title: How Do Spherical Diblock Copolymer Nanoparticles Grow during RAFT Alcoholic Dispersion Polymerization?
abstract: A poly(2-(dimethylamino)ethyl methacrylate) (PDMA) chain transfer agent (CTA) is used for the reversible addition-fragmentation chain transfer (RAFT) alcoholic dispersion polymerization of benzyl methacrylate (BzMA) in ethanol at 70 °C. THF GPC analysis indicated a well-controlled polymerization with molecular weight increasing linearly with conversion. GPC traces also showed high blocking efficiency with no homopolymer contamination apparent andMw/Mnvalues below 1.35 in all cases.1H NMR studies confirmed greater than 98% BzMA conversion for a target PBzMA degree of polymerization (DP) of up to 600. The PBzMA block becomes insoluble as it grows, leading to thein situformation of sterically stabilized diblock copolymer nanoparticles via polymerization-induced self-assembly (PISA). Fixing the mean DP of the PDMA stabilizer block at 94 units and systematically varying the DP of the PBzMA block enabled a series of spherical nanoparticles of tunable diameter to be obtained. These nanoparticles were characterized by TEM, DLS, MALLS, and SAXS, with mean diameters ranging from 35 to 100 nm. The latter technique was particularly informative: data fits to a spherical micelle model enabled calculation of the core diameter, surface area occupied per copolymer chain, and the mean aggregation number (Nagg). The scaling exponent derived from a double-logarithmic plot of core diameter vs PBzMA DP suggests that the conformation of the PBzMA chains is intermediate between the collapsed and fully extended state. This is in good agreement with1H NMR studies, which suggest that only 5-13% of the BzMA residues of the core-forming chains are solvated. TheNaggvalues calculated from SAXS and MALLS are in good agreement and scale approximately linearly with PBzMA DP. This suggests that spherical micelles grow in size not only as a result of the increase in copolymer molecular weight during the PISA synthesis but also by exchange of individual copolymer chains between micelles and/or by sphere-sphere fusion events.
authors.affiliation: Dainton Building, Department of Chemistry, University of Sheffield , Brook Hill, Sheffield, South Yorkshire S3 7HF, U.K.
authors.forename: E R
authors.initials: ER
authors.lastname: Jones
authors.affiliation: Dainton Building, Department of Chemistry, University of Sheffield , Brook Hill, Sheffield, South Yorkshire S3 7HF, U.K.
authors.forename: O O
authors.initials: OO
authors.lastname: Mykhaylyk
authors.affiliation: DSM Ahead , P.O. Box 18, 6160 MD Geleen, The Netherlands.
authors.forename: M
authors.initials: M
authors.lastname: Semsarilar
authors.affiliation: DSM Ahead , P.O. Box 18, 6160 MD Geleen, The Netherlands.
authors.forename: M
authors.initials: M
authors.lastname: Boerakker
authors.affiliation: DSM Ahead , P.O. Box 18, 6160 MD Geleen, The Netherlands.
authors.forename: P
authors.initials: P
authors.lastname: Wyman
authors.affiliation: Dainton Building, Department of Chemistry, University of Sheffield , Brook Hill, Sheffield, South Yorkshire S3 7HF, U.K.
authors.forename: S P
authors.initials: SP
authors.lastname: Armes