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The solvent-free ring-opening polymerization (ROP) of ε-caprolactone (ε-CL) with the tri-n-butyltin(IV) n-butoxide/aluminum(III) tri-s-butoxide mixed initiators [nBu3SnOnBu/Al(OsBu)3] was successfully studied by the non-isothermal differential scanning calorimetry for the first time. The nBu3SnOnBu/Al(OsBu)3 mixed initiators were completely dissolved in ε-CL and could be utilized to produce high molecular weight poly(ε-caprolactone) (PCL). The presence of the Al(OsBu)3 in the mixed initiators did not interfere with the initiation temperature and could increase the propagation rate of ε-CL. The activation energies (Ea) obtained from the peak methods of Kissinger and Ozawa for the ROP of ε-CL initiated by the nBu3SnOnBu/Al(OsBu)3 (1.0:2.0 mol%) (74.2–78.6 kJ/mol) were lower than nBu3SnOnBu/Al(OsBu)3 (1.0:1.0 mol%) (75.8–80.3 kJ/mol) and the single nBu3SnOnBu initiator (78.3–82.8 kJ/mol), respectively. From the proton-nuclear magnetic resonance spectroscopy (1H-NMR), the polymerization mechanism was proposed through the classic coordination–insertion mechanism that comprised: (i) the coordination of ε-CL and nBu3SnOnBu with Al(OsBu)3 and (ii) the nucleophilic attacked of n-butoxy group (–OnBu) from nBu3SnOnBu to the carbonyl carbon of ε-CL. From the small-scale synthesis (4 g) of PCL, our nBu3SnOnBu/Al(OsBu)3 mixed initiators could control the polymerization of ε-CL by adjusting the concentration of Al(OsBu)3. The number and weight average molecular weights (Mn and Mw) of PCL increased with decreasing concentration of mixed initiator. The nBu3SnOnBu/Al(OsBu)3 mixed initiators produced PCL with Mn, Mw, dispersity (Đ), and %yield in the range of 1.3 × 104–4.0 × 104 g/mol, 2.9 × 104–6.5 × 104 g/mol, 1.65–2.26 and 50–95%, respectively. The larger-scale polymerization (250 g) of ε-CL with the nBu3SnOnBu/Al(OsBu)3 mixed initiators was preliminary conducted at 150 °C for 48 h. PCL with higher Mn (7.3 × 104 g/mol) and Mw (1.2 × 105 g/mol) was synthesized. The nBu3SnOnBu/Al(OsBu)3 mixed initiators acted as an effective candidate for the production of the high molecular weight PCL via solvent-free polymerization. [ABSTRACT FROM AUTHOR]

Understanding the kinetics and mechanisms of polymerization, particularly the role of a catalyst or initiator used, allows for the manipulation and control of the fabrication of new materials by the most convenient, straightforward routes. The kinetics of the bulk ring‐opening polymerization (ROP) of d‐lactide, a useful monomer employed to control the properties of poly(l‐lactide), have been studied herein to identify a relatively quick (1 h), controlled, yet convenient route to moderately high molecular weight poly(d‐lactide). Tin(II) octoate (Sn(Oct)2), Sn(Oct)2/n‐butanol (nBuOH) and liquid tin(II) butoxide (Sn(OnBu)2) as initiating systems were investigated by non‐isothermal differential scanning calorimetry (DSC). Isoconversional methods were employed to determine the activation energy (Ea) for each reaction. The results showed that liquid Sn(OnBu)2 was a more efficient initiator than the commonly reported initiating systems of Sn(Oct)2 and Sn(Oct)2/nBuOH in terms of producing higher polymerization rates and polymer molecular weights. High‐molecular‐weight poly(d‐lactide) (1.8 × 105 Da) with moderate dispersity (Ð = 1.3) was obtained using 0.1 mol% liquid Sn(OnBu)2 as the initiator at 120 °C. This work describes the applications of non‐isothermal DSC and isoconversional methods in comparing the effectiveness of different initiators in the bulk ROP of d‐lactide for the first time. © 2023 Society of Chemical Industry. [ABSTRACT FROM AUTHOR]

