Polymerization with volume expansion

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 ... 

The van der Waals bonds between monomer molecules are replaced by covalent bonds between the monomeric units in polymerization. Since van der Waals bond lengths are about 0.3-0.5 nm and covalent bond lengths are, in contrast, about 0.14-0.19 nm, a general contraction occurs. The contraction increases with decreasing monomer molecule size, since more van der Waals bonds per unit mass must be eliminated. Thus, ethylene contracts by about 66%, vinyl chloride by about 34%, styrene by about 14%, and W-vinyl carbazole by as little as about 7.5%. Polymerization of ethylene oxide leads to a volume contraction of 23%, of tetrahydrofuran to one of about 10%, but that of octamethyl cyclotetrasiloxane, however, to a contraction of only 2%. Some strained bicyclic ring systems even polymerize with an expansion. With polycondensation, the volume contraction is smaller with decreasing size of eliminated residue. Polycondensation of hexamethylene diamine with adipic acid leads to a contraction of 22% (water elimination), that of hexamethylene diamine and dioctyl phthalate, on the other hand, to one of 66% (elimination of octanol). 

Experimentally the surface entropy, -dy/dT, of a polymeric liquid is smaller than for a low MW homologue. The surface entropy of a polymeric liquid may typically be 50% to 100% smaller than a corresponding low MW homologue. The primary reason for this phenomenon can again be related to density variations. A polymeric liquid has a smaller thermal expansion coefficient than a low MW homologue because entropy increases associated with volume expansion are smaller for a polymeric liquid. Since the poly-... 

Only a fraction of the chain segments will be present in this spherical shell, but whatever their number is, it will increase with the degree of polymerization n. Therefore, in the volume element associated with the expansion of the coil, the volume fraction of chain segments 0 is proportional to n/dV, or 0 n/a ro dro ... 

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... 

Here oth is the fraction of thermal expansion connected with changes in hole concentration (free-volume expansion), ), is the energy of hole formation, r=M/p0 Vn Na, where NA is the Avogadro number,M molecular weight, p0 the density of a liquid without holes at absolute zero, and Vn the hole volume. For polymeric systems r is very small, and then ahTis the function of E IRTalone. The value Of, is identified with experimentally observed changes in the thermal expansion coefficients A a at Tg, i.e. 

It was found that the total fraction of the free-volume in the system increases with increasing concentration of the polymeric filler. The temperature dependence of fg for the epoxy matrix was calculated on the supposition that free-volume is an additive value of the constituent components and using the temperature dependence of the fractional free-volume of polystyrene. It was found that with increasing filler concentration the fractional free-volume becomes greater than for pure epoxy resin. Since the fraction of the free-volume increases with increasing total surface area of the filler, it may be supposed that this effect is associated with the surface layers of polymer. It was found that the rate of free-volume expansion in a filled system is higher than in an unfilled one, which means that the expansivity of the free-volume... 

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. 

Bailey continues his series of papers in the area of ringopening polymerization with expansion in volume (109. 110). 

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

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). 

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... 

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. 

We have demonstrated, therefore, that polymerization with no change In volume or with expansion In volume Is a general phenomena possible with a wide variety of liquid and crystalline cyclic and blcycllc monomers. 

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