Aqueous fabrication of pH-gated, polymer-brush-modified alumina hybrid membranes.

In this Article, we studied the surface immobilization of five organic-acid-modified atom-transfer radical polymerization (ATRP) initiators based on salicylic acid, catechol, phthalic acid, and m- and p-benzoic acid on alumina, and we also investigated the growth of hydrophilic poly(2-hydroxyethyl methacrylate) (PHEMA) and poly(poly(ethylene glycol)methycrylate) (PPEGMA6) brushes from the resulting initiator-modified substrates. Whereas the surface immobilization of phthalic acid- and benzoic acid-based initiators results in only very thin brushes or no brush growth at all, SI-ATRP of HEMA and PEGMA6 from alumina surfaces modified with salicylate or catechol generates brushes with thicknesses comparable to those obtained using organosilane-based initiators. Most interestingly, the surface immobilization of the catechol- and salicylate based-initiators was found to be pH-dependent, which allowed facile variation of the ATRP initiator surface concentration and, concomitantly, the polymer brush grafting density by adjusting the pH of the aqueous solution that was used to immobilize the initiator. This is in contrast to organosilane-based initiators, where the variation of the grafting density is usually accomplished using mixtures of the ATRP initiator and an ATRP inactive "dummy". Another difference between the organosilane-based initiators and the organic acid analogues is the stability of hydrophilic brushes grown from alumina. After a certain threshold thickness was exceeded, organosilane-tethered PPEGMA6 brushes were observed to detach from the substrate, in contrast to brushes grown from catechol or salicylate initiators, which did not show signs of degradation. Finally, as a first proof-of-concept, the salicylate-based initiator was used to develop an all-aqueous protocol for the modification of alumina membranes with hydrophilic PHEMA and succinic anhydride post-modified polymer brushes. The water permeation properties of these hybrid membranes can be controlled by adjusting the brush thickness in the case of the neutral PHEMA brush coating or can be pH-gated after post-polymerization modification to introduce carboxylic acid groups.

A facile strategy for the modification of polyethylene substrates with non-fouling, bioactive poly(poly(ethylene glycol) methacrylate) brushes.

This manuscript reports a facile strategy for the modification of polyethylene, a widely used biomaterial, with a thin non-biofouling coating that can act as a platform to introduce biochemical cues to control and direct, e.g., cell adhesion and proliferation. The non-biofouling coating is produced, following a two-step strategy involving photobromination of the polyethylene substrate followed by surface-initiated ATRP of poly(ethylene glycol) methacrylate. The resulting coatings, which are referred to as polymer brushes, are robust and withstand prolonged exposure to aqueous ethanol and phosphate buffered saline and also do not show any signs of detachment or degradation in the in vivo studies over a period of 10 d. Functionalization of these polymer brush coatings with extracellular matrix derived peptide sequences, promotes adhesion and spreading of endothelial cells.

Chiral fluorous dialkoxy-diamino zirconium complexes: synthesis and use in stereospecific polymerization of 1-hexene.

New catalysts for the isospecific polymerization of 1-hexene based on cationic zirconium complexes incorporating the tetradentate fluorous dialkoxy-diamino ligands [OC(CF(3))(2)CH(2)N(Me)(CH(2))(2)N(Me)CH(2)C(CF(3))(2)O](2-) [(ON(2)NO)(2-)] and [OC(CF(3))(2)CH(2)N(Me)(1R,2R-C(6)H(10))N(Me)CH(2)C(CF(3))(2)O](2-) [(ON(Cy)NO)(2-)] have been developed. The chiral fluorous diamino-diol [(ON(Cy)NO)H(2), 2] was prepared by ring-opening of the fluorinated oxirane (CF(3))(2)COCH(2) with (R,R)-N,N'-dimethyl-1,2-cyclohexanediamine. Proligand 2 reacts cleanly with [Zr(CH(2)Ph)(4)] and [Ti(OiPr)(4)] precursors to give the corresponding dialkoxy complexes [Zr(CH(2)Ph)(2)(ON(Cy)NO)] (3) and [Ti(OiPr)(2)(ON(Cy)NO)] (4), respectively. An X-ray diffraction study revealed that 3 crystallizes as a 1:1 mixture of two diastereomers (Lambda-3 and Delta-3), both of which adopt a distorted octahedral structure with trans-O, cis-N, and cis-CH(2)Ph ligands. The two diastereomers Lambda-3 and Delta-3 adopt a C(2)-symmetric structure in toluene solution, as established by NMR spectroscopy. Cationic complexes [Zr(CH(2)Ph)(ON(2)NO)(THF)(n)](+) (n=0, anion=[B(C(6)F(5))(4)](-), 5; n=1, anion=[PhCH(2)B(C(6)F(5))(3)](-), 6) and [Zr(CH(2)Ph)(ON(Cy)NO)(THF)](+)[PhCH(2)B(C(6)F(5))(3)](-) (7) were generated from the neutral parent precursors [Zr(CH(2)Ph)(2)(ON(2)NO)] (H) and [Zr(CH(2)Ph)(2)(ON(Cy)NO)] (3), and their possible structures were determined on the basis of (1)H, (19)F, and (13)C NMR spectroscopy and DFT methods. The neutral zirconium complexes H and 3 (Lambda-3/Delta-3 mixture), when activated with B(C(6)F(5))(3) or [Ph(3)C](+)[B(C(6)F(5))(4)](-), catalyze the polymerization of 1-hexene with overall activities of up to 4500 kg PH mol Zr(-1) h(-1), to yield isotactic-enriched (up to 74 % mmmm) polymers with low-to-moderate molecular weights (M(w)=4800-47 200) and monodisperse molecular-weight distributions (M(w)/M(n)=1.17-1.79).