Cationic ring-opening copolymerization

Polyoxymethylene, also referred to as acetal resin or POM, is obtained either by anionic polymerization of formaldehyde or cationic ring-opening copolymerization of trioxane with a small amount of a cyclic ether or acetal (e.g., ethylene oxide or 1,3-dioxolane) [Cherdron et al., 1988 Dolce and Grates, 1985 Yamasaki et al., 2001]. The properties and uses of POM have been discussed in Sec. 5-6d. 

In many systems, however, the analysis of the cationic copolymerization of heterocyclic monomers is complicated by two factors (1) at least some of the homo- and cross-propagation reactions may be reversible (2) redistribution of the sequences of comonomers within the chain may occur as a result of chain transfer to polymer. Therefore, the conventional treatment involving four irreversible propagation steps is rarely applicable in cationic ring-opening copolymerization. Instead, the diad model should involve four reversible reactions, i.e., eight rate constants... 

Distinctive Features of the Cationic Ring-Opening Copolymerizations... 

Application of these methods to cationic ring-opening copolymerization sometimes gives erroneous results. This is because some of these copolymerizations involve more than merely four propagation reactions. 

Below we summarize the major reasons why Scheme (15-1) does not accurately describe at least some cationic ring-opening copolymerizations. 

Thus, in this chapter we will present a critical review of cationic ring-opening copolymerization on the basis of a restricted number of papers. 

Thus, it appears that steric hindrance in the active species governing the rates of monomer additions is of decisive influence in cationic ring-opening copolymerization within a given group of monomers whose basicities are similar. 

Structure-reactivity Correlation in Cationic Ring-opening Copolymerization... 

Several reports on copolymerization of cydosilazanes with other monomers have been published. A series of new poly (siloxane)s and poly(silazane)s were synthesized by cationic ring-opening copolymerization of the cydic monomers, octa-methylcydotetrasiloxane and hexamethylcydotiisilazane, obtaining PDMS-poly(dimethylsilazane) copolymers with different concentrations of the comonomer units. The polymers were thermally cured and pyrolyzed, produdng ceramic materials. ... 

CuAAC and used this for cationic ring-opening copolymerization (CROP) with 2-oxazoline-based monomers, yielding well-defined gly copolymers bearing functional groups for thiol-ene reactions to tune the properties [13]. 

Dreyfuss, P. andM. P. Dreyfuss, Cationic Ring-Opening Polymerization Copolymerization, Chap. 53 in Comprehensive Polymer Science, Vol. 3, G. C. Eastmond, A. Ledwith, S. Russo, and P. Sigwalt, eds., Pergamon Press, London, 1989. 

Cationic Copolymerization of 1,3>5-Trioxane with 1,3-Dioxolane (Ring-Opening Copolymerization)... 

In many instances in cationic ring-opening polymerization, all the reaction steps, however, are reversible. The final composition of copolymer (in equilibrium) is governed then by thermodynamics. Thermodynamic approaches have been developed [305] and recently reviewed [306]. Such thermodynamic approach has been used to analyze the copolymerization of pairs of cyclic acetals (1,3-dioxolane with 1,3-dioxepane and... 

The synthesis of polystyrene-g-polytetrahydrofurane [188] was achieved by ATR copolymerization of methacrylic PTHF macromonomer, MA-PTHF, with styrene (Scheme 105). The PTHF macromonomer was synthesized by cationic ring opening polymerization of THF with acrylate ions, formed by the reaction of methacryloyl chloride and AgC104. The polydispersity indices of the graft copolymers determined by SEC ranged between 1.3-1.4. Kinetic studies revealed that the relative reactivity ratio of the macromonomer to St was independent of the molecular weight of PTHF. 

The present paper deals broadly with the copolymerization of ethylene oxide and tetrahydrofuran using cationic ring-opening polymerization catalysts. A comparison is made of EO/THF polyether glycol with PTMEG and their respective polyurethanes. 

The above listed monomers polymerize exclusively by cationic ring-opening polymerization. Polymerization of cyclic imino ethers has been reviewed by Saegusa1,4,). In this section we follow mostly the conclusions of the Kyoto group summarizing the applied synthetic methods. Subsequently we describe initiating systems, peculiarities of chain growth, side reactions, copolymerization systems and possible applications, in this order. 

The classical scheme of copolymerization, discussed in the first paragraph of this section, cannot be used for the analysis of cationic ring-opening polymerization without important changes. 

In free radical copolymerization interconversion of the growing species proceeds exclusively by crosspropagation. In cationic ring-opening polymerization interconversion of the growing species may occur by two routes i.e., the incoming monomer may attack either the endo- or the exocyclic carbon atom ... 

Acetal (polyformaldehyde or polyoxymethylene, POM) is obtained by anionic or cationic polymerization of HCHO, or cationic ring-opening of trioxane. The ceiling temperature of POM is 127 °C and therefore the unzipping that would occur at the processing temperature (T 180 °C) has to be inhibited by end-capping with acetic anhydride or copolymerizing with 5-10% ethylene oxide (section 1.7.1). 

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