Ring-opening polymerization of ε-caprolactone initiated by tin(II) octoate/n-hexanol: DSC isoconversional kinetics analysis and polymer synthesis

Figures & data

Figure 1. Non-isothermal DSC curves for the ROP of ε-CL initiated by SnOct₂/n-HexOH (1:2): (a) 1.0, (b) 1.5, (c) 2.0 mol% at heating rates of 5, 10, 15 and 20°C/min and (d) non-isothermal DSC curve for the ROP of ε-CL initiated by 1.0, 1.5 and 2.0 mol% Sn(Oct₂)/n-HexOH (1:2) at a heating rate of 10°C/min.

Figure 2. Plots of monomer conversion against temperature for the ROP of ε-CL initiated by (a) 1.0, (b) 1.5 and (c) 2.0 mol% of Sn(Oct)₂/n-HexOH (1:2) at heating rates of 5, 10, 15, and 20°C min⁻¹.

Figure 3. Plots of polymerization rate against temperature for the ROP of ε-CL initiated by (a) 1.0, (b) 1.5 and (c) 2.0 mol% of Sn(Oct)₂/n-HexOH (1:2) at heating rates of 5, 10, 15, and 20°C min⁻¹.

Figure 4. The KAS plots for the ROP of ε-CL initiated by (a) 1.0, (b) 1.5 and (c) 2.0 mol% of Sn(Oct)₂/n-HexOH (1:2).

Figure 5. Plots of E_a against monomer conversion obtained from the ROP of ε-CL initiated by 1.0, 1.5 and 2.0 mol% of Sn(Oct)₂/n-HexOH (1:2): (a) Friedman and (b) KAS isoconversional method.

Table 1. Ideal reaction mechanism and kinetics model for solid state reaction [12,18,26]

Model	Symbol	f(α)	Model description
Reaction model	A1 (F1)	(1-α)	Unimolecular decay law (instantaneous nucleation and unidimensional growth)
Nucleation models	A2	2(1-α)[-ln(1-α)]^1/2	Avrami-Erofeev (random instant nucleation and 2D growth)
	A3	3(1-α)[-ln(1-α)]^2/3	Avrami-Erofeev (random instant nucleation and 3D growth)
	P2	2α^1/2	Power law (nuclei growth is a constant)
	P3	3α^2/3	Power law (nuclei growth is a constant)
Geometricalcontraction models	R2	2(1-α)^1/2	Phase boundary control reaction (contraction area, i.e., bidimensional shape)
	R3	3(1-α)^2/3	Phase boundary control reaction (contraction area, i.e., tridimensional shape)
Diffusion models	D1	1/(2α)	1D diffusion (disk particle shape)
	D2	1/[-ln(1-α)]	2D diffusion (cylinder particle shape)

Table 2. Compensation parameters for f(α) = m(1-α)^m[-ln(1-α)]^m−1/m (m = 1.5 and 2.0) for the ROP of ε-CL with Sn(Oct)₂/n-HexOH (1:2) at different heating rates

Initiating systems	Heating rate (°C min^−1)	a	b	lnA0
2.0 mol% Sn(Oct)2/n-HexOH (1:2)	5	0.279	−1.77	17.9
	10	0.275	−1.35	18.0
	15	0.269	−0.96	18.0
	20	0.275	−1.35	18.0
1.5 mol% Sn(Oct)2/n-HexOH (1:2)	5	0.289	−1.86	18.0
	10	0.282	−1.32	18.1
	15	0.278	−1.00	18.2
	20	0.273	−0.75	18.0
1.0% Sn(Oct)2/n-HexOH (1:2)	5	0.294	−2.06	17.0
	10	0.289	−1.37	17.4
	15	0.281	−1.00	17.2
	20	0.276	−0.74	17.2

Figure 6. Plots of f(α) against α for the reaction models shown in Table 1 (line) and the experimental plots of f(α) against α for the ROP of ε-CL initiated by 1.0, 1.5 and 2.0 mol% of Sn(Oct)₂/n-HexOH (1:2) at a heating rate of 5 °C min⁻¹ (dot).

Scheme 1. The proposed mechanism of ROP of ε-CL initiated with Sn(Oct)₂/n-HexOH.

Table 3. Number average molecular weight ($\overline{M_{\mathrm{n}}}$), weight average molecular weight ($\overline{M_{\mathrm{w}}}$), polydispersity index (PDI) and %yield of PCLs from bulk polymerization of ε-CL initiated by Sn(Oct)₂/n-HexOH at 140, 160 and 180 °C for 1 h

Entries	Temperature (°C)	[I] (mol%)	$\overline{{\mathit{M}}_{\mathbf{n}}}$^a (g/mol)	$\overline{{\mathit{M}}_{\mathbf{w}}}$^a (g/mol)	PDI^a	%Yield^b
1	140	0.1	4.8×10^4	7.8×10^4	1.6	78
2		0.2	4.1×10^4	5.8×10^4	1.4	79
3		0.3	3.6×10^4	6.0×10^4	1.7	91
4		0.4	3.4×10^4	5.8×10^4	1.7	95
5		0.5	2.7×10^4	4.6×10^4	1.7	96
6	160	0.1	9.0×10^4	15.5×10^4	1.7	86
7		0.2	5.9×10^4	10.4×10^4	1.8	96
8		0.3	5.2×10^4	9.2×10^4	1.8	95
9		0.4	4.9×10^4	8.8×10^4	1.8	91
10		0.5	4.1×10^4	7.2×10^4	1.7	97
11	180	0.1	6.7×10^4	12.7×10^4	1.9	95
12		0.2	6.5×10^4	11.8×10^4	1.8	95
13		0.3	5.0×10^4	8.6×10^4	1.7	91
14		0.4	4.9×10^4	8.3×10^4	1.7	96
15		0.5	3.7×10^4	6.3×10^4	1.7	91

^aGPC Measurements in THF at 40 °C calibrated with polystyrene standard. ^bAmount of polymer formed after precipitation in methanol.

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