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Issue 95, 2015
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Cardanol benzoxazines – interplay of oxazine functionality (mono to tetra) and properties

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Abstract

Cardanol, a sustainable origin phenol, was utilized as a reactive diluent to mediate solventless Mannich-type condensation reaction with para-formaldehyde and primary aromatic amines to form a homologous series of benzoxazine (Bz) monomers namely C-a, C-ddm, C-trisapm and C-tetraapm which differ in their degree of oxazine functionality as mono-, di-, tri- and tetra-oxazine respectively. A strong correlation is reflected between the number of oxazine rings in the monomer and the polymerization behavior, thermo-mechanical transitions, and properties of the polybenzoxazine synthesized. The monomer structure was confirmed by FTIR, 1H-, 13C-NMR spectroscopy and mass spectrometry. The curing, rheological, thermo-mechanical and thermal properties were determined using DSC, FTIR, rheometer, DMTA, LSS and TGA studies. The curing characteristic due to ROP of Bz monomers was supported both by DSC and FTIR studies. The presence of neighboring oxazine group in monomers (C-a to C-tetraapm) strongly attenuates the curing temperature (Ti = 225–140 °C), enhances Tg, thermal stability, and mechanical properties. Interestingly, DFT calculations also supported the lowest curing temperature for highest oxazine functionality monomer (C-tetraapm). The interplay between the degree of oxazine functionality in the monomer; extent of H-bonding and crosslink density values in sustainable origin synthesized polybenzoxazines is suggested. The thermoset showed an increasing trend (PC-a < PC-ddm < PC-trisapm < PC-tetraapm) in Tg (58–109 °C), thermal stability (355–391 °C), char yield (13–37%), LOI (23–31) and storage modulus (3.6–66.5 MPa) values. The monomers are liquid to semi-viscous paste at room temperature and showed potential for solventless processing in adhesive applications.

Graphical abstract: Cardanol benzoxazines – interplay of oxazine functionality (mono to tetra) and properties

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Supplementary files

Article information


Submitted
18 Jul 2015
Accepted
07 Sep 2015
First published
09 Sep 2015

RSC Adv., 2015,5, 78071-78080
Article type
Paper
Author version available

Cardanol benzoxazines – interplay of oxazine functionality (mono to tetra) and properties

S. Shukla, A. Mahata, B. Pathak and B. Lochab, RSC Adv., 2015, 5, 78071
DOI: 10.1039/C5RA14214H

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