Ring-opening polymerization volume expansion

Cationic Ring-Opening Polymerization with Expansion in Volume... 

S. R. Sandler and E. Karo, Polymer Syntheses, two vols.. Academic Press, New York, 1977. W. J. Bailey, Ring-opening polymerization with expansion in volume, Polym. Preprints 18, 17 (1977). 

At a recent symposium in his honour, Bailey reviewed the theory and chemistry of ring-opening polymerizations with expansion in volume. Monomers in... 

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... 

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). 

The same behavior was observed also for polymerization of other bicyclic esters. In all cases, opening of one ring leads to the decrease of volume (shrinkage), whereas the opening of both rings leads to slight increase of volume (expansion) [211]. 

Polymer structure-thermodynamic control. The polymers described above, containing dloxolane and dloxane rings, are the klnetlcally controlled products In these polymerizations. Bailey reported the polymerization of several bicyclic [2.2.2]orthoesters and also splro orthoesters under much harsher conditions (24). Simultaneous opening of both rings Is achieved In this way, leading to linear polyethers with ester branching. This Is usually accompanied by volume expansion. 

The polymerization is accompanied by approximately 6% shrinkage (calculated from densities of monomer and polymer at 25 °C). Upon heating the polymer solution in the presence of trifluoromethanesulfonic acid the substituted 1,3-dioxolane ring opens and linear polymer is formed. This is accompanied by a 9.7% expansion in volume. 

The same phenomenon, i.e. opening of one ring under mild conditions and opening of both rings (with volume expansion) under more drastic conditions, was observed in the polymerization of 2,6,7-trioxabicyclo 2.2.2. octane48). This monomer was obtained by reaction of the acyclic triol and orthoester ... 

If, hovewer, the same monomer is polymerized under more drastic conditions [in bulk with BF3 0(C2H5)2 at 5 °C or 70 °C], both rings open and a substituted polyether is obtained. The formation of this thermodynamic product is accompanied by volume expansion 47,49,50). 

According to these results expansion in volume during polymerization occurs only when both fused rings open upon polymerization. 

Since the double bonds in this compound are now reactive, part of the double bonds are incorporated into the polymer network to give a cross-linked material. The volume change can be controlled to some extent by the ratio of the cyclic ester added and the extent of polymerization that has taken place when the temperature is raised to 150°. Theoretically a large number of ring compounds and polymers could be used to control shrinkage or to promote expansion of polymers on ring-opening. 

In a program to develop monomers that expand on polymerization, we had prepared a series of spiro orthoesters, spiro orthocarbonates, trioxabicyclooctanes, and ketal lactones that could be polymerized with ring-opening by ionic catalysts to give either no change in volume or slight expansion... 

Monomers opening at least two rings in linear chains formation polymerize either without any volume change, or with a small expansion. ... 

It was reasoned from this study that if monomers were available in which at least two rings were opened for every new bond that was formed in the backbone, materials with either no change in volume during polymerization or slight expansion would be possible. It should be emphasized that this concept would eliminate from consideration the polymerization of a monomer, such as a dl-epoxlde or a dlanhydrlde, because, although two rings are opened during the polymerization, two new bonds are also formed at the same time. 

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