Ring opening polymerization of cyclic

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. 

This scheme is remarkably close to the coordination insertion mechanism believed to operate in the metal alkoxide-catalyzed ring-opening polymerization of cyclic esters (see Section 2.3.6). It shares many features with the mechanism proposed above for the metal alkoxide-catalyzed direct polyesterification (Scheme 2.18), including the difficulty of defining reaction orders. 

Polyesters from the Ring-Opening Polymerization of Cyclic Esters... 

In connection with studies on the ring-opening polymerization of cyclic acetals, we have undertaken investigations on the polymerization of bicyclic acetals, bicyclic oxalactone, and bicyclic oxalactam, which yield polysaccharide analogs, macrocyclic oligoesters, and a hydrophilic polyamide, respectively, some of which can be expected to be useful as novel speciality polymers. The monomers employed in the studies were prepared via synthetic routes presented in Scheme 1, starting from 3,4-dihydro-2H-pyran-2-carbaldehyde (acrolein dimer) I. 

Ring-opening polymerization of cyclic monomers, usually by anionic or cationic catalysts, is another route to elastomers. These include the polymerization of octamethylcyclotetrasiloxane... 

Here, lipase-catalyzed ring-opening polymerization of cyclic compounds giving polymers other than polyesters is described. l,3-Dioxan-2-one, six-membered cyclic carbonate, was polymerized in the presence of lipase catalysts (Fig. 13)... 

RING-OPENING POLYMERIZATION OF CYCLIC ESTERS 9.1.6.1 Introduction... 

Kress, J. D. Leung, P. G. Tawa, G. J. Hay, P. J. Calculation of a Reaction Path for KOH-Catalyzed Ring-Opening Polymerization of Cyclic Siloxanes. In Silicones and Silicone-Modified Materials Clarson, S. J., Fitzgerald, J. J., Owen, M. J., Smith, S. D., Eds. AGS Symposium Series 729 American Chemical Society Washington, DC, 2000 pp 81—97. 

Cypryk, M. Chojnowski, J. Kurjata, J. Tertiary Trisilyloxonium Ion and Silylenium Cation in Cationic Ring-opening Polymerization of Cyclic Siloxanes. In Organosilicon Chemistry VI From Molecules to Materials Auner, N., Weis, J., Eds. Wiley-VCH Weinheim, 2005 pp 85-92. 

Brunelle, D. J. and Serth-Guzzo, J. Titanate-catalyzed ring-opening polymerization of cyclic phthalate ester oligomers, Polym. Prep., 40(1), 566 (1999). 

Formation of cyclic oligomers is a characteristic feature of the cationic ring-opening polymerization of cyclic ethers (16-17). 

This indicates the possibility of making addition polymers biodegradable by the introduction of ester linkages in to the backbone. Since the free radical ring-opening polymerization of cyclic ketene acetals, such as 2-methylene-1,3-dioxepane (1, Scheme I), made possible the introduction of ester groups into the backbone of addition polymers, this appeared to be an attractive method for the synthesis of biodegradable addition polymers. 

The cationic ring-opening polymerization of cyclic ethers has been the subject of many recent investigations (1.. Nuclear magnetic resonance (NMR) methods, particularly carbon-13 techniques, have been found most useful in studying the mechanism of these polymerizations ( ). In the present review we would like to report some of our recent work in this field. 

Agarwal S (2010) Chemistry, chances and limitations of the radical ring-opening polymerization of cyclic ketene acetals for the synthesis of degradable polyesters. Polym Chem 1 953-954... 

Zhong Z, Dijkstra PJ, Birg C, Westerhausen M, Feijen J (2001) A novel and versatile calcium-based initiator system for the ring-opening polymerization of cyclic esters. Macromolecules 34 3863-3868... 

Connor EE, Nyce GW, Myers M, Mock A, Hedrick JL (2002) First example of N-heterocyclic carbenes as catalysts for living polymerization organocatalytic ring-opening polymerization of cyclic esters. J Am Chem Soc 124 914-915... 

The ring-opening polymerizations of cyclic monomers such as propylene oxide... 

The ring-opening polymerization of cyclic ethers having 3-, 4-, and 5-membered rings (e.g., epoxides, oxetanes, THF) yields polymeric ethers. Six-membered rings (1,4-dioxane) are not capable of polymerization. 

Ring-opening polymerization of cyclic siloxanes with cationic initiators allows the possibility of introducing stable end groups by the use of suitable chain transfer agents. Thus, polysiloxanes with trimethylsilyl end groups are formed when the cationic polymerization of octamethylcyclotetrasiloxane is carried out in the presence of hexamethyldisiloxane as transfer agent ... 

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