Macrocyclic cyclic siloxanes

Eq. (6) with oji = 2x. A rotational isomeric state model for polyphosphate chains (2 76,187) was used to compute values of < rj >o required by Eq. (6). Comparison of the experimental values with the theoretical values, as well as with the values for the corresponding cyclic siloxanes (R(CH3)SiO)x [see Section III.(A)5] stronj y supports the contention that polyphos diate chains in sodium phosphate melts adopt random-coil conformations. Further evidence for the structure of sodium phosphate melts would come from precise data for macrocyclic concentrations in quenched sodium phosphate ring-chain equilibrates, if these became available. 

There are numerous reports of the uses of cyclic oligomeric carbonates for copolymerization. Evans and Carpenter reported the preparation of PC/PDMS copolymers (Scheme 103). Two approaches were used in the preparation of the copolymers the first one used direct reaction of macrocyclic carbonates with cyclic siloxanes, the second one reaction of hydroxy-terminated linear PCs with chlorosilane-terminated PDMSs. 

Similar effects are found for R = C4H5 (48) but they cannot be observed for CF3CH2CH2 over the limited dihition range (see Fig. 7). In all these systems the values for the larger cyclics with x>ca. 10 remain constant within experimental error [see, however. Section HI. (A) 4 above for dilution effects on macrocyclic siloxanes]. 

Thus, we first discuss thermodynamics, paying attention to features that are important for polymer synthesis (e.g., dependence of equilibrium monomer concentration on polymerization variables) then we describe kinetics and thermodynamics of macrocyclization, trying to combine these two related problems, usually discussed separately. In particular we present the new theory of kinetic enhancement and kinetic reduction in macrocyclics. Thereafter, we describe the polymerization of several groups of monomers, namely cyclic ethers (oxiranes, oxetanes, oxolanes, acetals, and bicyclic compounds) lactones, cyclic sulfides, cyclic amines, lactams, cyclic iminoethers, siloxanes, and cyclic phosphorus-containing compounds, in this order. We attempted to treat the chapters uniformly we discuss practical methods of synthesis of the corresponding polymers (monomer syntheses and polymer properties are added), and conditions of reaching systems state and reasons of deviations. However, for various groups of monomers the quality of the available information differ so much, that this attempt of uniformity can not be fulfilled. 

Fig. 1. Gel permeation chromatogram (g-p.c.) of an undiluted equilibrate of poly(phenylmethyl-siloxane) showing regions corresponding to small cyclics, macrocyclics and linear polymer...

Cationic and anionic polymerizations of heterocyclic monomers provide many examples in which the concurrent formation of cyclics of various sizes is observed during the ring-opening polymerization. As illustrated in Scheme 1, in these systems active species follow three pathways they can react with a functional group of the monomer, of its own polymer chain, or of other chains. When the function / involved belongs to a linear polymer chain, intramolecular chain saambling or intermolecular macrocycle formation takes place, as observed in the cationic polymerization of cyclic ethers, acetals, esters, amides, siloxanes, and so forth. 

In 1976, Hory et al. [7-9] returned to the problem of macrocyclization equilibria, presenting a new mathematical approach called Direction Correlation Factor theory, to improve the agreement between calculated and experimental data for rings of DP < 15. Cyclization equilibrium constants ( ) for the formation of cyclic poly(dimethyl siloxane)s, PDMS, were calculated for 6 < c < 31 and compared with experimental data. Similar calculations were performed for cyclic oligomers of Nylon-6, but the agreement with the experimental data was not satisfactory for the smaller rings. Remarkably, Hory presented a positive citation of two papers of Andrews and Semiyen (see below) who reported that equilibrated Nylon-6 contains around 12 % of cyclic species in the melt at 500-560 K. Unfortunately, he did not comment, how this relatively large value fits in with the much lower values he had previously calculated from the J - - S theory (see text above and p. 328 in Ref. [5]). 

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