Silica cation polymerization

According to Tsubokawa et al. (18), the molecular weight of grafted polystyrene from radical polymerization at the surface of silica is considerably higher than that from cationic polymerization. 

Scheme 12.13 Cationic polymerization from an ion pair formed from silanol and diaryl halide on silica surface.

By following the known synthetic route to cationically polymerized VFA [61] it should also have been feasible to co-polymerize this monomer we showed, however, that co-polymerization of VFA in the presence of silica was impossible for mechanistic reasons [62]. Therefore we co-polymerized VFA radically using two different synthetic strategies. In the first we polymerized VFA with l,3-divinylimidazolidin-2-one (BVU) as co-monomer in... 

R548 S. Spange, Silica Surface Modification by Cationic Polymerization and Carbenium Intermediates , Prog. Polym. Sci., 2000, 25, 781... 

Zinc, calcium and magnesium oxides, silica gel, and other compounds are used as solid additives in radiation-induced polymerization carried out by a cationic mechanism. Recently, Crivello shown that very useful for electron-beam induced cationic polymerization are onium salts, which presence in the systems allow to achieve high conversion of monomers at very low doses [5, 6],... 

Porous silica-supported polymeric catalysts were prepared by sulfonation of divinylbenzene (DVB) or styrene-DVB copolymers with chlorosulfonic acid. The resultant acidic polymers had an ion-exchange capacity of up to 0.41 mequiv. g. ° Treatment of the styrene-divinylbenzene copolymer (one part) with chlorosulfonic acid (three to four parts) in 1,2-dichloroethane at 10-25 afforded the cation-exchange resin. ... 

The polymerization of alloocimene [121] is reported in the patent literature I39-I41). Silica gel, synthetic silicates, and various Lewis acids were used as the catalysts. However, no details concerning the structure of the polymeric products were given. More recently, the cationic polymerization of alloocimene was investigated by Jones (71). An intra-intermolecular polymerization mechanism was postulated (11-57). The iodine number of the polymer indicated the loss of two double bonds per monomer unit during polymerization. Interestingly, the use of Ziegler-type catalysts did not yield cyclic polymeric structures (95, 96). 

Copper triflate is an efficient catalyst in the cationic polymerization of styrene. However, its grafting onto a silica surface enhanced the overall reactivity of the catalyst providing faster conversions and polymers with higher molecular weight [98]. Only little leaching of species from the supported catalyst was reported. The initiation with Cu(OTl)2-silica catalyst occurs via a catalyst/cocatalyst process between the Lewis acid species and mostly the water present in the system. The latter originated from both the hydration water molecules of Cu(OTf)2 and the adventitious moisture. The surface silanol groups of the catalyst and the physisorbed solvent (methanol) from the catalyst preparation were also mentioned to play a cocatalytic role [98]. 

Silica Polymei Metal Ion Interactions in Solution. The reaction of metal ions with polymeric sihcate species in solution may be viewed as an ion-exchange process. Consequently, it might be expected that sihcate species acting as ligands would exhibit a range of reactivities toward cations in solution (59). Sihca gel forms complexes with multivalent metal ions in a manner that indicates a correlation between the ligand properties of the surface Si-OH groups and metal ion hydrolysis (60,61). For Cu +, Fe +, Cd +, and Pb +,... 

The use of bonded, silica column supports has also become a useful way to characterize cationic, water-soluble polymers. CATSEC SEC columns from Micra Scientific contain a silica support with a polymerized polyamine-bonded phase. This imparts a cationic surface charge on the packing that can be... 

The insolubilization of cations and anions during the setting and hardening process is thus paralleled by that of silica. Under add conditions orthosilicic add condenses first to form polymeric silidc add and then silica gel (Her, 1979 Andersson, Dent Glasser Smith, 1982). These processes are discussed more fully in Section 6.5.4. Gelation of silica, like the formation of salt gels, is enhanced by a reduction in the acidity of solutions. 

The first reversed-phase SPE sorbents were based on silica gel particles, similar to the particles used in HPLC. A number of phases are available ranging from C8 to C18 to anion- and cation-exchange functionalities. Recent advances in particle technology have included polymeric materials that combine the benefits of a water-wettable particle to retain polar analytes with a reversed-phase, hydrophobic moiety to... 

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