Examining structure property relationships in coatings based on substituted linear aromatic polycyanurates
Introduction
The reactivity of chlorotriazines towards alcohols in the presence of base was first used to obtain polymeric products by Picklesmeyer in 1965 [1], albeit insoluble and intractable crosslinked films. However, from these beginnings efforts were directed towards a more controlled approach involving capped dichlorotriazines to prevent crosslinking. Historically, the formation of linear polycyanurates was undertaken from single solvent systems and high temperatures to condense aromatic bisphenols with a number of 2-substituted-4,6-dichloro-s-triazines in the presence of base [2]. Nakamura et al. showed [3] that similar results could be obtained at much lower temperatures using a water-immiscible organic solvent in the presence of a cationic phase transfer catalyst (PTC), typically quaternary salts of organic amines. However, despite the wide scope of the work (some 40 polycyanurates were produced to achieve high thermal stability and good mechanical properties), little attention was paid to the processibility of the resulting polymers or the refinement of the synthesis. It was reported that all alkoxy-cyanurates either decomposed or crosslinked on heating at 200 °C for 60 min and some limited data examining the reduced solubility of the polymers was presented in support. The present work concentrates on examining polycyanurates for their potential use as thermally stable coating materials or pigment binders. Consequently, our study presents data to show the effects of the structure of the polycyanurate backbone and the degree of halogenation on the resulting thermal and mechanical properties and the kinetics of crystallisation.
Section snippets
Equipment
Fourier transform infrared (FTIR) spectra were obtained using a Perkin Elmer 1750 FTIR spectrometer interfaced with a Perkin Elmer 7300 computer; a minimum of 24 scans was collected at a resolution of 2 cm−1. Materials that could be cast from solution were analysed directly as films, otherwise diffuse reflectance infrared spectroscopy (DRIFTS) was used. The spectral data are presented in absorbance units to allow easy comparison of the normal transmission spectra with DRIFTS data in Kubelka–Munk
Results and discussion
All of the interfacial polymerisations were performed under phase transfer (PT) conditions using Cetrimide as the phase transfer catalyst (PTC). Initially, the polymerisation was performed using a reported method [10] in which a phase-volume ratio (PVR) of 1 was used and the PTC (6 mol%) was added, but later studies suggested that a PVR of 0.25 [11] yielded a high molecular weight product. All reactions were carried out under nitrogen to prevent termination by oxidation of phenoxide (to a
Conclusions
Some materials formed from m-dichlorotriazine and a variety of bisphenols can be cast into films with good resilience and these films exhibit good thermo-oxidative stability. Problems were encountered with solubility, particularly aromatic substituted dichlorotriazines and those containing high halogen content, which led to the formation of polymers with limited molecular weights. In order to ensure adequate solubility throughout the polymerisation range, it was found necessary to use aromatic
Acknowledgement
We thank the Ministry of Defence (formerly DRA, Malvern) for providing sponsorship in the form of a studentship (DAT).
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