Eur. Phys. J. E 19, 37–45 (2006) DOI: 10.1140/epje/e2006-00009-4 T HE EUROPEAN P HYSICAL JOURNAL E Glass transition and the origin of poly(p-phenylene sulfide) secondary crystallization L. D’Ilario a and A. Martinelli Dipartimento di Chimica, Universit`a di Roma “La Sapienza”, PO Box 34-ROMA 62, Roma, Italy Received 23 June 2005 / Received in final form 24 October 2005 Published online 17 January 2006 – c  EDP Sciences, Societ`a Italiana di Fisica, Springer-Verlag 2006 Abstract. The effect of low temperature cold-crystallization on quenched poly(p-phenylene sulfide) (PPS) amorphous phase behaviour was systematically investigated by differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA) over the entire range of the process, from its early stage to the end. For the first time a well resolved double glass transition of partially cold-crystallized samples was evidenced. A Tg steady increase was observed during the primary crystallization process, due to the reduction of amorphous chain segmental mobility imposed by the growing rigid phase. A shift of the relaxation temperature of about 10 ◦ C was recorded at the end of the primary crystallization process. As the secondary crystallization takes place a new glass transition appears at higher temperature. For longer annealing time the lower Tg disappears while the intensity of the upper one increases. The upper temperature glass transition of semi-crystalline PPS is explained as a consequence of the PPS secondary cold-crystallization process. In the light of the thermal and dynamic mechanical results, an interpretation is given of step-wise double crystallization, evidenced in non-isothermal cold-crystallization experiments carried out at low heating rate and followed by means of FT-IR techniques. PACS. 65.60.+a Thermal properties of amorphous solids and glasses: heat capacity, thermal expansion, etc. – 64.70.Pf Glass transitions – 81.10.Aj Theory and models of crystal growth; physics of crystal growth, crystal morphology and orientation 1 Introduction Poly(p-phenylene sulphide) (PPS) is a semi-crystalline en- gineering thermoplastic polymer which exhibits outstand- ing mechanical properties, high thermal stability, good sol- vent resistance and can be rendered electrically conductive through doping with strong oxidizing agents. Moreover, PPS can be easily obtained as closely amorphous by rapid quenching from the melt state and its crystallinity may be subsequently increased by controlled annealing at tem- perature above T g . In this a way it is possible to investi- gate the influence of crystalline domains on the amorphous phase relaxation phenomena at T g . In general a semi-crystalline polymer may be consid- ered as a heterogeneous material whose amorphous frac- tion displays different behaviours depending on the di- mensions and location of the disordered domains respect to the crystalline phase. Amorphous chains characterized by different mobility have been observed by relaxation and calorimetric experiments, as widely described in liter- ature [1–14]. Usually the crystalline phase strongly affects the amorphous phase relaxation, extending its influence well above the ordered regions. As for other semi-rigid a e-mail: lucio.dilario@uniroma1.it para-linked aromatic polymers, PPS chain segments close to the crystalline lamellae behave rigidly, do not relax at T g and do not contribute to the increase of the heat capac- ity during the glass transition [15,16]. This phase, referred as the rigid amorphous phase (RAP), may be estimated from calorimetric experiments by assuming a three phase model (crystalline, mobile amorphous, rigid amorphous). It undergoes a progressive mobilization above the glass transition, as demonstrated by Huo and Cebe in dielec- tric relaxation analysis [1]. The relative fraction of RAP (X RAP ) depends on the crystallization condition, being higher at the lower cold-crystallization temperature. PPS samples cold-crystallized in the T c range 107–135 ◦ C show a X RAP =0.43–0.55, twice as much the crystalline frac- tion [17]. Lower amount of rigid amorphous phase may be reached at higher crystallization temperature. A de- crease of X RAP from 0.42 to 0.33 was observed increasing T c from 150 to 210 ◦ C [1]. As far as the mobile amorphous fraction is concerned, DSC and dielectric spectroscopy ex- periments have evidenced that cold-crystallization at pro- gressively higher T c leads to a steady T g increase. However the amorphous polymer glass transition at the lowest tem- perature still continues to be evident.