On the Effect of Alkyl End Group in Poly(ϵ-caprolactone) Oligomers: Preparation and Characterization

Abstract

Poly(ϵ-caprolactone) (PCL) oligomers with α-hydroxyl-ω-alkyl end groups (alkyl =–CH₂–[CH₂–CH₂]_m–CH₃, where m = 1, 2, 4, 5, 6, 7, 8, 9, and 10) were synthesized by ring-opening polymerization (ROP) of ϵ-caprolactone (CL) catalyzed by ammonium decamolybdate (NH₄)₈[Mo₁₀O₃₄] and using aliphatic primary alcohols as initiators (HO–CH₂–[CH₂–CH₂]_m–CH₃, where m = 1, 2, 4, 5, 6, 7, 8, 9, and 10). The characterizations of the PCL oligomers were determined by MALDI-TOF, GPC, FT-IR, SAXS and ¹H and ¹³C NMR. The effects of alkyl end groups on thermal properties of the PCL oligomers were analyzed by DSC and TGA.

Keywords:

• Alkyl end group
• Crystallinity
• Oligomer
• Poly(ϵ-caprolactone)

ACKNOWLEDGMENTS

J.E.B. is much indebted to the Instituto de Ciencia y Tecnología de Polímeros (CSIC), Consejo Nacional de Ciencia y Tecnología (CONACYT, México) and Sistema Nacional de Investigadores (SNI, México). J.E.B. thanks MA. Jennifer Lee Ó'Donnell for her assistance. A.M.F. and J.E.B. thank the Ministerio de Ciencia e Innovación for its financial support of the work (MAT 2008-00619/MAT) and in accessing the synchrotron radiation source (experiment 16-2-70) in the European Synchrotron Radiation Facility (ESRF) in Grenoble (France), and François Fauth and Ana Pastor for their help on the beamline BM16. J.E.B. thanks to Mario Luzón and Jesús L. Pablos for obtaining GPC chromatograms. Finally, J.E.B. thanks A.M.F. for believing in the ideas and financial support of the reagents and Dr. José Luis Chiara for advising in the use of glovebox.

Notes

^a Polymerization at 150°C for 1 h with 50 mmol of CL, a CL/Initiator molar ratio of 10 was used.

^b Determined by ¹H NMR in CDCl₃.

^c After recrystallization with chloroform/methanol.

^d Obtained from the equation M _n(calcd) = (MW(CL)).(mmolCL/mmolROH) +MW(ROH), where MW is the molecular weight of ϵ-caprolactone (CL) monomer or hydroxylic compound (ROH).

^e Obtained from the equation M _n(NMR) = (DP_PCL x MW(CL)) +MW(ROH), where MW is the molecular weight of ϵ-caprolactone (CL) monomer or hydroxylic compound (ROH).

^f Determined by gel permeation chromatography (GPC) using polystyrene standars.

^g Obtained from the equation % End group (% EG) = (MW_initiator/M _n(NMR)) × 100, where MW_initiator is the molecular weight of initiator (ROH).

^h Respect to feed monomer (CL) and initiator (ROH).

ⁱ non-linear alcohol.

^a Oligo-esters obtained by ammonium decamolybdate as catalyst (except PCL10a) and after recrystalization with chloroform/methanol.

^b Obtained from the equation % End group (% EG) = (MW_initiator/M _nPCL) × 100, where MW_initiator is the molecular weight of initiator (ROH).

^c Obtained by DSC analysis.

^d Obtained from the equation ΔH _mPCL = ΔH _m – (ΔH _m. x_EG) where x_EG is the weight fraction of end group in the PCL oligo-ester.

^e Obtained from ΔH _mPCL.

^f oligomer obtained by Al(OiPr)₃ as catalyst.

^g second peak.

^a Oligo-esters obtained by ammonium decamolybdate as catalyst and after recrystalization with chloroform/methanol.

^b Determined by ¹H NMR in CDCl₃.

^c Obtained from the equation M _n(NMR) = (DP_PCL x MW(CL)) +MW(ROH), where MW is the molecular weight of ϵ-caprolactone (CL) monomer or hydroxylic compound (ROH).

^d Obtained from the equation % End group (% EG) = (MW_initiator/M _n(NMR)) × 100, where MW_initiator is the molecular weight of initiator (ROH).

^e Obtained by DSC analysis.

^f Obtained from the equation ΔH _mPCL = ΔH _m – (ΔH _m. x_EG) where x_EG is the weight fraction of 1-docosanol in the PCL oligo-ester.

^g Obtained from ΔH _mPCL.