Friedel-Craft crosslinking

Acyclic C5. The C5 petroleum feed stream consists mainly of isoprene which is used to produce rubber. In a separate stream the linear C5 diolefin, piperylene (trans and cis), is isolated. Piperylene is the primary monomer in what are commonly termed simply C5 resins. Small amounts of other monomers such as isoprene and methyl-2-butene are also present. The latter serves as a chain terminator added to control molecular weight. Polymerization is cationic using Friedel-Crafts chemistry. Because most of the monomers are diolefins, residual backbone unsaturation is present, which can lead to some crosslinking and cyclization. Primarily, however, these are linear acyclic materials. Acyclic C5 resins are sometimes referred to as synthetic polyterpenes , because of their similar polarity. However, the cyclic structures within polyterpenes provide them with better solvency power and thus a broader range of compatibility than acyclic C5s. 

Friedel—Crafts reactions with halomethyl aromatic compounds have been used to prepare several types of polymers. The reaction is usually unsatisfactory because of the formation of either low-molecular-weight or crosslinked polymers. Rate studies are complicated by the multifunctional nature of the reactants, and often by limited solubility of the products. The kinetics of the first two steps of the reaction between benzene and p-bis-chloromethylbenzene with SnC catalysts were investigated by Grassie and Meldrum [212]. The activation energy was found to be about 10 kcal mole . ... 

Topchiev has reported obtaining a 1,6 polymerization with styrene, resulting in a polymer with structure II. Catalysts used included AICI3-VOCI3 (41). It has been suggested that the product is not II, but rather a crosslinked self-alkylation product brought about by Friedel-Crafts reaction (12). 

Ando et al. [62, 63] suggested using unreacted double bonds in swollen styrene-DVB copolymers, which also react with aromatic rings via Friedel-Crafts reaction forming rigid crosslinks ... 

Friedel-Crafts reaction can proceed in a rather limited number of inert solvents, such as aliphatic hydrocarbons, benzene, nitrobenzene, CS2, and chlorinated or fluorinated hydrocarbons. Among these solvents, however, only chlorinated hydrocarbons, particularly EDC, nitrobenzene, as well as cyclohexane at an elevated temperature, are suited for the synthesis of hypercrosslinked polystyrene, since they are thermodynamically good solvents for both the initial polystyrene and the final products of crosslinking. 

Spectrum. On the other hand, this band is revealed in the spectrum of the styrene-0.6% DVB copolymer intensively crosslinked with 1 mol of MODE, which contains a comparable amount (1%) of pending chlorine. It is quite possible that industrial MN-200 contains chlorine of a different kind. A part of rather inert chlorine in the form of chloroethyl groups may have originated by the involvement of EDO into the Friedel—Crafts reaction. One may also assume that the initial copolymer of that product incorporates more DVB thus the unreacted pendent double bonds may have interacted with MCDE during the post-crosslinking reaction, leading to the formation of methyl chloropropyl ether fragments [105] ... 

As already mentioned in Chapter 6, Section 4, appropriate solvents for conducting Friedel—Crafts crosslinking reaction of polystyrene are EDC, tetrachloroethane, nitrobenzene, and cyclohexane (at an elevated temperature). While the products prepared in the first two solvents are identical in aU their swelling behavior, the character of swelling of materials obtained in nitrobenzene is different. 

Other types of hypercrosslinked sorbents, namely commercial Lewatit EP63, laboratory samples obtained by post-crosslinking styrene-DVB copolymer with CCI4 [55], by self-crosslinking macroporous copolymer of vinylbenzyl chloride with 20% DVB via Friedel-Crafts reaction [56], or by bridging preliminary chloromethylated macroporous styrene-DVB copolymer [57, 58], are all superior to XAD-2, XAD-4, and activated carbon Ambersorb XE340 with respect to phenol and nitrophenol removal. Material [20%-VBC(F.C.)] retains 2,4-dichlorophenol much stronger than unsubstituted phenol, and, therefore, the presence of phenol in the solution does not impact the retention of the chlorinated phenol. On the contrary, the sorption of phenol from the binary solution depends heavily on the concentration of 2,4-dichlorophenol. 

Jefabek et al. [79] reported the adsorption of furfural onto the hypercrosslinked sorbents prepared by post-crosslinking both chloro-methylated gel-type styrene-5% DVB copolymer and chloromethylated macroporous copolymer of styrene with 8% DVB via Friedel-Crafts... 

The resins can be crosslinked by heating with Friedel-Crafts catalysts. It is assumed that the nitrile groups are forming triazines by heating. Even without Friedel-Crafts catalysts crosslinking is possible however, the reaction proceeds slowly. The materials are intended for use as laminating... 

Polystyrene can also crosslink by a Friedel-Craft reaction ... 

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