Exploring the Upper Size Limit for Sterically Stabilized Diblock Copolymer Nanoparticles Prepared by Polymerization-Induced Self-Assembly in Non-Polar Media

Abstract

Reversible addition–fragmentation chain transfer (RAFT) dispersion polymerization of benzyl methacrylate is used to prepare a series of well-defined poly­(stearyl methacrylate)–poly­(benzyl methacrylate) (PSMA–PBzMA) diblock copolymer nanoparticles in mineral oil at 90 °C. A relatively long PSMA54 precursor acts as a steric stabilizer block and also ensures that only kinetically trapped spheres are obtained, regardless of the target degree of polymerization (DP) for the core-forming PBzMA block. This polymerization-induced self-assembly (PISA) formulation provides good control over the particle size distribution over a wide size range (24–459 nm diameter). 1H NMR spectroscopy studies confirm that high monomer conversions (≥96%) are obtained for all PISA syntheses while transmission electron microscopy and dynamic light scattering analyses show well-defined spheres with a power-law relationship between the target PBzMA DP and the mean particle diameter. Gel permeation chromatography studies indicate a gradual loss of control over the molecular weight distribution as higher DPs are targeted, but well-defined morphologies and narrow particle size distributions can be obtained for PBzMA DPs up to 3500, which corresponds to an upper particle size limit of 459 nm. Thus, these are among the largest well-defined spheres with reasonably narrow size distributions (standard deviation ≤20%) produced by any PISA formulation. Such large spheres serve as model sterically stabilized particles for analytical centrifugation studies.

Influence of the Polymer Microstructure over the Phase Separation of Thermo-Responsive Nanoparticles

“…It is worth mentioning that a broad range of Dn can be accessed with this strategy, from around 50 nm up to 1 μm (i.e., 40EG 4 -3000BMA). This is a remarkable result for colloids produced via RAFT emulsion polymerization, which typically leads to NPs with an upper size limit of 500 nm [ 42 ].…”

Synthesis of well-defined diblock copolymer nano-objects by RAFT non-aqueous emulsion polymerization of N-(2-acryloyloxy)ethyl pyrrolidone in non-polar media

“…43 However, our prior PISA experience suggested that selecting a sufficiently long PSMA stabilizer should confer colloidal stability. 13,[45][46][47] Aliquots were periodically extracted during the RAFT solution homopolymerization of SMA in toluene when targeting a DP of 60 at 70°C, with monomer conversions being determined by 1 H NMR spectroscopy (Fig. S3a †) and molecular weight data being obtained by GPC analysis using chloroform as an eluent (Fig.…”

Bromoform-assisted aqueous free radical polymerisation: a simple, inexpensive route for the preparation of block copolymers

“…It should be noted that the molar mass dispersity, Ð, of the final polymers was high in all cases (2.8-3.5), with no suggested relationship between Ð and bromoform content. As previously discussed, high Ð values may not inherently have an adverse impact on the desired application 15,[23][24][25][26][27][28][29][30] .…”

“…Such well-defined macromolecules are crucial for structure-property relationship studies 15 , bulk block copolymer self-assembly (where low mass dispersities are required to produce sharp nanophase boundaries [16][17][18][19] ) and in the pursuit of sequence-controlled macromolecules for biomimicry [20][21][22] . Despite the drive for narrow molar mass distributions, this is not always necessary to prepare materials with desired characteristics and performance [23][24][25][26][27][28][29][30] . In industrial settings, polymers with broader molar mass distributions are often easier to process 31 and the breadth and shape of the molar mass distribution 32 can impart desirable physical properties (e.g.…”

“…processability) 33,34 . Indeed, Parker et al 35 reported the synthesis of block copolymers via RAFT dispersion polymerisation with high molar mass dispersity values (Ð > 3) that self-assembled into extremely well-defined spherical nanoparticles which show promise as friction reduction agents in automotive engine oil 36 .…”