Structure development in aromatic polycyanurate networks modi®ed with hydroxyl-terminated polyethers A.M. Fainleib a, * , D.J. Hourston b , O.P. Grigoryeva a , T.A. Shantalii a , L.M. Sergeeva a a Department of Interpenetrating Polymer Networks and Systems, Institute of Macromolecular Chemistry, National Academy of Sciences of Ukraine, 48, Kharkivs'ke shose, 02160 Kyiv-160, Ukraine b Institute of Polymer Technology and Materials Engineering, Loughborough University, Loughborough, Leicestershire LE11 3TU, UK Received 11 September 2000; received in revised form 10 April 2001; accepted 7 May 2001 Abstract A series of polycyanurate networks PCN), based on the dicyanate of bisphenol A monomer DCBA), was synthesized in the presence of different contents of hydroxyl-terminated polyethers PEth), such as polyoxypropylene glycol PPG) and polyoxytetramethylene glycol PTMG). We studied the in¯uence of the nature of the oligomeric modi®er, initially miscible with DCBA, on the chemical structure, glass transition behaviour, phase morphology and mechanical properties of modi®ed PCN. The possibility of PEth incorporation into the PCN structure through mixed cyanurate ring formation is discussed. A maximum PEth incorporated content of 0.1 mol of PEth per mol of DCBA irrespective of PEth type has been detected. Dynamic mechanical thermal analysis DMTA) analysis showed the formation of multiphase polymer compositions due to microphase separation of the components occurring during DCBA/PPG curing. The formation of very ®nely divided morphologies with highly interpenetrated phases, i.e. a PCN-rich phase, a mixed phase of PCN/PPG components and a PPG-rich phase was determined. On the other hand, all PCN/PTMG cured compositions exhibited a single, broad glass transition that shifted to lower temperature as the modi®er content was increased and the experimental T g versus modi®er content showed a slight positive deviation from the Fox equation for miscible polymer systems. It can be concluded that the PCN and the PTMG have a higher degree of compatibility than PCN and PPG. The introduction of small additions of modi®er ,10 wt%) allow production of the thermosets with high T g and good strength properties. q 2001 Elsevier Science Ltd. All rights reserved. Keywords: Polycyanurate network; Polyether; Polyoxypropylene glycol 1. Introduction Since the late 1970s, cyanate ester resins have been used with glass or aramid ®bre in high-speed multilayer circuit boards and this remains their primary application. In this application, the primary performance considerations of a glass transitions temperature T g ) matching or exceeding molten solder temperatures 220±2708C), low dielectric loss properties to increase signal speed and facilitate miniaturization) and good peel strength made cyanate esters pre-eminently suitable [1]. Cyanate ester monomers polymerize by a cyclotrimerization reaction to yield cyanu- rate-linked network polymers Scheme 1, generalised monomer structure and polycyanurate network formation). Currently, this polymerization and the physical properties of the resulting polymers have attracted substantial commercial and scienti®c interest. Polycyanurate matrices resulting from the cure of pure dicyanate monomers have excellent thermal and dielectric properties, but are often very brittle [2]. Several attempts are currently being under- taken in order to improve this particular aspect. There are two basic ways to decrease the high brittleness of high crosslink density polymer networks. Reaction of cyanate group with active hydrogen-containing functional groups to form modi®ed polycyanurates is a developing area. The particularly important examples are the reactions of dicyanates with epoxies to form an oxazolidinone-linked polycyanurates [3±6], with mono- and bis-phenols [3,5± 8], diamines [5,7] and with bismaleimides [9±11]. Brittle thermosets are also toughened by the introduction of a rubbery or a thermoplastic dispersed phase [7,12±15]. Generally, at the curing temperature, the initial mixture of monomers) and additive is homogeneous. The dispersed phase results from the phase separation induced by the step-growth polymerization of the monomers). The studies show that the morphology formed diameters, number and Polymer 42 2001) 8361±8372 0032-3861/01/$ - see front matter q 2001 Elsevier Science Ltd. All rights reserved. PII: S0032-386101)00333-0 www.elsevier.nl/locate/polymer * Corresponding author. Tel.: 1380-44-551-03-22; fax: 1380-44-552- 40-64. E-mail address: fainleib@i.kiev.ua A.M. Fainleib).