Synthesis and characterization of thermostable hyperbranched epoxy resin for surface coating applications

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A hyperbranched epoxy resin has been synthesized by using epichlorohydrin, bisphenol-A, and hyperbranched polyether polyol by a low-temperature polycondensation technique in the presence of a base. The reaction parameters of this polycondensation reaction were optimized, and 5 N aqueous sodium hydroxide solution, (54 6 1) °C reaction temperature and 3 h reaction time were found to be the best. The degree of branching of the resin was found to be 0.57 as determined from 13C nuclear magnetic resonance spectroscopy (Fig. 3). This hyperbranched epoxy resin was cured with poly(amido amine) hardener at 120 °C for a specified period of time. The resin exhibits very good crosscut adhesive strength (100%). The cured films showed moderate impact strength (60 cm), good scratch resistance (5.5 kg), good gloss (82 at 60°), thermostability up to 270 °C, and good chemical resistance in various chemical media. All these results indicate its suitability to be used as an advanced surface coating material.

I. INTRODUCTION

Distinctive structure-property accord has instigated research for newer synthesis routes of hyperbranched polymers (HBPs), a novel class of dendritic macromolecules. Their hallmark architectural attribute is a highly branched structure with a large number of peripheral functional groups responsible for their excellent flow and processing properties.1–4 The structure of the repeating unit, the nature of their end groups, the degree of branching (DB), and the molar mass dictate their final properties. In this context, it is pertinent to mention that HBPs with s-triazine moiety in their structure have many advantages in practical field of applications.5 These include high thermostability, flame retardancy, rigidity and good electronic properties, and so on. Moreover, s-triazine containing cyanuric chloride is a low-cost commercially available product with applications attested in various sectors including textiles, plastics, and rubber industries. Thus, synthesis of a new HBP with s-triazine unit from cyanuric chloride is an interesting proposition to develop materials with desirable advanced properties. Again, epoxy resins are a class of versatile thermosetting polymers because of their high strength, low creep, very low cure shrinkage, excellent resistance to corrosion, good adhesion to many substrates, and appropriate electrical properties. These attributes make them applicable in different industries (e.g., electronics, aeronautics, a)

Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2012.86 1806

J. Mater. Res., Vol. 27, No. 14, Jul 28, 2012

http://journals.cambridge.org

Downloaded: 02 Dec 2014

or astronautics) as protective coatings, fiber-reinforced plastics, adhesives, binder for composites, etc.6–9 However, the existing epoxy resins have inherent brittle character that inhibits their further proliferation into various advanced industrial applications including active surface coatings.10 Hence, the synthesis of a new epoxy resin or modification of existing epoxy resins t

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