Collapsed polymer nanoparticles

This approach has recently been extended by the same group for the synthesis of noncovalently cross-linked nanoparticles, which can be formed reversibly on application of external stimuli. In this strategy, self-complimentary hydrogen-bonding units are incorporated into the polymer chain at relatively low loadings (about 6%) to afford nanoparticles with sizes around 20 mn. This group has also reported the use of microwave cross-hnking chemistries for the synthesis of collapsed and functionalized polymer nanoparticles. ... 

Meijer et al. [64] described an unusual strategy to obtain metastable supramolecular polymer nanoparticles. Each nanoparticle arose from the collapse of a single polymer chain. This approach relied on a PNBE chain functionalized with a photoactivable quadruple hydrogen-bonding unit, which is able to create intramolecular cross-linking of single chains after deprotection. 

FIG. 13 TEM micrograph of a hollow composite nanoparticle/polymer capsule dried on a carbon grid. The hollow composite capsule was obtained after removal of the ME core from Si02/PDAD-MAC-coated ME particles by treatment with hydrochloric acid. The shadowing seen is a result of collapse and overlapping of the hollow capsule upon drying. (From Ref. 110.)... 

Dendrimer-protected colloids are capable of adsorbing carbon monoxide while suspended in solution, but upon removal from solution and support on a high surface area metal oxide, CO adsorption was nil presumably due to the collapse of the dendrimer [25]. It is proposed that a similar phenomena occurs on PVP-protected Pt colloids because removal of solvent molecules from the void space in between polymer chains most likely causes them to collapse on each other. Titration of the exposed surface area of colloid solution PVP-protected platinum nanoparticles demonstrated 50% of the total metal surface area was available for reaction, and this exposed area was present as... 

Those nanoparticles (3LNPs) were fabricated via a pH-controlled hierarchical self-assembly of a tercopolymer brush (Schemes 10.2 and 10.3), which contained hydrophilic polycaprolactone (PCL) chains, water-soluble PEG chains, and pH-responsive poly[2-(iV,iV-diethylamino)ethyl methacrylate] (PDEA) chains. PDEA is a polybase that is soluble at low pH but insoluble at neutral pH [167-169]. The brush polymer was initially dispersed in a pH 5.0 solution where the PDEA chains were protonated and hence water-soluble. The hydrophobic PCL chains and drug molecules associated to form the hydrophobic core. The PEG and protonated PDEA chains formed a hydrophilic corona surrounding the core. After the solution pH was raised to 7.4, the PDEA chains were deprotonated and became hydrophobic, collapsing on the PCL core as a hydrophobic middle layer with only the PEG chains forming the hydrophilic corona (Scheme 10.3). 

Polyplexes are formed by mixing a poly(nucleic acid) salt (typically the sodium salt) and a cationic polymer. Electrostatic attraction and counterion release leads to a hydrophobic collapse of the polymer-nucleic acid complex into a nanoparticle called a polyplex. 

A similar breaking of the symmetry of the high temperature (good solvent) phase upon side-chain collapse also occurs for an even simpler kind of brush stmcture, a spherical polymer bmsh, and there it also leads to a specific form of intermolecular aggregation. Spherical polymer bmshes formed from (spherical) nanoparticles to... 

Figure 22 Schematic representation of the intramolecnlar collapse of a linear polymer to form a stable nanoparticle. (Reproduced from Ref. 56. American Chemical Society, 2002.)...

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