Isoconversional kinetic analysis of ring-opening polymerization of ε-caprolactone: Steric influence of titanium(IV) alkoxides as initiators

Abstract

Four titanium(IV) alkoxides, namely: Ti(IV) npropoxide (1), Ti(IV) n-butoxide (2), Ti(IV) tert-butoxide (3), and Ti(IV) 2-ethylhexoxide (4), have been used as initiators in the bulk ring-opening polymerization (ROP) of ε-caprolactone (ε-CL). The influence of the alkoxide group on the course of the ROP of ε-CL was investigated by means of 1 H-NMR and differential scanning calorimetry (DSC). The 1 H-NMR spectra confirmed that the ROP reaction of ε-CL proceeded via the widely accepted coordinationinsertion mechanism for each of the four initiators. Isoconversional methods have been used to evaluate non-isothermal DSC data via the equations of Friedman, Kissinger-AkahiraSunose (KAS) and Ozawa-Flynn-Wall (OFW). The kinetic studies showed that the polymerization rate for the four initiators (1-4) was in the order of 1>2≈4>3. The lowest activation energies (40-47, 42-44, and 49-52 kJ/mol for the Friedman, KAS and OFW methods respectively) were found in the polymerizations using Ti(IV) n-propoxide (1), while the highest activation energies (84-107, 77-87, and 80-91 kJ/mol for the Friedman, KAS and OFW methods respectively) were obtained using Ti(IV) tert-butoxide (3). Differences in the rates of polymerization and the activation energies amongst the four initiators appeared to be governed mainly by the different degrees of steric hindrance in the initiator structure. These results represent important findings regarding the steric influence of the alkoxide groups on the kinetics of the ROP of ε-CL initiated by titanium(IV) alkoxides.

DSC Kinetics Analysis for the Synthesis of Three‐Arms Poly(ε‐caprolactone) Using Aluminum Tri‐sec‐Butoxide as Initiator

“…1a. The results show that the polymerization exotherms shift to a higher temperature range as the heating rate increases, which is similar to those reported in the literature [9,13]. The polymerization process occurred at a high-temperature range indicating the slow initiation step due to the steric interference of the methyl (CH 3 ) group connected to aluminiumoxygen (Al-O).…”

“…The DSC technique is frequently used to study the kinetics of the polymerization process [9,13,26,27]. It is accepted that this technique is fast to study the kinetics of polymerization reactions [9,13]. In this work, this technique is first applied to determine the important kinetic parameters for ROP of ε-CL using Al(OsecBu) 3 as the initiator.…”

Chemical Processes

“…An example of such behavior has been reported [18] for ring-opening polymerization of ε-caprolactone initiated by a series of titanium (IV) alkoxides. As seen in Fig.…”

“…However, it should not be entirely unexpected if one considers the temperature of polymerization relative to the temperatures of the glass transition and melting of poly(ε-caprolactone). Polymerization of ε-caprolactone commences above 150 °C [18]. This temperature is significantly higher than T g = −64 °C and T m = 69 °C of poly(ε-caprolactone) [19].…”

Chemical synthesis of a biodegradable PEGylated copolymer from ε-caprolactone and γ-valerolactone: evaluation of reaction and functional properties

“…Some biodegradable polyesters, such as polyhydroxyalkanoates (e.g., poly 3-hydroxybutyrate (P3HB) and poly 3-hydroxybutyrateco-3-hydroxyvalerate (P3HB3HV)), are produced via the biological route [11][12][13], more expensive and less controlled than a conventional chemical polymerisation. The most common chemical strategy to synthesise biodegradable polyesters is the Ring-Opening Polymerisation (ROP) starting from cyclic esters (lactones); ROP is a well-consolidated reaction scheme for the polymerization of lactide [14][15][16][17][18] and glycolide [19] (6-membered dimers of lactic and glycolic acids respectively), ε-caprolactone (7-membered ring [20][21][22][23]), δ-valerolactone (6-membered [24]) and β-butyrolactone (4-membered [25][26][27][28]). …”