Macroinitiators reaction with ethylene

A conceptually similar approach was used by Muhlbach and Schulz [96] to prepare a styrene and l-azabicyclo[4.2.0]octane block copolymer. By end-capping living PSt with ethylene oxide, and subsequent reaction with bromoacetyl bromide, a polymer with bromoacetyl groups was obtained which, together with AgCl04, acted as a macroinitiator for a living polymerization of the cyclic monomer (Scheme 11.26). Very little homopolymer was formed, however. Two distinct glass transition temperatures, at 10 and 94 °C, were observed with the block copolymer that corresponded to the poly(l-azabicyclo[4.2.0]octane) and PSt sequences, respectively, and indicated that the blocks were incompatible and phase-separated. 

Recently, several other aminopolymers were synthesized for the NCA polymerization. Ichie and coworkers used copolymers of styrene-vinyl benzylamine and methyl methacrylate-vinyl benzylamine for NCA polymerization to study the kinetics of NCA polymerization with macroinitiators. 2 The polymerization was Ist-order with respect to monomer concentration and was much faster in nitrobenzene than in dioxane or THF. Kiba patented a new system for NCA polymerization with the different aminopolymers [38] produced according to Scheme 5. He also claimed the ester exchange reaction of the resulting graft copolymer with ethylene cyanohydrin over p-toluene sulfonic acid. 

In the second method, the alkoxyamine-ftmctionalized backbone is prepared by a chemical modification of a preformed polymer. Abbasian and Entezami prepared alkoxyamine-functionalized poly(vinyl chloride) (PVC) in a three-step procedure. PVC was first arylated with toluene by Friedel-Crafts acylation followed by a bromination step using N-bromosuccinimide. The bromine atom was finally reacted via nucleophilic substitution by the TEMPO hydro-xylamine anion. PVC-g-PS was finally obtained after TEMPO-mediated polymerization of styrene. A TEMPO-functionalized isotactic poly(l-butene) macroinitiator was synthesized by Jo et al. who used a rhodium-catalyzed activation of the alkane C-H bonds and subsequent transformations of the boronate ester group into an hydroxyl pendant group. This reactive moiety was then used to attach a TEMPO-based alkoxyamine bearing another hydroxy function by an ether linkage. A method to prepare PE-g-PS from a poly(ethylene-co-m,p--methylstyrene) obtained by metallocene-catalyzed polymerization was also reported. The macroalkoxya-mine was synthesized after bromination with N-bromosuccinimide followed by a nucleophilic reaction with the TEMPO hydroxylamine anion. 

Considerable effort has been carried out by different groups in the preparation of amphiphihc block copolymers based on polyfethylene oxide) PEO and an ahphatic polyester. A common approach relies upon the use of preformed co- hydroxy PEO as macroinitiator precursors [51, 70]. Actually, the anionic ROP of ethylene oxide is readily initiated by alcohol molecules activated by potassium hydroxide in catalytic amounts. The equimolar reaction of the PEO hydroxy end group (s) with triethyl aluminum yields a macroinitiator that, according to the coordination-insertion mechanism previously discussed (see Sect. 2.1), is highly active in the eCL and LA polymerization. This strategy allows one to prepare di- or triblock copolymers depending on the functionality of the PEO macroinitiator (Scheme 13a,b). Diblock copolymers have also been successfully prepared by sequential addition of the cyclic ether (EO) and lactone monomers using tetraphenylporphynato aluminum alkoxides or chloride as the initiator [69]. 

Pan et al. prepared a macroinitiator by chloromethylation of a commercially available AB block copolymer of poly (styrene-fe-ethylene-co-propylene) (SEP) and used it as a macroinitiator for the ATRP of ethyl methacrylate (EM A) [302]. The kinetic plot showed little evidence of termination during the reaction and the molecular weight of the graft copolymer increased linearly with the monomer conversion, resulting in a final Mn=73,200 and Mw/Mn=1.22. The weight ra-... 

Polymerizations of benzyl methacrylate (BzMA) were carried out in a toluene- /g solution with (i) a PEG-based macroinitiator, MeOPEG-lin, and (ii) ethylene glycol diethyl ether as co-solvent. According to the previous study, the reaction temperature was kept at 50°C in order to keep control over the polymerization. 

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