di[methylamine]ethyl methacrylate) amphiphilic triblock copolymers by ATRP: Condensed‐phase and solution properties

“…This larger interfacial thickness can be responsible of the lack of reflections. 64,65 In addition, there is other important aspect that can reduce the ordering capability at large scale in these copolymers together with the just mentioned diffuseness of the phase boundaries. This is the polydispersity (see Table 1), although the values reached are quite low, they are higher than those that can be obtained through living anionic polymerisation.…”

“…Therefore, differences in the macrochain length make difficult the development of ordered arrangements and longer annealing at temperature higher than glass transition temperature of the rigid block are often necessary to promote ordering, this being even impossible sometimes. 65 However, the amphiphilic nature of these copolymers makes the existence of self-assembly more interesting in solution than in condensed matter.…”