In situ monitoring of cyclic butylene terephtalate polymerization by dielectric sensing C. Hakme´ * , I. Stevenson, A. Maazouz, P. Cassagnau, G. Boiteux, G. Seytre Universite´ de Lyon, Universite´ Lyon 1, Laboratoire des Mate´riaux Polyme`res et des Biomate´riaux, IMP, UMR CNRS 5223, 43 Bd. du 11 novembre 1918, 69622 Villeurbanne cedex, France Available online 17 October 2007 Abstract The in situ monitoring of the polymerization of cyclic butylene terephtalate (CBT) oligomers by dielectric sensing has been investi- gated under isothermal conditions at different processing temperatures. The change in conductivity depends on the increase of molecular weight but is also influenced by crystallization of the obtained c-PBT during or after polymerization. Dielectric sensing investigations are in good agreement with SEC and DSC analysis which confirm the observation of polymerization and crystallization kinetics. Unfortu- nately, the conductivity signal could not distinguish between the polymerization and crystallization when they occur simultaneously at lower temperatures (<210 °C) but the crystallization remains detectable by the MWS relaxation which is related to the crystalline/amor- phous interface. Ó 2007 Elsevier B.V. All rights reserved. PACS: 61.41.+e; 66.10.Ed; 77.84.Jd; 77.22.Ch; 77.22.Gm Keywords: Crystallization; Electrical and electronic properties; Dielectric properties, relaxation, electric modulus; Fast ion conduction; Polymers and organics; Thermal properties 1. Introduction Interest in recently developed macrocyclic polyester olig- omers such as cyclic poly(butylene terephtalate) (c-PBT) has increased steadily over recent years due to their advan- tages over thermosets. The main advantages making them attractive as matrix materials for thermoplastic composite engineering are: low viscosity (water-like), the capability of rapid polymerization and the ability to be processed like thermoset resins [1,2].The c-PBT is prepared by the poly- merization of cyclic butylene terephtalate (CBT) in the presence of transesterification catalysts. The usual catalysts used for this polymerization include various organotin compounds and titanium esters [3–5]. Tripathy et al. [6,7] have studied the polymerization by light transmittance measurements of CBT using different catalysts and have reported that the choice of catalyst has a large effect on the polymer conversion and the time required for polymerization. Patron et al. [2,8] have charac- terized the crystalline structure of c-PBT and have shown that c-PBT has thick and well oriented crystalline lamellae. They also report that the mechanical properties of resulting materials are not at all affected by the lamellae orienta- tions. Other works [9,10] show the ability to synthesize PBT/clay nanocomposites with a good thermo-stability using organically moulding clay via in situ polymerization in the solution method. The in situ monitoring by dielectric sensing has been described in several papers [11–14] and it was shown that this technique can detect different physico- chemical phenomena in thermoplastics and thermoset composites. However, very little research has been devoted to the electrical properties of CBT, which is why as a part of an on-going research program, the work reported here was focused on the in situ monitoring of CBT polymerization 0022-3093/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.jnoncrysol.2007.04.051 * Corresponding author. E-mail address: chady.hakme@univ-lyonl.fr (C. Hakme´). www.elsevier.com/locate/jnoncrysol Available online at www.sciencedirect.com Journal of Non-Crystalline Solids 353 (2007) 4362–4365