Ring-opening polymerization general

Ring Opening Polymerization General Considerations Initiation Propagation... 

Ring-opening polymerization generally yields high molecular weight (MW) polymers, whereas direct polycondensation leads to low MW products. 

The use of an unsaturated anionic initiator—such as potassium p-vinyl benzoxide—is possible for the ring opening polymerization of oxirane [43]. Although initiation is generally heterogenous, the polymers exhibit the molecular weight expected and a low polydispersity. In this case, the styrene type unsaturation at chain end cannot get involved in the process, as the propagating sites are oxanions. 

The most general and frequently used method to synthesize long chains of block copolypeptides for vesicle assembly is successive ring opening polymerizations of a-amino acid-Ai-carboxyanhydride (NCA) monomers [18, 20, 21, 39-51]. NCA monomers are readily prepared from commercially available amino acids, most commonly through direct phosgenation [52]. 

The conventional route to prepare I generally involves a high temperature melt polymerization of hexachlorocyclotriphosphazene, or trimer (IV). Recent studies have demonstrated the effectiveness of various acids and organometalllcs as catalysts for the polymerization of IV (8). Alternate routes for the preparation of chloro-polymer which do not involve the ring opening polymerization of trimer have been reported in the patent literature (9. 10). These routes involve a condensation polymerization process and may prove to be of technological importance for the preparation of low to moderate molecular weight polyphosphazenes. 

The hybrid polymer 140 is generated by a thermal ring-opening polymerization (ROP) process (Scheme 10).300,301 Polymers containing three-coordinate sul-fur(IV) are generally hydrolytically sensitive even when the chloro substituents are replaced by phenoxy groups.302... 

Fig.3A-D. Use of ring-opening polymerization (ROP) for neobiopolymer synthesis A General mechanism of cationic ROP. B Okada s use of cationic ROP to generate polymers with carbohydrate substituents at the terminus. C General mechanism for anionic ROP. D Okada s application of anionic ROP to generate carbohydrate-substituted polymers... 

Peduoropolyethers, which constitute special class of fluoropolymer, are useful as lubricants,1 elastomers,2 and heat-transfer fluids under demanding conditions. Several commerical products are available, which are generally prepared by ring-opening polymerization of hexafluoropropylene oxide or by the random copolymerization oftetrafluoroethylene and hexafluoropropylene with oxygen under ultraviolet irradiation.3 Direct fluorination of hydrocarbon ethers has been reported4 but must be done very slowly under carefully controlled... 

Save M, Schappacher M, Soum A (2002) Controlled ring-opening polymerization of lactones and lactides initiated by lanthanum isopropoxide, 1 general aspects and kinetics. Macromol Chem Phys 203 889-899... 

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