• AHAs acted as the green and metal-free initiator for the ROP of ε -CL. • Non-isothermal DSC kinetics showed that the reactivity of CA > MA > MDA. • Solvent-free ROP of ε -CL with AHAs occurs via the activated monomer mechanism. • Microwave irradiation reduces the synthesis time of PCL. • AHAs produces PCL with M n values of 4.28×103 – 1.43×104 g/mol. Metal-free and green α ‑hydroxy acids (AHA) such as l -malic (MA), DL-mandelic acid (MDL), and citric acid (CA) were successfully and effectively utilized as an effective initiator for the solvent-free ring-opening polymerization (ROP) of ε -caprolactone (ε -CL). The performance of AHAs in the polymerization of ε -CL was completely and powerfully investigated via the non-isothermal differential scanning calorimetry (DSC). The proceed of ROP of ε -CL with AHAs could be real-time monitored by the obtained polymerization exotherms at different heating rates. The polymerization exotherms obtained from the ROP of ε -CL with CA occurred at a lower temperature range than MA, and MDA, respectively. From the kinetics study, the average activation energy (E a) values for the ROP of ε -CL with CA (38.0 ± 1.8 kJ mol−1) were lower than MA (45.2 ± 3.6 kJ mol−1) and MDA (48.8 ± 6.2 kJ mol−1). Using the first-order model fitting, the values of pre-exponential factor (ln A 0) for the ROP of ε -CL with CA, MA, and MDA were 7.0 ± 0.3, 8.5 ± 0.2, and 8.9 ± 0.3, respectively. The effectiveness of AHAs in the synthesis of PCL was clarified by conducting a larger-scale (4.0000 g) polymerization using conventional heating and microwave (MW) irradiation methods. From conventional heating, the green AHAs produced PCL with the number average molecular weight (M n) and dispersity (Đ) values in the range of 5.18 × 103 - 1.43 × 104 g mol−1 and 1.14–2.02, respectively. The irradiation by MW could enhance the synthesis of PCL by reducing the synthesis time. By using the MW power of 450 W and irradiation time of 30 min, the PLC was obtained from the ROP of ε -CL with MA and MDA initiators, and the M n of the obtained PCL from MW heating was 4.28 × 103 - 8.45 × 103 g mol−1. The mechanism for the ROP of ε -CL with all AHAs was proposed through the activated monomer mechanism. [Display omitted] [ABSTRACT FROM AUTHOR]

Biodegradable poly(ε-caprolactone) (PCL) was successfully synthesized by the green polymerization process that was conducted in the absence of heavy metal catalyst and toxic solvent. L-Lactic (LLA) and glycolic acids (GA) were utilized as green initiator for the bulk ring-opening polymerization (ROP) of ε-caprolactone (ε-CL). These organic initiators could produce PCL with number average molecular weight (Mn) in the range of 8.46 × 103–1.98 × 104 g/mol and molecular weight distribution (MWD) of 1.71–1.81. GA could produce higher molecular weight PCL than LLA under identical synthesis condition. The catalytic performance of these initiators in the ROP of ε-CL was completely investigated by the non-isothermal differential scanning calorimetry (DSC). From non-isothermal DSC kinetics analysis, the reactivity of GA was higher than LLA in the bulk ROP of ε-CL as supported by the lower values of activation energy (Ea) and frequency factor (A) of GA than LLA initiator. The polymerization mechanism for the ROP of ε-CL initiated by LLA and GA was proposed through the activated monomer mechanism. [ABSTRACT FROM AUTHOR]

