Radical Ring-Opening Polymerization Mechanism

Functional Polyesters by Conventional and Controlled Radical Homopolymerization ofCKAs 

R = R = Ph l-viny1-5-phenyl-4,7-dioxaspiro[2.4]heptane R = H, R =1 y l-vinyl-6,7-benzo-4,9-dioxaspiro[2,6]nonane 

cross-linked polyesters can be easily made by reaction of CKAs with vinyl cross-linkers with more than one double bond. In one of the studies, porous monolithic supports for tissue engineering were made by electron-beam-initiated free-radical polymerization of 2-methylene-4-phenyl-l,3-dioxolane with trimethylolpropane triacrylate as a cross linker [24]. 

Functional Polyesters by Copolymerization of CKAs and Vinyl Monomers 

2 Funcdaial (Bio)degradable f ytyestefs by Radical Ring-Opening Polymerization 

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Bailey WJ, Ni Z, Wu S-R (1982) Synthesis of poly-e-caprolactone via a free radical mechanism. Free radical ring opening polymerization of 2-methylene-l,3-dioxepane. J Polym Sci A Polym Chem 20 3021-3030... 

Very recently, Bailey and Endo have enlarged the scope of the free-radical ring-opening polymerization.13 15> Several examples of their studies are described below. All the polymerizations are represented by the following general pattern of fundamental reaction. It is seen that the free-radical ring-opening by a P-scission mechanism is coupled with the addition of a free radical to the carbon-carbon double bond 13). 

The above examples of free-radical ring-opening polymerization, which have been explored by Bailey and Endo, produce polymers containing ketonic carbonyl and/or ester groups in the main chain. In addition, these cyclic monomers can be copolymerized with vinyl monomers by free-radical mechanism. Thus, the variety of the polymers produced by radical polymerization has been enlarged. 

There are some reports in the literature of ring-opening polymerizations by free-radical mechanism. One is a polymerization of substituted vinyl cyclopropanes.The substituents are radical stabilizing structures that help free-radical ring-opening polymerizations of the cyclopropane rings. This can be illustrated as follows ... 

Controlledriiving" radical ring-opening polymerization of 5,6-benzo-2-methylene- 1,3-dioxepane based on reversible Addition fragmentation chain transfer mechanism. Polym. /.,... 

Here we discuss dispersion polymerizations that are not related to vinyl monomers and radical polymerization. The first one is the ring-opening polymerization of e-caprolactone in dioxane-heptane (30). A graft copolymer, poly(dodecyl acrylate)-g-poly(e-caprolactone), is used as a stabilizer. The polymerization proceeds via anionic or pseudoanionic mechanism initiated by diethylaluminum ethoxide or other catalysts. The size of poly(caprolactone) particles depends on the composition of stabilizer, ranging from 0.5 to 5 i,m. Lactide was also polymerized in a similar way. Poly(caprolactone) and poly(lactide) particles with a narrow size distribution are expected to be applied as degradable carriers of drugs and bioactive compounds. 

Most cyclic monomers of interest in the field of composites happen to be heterocyclic in nature. Polymerizability of some monomers is summarized in Table 1.1. Ring opening polymerizations invariably follow ionic mechanisms, although a few are known to proceed via the free radical route and some via metathesis involving metallocarbene intermediates. 

Ring-opening polymerization is an important field of research in the chemistry of polymer synthesis. Usually, it proceeds by ionic mechanisms, i.e. cationic, anionic and coordinate anionic mechanisms. Research on ring-opening polymerization proceeding via free-radical propagating species in which the so-called molecular design of monomer plays an important role has recently been reported. 

Several examples of ring-opening polymerization proceeding via free-radical mechanism have been reported, e.g. the free-radical polymerization of vinylcyclo-propane 7 and its derivatives having alkoxycarbonyl substituents 98,9) ... 

The subjects Include fundamental and applied research on the polymerization of cyclic ethers, slloxanes, N-carboxy anhydrides, lactones, heterocycllcs, azlrldlnes, phosphorous containing monomers, cycloalkenes, and acetals. Block copolymers are also discussed where one of the constituents is a ring opening monomer. Important new discussions of catalysis via not only the traditional anionic, cationic and coordination methods, but related UV Initiated reactions and novel free radical mechanisms for ring opening polymerization are also Included. 

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