Effects of Residual Zinc Compounds and Chain-End Structure on Thermal Degradation of Poly(ε-caprolactone)

Abstract

Effects of chain-end structure and residual metal compounds on thermal degradation of poly(epsilon-caprolactone) (PCL) were investigated by means of thermogravimetric and pyrolysis-gas chromatograph mass spectrometric analyses. Four types of PCL samples with different chain-end structures (alpha-carboxylic acid-omega-hydroxyl-PCL, alpha-dodecyl ester-omega-hydroxyl-PCL, alpha-carboxylic acid-omega-acetyl-PCL, and alpha-dodecyl ester-omega-acetyl-PCL) were prepared by ring-opening polymerization of epsilon-caprolactone in the presence of zinc-based catalyst and by subsequent acetylation reaction of polymers with acetic anhydride. PCL samples with different zinc contents were obtained by washing with acetic acid in chloroform solution of polymer. Thermal degradation behaviors of these PCL samples with different chain-end structures were examined under both isothermal and nonisothermal conditions. From both the isothermal and nonisothermal experiments, the thermal degradation of PCL samples containing high amounts of residual zinc compounds from synthesis process revealed the selective unzipping depolymerization step below 300 degrees C producing epsilon-caprolactone exclusively. In contrast, zinc-free PCL samples were stable at temperatures below 300 degrees C, and the thermal degradation occurred only at temperatures above 300 degrees C regardless of the chain-end structure. From (1)H NMR analysis of the residual molecules after isothermal degradation of zinc-free PCL, it was confirmed that the omega-chain-end of residual molecules was 5-hexenoic acid unit. However, the cyclic monomer and oligomers were detected as the volatile products of zinc-free PCL samples. These results suggest that the dominant reaction of thermal degradation for PCL above 300 degrees C is a competition between the random chain scission via cis elimination reaction and the cyclic rupture via intramolecular transesterification of PCL molecules.

Thermal Degradation of Environmentally Degradable Poly(hydroxyalkanoic acid)s

“…Purified PCL sample containing 3 ppm of Zn compounds (M n ¼ 113 000, M w =M n ¼ 1.6), PCL sample containing 2 600 ppm of Zn compounds (M n ¼ 113 000, M w =M n ¼ 1.5). [62] P(4HB) and PVL, each of the DTG curves of PCL recorded at different heating rates revealed only one peak. In addition, the TGA and DTG curves of PCL sample protected with acetyl groups at o-hydroxyl chain-ends showed profiles that were identical to the non-end-capped PCL sample.…”

“…Several groups investigated the thermal stability of PCL in the high temperature region by using various analytical techniques, although there is no consistency in the mechanism. [57][58][59][60][61][62] We also prepared PCL (M n ¼ 113 000, M w =M n ¼ 1.6) by a ring-opening polymerization of e-CL in the presence of Zn(CH 2 CH 3 ) 2 /H 2 O catalyst. [62] Figure 12 shows the TGA and DTG curves of purified PCL at a heating rate of 10 8C Á min À1 under nitrogen atmosphere.…”

“…TIC of Py-GC/MS of PCL at various temperatures (A) and relative mass spectra of PCL pyrolysis products (B). [62] Thermal Degradation of Environmentally Degradable Poly(hydroxyalkanoic acid)s…”

Fire and Gas Barrier Properties of Poly(styrene-co-acrylonitrile) Nanocomposites Using Polycaprolactone/Clay Nanohybrid Based-Masterbatch

“…Previous studies have shown [28,29] the possible degradation of PCL in the presence of catalytic residues. In order to avoid any undesirable parallel effect, Irganox MD1024 (0.05 wt%), a metal deactivator, was blended with SAN using a Brabender internal mixer operating at 220…”

Pyrolysis of polyphenylenes with PCL or/and PSt side chains

“…Taking into account that GPC apparatus was calibrated with PSt standards, in the case of macromonomers 1-3, the value calculated from 1 H NMR was considered more reliable and was used for further calculations. Though there were inconsistencies in the proposed thermal degradation mechanism for PCL in the literature, the formation of v-hydroxyl and ketene end-groups have been confirmed by several groups [26][27][28][29][30]. It has been determined that on isothermal heating PCL degrades by pure unzipping of the monomer from the hydroxyl end of the polymer, whereas a parallel mechanism including random chain scission via cis-elimination reaction and cyclic rupture via trans-esterification of PCL molecules was suggested under non-isothermal conditions.…”