The kinetics of ring-opening polymerization (ROP) of ε-caprolactone (ε-CL) initiated by 1.0, 1.5 and 2.0 mol% of stannous(II) octoate/n-hexanol (Sn(Oct)2/n-HexOH) wase successfully studied by non-isothermal differential scanning calorimetry (DSC) at heating rates of 5, 10, 15 and 20 °C/min. The DSC polymerization kinetic parameters of ε-CL were calculated using differential (Friedman) and integral isoconversional methods (Kissinger-Akahira-Sunose, KAS). The average activation energy (Ea) values obtained from Friedman and KAS methods were in the range of 64.9–70.5 kJ/mol and 64.9–80.4 kJ/mol, respectively. The values of frequency factor (A) were determined from model fitting method using Avrami-Erofeev reaction model. The average values of A for the ROP of ε-CL initiated by 1.0, 1.5 and 2.0 mol% of Sn(Oct)2/n-HexOH (1:2) were 7.3x107, 2.8x106 and 1.2x106 min−1, respectively. From kinetics studied, the polymerization rate of ε-CL increased with increasing initiator concentration. The performance of Sn(Oct)2/n-HexOH in the synthesis of poly(ε-caprolactone) (PCL) was investigated by bulk polymerization at temperatures of 140, 160 and 180 °C. Sn(Oct)2/n-HexOH (1:2) could produce high number average molecular weight ( M n ‾ = 9.0 × 104 g/mol) and %yield (89%) of PCL in a short period of time at Sn(Oct)2 concentration of 0.1 mol% and temperature of 160°C. The mechanism of the ROP of ε-CL with Sn(Oct)2/n-HexOH was proposed through the coordination-insertion mechanism. [ABSTRACT FROM AUTHOR]

ABSTRACT The kinetics of the ring-opening polymerization (ROP) of ε-caprolactone ( ε-CL) initiated by soluble aluminum tri- sec-butoxide (Al(O secBu)3) has been investigated by the differential scanning calorimetry (DSC). The DSC polymerizations were carried out under nonisothermal and isothermal conditions to obtain three-arms poly( ε-caprolactone) (PCL). From nonisothermal DSC, the polymerization rate (d α/d t) increased with increasing heating rates. The values of Ea were determined from Kissinger ( [ABSTRACT FROM AUTHOR]

• Activation parameters for ROP of ε -caprolactone can be rapidly obtained from DSC. • Reactivity of SnCl 2 is higher than ZnCl 2 in the polymerization of ε -caprolactone. • SnCl 2 produces very high molecular weight PCL in a short time. • Effectiveness of ZnCl 2 in PCL synthesis can be improved by increasing temperature. The kinetics of the ring-opening polymerization (ROP) of ε -caprolactone (ε -CL) initiated by 1.0 mol% of tin(II) chloride (SnCl 2) and zinc(II) chloride (ZnCl 2) was completely investigated by the differential scanning calorimetry (DSC) technique. The fast method to determine the activation parameters such as activation enthalpy (∆ H ≠) and activation entropy (∆ S ≠) was successfully developed basing on the transition state theory and isoconversional method. From Friedman isoconversional method, the values of activation energy (E a) for the ROP of ε -CL initiated by SnCl 2 (36.2 ± 1.5 to 40.8 ± 1.5 kJ/mol) were lower than ZnCl 2 (51.9 ± 2.8 to 62.3 ± 2.8 kJ/mol). From Starink isoconversional method, the E a values for the ROP of ε-CL initiated by SnCl 2 (32.3 ± 1.1 to 35.8 ± 1.1 kJ/mol) were also lower than ZnCl 2 (59.2 ± 0.8 to 62.1 ± 0.8 kJ/mol). By using the compensation parameters, the reconstructed monomer conversion function (f (α)) was fitted with the Avrami-Erofeev nucleation model (A2, f (α) = 2(1- α)[- ln (1- α)]1/2). The values of frequency factor (A) for the ROP of ε -CL with SnCl 2 and ZnCl 2 were 4.3 × 103to 1.6 × 104 min−1 and 2.1 × 105 to 5.3 × 105 min−1, respectively. From the developed rate equation, the values of ∆ H ≠ and ∆ S ≠ could be conveniently determined from dynamic heating. The obtained ∆ H ≠ values for the ROP of ε -CL initiated by SnCl 2 and ZnCl 2 were similar to the E a values. The ∆ S ≠ values for the transition state of the ROP of ε -CL initiated by SnCl 2 (-152.0 to -161.7 J/mol.K) were lower than ZnCl 2 (-129.6 to -153.1 J/mol.K). The kinetics and the stability of transition state information demonstrated that the reactivity of SnCl 2 in the ROP of ε -CL was higher than ZnCl 2. The mechanism of the ROP of ε -CL with SnCl 2 and ZnCl 2 was proposed through a classical coordination-insertion mechanism. From poly(ε -caprolactone) (PCL) synthesis via solvent-free polymerization, SnCl 2 acted as the highly effective initiator than ZnCl 2. The highest number average molecular weight (M n) of PCLs obtained from the SnCl 2 and ZnCl 2 initiator were 1.8 × 105 g/mol and 3.6 × 104 g/mol, respectively. The effectiveness of the slow ZnCl 2 initiator in the production of high molecular weight and %yield of PCL could be improved by increasing the synthesis temperature. These SnCl 2 and ZnCl 2 compounds acted as a powerful initiator for the synthesis of PCL. The obtained results from this work were useful for understanding the transition state formulation in the ROP of other cyclic esters with various initiating systems that still in our attention and would be described in our future work. [Display omitted] [ABSTRACT FROM AUTHOR]

