Synthesis and characterization of a novel flame retardant, poly(lactic acid-<i>co</i>-3,3′-diaminobenzidine)

Abstract

Directly starting from D,L-lactic acid (LA) and 3,3′-diaminobenzidine (DAB), poly(lactic acid-co-3,3′-diaminobenzidine) [P(LA-co-DAB)] as a kind of potential flame retardant is synthesized via melt polycondensation. When the molar feed ratio LA/DAB is 80/1, the optimal synthetic conditions, including type and dosage of catalyst, temperature, and time of copolymerization, are discussed. After the prepolymerization at 140 °C for 8 h, using 0.7 wt.% stannous oxide (SnO) as the catalyst, the melt copolymerization for 6 h at 160 °C gives the polymer with the biggest intrinsic viscosity ([η]) 0.71 dL • g−1. The structure and properties of P(LA-co-DAB)s at different molar feed ratios are systematically characterized by Fourier transform infrared spectroscopy, proton nuclear magnetic resonance (1H NMR), gel permeation chromatography, differential scanning calorimetry, and X-ray diffraction (XRD). With the increase of the molar feed ratio LA/DAB, the crystallinity and [η] of P(LA-co-DAB) increase gradually. When LA/DAB is 120/1, the biggest weight-average molecular weight (M w) is 5900 Da. The results of thermogravimetric analysis show that the decomposition temperature at 5% weight loss (T 5%) and char yield of the copolymers are higher than those of homopolymer poly(D,L-lactic acid). Furthermore, the more DAB in the feed content, the higher char yield. These indicate that P(LA-co-DAB) may play a flame retardant role when it is blended with polylactic acid.