Acid-initiated ring-opening polymerization

Yu, Z.J. and Liu, L.J. 2004. Effect of microwave energy on chain propagation of poly (e-caprolactone) in benzoic acid-initiated ring opening polymerization of e-caprolactone. European Polymer Journal, 40 2213-20. 

Both protonic and Lewis acids initiate ring-opening polymerization of siloxanes. In spite of the practical importance [240] and the very extensive studies of this system, the mechanism of the polymerization is not completely understood. Even the nature of ionic propagating species is still a matter of controversy. The silicenium [241] or oxonium [242,243] ion structure has been postulated. 

Acheson process, 566 Acid-initiated ring-opening polymerization comparison widi base-initiated process, 79 kinetics, 79-80 mechanism, 79-81 rate retardation by water, 81 relative reactivities of cyclosiloxanes, 79 step-growth process, 79 Acyclic oligosilanes, photochemical transformations, 432/-433/ Acylsilanes... 

Common initiators are Li and K alkoxides. In additimi to that, it was reported that phosphazene bases can be used to cany out polymerizations of cyclic esters [92]. Also, commercially available materials, like tert-butoxybis(dimethylamino)methane and tris(dimethylamino)methane yield high molecular weight polylactic acid by ring-opening polymerization with narrow molecular weight distribution ... 

Oxidative addition of a-amino acid-jV-carboxyanhydrides to a Pt(0) complex leads to a six-membered platinacycle 437 (Equation (110)). The complex initiates ring-opening polymerization of 7-benzyl-L-glutamate-iV-carboxyanhydride. 

Messersmith and GianneUs [303] developed bionanocomposites of PCL and MMT organically modified with a protonated amino acid to promote delamination/dispersion of the host layers and initiate ring-opening polymerization of s-caprolactone monomer. This resulted in PCL chains that were ionically bound to the siUcate layers (Figure 11.22). Films with a significant reduction... 

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. 

Nylon-6 is the polyamide formed by the ring-opening polymerization of S-caprolactam. The polymerization of S-caprolactam can be initiated by acids, bases, or water. Hydrolytic polymerization initiated by water is often used in industry. The polymerization is carried out commercially in both batch and continuous processes by heating the monomer in the presence of 5—10% water to temperatures of 250—280°C for periods of 12 to more than 24 h. The chemistry of the polymerization is shown by the following reaction sequence. 

Group 4 metal complexes of the dianion [ BuNP( -N Bu)2PN Bu] polymerize ethylene in the presence of a co-catalyst, but they are readily deactivated [10,14]. This behaviour is attributed to coordination of the lone-pair electrons on the phosphorus(III) centers to Lewis acid sites, which initiates ring opening of the ligand [15]. 

Liu J, Liu L (2004) Ring-opening polymerization of e-caprolactone initiated by natural amino acids. Macromolecules 37 2674—2676... 

Previously, PLAs were obtained via condensation of lactic acid by heating and driving off water, which produced a gummy polymeric material of ill-dehned molecular weight and microstmcture [6]. Ring-opening polymerization (ROP) of dilactones, pioneered by Carothers in 1932 [7], was the hrst initiative for an... 

The overall rate of conversion of e-caprolactam to polymer is higher than the polymerization rate of e-aminocaproic acid by more than an order of magnitude [Hermans et al., 1958, I960]. Step polymerization of e-aminocaproic acid with itself (Eq. 7-57) accounts for only a few percent of the total polymerization of e-caprolactam. Ring-opening polymerization (Eq. 7-58) is the overwhelming route for polymer formation. Polymerization is acid-catalyzed as indicated by the observations that amines and sodium e-aminocaproate are poor initiators in the absence of water and the polymerization rate in the presence of water is first-order in lactam and second-order in COOH end groups [Majury, 1958]. 

The ring-opening polymerization of dilactide (dimeric cyclic ester of lactic acid) allows the preparation of high molecular weight, optically active polyesters of lactic acid. The configuration of the asymmetric carbon atoms of the monomer is retained when the polymerization is initiated with SnCl4 or Et2Zn, for example ... 

Ring-Opening Polymerization of Epoxide with Various Aluminum Complexes as Initiators in the Presence of a Lewis Acid... 

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