Intramolecular Reaction in Polycondensations. II. Ring-Chain Equilibrium in Polydecamethylene Adipate

Abstract

Decamethylene adipate polymers prepared in the absence of solvent undergo a reversible decrease in solution viscosity when heated for long times in chlorobenzene. This phenomenon is shown to be due to ester interchange reactions which establish equilibrium between ring and chain molecules. Quantitative agreement with the equilibrium theory of the previous paper is obtained if the effective length of a chain link is taken as 4.5±0.2A, which is of the order of magnitude to be expected from hindered rotation and steric effects. Measurements of ring-chain equilibrium thus appear to offer a useful method for characterizing the stiffness of relatively short and flexible chains.

Cyclic polymers: Synthetic strategies and physical properties

“…The main purpose of those studies was determination of frequency distribution (or weight fraction) of the individual cyclic oligomers in correlation with the Jacobson-Stockmayer theory of TCP. 120,121 Nonetheless, several authors determined the total weight fraction of all cyclic species in the virgin reaction mixtures and reported the following data. 176,179,181 The equilibrate of neat cyclo(dimethyl siloxane) contains at 110 C 15 6 1% of cyclics.…”

“…169 Ring-ring equilibration is also related to the theory of TCPs. 120,121 At 100% conversion, a clean TCP should yield the same mixture of cyclic products as an equilibration of a cyclic monomer or oligomer as exemplarily illustrated for poly(dimethyl siloxane)s in Scheme 47. Equilibrations of polysiloxanes and cyclosiloxanes were intensively studied by several research groups [169][170][171][172][173][174][175][176][177][178][179][180][181][182][183][184][185][186][187] either promoted by heating [169][170][171][172] or by strong protic acids or by potassium silanolates.…”

“…First, the frequency of cycles based on flexible chains [e.g., aliphatic polyesters or poly(dimethyl siloxane)] will decrease with DP À3/2 in the case of a KCP, but with DP À5/2 in the case of a TCP. 120,121 Second, at low and moderate conversions (e.g., up to 99.9%), a TCP yields more cycles than a KCP, when similar polymers are compared under similar conditions, because in the case of a TCP, the cycles are formed by two processes, ''back-biting'' and ''end-to-end'' cyclization, whereas only ''end-to-end'' cyclization is relevant in the case of a KCP, since, to the best of our knowledge, this difference has never been demonstrated before, an example should be presented by the mass spectra of Figure 4. 122 Spectrum A represents a poly(butylenes terephthalate), PBT, prepared from dimethyl terephthalate and an excess of 1,4-butane diol in bulk under the conditions of a TCP, whereas spectrum B is based on a PBT resulting from a KCP conducted again with an excess of 1,4-butane diol in bulk.…”

“…The most frequent type of equilibration reaction is the reversible formation of cyclic monomers and oligomers by ''back-biting'' from the most reactive chain end as illustrated in Scheme 36. 120,121 This type of equilibration involves the lowest energy of activation and has the consequence that three equilibria will be established: a chain-chain, a ring-chain, and a ring-ring equilibrium. According to the law of self dilution (eq 4), more and more cycles will be formed with increasing conversion, so that at conversion beyond 99%, the ring-ring equilibrium will dominate the thermodynamic parameters.…”

When Polymer Science Looked Easy

“…Experimentally, Jacobson was able to give support to the theory by observing changes in solution viscosity of the predicted magnitude upon dilution and reequilibration (54). In this part of his work he was advised by Charlie Beckmann, for I had by then left Columbia.…”