Catalytic Ring-Opening (Co)polymerization of Semiaromatic and Aliphatic (Macro)lactones

Abstract

The ring-opening polymerization (ROP) of cyclic butylene terephthalate oligomers (cBT) using an aluminum salen catalyst was investigated. The kinetic analysis of the ROP of cBT in tetrachloroethane (TCE) revealed a firstorder dependence of the rate constant in catalyst as well as monomer concentration. Comparison with the ROP in other solvents showed that TCE significantly retards the reaction by short-term reversible catalyst deactivation and by long-term permanent deactivation. The apparent activation energy for the ROP of cBT and ε-caprolactone (CL) were determined independently, and the difference in reactivity was used to investigate the possibility to synthesize blocky copolymers. Sequence distribution analysis of the copolymers obtained over a period of time from a single feed copolymerization revealed that over the full reaction range the degree of randomness was high. A sequential feed approach, in which CL was added after the polymerization of cBT was completed, showed that the propagation reaction was not fast enough to avoid transesterification, yielding copolymers with an increasing degree of randomness over time. Additionally, the copolymerization of cBT with ω-pentadecalactone (PDL) was performed in bulk at temperatures above the crystallization temperature of poly(butylene terephthalate) (PBT), yielding random copolymers over the full composition range between polypentadecalactone (PPDL) and PBT. Copolymerizations using aluminum salen as catalyst were rapid and high molecular weights could be achieved. The melting temperature of both PPDL and PBT decreased upon the introduction of either counit, reaching a eutectic point between 50 and 70 mol % PDL. Furthermore, a combination of thermal analysis and X-ray diffraction shows that PDL units are fully excluded from the PBT crystal lattice, while butylene terephthalate units are partially incorporated into the PPDL crystal lattice.

Organocatalyzed ring‐opening polymerization of cyclic butylene terephthalate oligomers

“…S1), size exclusion chromatography has been the preferred analytical technique employed to determine monomer conversion. As reported previously by Brunelle et al and Duchateau et al, the latter can be directly obtained from the ratio of the integration areas below the peaks attributed to CBT and PBT in chromatograms of crude reaction samples. For this purpose the PBT and CBT peaks have to be well separated and identified, as represented in Figure , and monomer conversion can then be directly obtained from eq : in which and are the areas under the peaks attributed to CBT and PBT, respectively.…”

“…Because CBT is a mixture of cyclic oligomers possessing 2–7 butylene terephthalate units (BTu), the determination of monomer conversion appears less straightforward than with well‐defined cyclic esters. Consequently, polymerization rates and monomer conversions have often been expressed with regards to the number of BTu involved in the reaction and not with regards to the concentration of each type of cyclic oligomer . In addition, because CBT and PBT have very similar chemical shifts in 1 H NMR (see Fig.…”

“…However, it also induces an increase in Đ which suggests that side reactions (transesterification) occur. Because polymerization of CBT has been reported to proceed extremely fast when employing other catalysts, it can be envisaged that these transesterification reactions only take place after polymerization completion and not during the course of the polymerization . We thus studied the influence of polymerization time and TBD content on the ROP of CBT in bulk.…”

“…Such phenomenon has also been observed by Duchateau et al, and has been attributed to the presence of impurities, in the form of linear oligomeric butylene terephthalates, in the commercial monomer. Because some linear oligomeric butylene terephthalates possess hydroxyl end‐groups, they can directly initiate the ROP of CBT or induce chain‐transfer reactions, and thus contribute to the polymerization system . Nevertheless, the possibility of synthesizing PBT up to 50 kg·mol −1 with desired chain length and chain‐end functionality prompted us to employ this system for the synthesis of a PEO‐ b ‐PBT block copolymer.…”

Tuning the thermal properties of poly(ethylene)‐like poly(esters) by copolymerization of ε‐caprolactone with macrolactones, in the presence of a pyridylamidozinc(II) complex

“…Conversely, the copolymerization of other macrolactones, such as ethylene brassilate, with smaller lactones was also described in the literature . Copolymerization of semiaromatic macrolactones, the cyclic butylene terephthalate oligomers, with pentadecalactone has been also reported . To the best of our knowledge, the copolymerization of 6HDL with ω‐PDL has not been described in the literature, and it is reported herein for the first time.…”