Transesterification in Mixtures of Poly(ethylene terephthalate) and Poly(ethylene naphthalene-2,6-dicarboxylate):  An NMR Study of Kinetics and End Group Effects

Abstract

Mixtures of poly(ethylene terephthalate) and poly(ethylene naphthalene-2,6-dicarboxylate) have been transesterified at temperatures between 553 and 573 K. The partially transesterified polymers were analyzed using 1 H NMR, and the rate constants for transesterification were obtained using a kinetic expression based on a second-order reversible reaction mechanism. The hydroxyl end groups have been shown to have a significant effect on the kinetics of the reaction by comparing rate constants obtained for the same polyester mixture but with hydroxyl end groups quantitatively esterified by trifluoroacetic acid. Carboxyl end groups do not have such a significant role in transesterification, and from the variation of rate constant at one temperature for a series of PET polymers with differing carboxyl to hydroxyl end groups, it appears that transesterification by direct ester-ester interchange is very small. The NMR data have also been used to calculate the randomness factor and number-average sequence length of the terephthalate sequences in the copolymer as transesterification progresses. The initially immiscible polyester mixture becomes miscible after a critical amount of transesterification takes place; no matter what reaction temperature is used, this homogenization takes place when the randomness factor has a value of 0.5. This does not correspond to completely random copolymer formation but suggests that the number-average sequence length of the terephthalate units in the copolyester is ca. 4-8.

The Effect of Molecular Weight of Polycaprolactone on the Ester Interchange Reactions during Melt Blending with Poly(ethylene terephthalate)

“…The ester interchange reactions between PET and PCL gave a result similar to PET and PEN blend systems. [16][17][18] On the other hand, if ester interchange in the PET/PCL blend is only done by direct transesterification, the degree of ester interchange reactions should be identical because the population of ester groups in the blends is the same regardless of the MW of PCL at given composition. In fact, however, the degree of ester interchange reactions in PET/PCL blends is influenced by the MW of PCL.…”

“…Recently, it is reconfirmed the fact that the importance of the role of alcoholysis by hydroxyl end group via the control of molecular weight (MW) of PET in the kinetics of the ester interchange reactions between PET and poly(ethylene naphthalene-2,6-dicarboxylate) (PEN). [16][17][18] Taking into account the aforementioned reports, one of the possible solutions for the problems in melt blending of PET and PCL may be the control of the MW of PCL component. Thus, lower MW of PCL component can lead to higher degree of ester interchange reactions in short blending time because it increases the concentration of hydroxyl end group as presented in Figure 1.…”

Addition‐Fragmentation Chain Transfer to Polymer in the Free Radical Ring‐Opening Polymerization of an Eight‐membered Cyclic Allylic Sulfide Monomer

“…It was suggested that interchange reactions analogous to those in polyester [3,4,17] and polyamide [18] systems may occur in case of the eight-membered disulfide monomer, 2-methyl-7-methylene-1,5-dithiacyclooctane (MDTO). [13] The idea of these interchange reactions was put forward based on the finding of bimodal MWDs, which were speculated to originate from backbiting via addition of the propagating sulfur radical species to one of the double bonds on the polymer backbone, with subsequent b-fragmentation (i.e.…”

End-group interchain exchange reaction in polymer blends: evolution of the block weight distribution

“…To this aim, they examine whether the rate constant (extracted from the above-mentioned kinetic equation for dyads) depends on the average MW of the initial blend components [9][10][11], study the interchange kinetics in blends of model compounds [12,13] or in polymer end-capped blends [14,15], or detect the difference in composition between the copolymer and the blend as a whole [16]. However, the results are not always easy to interpret, e.g., the discussion on the main interchange mechanism in the popular blend PET/PEN still lasts [13,14,17,18].…”