Ring-opening polymerizations propagation step

A mechanism of ring opening and propagation step in the polymerization of p-sub-stituted-benzenesulfonamido- 3-thiolactones with methylamine as initiator as illustrated in Figure 7 was proposed by Fle and Tomasic [5]. 

The key initiation step in cationic polymerization of alkenes is the formation of a carbocationic intermediate, which can then interact with excess monomer to start propagation. We studied in some detail the initiation of cationic polymerization under superacidic, stable ion conditions. Carbocations also play a key role, as I found not only in the acid-catalyzed polymerization of alkenes but also in the polycondensation of arenes as well as in the ring opening polymerization of cyclic ethers, sulfides, and nitrogen compounds. Superacidic oxidative condensation of alkanes can even be achieved, including that of methane, as can the co-condensation of alkanes and alkenes. 

Polymerization of the dithiocins 838f,g proceeded, in benzene at 40-70 °C, with complete ring opening. A two-step mechanism was involved in the first step, addition of sulfanyl radical onto monomer exocyclic double bond formed the intermediate carbon-centered radicals 841, which do not propagate in the second step, a rapid fragmentation of 841 yielded new propagating sulfanyl radicals 842 and 843 and polymer backbone double bonds (Scheme 168) <2005MM2143>. 

This review summarizes all the data we obtained on the synthesis and cationic ring-opening polymerization of bicyclic acetals and orthoesters, and discusses the relationship between ring-strain and poly-merlzablllty. This ties In with earlier work on the polymerlzabll-Ity of monocyclic and bicyclic lactams ( - ). A new mechanism for the propagation step In the polymerization of bicyclic orthoesters Is supported. 

As discussed by Ruckel et al., (14) the catalytic cationic polymerizations of a-plnene oxide and B-plnene oxide both Involve the concomitant opening of the epoxide and cyclobutane rings In the propagation step. This rearrangement mechanism also clearly operates In the radlatlon-lnduced polymerization of these monomers, and Is depicted below for a-plnene oxide (Scheme ). 

Scheme 8.1 Schematic representation of the propagation step, that is, monomer addition, in carhocationic polymerizations (top) and cationic ring-opening polymerizations (hottom). Connteran-ions have been omitted for clarity.

The generally accepted propagation mechanism for cationic ring-opening polymerization for ethylene oxide is shown in Figure 5. According to this mechanism, the proton of the superacid (produced from the initiation step as explained in... 

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