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.
Highlights
Polymerization-induced self-assembly (PISA) has become widely recognized as a powerful platform technology for the rational synthesis of sterically stabilized diblock copolymer nano-objects with various morphologies.[1−5] One of the main advantages of PISA is its versatility: it can be conducted in water,[6−11] polar solvents,[12−19] or non-polar media.[20−29] In essence, PISA involves growing AB diblock copolymer chains in a suitable solvent, i.e. a good solvent for the precursor (A) block but a bad solvent for the growing second (B) block
The upper size limit has been established for the preparation of PSMA54−PBzMAx nanoparticles via PISA at 20% w/w solids
The power-law relationship between hydrodynamic diameter and PBzMA degree of polymerization (DP) enables convenient targeting of any desired particle size up to this limiting value
Summary
Polymerization-induced self-assembly (PISA) has become widely recognized as a powerful platform technology for the rational synthesis of sterically stabilized diblock copolymer nano-objects with various morphologies.[1−5] One of the main advantages of PISA is its versatility: it can be conducted in water,[6−11] polar solvents,[12−19] or non-polar media.[20−29] In essence, PISA involves growing AB diblock copolymer chains in a suitable solvent, i.e. a good solvent for the precursor (A) block but a bad solvent for the growing second (B) block This scenario leads to in situ self-assembly to produce sterically stabilized diblock copolymer nanoparticles whose final copolymer morphology (e.g., spheres, worms/cylinders, or vesicles) should be primarily governed by the relative block volume fractions.[29,30] In practice, using a relatively long A block usually leads to the formation of kinetically trapped spheres.[31] In principle, the design rules for PISA are generic, and various (pseudo)living polymerization chemistries should be applicable. There are at least two examples of anionic polymerization being utilized for the formation of diblock copolymer nano-objects.[32,33] the vast majority of the PISA literature is based on reversible addition−fragmentation chain transfer (RAFT) polymerization, which offers exceptional tolerance of monomer functionality and can be conducted directly in protic solvents.[34−38]
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