Macromonomers cationic transfer reactions

It seems that instead protonated species (anhydride or ester molecules) play a major role in the process. The protons originate from some added acid (e.g. acrylic or methacrylic acid). The characterization of the formed macromonomers revealed that the number of ester functions per molecule is close to 2. The role of the protons is evidenced by the increase of the reaction rate with increasing amount of methacrylic acid in the system. In the absence of a protonic acid high molecular weight poly-THF is produced, no anhydride is consumed and reshuffling does not take place. This mechanism which remains to be confirmed is in any case completely different from the inifer -type cationic transfer which may occur with unsaturated monomers. It is discussed in the next section. 

The reaction of an unsaturated compound with an antagonist function located at the end of a polymer chain is still the most commonly used method to synthesize macromonomers. We have already mentioned some processes that can be used to introduce into the chain end of a macromolecule a functional group, e.g. by deactivation of living carbanionic sites and transfer reactions of various kinds in cationic polymerization. We have also described some methods used to link an active terminal double bond to the chain end originally bearing hydroxy groups. 

Termination of the cationic ring-opening polymerization of iV-t-butylaziridine with methacrylic acid yields macromonomers according to equation (20). Because N-t-butylaziridine is sterically hindered, polymerization is not complicated by the transfer reaction of two growing chains that results in one chain growing in two directions and one dead chain. 

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