Synthesis and characterization of non-isocyanate polyurethane from natural and poly (Iactic acid)

Abstract

Non-isocyanate polyurethane (NIPU) based on natural rubber (NR) and poly(lactic acid) (PLA) were synthesized by polyaddition without catalyst and solvent. Two new oligoisoprenes (amino telechelic natural rubber (ATNR) and cyclic carbonate telechelic natural rubber (CCTNR)) have synthesized from carbonyl telechelic natural rubber (CTNR) obtaining from the control oxidative degradation of NR with the targeted chain length of 1000 and 2000 g/mol. A cyclic carbonate telechelic PLA (CCPLA) was synthesized from lactic acid by melt condensation in the presence of catalyst and succinic acid then it was subsequently reacted with glycerol carbonate in Steglish esterification. The Mn of CCPLA was in the range from 1000 to 2000 g/mol. The NIPU from NR were successfully synthesized by two approaches. The first approach was the reaction of ATNR and aromatic or aliphatic dicyclic carbonates corresponding to linear NIPU (NIPU#1). The second approach was the reaction of CCTNR and di- or tri- amines corresponding linear and cross-linked NIPU depending on type of amine (NIPU#2). The homogenous films were obtained in cross-linked NIPU#2. The reaction of CCPLA and various diamines produced NIPU#3. The evolution of the reaction was studied by FTIR analysis. The amide formation did not occur in both of NIPU#1 and NIPU# 2 except in NIPU#3. The aminolysis of amine and ester as a side reaction could not prevent from the reaction of NIPU#3; therefore, it has no further analysis. No influence of Mn of ATNR, CCTNR and CCPLA on the reactivity to form NIPU was observed. The single Tg was observed in NIPU#1 and NIPU#2 and depended on the molecular weight of ATNR and CCTNR. The types of amine were not influence on Tg. NIPU#2 was a fully amorphous while the NIPU#1 has a low crystallization rate. DMTA analysis of cross-linked NIPU#2 showed the one a transition temperature. Two decomposition steps were found in both NIPU#1 and NIPU# 2. The first and second steps were the rupture of urethane linkage and hydrocarbon chain, respectively.