Shell Cross-Linked Knedels:  A Synthetic Study of the Factors Affecting the Dimensions and Properties of Amphiphilic Core-Shell Nanospheres

Abstract

Shell cross-linked knedels (SCK's), nanometer-sized spherical particles that are composed of a core-shell morphology, were prepared by intramicellar polymerization of side chain functionalities along the backbone of the hydrophilic block of amphiphilic polystyrene-b-poly(vinylpyridine) block copolymers organized into micellar assemblies. Control over the size of the SCK's was demonstrated through variation of the chemistry and processing conditions. The solid-state SCK diameters (from atomic force microscopy) ranged from 8 to 30 nm, depending upon the chemical composition and micellization time. The relative amount and nature of hydrophilicity in the amphiphilic block copolymer precursor to the SCK's affects the propensity for aggregation, leading to differences in the aggregation numbers of polymer chains within the micelles and to differences in the dimensions of the SCK's. Therefore, increased lengths of the PS (hydrophobic) block in comparison to the PVP (hydrophilic) block gave larger aggregation numbers and larger SCK's. Alternatively, the incorporation of more quaternized sites along the PVP backbone (increased hydrophilicity) gave smaller SCK's. Quaternization of the PVP using poly(ethylene oxide) (PEO) to give water soluble side chain grafts also resulted in decreased SCK diameters and more narrow size distributions, in comparison to the SCK with no PEO. Allowing longer times for micelle formation prior to cross-linking gave larger SCK's and broader size distributions, due to coalescence of the polymer micelles.

Design of naltrexone-loaded hydrolyzable crosslinked nanoparticles

“…They obtained cylindrical structures in water as a selective solvent for poly(ethylene oxide). Thrumond et al (1997) reported on crosslinking of the shell of amphiphilic diblock copolymer micelles. Nanometer-sized spherical particles composed of a core-shell morphology were prepared by intramicellar polymerization of side chain functionalities along the backbone of the hydrophilic block of amphiphilic polystyrene-bpoly(vininylpyridine) block copolymer organized into micellar assemblies.…”

Packaging of DNA by shell crosslinked nanoparticles

“…The SCKs are prepared in a three-step process, including: (i) the synthesis of a linear amphiphilic block copolymer; (ii) self-assembly into spherical micelles in aqueous solution; (iii) stabilization by intramicellar crosslinking of functionalities located within the shell domain. The SCKs used in this study consisted of hydrophobic PS cores and hydrophilic, crosslinked p-chloromethylstyrene-quaternized PVP shells (21). SCKs prepared from polymer chains of 20 700 Da molecular weight and a ratio of PS:PVP repeat units of 1:2 have a solid-state diameter of 9 ± 3 nm and a hydrodynamic diameter of 16 ± 2 nm, determined by AFM and DLS, respectively.…”

“…Tris base (Sigma), sodium acetate (Sigma), EDTA dihydrate (Sigma) and agarose (Fisher) were used as received. The experimental details for the preparation of the SCK nanospheres are described elsewhere (21). The SCK composition consisted of a polystyrene (PS) core encapsulated within a layer of poly(4-vinyl pyridine) (PVP) that had been quaternized with 4-chloromethylstyrene to provide crosslinking throughout the shell layer.…”

“…The SCK composition consisted of a polystyrene (PS) core encapsulated within a layer of poly(4-vinyl pyridine) (PVP) that had been quaternized with 4-chloromethylstyrene to provide crosslinking throughout the shell layer. The ratio PS:PVP was 1:2, with 46% of the pyridyl nitrogens quaternized by reaction with 4-chloromethylstyrene (21).…”

Synthesis and Solution Self‐Assembly of Polyisoprene‐block‐poly(ferrocenylmethylsilane): A Diblock Copolymer with an Atactic but Semicrystalline Core‐Forming Metalloblock

“…[340][341][342] BCPs that have corona-forming blocks such as PI and PMVS with pendant vinyl groups within the polymer backbone have been shown to undergo Ptcatalysed hydrosilylation crosslinking with tetramethyldisiloxane and Karstedt's catalyst, 221,[343][344][345][346] or by UV-initiated crosslinking. 34,347 As a result of this shell-crosslinking, the micellar structures are essentially locked in and are preserved even if they are transferred from a corona-selective solvent into a common solvent for both blocks.…”