High molecular weight polymers ring-opening polymerization

In polyester synthesis via ring-opening polymerizations, metal catalysts are often used. For medical applications of polyesters, however, there has been concern about harmful effects of the metallic residues. Enzymatic synthesis of a metal-free polyester was demonstrated by the polymerization of l,4-dioxan-2-one using Candida antarctica lipase (lipase CA). Under appropriate reaction conditions, the high molecular weight polymer (molecular weight = 4.1 x 10" ) was obtained. 

Arylene ether/imide copolymers were prepared by the reaction of various amounts 4,4 -carbonylbis[Ar-(4 -hydroxyphenyl)phthalimide] and 4,4 -biphenoi with a stoichiometric portion of 4,4 -dichlorodiphenyl sulfone in the presence of potassium carbonate in NMP/CHP [55]. To obtain high molecular weight polymer, the temperature of the reaction was kept below 155 °C for several hours before heating to >155°C in an attempt to avoid undesirable side reactions such as opening of the imide ring. The imide ring is not stable to conditions of normal aromatic nucleophilic polymerizations unless extreme care is exercised to remove water. Special conditions must be used to avoid hydrolysis of the imide as previously mentioned in the section on Other PAE Containing Heterocyclic Units and as practiced in the synthesis of Ultem mentioned in the Historical Perspective section. 

The copolymerization of trioxane with cyclic ethers or formals is accomplished with cationic initiators such as boron trifluoride dibutyl etherate. Polymerization by ring opening of the six-membered ring to form high molecular weight polymer does not commence immediately upon mixing monomer and initiator. Usually, an induction period is observed during which an equilibrium concentration of formaldehyde is produced. 

Ring-opening Olefin Metathesis Polymerization (ROMP) gives a mixture of linear high molecular weight polymer and a series of cyclic oligomers for a number... 

As already mentioned, cationic ring-opening polymerization offers several possibilities of preparing useful high molecular weight polymers, which may find applications as such. The main interest, however, is in preparation of reactive polymers, which are used in synthesis of block or graft copolymers. 

The necessary, but not sufficient criterion of the living character of polymerization is the possibility of preparation of high molecular weight polymers (M > 10s). This has been achieved in several systems in cationic ring-opening polymerization, e.g., in the polymerization of some cyclic ethers 3,3-bis(chloromethyl)oxetane, tetrahydrofuran, 1,3-dioxo-lane, and 1,3,5-trioxane. 

When certain cycloalkanes are used in metathesis reactions, ring-opening metathesis polymerization (ROMP) occurs to form a high molecular weight polymer, as shown with cyclopentene as the starting material. The reaction is driven to completion by relief of strain in the cycloalkene. 

Ring-opening metathesis polymerization (Problem 26.28) An olefin metathesis reaction that forms a high molecular weight polymer from certain cyclic alkenes. 

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