Grafting from reactions

Systems examined include copolymerizations of 349 with MMA using RAFT agent 175,548,711 348 with AA using 2207 0 and 348 with 352 using 176.7 4 The latter copolymerization created a precursor for a grafting from reaction by ATRP using the bromoisobutyrate group as an initiator/34... 

More recently, the scope of using hyperbranched polymers as soluble supports in catalysis has been extended by the synthesis of amphiphilic star polymers bearing a hyperbranched core and amphiphilic diblock graft arms. This approach is based on previous work, where the authors reported the synthesis of a hyperbranched macroinitiator and its successful application in a cationic grafting-from reaction of 2-methyl-2-oxazoline to obtain water-soluble, amphiphilic star polymers [73]. Based on this approach, Nuyken et al. prepared catalyticaUy active star polymers where the transition metal catalysts are located at the core-shell interface. The synthesis is outlined in Scheme 6.10. 

Starting from a hyperbranched polyester based on 4,4 -bis(hydroxyphenyl)valeric acid, terminal -OH groups were derivatized to yield the hyperbranched macroinitiator. The Hgand precursor was introduced as the first block in the grafting from reaction, followed by 2-methyl-2-oxazoHne polymerization to give the second block and allow for water-soluble polymers. The triphenylphosphine-functionalized am-phiphihc star block copolymer was obtained after transformation of the iodoaryl... 

A special case of "grafting from" reaction is the chemical modification that can be induced on a metalated backbone chain by micromolecular reagents. A recent example of such reactions is the oxidation of metalated sites on a polystyrene chain, yielding vinylphenol units. It has been shown that in this case metalation (using BuLi, TMEDA) is located on the phenyl rings. 

PE Graft Copolymers Prepared by Graft-from Reactions... 

The lithiated polyethylene copolymer was then suspended in hexane or THF solvent. The graft-from reactions were carried out in slurry solution by reacting the lithiated polyethylene copolymer with anionic polymerizable monomers, such as styrene and p-methylstyrene. After certain reaction time, 10 ml of isopropanol was added to terminate the graft-from reaction. The precipitated polymer was filtered and then subjected to fractionation. Good solvents for backbone and side chain polymers were used during the fractionization, using a Soxhlet apparatus under N2 for 24 hours. The soluble fractions were isolated by vacuum-removal of solvent. Usually, the total soluble fractions were less than 5 % of the product. The major insoluble fraction was PE graft copolymer, which was completely soluble in xylene or trichlorobenzene at elevated temperatures. 

Anionic sites suitable for grafting from reactions can be introduced by met-allation, involving the complexation of a hydrocarbon polymer by oiganolithium compounds. The reaction is assisted by complexing the lithium first with tetrame-thylenediamine, which acts as a solvating base. Aromatic chlorine is readily exchanged for lithium, which then acts as an initiator for the anionic polymraization of suitable monomers. 

Scheme 7.8 Grafting from reaction of MMA onto alginate backbone...

Lu, H. L. and Chung, T. C. 1999. Synthesis of PP graft copolymers via anionic living graft-from reactions of polypropylene containing reactive p-methylstyrene units. Journal of Polymer Science, Part A Polymer Chemistry 37 4176—4183. 

Graft Polymerizations.—Cationic graft polymerizations may be classified under two principal headings (/) grafting onto reactions in which propagating macrocations are terminated on a substrate, and (h ) grafting from reactions in which the substrate is employed as a macro-initiator for cationic polymerization. 

Examples of grafting from reactions are far more numerous in the recent literature. Poly(vinyl chloride) (PVC) has been used frequently as a macro-initiator for cationic polymerizations. Active centres on the PVC backbone can be generated by radiolytic or chemical methods. Various chemical coinitiators including EtjAlCl, AgPF, and AgSbFe have been employed to induce the cationic polymerization of vinyl and heterocyclic monomers from the backbone. 

A suitable functional group on the surface of the microgel could be an azo-moiety which can be utilized to start a grafting from reaction in order to synthesize core-shell or star-like... 

The primary requirement for a successful grafting from reaction is a preformed macromolecule with distributed initiating functionality (Scheme 19). 

Grafting from reactions have been conducted from polyethylene, poly(vinyl chloride),and polyisobutylene. ... 

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