Cationic ring-opening polymerization CROP

The living cationic ring opening polymerization (CROP) of 2-oxazolines was first reported in the 1960s [61, 62]. The polymerization can be initiated by an electrophile such as benzyl halides, acetyl halides, and tosylate or triflate derivatives. The typical polymerization mechanism for 2-alkyl-2-oxazoline initiated by methyl tosylate is shown in Scheme 6. 

Cationic Ring-Opening Polymerization (CROP) of Oxetanes... 

Living cationic ring-opening polymerization (CROP) techniques represent important methods for the polymerization of a wide variety of heterocyclic monomers, such as cyclic ethers, cyclic amines, and cyclic imino ethers [7, 84-87]. The main differences between carbocationic polymerization of vinyl monomers and CROP of heterocyclic monomers arise from the nucleophilic heteroatoms... 

A transformation from cationic ring-opening polymerization (CROP) to ATRP, or vice versa, can also be effected, as shown below. 

FIGURE 3.6 Cationic ring-opening polymerization (CROP) of meso-lactic acid dimer toward poly(D,L-lactide). 

The earliest reported PHAI was hyperbranched PEI (B-PEI), synthesized by the cationic ring-opening polymerization (CROP) of aziridine in water. The formation of a hyperbranched structure is due to the high nucleophilicity of the amino groups in both the monomer and the polymer causing significant chain transfer of cationically growing chains to already formed polymer chains, followed by reinitiation of a new chain by so-called proton transfer (Scheme 2.2). 

Yoshida and Sugita [72, 73] have described the synthesis of polytetrahydrofuran (PTH F) possessing a nitroxy radical by terminating the Hving cationic ring-opening polymerization (CROP) of THF with sodium 4-oxy TEMPO. The polymer obtained in this way acted as a counter-radical in the polymerization of styrene, in the presence of a free radical initiator, to yield PSt-f)-PTHF (Scheme 11.16). 

Transformation of cationic polymerization to ATRP is one of the most widely utilized methodologies in this approach. The method is simply based on the synthesis of a segment with halide functionality at its one or both ends by cationic polymerization, and utilization of this segment as a macroinitiator for ATRP. There are several reports on such block copolymer preparation. The most recently published article by Becer et provides a representative example of the system. Cationic ring-opening polymerization (CROP) of EtOx was... 

Cyclic ethers are the class of heterocyclic monomers that provide suitable models for mechanistic studies. Polymerization of several monomers of this class leads to polymeric materials that are produced on an industrial scale. The most prominent examples are polymers of ethylene oxide (EO), propylene oxide (PO), epichlorohydrin (ECH), or tetra-hydrofiiran (THE). Cationic ring-opening polymerization (CROP) of cyclic ethers is thus interesting from both an academic and industrial point of view. 

There are certain similarities between cationic ring-opening polymerization (CROP) of cyclic acetals and cyclic ethers. Essentially the same group of initiators may start the polymerization and in both cases the major growing species are tertiary oxonium ions of similar stmcture as shown below for polymerization of five-membered cyclic ether and cyclic acetal ... 

Scheme 6 A general scheme of cationic ring-opening polymerization (CROP) involving covalent propagating species in equilibrium with ionic...

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