Hydroxy‐terminated poly(ε‐caprolactone‐co‐δ‐valerolactone) oligomers: Synthesis, characterization, and polyurethane network formation

Abstract

AbstractDifunctional hydroxy‐terminated poly(ε‐caprolactone‐co‐ε‐valerolactone) (PCV) oligomers were synthesized by the diol‐initiated bulk copolymerization of ε‐caprolactone (C) and δ‐valerolactone (V). The two homopolymers were semicrystalline, with almost identical melting temperatures; copolymerization significantly lowered the melting point (Tm) compared to either homopolymer. Copolymer melting points were found to decrease with decreasing molecular weight and to be dependent on composition, i.e., the incorporation of a comonomer into either homopolymer resulted in a decrease in Tm, with the maximum decrease occurring at a copolymer composition of about 60 mol % ε‐caprolactone. The molar compositions of the copolyesters were determined from 13C‐NMR spectra. The reactivity ratios of the two monomers (M1 = C, M2 = V) were determined to the r1 = 0.25 and r2 = 0.49. Number average molecular weight (M̄n) of the PCV diols was inversely proportional to the initial diol concentration within the studied molecular weight range of 900 to 11,100 g/mol. Crosslinked polyurethane networks were prepared by reacting PCV diols with triphenylmethane triisocyanate. Network characterization included determination of sol content by solvent extraction, glass transition (Tg) and Tm by DSC, and tensile properties by stress‐strain measurements. Completely amorphous networks resulted from PCV diols of M̄n ≤ 2,400; semicrystalline networks resulted from PCV diols of M̄n ≥ 3,600.