Effects of the curing atmosphere on the structures and properties of polybenzoxazine films
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Effects of the curing atmosphere on the structures and properties of polybenzoxazine films Shuai Zhang1,2
, Qichao Ran1,*
, Xiaokun Zhang2, and Yi Gu1
1
College of Polymer Science and Engineering, State Key Laboratory of Polymer Materials Engineering, Sichuan University, Chengdu 610065, China 2 State Key Laboratory of Electronic Thin Films & Integrated Devices, School of Energy Science and Engineering, University of Electronic Science and Technology of China, 2006 Xiyuan Avenue, West High-Tech Zone, Chengdu 611731, Sichuan, China
Received: 23 July 2020
ABSTRACT
Accepted: 2 October 2020
The effects of four different curing atmospheres, i.e., static air, circulating air, nitrogen and vacuum, on the polymerization mechanism, chemical structure, hydrogen bonding, mechanical property, thermal property, water contact angle, etc., of the polybenzoxazine films were systematically studied. It was found that curing in air caused more oxidation and decomposition, generating more benzoquinones, carbonyl groups and iminium ions in the resultant polybenzoxazine films. Consequently, the films cured in air were less cross-linked, darker in color and more brittle. The films cured in static air (SA) showed tensile strength and elongation at break of 12.59 MPa and 2.16%, respectively, which were 61.24 MPa and 2.74% lower than those of the films cured in nitrogen (N2). Moreover, it was demonstrated that more intramolecular rigid –OHN hydrogen bonding was formed in the films cured in air, which was believed to be the fundamental reason for the lower chemical cross-linking density and poorer toughness. Nevertheless, these films showed higher char yield due to the formation of more thermally stable groups in oxidation process. Further investigation on chemical structures, hydrogen bonding and water contact angles of the upper and lower surfaces of the films revealed that the upper surfaces were more inclined to be oxidized and decomposed during curing and more intramolecular hydrogen bonding (–OHN HB) was formed on upper surfaces, which led to increased water contact angles.
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Springer Science+Business
Media, LLC, part of Springer Nature 2020
Handling Editor: Gregory Rutledge.
Address correspondence to E-mail: [email protected]
https://doi.org/10.1007/s10853-020-05425-5
J Mater Sci
GRAPHIC ABSTRACT
Introduction Polybenzoxazines that can be formed by ring-opening polymerization (ROP) of nitrogen and oxygen containing six-membered heterocyclic compounds have drawn much attention and research interest from industrial and academic communities, especially in recent 30 years [1–11]. Polybenzoxazines are versatile resins which meet a variety of application scenarios. Firstly, their high Tgs, high strength, high modulus and good thermal stability ensure their application in harsh environments like aeronautics and astronautics [12–15]. Secondly, their good dielectric properties, dimensional stability, flame retardance and low water uptake make them good candidates for electronic devices [16–21]. Moreover, the tremendous
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