Application of cationic polymerization to grafting and coating of silica particles

Abstract

The cationic polymerization of electron rich monomers such as vinyl ethers, vinyl furane, and cyclopentadiene on silica surfaces can be initiated by aryl methyl halides. The reactions yield always soluble polymers (by heterogeneous catalysis) and novel polymer/silica hybrid materials. The link between polymer and solid is caused by covalent Si‐O‐C bonds, by network formation of the polymers during the chain growth, or by a combination of both of them. The analysis of the polymer structures on the surface by 1H MAS NMR spectroscopy in suspension and by solid state 13C CP MAS NMR spectroscopy is described. Proof of Si‐O‐C bonds via DRIFT spectroscopy and 13C CP MAS NMR spectroscopy is given. The most effective method of irreversibly linking the polymer to the silica surface is the network formation. Polyvinyl ethers are bound strongly to the surface, as can be shown by FTIR measurements, but the linkage is not stable due to the Si‐O‐C bonds' susceptibility to hydrolysis. Poly‐cyclopentadienes (PCPD) are linked to the surface by Si‐O‐C bonds, which show an extraordinary high resistance to acids and bases. Si‐O‐C bond formation of poly‐2‐vinyl furane could not yet be detected by 13C CP MAS NMR spectroscopy and DRIFT spectroscopy. In this case the high degree of coating derives from the bifunctionality of 2‐vinyl furane: it may undergo Friedel‐Crafts‐alkylation at the 5‐position of the furane ring as well as chain polymerization via the vinyl group at the 2‐position.

Cationic surface polymerization of 1,3-divinylimidazolid-2-one for immobilization on silica gel particles

“…Therefore, the propagating cationically active chain is strongly located on the particle surface. However, both types of ion pairs, silanolate and halide silanol bridges, can contribute to the propagation mechanism when an excess of (C 6 H 5 ) 3 CCl is used in conjunction with silica [19][20][21][22] . Due to the high cationic reactivity of the BVH, the surface polymerization proceeds effectively even at room temperature.…”

“…From solid state 1 H-MAS-NMR investigations, a silanolate-carbenium ion pair should be present as reactive intermediate 22) . Therefore, the propagating cationically active chain is strongly located on the particle surface.…”

“…Cationic surface polymerization as tool for functionalization of neat silica particles is suitable when Si1O1C bonds are formed associated with controlled structure formation 17,18) or by a defined surface polymerization of the monomer on silica particles 19) . A combination of both processes is advantageous because the hydrolytically unstable Si1O1C -linkages are shielded by crosslinked polymer [20][21][22] . In a previous paper we reported that it is possible to polymerize cationically vinylformamide (VFA) by arylmethyl halides supported on a silica gel surface or by iodine 23) .…”

Formation of surface-grafted polymeric amphiphilic coatings comprising ethylene glycol and fluorinated groups and their response to protein adsorption

“…One concern when working with organosilane modifiers involves the stability of the Si-O-C bond, which is known to be susceptible to large variations in solution pH. 20 In Appendix C we provide details of stability experiments, which indicate that both mF8H2-PHEMA and tF8H2-PHEMA remained stable for many hours when exposed to solutions whose pH ranged from 4 to 9.…”

“…52 In order to test the stability of the organosilane-modified PHEMA, we exposed mF8H2-and tF8H2-based PHEMA samples to solutions of various pH ranging from 4 to 9. We measured the thickness of the layer before and after the deposition for extended periods of time.…”