STUDIES ON SYNTHESES, SPECTRAL, THERMAL AND HYDROPHOBIC BEHAVIOR OF CARDANOL BASED TETRA FUNCTIONAL BENZOXAZINES

Abstract

In the present work, the tetra-functional benzoxazine was prepared using the calculated stoichiometric quantities of cardanol (C), 4-aminophenol (ap), paraformaldehyde, isophoronediamine (ipda) and diaminodiphenylmethane (ddm) under an appropriate experimental conditions. The molecular structure of benzoxazines synthesized namely cardanol-aminophenol-isophoronediamine (C-ap-ipda) and cardanol-aminophenol-diaminodiphenylmethane (C-ap-ddm) was ascertained from FTIR and 1H NMR spectral analyses. The curing behavior of C-ap-ipda and C-ap-ddm benzoxazines was studied using differential scanning calorimetry (DSC). From DSC thermograms, the polymerization temperatures Tp observed for C‑ap-ipda and C-ap-ddm are 246 and 254°C respectively. It was noticed that the benzoxazine with cycloaliphatic ring (C-ap-ipda) possesses the lower curing temperature than that of aromatic substituted (C-ap-ddm) benzoxazine. The cleavage of benzoxazine ring and the occurrence of ring-opening polymerization were confirmed by FTIR analysis after the thermal curing. The thermal stability of cured poly(C-ap-ipda) and poly(C-ap-ddm) benzoxazines was studied by TGA analysis. The values of char yield observed for poly(C-ap-ipda) and poly(C-ap-ddm) at 850°C are 27 and 30%, respectively. Further, the values of LOI calculated for poly(C-ap-ipda) and poly(C-ap-ddm) are 28.3 and 29.5 respectively and these values suggest that both poly(C-ap-ipda) and poly(C-ap-ddm) possess good flame retardant characteristics. The values of water contact angle obtained for poly(C-ap-ipda) and poly(C-ap-ddm) are 128° and 137° respectively and these values infer that both the polybenzoxazine matrices exhibit very good hydrophobic behavior. Among the synthesized polybenzoxazines, poly(C-ap-ddm) possesses better thermal and hydrophobic character than those of poly(C-ap-ipda), however both the samples qualify for high performance thermal and moisture resistant applications.