Pyridine containing polymers cross-linked

A very interesting technique that has been used widely in the MTO-catalyzed olefin oxidation reaction is the microencapsulation technique. This technique uses poly(4-vinylpyridine) (PVP), either 2% or 25% cross-linked with divinylbenzene (PVP-2% or PVP-25%, Fig. 4), as well as poly(4-vinylpyridine-/V-oxide) (PVPN-2%, Fig. 4). In addition, 2% cross-linked PS (PS-2%, Fig. 4, X = CH2) and a mixture of PS-2% and PVP-2% (5 1, Fig. 4, X = N) have been used as support polymers. This approach is based on the physical envelopment of the Lewis-acidic MTO by the PS polymer, enhanced by interactions of the 7t-electrons of the phenyl rings with MTO. In the case of the pyridine-containing polymers, Lewis acid-Lewis base interactions between the pyridine moiety and MTO obviously play an important role. In the case of the PVP and PVPN polymers, MTO can be incorporated in the support matrix by mixing the polymer and MTO in ethanol to obtain the desired immobilized catalyst. 

In the case of dense, surface-grafted polymer brush thin hlms, cross-links are introduced by the simple addition of solutions containing bis(Pd -pincer) compounds 4a or 4b to grafted PVP brushes (Loveless et al. 2006). Because the association constants for pyridine coordination are similar, the uptake of 4a and 4b from equimolar solutions into the PVP brushes (at constant grafting density and molecular weight) is effectively equivalent, producing samples with comparable structure (number and placement of cross-links). 

Similar conductivities are also shown by free radical ions. For example, systems from vinyl pyridine containing copolymers with tetracyano-p-quinodimethane belong to this group. In contrast to cross-linked semiconductor polymers, these systems are soluble and can be cast into films. But they decomposed slowly in air and lose thereby their conductivity. 

The second general approach for the covalent cross-linking was the use of side double bond functionalized copolymers [24]. In this case the synthesis of aromatic polyethers containing polar pyridine units in the main chain and side cross-linkable propenyl groups was the key step. These polymers were subjected to thermal cross-linking with the use of a cross-linker. The effect of the cross-linking on the thermal and mechanical... 

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