The catalytic behavior of the novel tin(II) n -butyl l -lactate (Sn(OCH(CH 3 )COO n C 4 H 9 ) 2 ) initiator in the ring-opening polymerization (ROP) of ε- caprolactone ( ε -CL) was firstly investigated by non-isothermal DSC. The Sn(OCH(CH 3 )COO n C 4 H 9 ) 2 initiator was successfully synthesized from the reaction of tin(II) chloride (SnCl 2 ), diethylamine (Et 2 NH) and n -butyl l -lactate (CH 3 CH(OH)COO n C 4 H 9 ). The synthesized Sn(OCH(CH 3 )COO n C 4 H 9 ) 2 was characterized by FT-IR, 1 H NMR and 13 C NMR techniques. The advantages of this initiator were high oxygen-moisture stability and solubility in common organic solvent. From DSC analysis, the polymerization rate of ε -CL was controlled by Sn(OCH(CH 3 )COO n C 4 H 9 ) 2 concentration. The average values of activation energy ( E a ) obtained from Starink isoconversional method for the ROP of ε -CL initiated by 1.0, 2.0 and 3.0 mol% of Sn(OCH(CH 3 )COO n C 4 H 9 ) 2 were 74 ± 5, 72 ± 5 and 68 ± 2 kJ/mol, respectively. Furthermore, the aggregation and non-aggregation equilibrium of Sn(OCH(CH 3 )COO n C 4 H 9 ) 2 initiator in the ROP of ε -CL was also investigated by non-isothermal DSC. The degree of aggregation ( m ) of initiator was rapidly determined using new derived equation based on non-isothermal DSC approach. The polymerization mechanism was also studied and proposed through the coordination-insertion mechanism. [ABSTRACT FROM AUTHOR]

The kinetics of ring-opening polymerization (ROP) of ϵ- caprolactone ( ϵ -CL) initiated by 1.0 mol% of the tributyltin alkoxides (Bu 3 SnOR; R = Me, Et, n Pr and n Bu) was investigated by non-isothermal DSC technique. The DSC curves showed the dependency of polymerization exotherms with the heating rate. The polymerization rate increased with increasing of heating rate for all initiating systems. The values of activation energy ( E a ) obtained from the peak method of Kissinger for Bu 3 SnOMe, Bu 3 SnOEt, Bu 3 SnO n Pr and Bu 3 SnO n Bu initiated ROP of ϵ -CL were 52.4, 70.3, 75.9 and 78.0 kJ/mol, respectively. The values of E a increased with increasing of alkoxy chain length but polymerization rate decreased. The variation of E a with monomer conversion was investigated by Friedman and Starink isoconversional methods. The Bu 3 SnO n Bu initiator produced the highest molecular weight and %yield of poly( ϵ- caprolactone) (PCL). [ABSTRACT FROM AUTHOR]