Exploring the effect of alkyl end group on poly(L-lactide) oligo-esters. Synthesis and characterization |
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Authors: | José E Báez Ángel Marcos-Fernández Plácido Galindo-Iranzo |
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Affiliation: | 1.Departamento de Química y Tecnología de Elastómeros,Instituto de Ciencia y Tecnología de Polímeros (CSIC),Madrid,Spain;2.Instituto de Química-Física “Rocasolano” (CSIC),Madrid,Spain |
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Abstract: | Poly(L-lactide) (PLLA) oligo-esters with α-hydroxyl-ω-alkyl (alkyl = −CH2−CH2−CH2]m−CH3, where m = 1, 2, 4, 5, 6, 7, 8, 9, and 10) end groups were synthesized by ring-opening polymerization of L-lactide (L-LA)
catalyzed by tin(II) 2-ethylhexanoate Sn(Oct)2 in the presence of aliphatic alcohols as initiators (HO−CH2−CH2−CH2]m−CH3, where m = 1, 2, 4, 5, 6, 7, 8, 9, and 10). High yields (~ 62 to 71%) and M
n(NMR) in the range of 2120–2450 Da (PLLA) were obtained. Effects of alkyl end groups on thermal properties of the oligo-esters
were analyzed by DSC, TGA and SAXS. Glass transition temperature (T
g) gradually decreases with increase in the percent of−CH2−CH2−CH2]m−CH3 end group, as results alkyl end group provides most flexibility to PLLA. An important effect of alkyl end group on a double
cold crystallization (T
c1 and T
c2) was observed, and is directly related with the segregation phase between alkyl end group and PLLA. TGA analysis revealed
that PLLA oligo-esters are more thermally stable with docosyl (−C22H45) respect to the butyl (−C4H9) end group, probably is due to steric hindrance of the end group (docosyl respect to butyl) toward intermolecular and intramolecular
transesterification. SAXS analysis showed that alkyl end group as docosyl restricted the growth of lamellae thickness (D)
due to steric hindrance. Characterization of hydroxyl and alkyl end groups in the PLLA oligo-esters was determined by MALDI-TOF,
GPC, FT-IR and 1 H and 13 C NMR. |
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