SYNOPSISThe isothermal cure of a dicyanate ester monomer has been studied under different atmospheres (air and argon) without any catalyst, by following the evolutions of both glass transition temperature and conversion. Independently of both atmosphere and temperature of cure, there is a unique one-to-one relationship between these two parameters, correctly described by a restated DiBenedetto's equation. The chemical kinetics are satisfactorily modeled with two competing reactions schemes, which are second-order and second-order autocatalyzed, the latter displaying more relative importance under air-curing conditions. Whatever the cure temperature may be, gelation occurs around 0.60 conversion under air, whereas the theoretical rgel = 0.50 is experimentally observed under argon. The timetemperature-transformation diagrams have been established. 0

No abstract

No abstract

The dynamic mechanical behavior of a series of polycyanurate networks has been studied in the glassy state as a function of cyanate conversion. Two relaxations, p and y. were defined and the Arrhenius dependence and Starkweather treatments were applied. To understand the origin of these sub-T, relaxations, molecular modeling (both mechanics and dynamics) was used on model molecules representative of the network structure. Two types of molecular motion were examined: rotation of the phenylene ring and crankshaft of the chain segment between crosslinks We., triazine rings). -O---C=Nfunctionality, which cyclotrimerizes upon heating, leading to a polycyanurate network with triazine rings as branching units, as shown in Fig. 1. Our group carried out a complete investigation of this kind of material. Results about polymerization kinetics, network buildup statistics, volumetric, and mechanical properties are available elsewhere (23-25). In addition, numerous studies on polymerization kinetics have also been reported, as well as a review of the chemistry, properties, and applications of this range of resins (26). Nevertheless, no detailed investigations of their relaxation behavior have yet been published.In this work we intend to present both technical and