Abstract
The effect of three different cerium salts (Ce(NO3)3·6H2O, CeCl3·7H2O and Ce(OOCCH3)3·5H2O) on the ring-opening polymerization (ROP) of a model diamine-based benzoxazine (4EP-pPDA) was investigated. With the incorporation of the cerium salts, the curing temperature of 4EP-pPDA is reduced substantially, and the glass transition temperatures of the resulting networks are increased significantly. The three cerium salts exhibit different catalytic activities, which were analyzed by FT-IR, NMR, and energy-dispersive X-ray (EDX). Ce(NO3)3·6H2O was found to exhibit the best catalytic effect, which seems to be related to its better dispersibility within 4EP-pPDA benzoxazine precursors.
Highlights
Benzoxazine resins are relatively new incomers in the field of thermosetting materials [1,2] and they are obtained from the ring-opening polymerization of 1,3-benzoxazine precursors [3]
It is not fully elucidated, it is commonly accepted that the thermal ring-opening polymerization of benzoxazine monomers occurs via cationic polymerization and the mechanism includes mainly three steps: coordination ring-opening of the oxazine ring, an electrophilic attack, and, rearrangement [17]
We report the synthesis of a new diamine-based benzoxazine (4EP-pPDA) synthesized by the reaction of bio-basable reactants (4-ethylphenol, 1,4-phenylenediamine, and paraformaldehyde) and its thermal ring-opening polymerization in the presence of different kinds of cerium salts
Summary
Benzoxazine resins are relatively new incomers in the field of thermosetting materials [1,2] and they are obtained from the ring-opening polymerization of 1,3-benzoxazine precursors [3]. The search for reaction paths reducing the curing temperature has become one of the main focuses to overcome in this field It is not fully elucidated, it is commonly accepted that the thermal ring-opening polymerization of benzoxazine monomers occurs via cationic polymerization and the mechanism includes mainly three steps: coordination ring-opening of the oxazine ring, an electrophilic attack, and, rearrangement [17]. Another study reported the preparation and use of a polyamine-based oligomer to accelerate benzoxazine polymerization In this case, the polyamine was able to promote both the curing and, simultaneously, enhance the glass transition temperature as well as the thermal stability of the cured network [33]. To the best of our knowledge, the ability of these metallic salts to accelerate benzoxazine polymerization has never been tested
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