Creating Surfactant Nanoparticles for Block Copolymer Composites through Surface Chemistry

Abstract

A simple strategy to tailor the surface of nanoparticles for their specific adsorption to and localization at block copolymer interfaces was explored. Gold nanoparticles coated by a mixture of low molecular weight thiol end-functional polystyrene (PS-SH) (Mn = 1.5 and 3.4 kg/mol) and poly(2-vinylpyridine) homopolymers (P2VP-SH) (Mn = 1.5 and 3.0 kg/mol) were incorporated into a lamellar poly(styrene-b-2-vinylpyridine) diblock copolymer (PS-b-P2VP) (Mn = 196 kg/mol). A library of nanoparticles with varying PS and P2VP surface compositions (FPS) and high polymer ligand areal chain densities was synthesized. The location of the nanoparticles in the PS-b-P2VP block copolymer was determined by transmission electron microscopy. Sharp transitions in particle location from the PS domain to the PS/P2VP interface, and subsequently to the P2VP domain, were observed at FPS = 0.9 and 0.1, respectively. This extremely wide window of FPS values where the polymer-coated gold nanoparticles adsorb to the interface suggests a redistribution of PS and P2VP polymers on the Au surface, inducing the formation of amphiphilic nanoparticles at the PS/P2VP interface. In a second and synthetically more challenging approach, gold nanoparticles were covered with a thiol terminated random copolymer of styrene and 2-vinylpyridine synthesized by RAFT polymerization. Two different random copolymers were considered, where the molecular weight was fixed at 3.5 kg/mol and the relative incorporation of styrene and 2-vinylpyridine repeat units varied (FPS = 0.52 and 0.40). The areal chain density of these random copolymers on Au is unfortunately not high enough to preclude any contact between the P2VP block of the block copolymer and the Au surface. Interestingly, gold nanoparticles coated by the random copolymer with FPS = 0.4 were dispersed in the P2VP domain, while those with FPS = 0.52 were located at the interface. A simple calculation for the adsorption energy to the interface of the nanoparticles with different surface arrangements of PS and P2VP ligands supports evidence for the rearrangement of thiol terminated homopolymers. An upper limit estimate of the adsorption energy of nanoparticles uniformly coated with a random arrangement of PS and P2VP ligands where a 10% surface area was occupied by P2VP -mers or chains was approximately 1 kBT, which indicates that such nanoparticles are unlikely to be segregated along the interface, in contrast to the experimental results for nanoparticles with mixed ligand-coated surfaces.

Living Radical Polymerization by the RAFT Process - A Second Update

“…St [184] MMA [88] 323 [185] 40 [186] S S O O St [186] St-b-MAH [186] St-b-MAH-b-NIPAM [186] 41* [187,188] S S (MMA) [64,187,189] BA [187] EHA [188] St [190] TBAM [191] DEAM [187] DMAM [187] NAM [191] NIPAM [187,189] BA/St [192] EHA-b-MA [188] TBAM-b-NAM [191] DMAM/NAS [193] NAM-b-TBAM [191] 42* S S Ph CN MMA [194] 376 [195] 376-b-MMA [195] BA [196] MMA [189] NIPAM [189] MMA-b-NIPAM [189] MMA/283 [197] MMA/284 [197] St/2VP [198] St/348 [199] THPA-b-St [200] THPA-b-St/373 [201] 44 [202] [200] 47 [203] …”

“…This approach has been used to make inorganic (TiO 2 , SnO 2 or ZnO) nanorods [102] or CdSe/ZnS quantum dots [538] with PAA-b-PSt, [539] P(AEME-co-328-co-342) [278] or semiconductor (P364 or P365) arms, gold nanoparticles with PSt, [476] PSt-b-P2VP, [198] PDMAEMA, PAA, or PSt, [91] P(340-co-AM) or P(341-co-AM), [239] PPEGA-b-PNIPAM, [217] PMMAb-PNIPAM, [189] or P(DEGMA-co-tBA), P(DEGMA-co-tBA)-b-PGMA, PGMA, PSt [398] grafts, magnetic iron with PNIPAM grafts, [305] silver nanoparticles with PSt grafts, [409] chitosan with PAA grafts, [487] and silicon wafers with NIPAM grafts. [273] Silicon wafers and silica particles have also been modified with multiple layers of an amine-functional polymer, polyethyleneimine or poly(allylamine hydrochloride), respectively, and PAA-bPSSO3Na in a layer-by-layer assembly process.…”

Modification of RAFT‐polymers via thiol‐ene reactions: A general route to functional polymers and new architectures

“…1,[9][10][11][12][13][14][15] Like other living radical polymerizations, [16][17][18][19] reversible addition-fragmentation chain transfer polymerization (RAFT) has been increasingly used to create functional polymers and architectures for biological and nanotechnology applications. 9,10, Polymers synthesized by RAFT polymerization contain thiocarbonylthio end groups that can impart instability to the final polymers.…”

Preparation of Neutral Wetting Brushes for Block Copolymer Films from Homopolymer Blends

“…This method provides a general approach to screen neutral blend composition windows for block copolymers without the need to synthesize functionalized random copolymers, and also makes it possible to prepare neutral brushes for copolymers with monomer pairs that are difficult to be randomly copolymerized. Such a technique could find application anywhere where it is desirable to have both blocks of a copolymer interacting with a surface equally, such as in the surface modification of particles [61,62] or in coating applications.…”