Styrene multifunctional catalysts

Epoxy resins and other polymers (tetrahydrofuran, vinyl ethers, styrene, etc.) can be cured when exposed to an acid or cation intermediate species. The photoactive catalyst system commonly used to cure epoxy resins and multifunctional vinyl ether materials is composed of salts of aryldiazonium, triarylsulfonium, and diaryliodonium. These systems are commonly employed in coatings and adhesives for electronic products. The acid initiator generated from the photoinitiator continues to be active even after uv curing, and so conversion of reactants and crosslinking continue even in the absence of uv light. This phenomenon is typically referred to as dark cure. 

If the epoxide rearrangement (see chapter 15.2.1) of styrene oxide is carried out in the presence of hydrogen and by use of a bifunctional boron-pentasil zeolite catalyst having a hydrogenation component such as Cu, then 2-phenylethanol is obtained in one step. This hydro-isomerization renders high yields (> 85%) at 250 °C under the gas phase conditions. It is an example for multifunctional catalysis in a one pot-reaction, that means simultaneous rearrangement and hydrogenation. 

Block copolymers between alkyl acrylates such as B-4,358 B-5,202,203 and B-6,203 on the other hand, have been synthesized by the macroinitiator methods mostly with copper catalysts. Star block copolymers with a soft poly(MA) core and a hard poly(isobomyl acrylate) shell were synthesized by using multifunctional initiators.358 Poly(tBA) segments in B-5 and B-6 can be converted into hydrophilic poly(acrylic acid).203 Block copolymers between />methylstyrene and styrene (B-7) were also prepared by the rhenium-catalyzed living radical polymerization in conjunction with an alkyl iodide initiator.169... 

Vinylester (VE) resins are prepared by an addition reaction between epoxy resin (difunctional or multifunctional) with an unsaturated carboxylic acid such as acrylic acid or methacrylic acid [77]. The simplest form of VE is the product of the reaction between one mole of diglycidyl ether of BPA and 2 moles of methacylic acid (Figure 2.21). The reaction is carried out at about 100 °C using a catalyst such as triphenyl phosphine. To stop the polymerisation of methacylic acid, an inhibitor such as hydroquinone is used. By changing the nature of base epoxy resin, various types of VE resins can be produced. The vinyl-ended prepolymer is then dissolved in styrene to produce a polymerisable resin similar to an unsaturated polyester resin. Styrene content is adjusted to provide a wide range of viscosities, typically 0.1-4 Pa-s. 

Using C6o(Cl) (n = 16 to 20) [88] as a multifunctional initiator under ATRP conditions (CuCl/2,2 -bipyridine, toluene, 130 °C), styrene [89] and N-vinylcarbazole [90] could be polymerized (Scheme 5.15). There is experimental evidence that the resulting compounds are star shaped, but the number and length of the arms or the number of residual Cl on the fullerene could not be determined. A thermal polymerization, producing a non-negligible amount of polymer containing no fullerene, is always observed. Nevertheless, the optical-limiting behavior of (PVK)j,C6o(Cl). y approached that of pristine Ca> [90]. This work was further extended to a Ni-based ATRP catalyst system and it was estimated that about two PS arms were attached to C6o(Cl) [91]. 

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