Other Ring-Opening Polymerizations

The polymerization of a variety of other monomers, such as vinyloxiranes, vinyllactones, dihydrofurans, and bicyclobutanes, have been studied [Cho, 2000]. 

Kricheldorf and coworkers have found that some heterocyclic compounds containing two reactive bonds behave as bifunctional reactants in a ROP that proceeds by a step polymerization mechanism [Kricheldorf, 2000]. An example is the polymerization of 2,2-dibutyl-2-stanna-l,3-dioxepane with an aliphatic diacid chloride  

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If, however, radicals add preferentially to the vinyl group of 48, ring-opening polymerization w-ould give the polymer with in-chain double bonds specifically via resonance structure 49 (Scheme 4.31). Thus, the two pathways are readily distinguishable. No other ring-opening polymerizations of vinyl dioxolane derivatives appear to have been reported to date. 

The grafting from method is also successful in other ring opening polymerizations. For example, -caprolactone polymerization is initiated from polypropylene imine) dendrimers with n=2-16 end-standing amine groups [135]. To be... 

Apart from the above-mentioned chemical factors of course physical factors such as temperature or solvent are very important, too. Generally, as in most other ring-opening polymerizations a ceiling temperature at a given concentration and an equilibrium monomer concentration at a given temperature exists. 

Unlike other ring-opening polymerizations, most C-C single bond polymerizations have been carried out by free radical initiation, even though examples of cationic, anionic, and coordination polymerizations have been presented. The bicyclobutane monomers, such as bicyclobutane-1-carbonitrile (la X = CN), are as reactive in free radical polymerization as vinyl monomers ( ). 

Ring-Opening Polymerization. As with most other inorganic polymers, ring-opening polymerization of cyclotetrasilanes has been used to make polysilanes (109,110). This method, however, has so far only been used for polymethylphenylsilane (eq. 12). Molecular weights (up to 100,000) are higher than from transition-metal catalyzed polymerization of primary silanes. 

The chemistry of polymerization of the oxetanes is much the same as for THE polymerization. The ring-opening polymerization of oxetanes is primarily accompHshed by cationic polymerization methods (283,313—318), but because of the added ring strain, other polymerization techniques, eg, iasertion polymerization (319), anionic polymerization (320), and free-radical ring-opening polymerization (321), have been successful with certain special oxetanes. 

Much of the interest in ring-opening polymerizations stems from the fact that the polymers formed may have lower densities than the monomers from which they are derived (i.e. volume expansion may accompany polymerization).168-171 This is in marked contrast with conventional polymerizations which typically involve a nett volume contraction. Such polymerizations are therefore of particular interest in adhesive, mold filling, and other applications where volume... 

Various methylene derivatives of spiroorthocarbonates and spiroorthocstcrs have been reported to give double ring-opening polymerization e.g. Scheme 4.36). Like the parent monocyclic systems, these monomers can be sluggish to polymerize and reactivity ratios are such that they do not undergo ready copolymerization with acrylic and styrenic monomers. Copolymerizations with VAc have been reported.170 These monomers, like other acetals, show marked acid sensitivity. 

Thus, confirmation of whether the product obtained in an attempted reaction in a true random copolymer is important to clarify the mechanism of the propagation reaction and to correlate structure and reactivity in ring-opening polymerizations. Considering that apparent copolymers may be formed by reactions other than copdymerization, for example, by ionic grafting or by combination of polymer chains, characterization of cross-sequences appears to be one of the best ways to check the formation of random copolymers. 

Poly (dimethyl siloxane) obtained by anionic ring-opening polymerization of hexamethylcyclotrisiloxane (D3) can also be end-capped with vinylbenzyl bromide or other electrophiles, such as p. (chlorodimethylsilyl)styrene80). 

Three other MEEP-type polyphosphazenes were synthesized by Allcock [622]. Polymers XIII and XIV were prepared via the cationic living polymerization of phosphoranimines, and polymers XV by ring opening polymerization. 

Furthermore, formation of these products occurs with much greater ease than linear polymerization of units of six or more chain members, and they are more stable to hydrolysis or other ring-opening reactions. 

Quite often in the ring-opening polymerization, the polymer is only the kinetic product and later is transformed to thermodynamically stable cycles. The cationic polymerization of ethylene oxide leads to a mixture of poly(ethylene oxide) and 1,4-dioxane. In the presence of a cationic initiator poly(ethylene oxide) can be almost quantitatively transformed to this cyclic dimer. On the other hand, anionic polymerization is not accompanied by cyclization due to the lower affinity of the alkoxide anion towards linear ethers only strained (and more electrophilic) monomers can react with the anion. 

Polyester syntheses have been achieved by enzymatic ring-opening polymerization of lactide and lactones with various ring-sizes. Here, we focus not only on these cyclic esters but also other cyclic monomers for lipase-catalyzed ringopening polymerizations. Figure 8 summarizes cyclic monomers for providing polyesters via lipase catalysis. 

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 Metathesis Polymerization (ROMP) and other Ring-Opening Reactions... 

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