Acid-catalyzed ring-opening polymerization

Poly(tetramethylene oxide) polyols (see Scheme 4.4) are a special class of polyethers syndiesized via acid-catalyzed ring-opening polymerization of tetrahy-drofuran. Although less susceptible to side reactions, the synthesis of these C4 ethers is less flexible in terms of product composition and structure. Thus, because of diis syndietic route, only two-functional glycols are available and copolymers are not readily available. Molecular weights of commercial C4 glycols range up to about 3000 g/m. 

Base and acid catalyzed ring opening polymerization of cyclotri-siloxane, -[Me2SiO]3- [e.g. reaction (10)], is a well-known method of generating high molecular weight polysiloxanes. 

Rochow et al. (27-28) have examined acid catalyzed ring opening polymerization as an approach to the formation of polysilazanes. 

Scheme I Synthesis of hyperbranched poly(ethylene imine) (PEI) via acid catalyzed ring-opening polymerization of aziridine. Each color represents a different branching unit blue for linear units (L), black for dendritic units (D), red for terminal units (T). PEI has a degree of branching (DB) of 62-73%, the depicted structure represents only a small idealized fragment. Reproduced with permission from [91]...

An alternative approach to such materials involves acid-catalyzed ring-opening polymerization of macrocyclic stannasiloxane rings to produce waxy solids. The molecular weight of these materials could not be determined. 

Polymers with composition [NP(02Ci2Hg)] .x(0C4H8) have been formed in the reaction of (NPCl2) with 2,2 -diphenol in thf. Polytetrahydrofurane (OC4Hg) arises from acid-catalyzed ring opening polymerization of thf. ... 

The functional group compatibility of the click cyclization approach also makes it amenable to a variety of other polymerization techniques. For example, cyclic polyesters have been prepared using the Lewis acid-catalyzed ring-opening polymerizations (ROPs) of lactone monomers, including e-caprolactone [47, 48] and 5-valerolactone [49] from an azide-functionaUzed alcohol. Esterification of the terminal alcohol with pentynoic anhydride provided the complementary functional groups to enable an efficient click cycHzation for molecular weights up to 15 kDa. 

Scheme 15 General mechanism for Bronsted acid-catalyzed ring-opening polymerizations.

Polydlmethylslloxane oligomers may be easily prepared by the acid or base catalyzed ring opening polymerization of the cyclic tetramer, octamethylcyclotetraslloxane. The molecular weight of the polymer prepared may be controlled by the addition of a linear dlslloxane as an endblocker > When the dlslloxane Is... 

Okumara et al. [10] were the first to attempt the enzyme-catalyzed synthesis of oligoesters from a reaction between dicarboxylic acids and diols. Gutman et al. [11] reported the first study on polyester synthesis by enzyme-catalyzed polymerization of A-B type monomers. Two independent groups in 1993 [12, 13] were first to report enzyme-catalyzed ring-opening polymerization (ROP). Their studies focused on 7- and 6-membered unsubstituted cyclic esters, e-caprolactone (e-CL) and 8-valerolactone (8-VL), respectively. 

By attaching formyl groups [106] and reducing them to hydroxymethyl moieties, benzylic alcohol functions can be formed [108], which enhances the polymerization rates when used with epoxides in Brpnsted-acid-catalyzed ring-opening cationic polymerizations. As termed by Penczek and Kubisa, the polymerization follows a mechanism called the activated monomer mechanism (Scheme 11.29) [109-112],... 

Base catalyzed ring opening polymerization reactions of A -carboxy-a-amino acid anhydrides also result in formations of polypeptides ... 

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