Branching cationic chain polymerization

The use of nanofiltration membranes as supporting membranes have been also reported [28]. In this case, direct filtration of ionic liquids through the nanofiltration membrane was not possible at a gas pressure up to 7 bars. The ionic liquids with cations associated with straight or branched hydrocarbon chains were easily absorbed into the polymeric membrane allowing the nanoporous structure saturated with the ionic liquids. 

Monomer Reactivity. The nature of the side chain R group exerts considerable influence on the reactivity of vinyl ethers toward cationic polymerization. The rate is fastest when the alkyl substituent is branched and electron-donating. Aromatic vinyl ethers are inherently less reactive and susceptible to side reactions. These observations are shown in Table 2. 

Chain growth occurs through a nucleophilic attack of the carbanion on the monomer. As in cationic polymerizations, lower temperatures favor anionic polymerizations by minimizing branching due to chain transfer reactions. 

Indeed, cumyl carbocations are known to be effective initiators of IB polymerization, while the p-substituted benzyl cation is expected to react effectively with IB (p-methylstyrene and IB form a nearly ideal copolymerization system ). Severe disparity between the reactivities of the vinyl and cumyl ether groups of the inimer would result in either linear polymers or branched polymers with much lower MW than predicted for an in/mcr-mediated living polymerization. Styrene was subsequently blocked from the tert-chloride chain ends of high-MW DIB, activated by excess TiCU (Scheme 7.2). 

One chapter in this series deals with the newer use of cationic polymerization to form polymers and copolymers with controlled long-chain branched struc-... 

Unwanted branching of many polymers probably occurs through such isomerizations. PP, formed using cationic polymerization, has methyl, ethyl, w-propyl, w-butyl, isopropyl, gem-dimethyl, isobutyl, and t-butyl groups connected to the main chain. 

Propylene has been polymerized with highly cationic catalysts such as aluminum chloride plus ethyl chloride (61). However, this polypropylene was amorphous and considerably different from the Ziegler-Natta polypropylene. It had large amounts of chain branching which resulted from the highly cationic nature of this catalysts. Olah, Quinn and Kuhn (62) have studied the cationic polymerization of propylene utilizing complexes of BF3 with various alkyl fluorides. Apparently these cationic catalysts produced only amorphous polymers. 

A macromonomer is a macromolecule with a reactive end group that can be homopolymerized or copolymerized with a small monomer by cationic, anionic, free-radical, or coordination polymerization (macromonomers for step-growth polymerization will not be considered here). The resulting species may be a star-like polymer (homopolymerization of the macromonomer), a comblike polymer (copolymerization with the same monomer), or a graft polymer (copolymerization with a different monomer) in which the branches are the macromonomer chains. 

This article surveys the research work on the synthesis and modification reactions of poly(ethyleneimine) as well as its applications to metal complexation processes. Poly-(ethyleneimine), one of the most simple heterochain polymers exists in the form of two different chemical structures one of them is branched, which is a commercially available and the other one linear which is synthesized by cationic polymerization of oxazoline monomers and subsequent hydrolysis of polyf(/V acylimino)cthylcne]. The most salient feature of poly(ethyleneimine) is the simultaneous presence of primary, secondary, and tertiary amino groups in the polymer chain which explains its basic properties and gives access to various modification reactions. A great number of synthetic routes to branched and linear poly(ethyleneimine)s and polymer-analogous reactions are described. In addition, the complexation of polyfethyleneimine) and its derivatives with metal ions is investigated. Homogeneous and heterogeneous metal separation and enrichment processes are reviewed. 

Chain branching occurs in cationic polymerization much as it does in free-radical polymerization. Propose a mechanism to show how branching occurs in the cationic polymerization of styrene. Suggest why isobutylene might be a better monomer for cationic polymerization than styrene. 

Chain branching is not as common with anionic polymerization as it is with free-radical polymerization and cationic polymerization. 

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