Journal of Photochemistry and Photobiology A: Chemistry 187 (2007) 222–232 Study of secondary relaxations in poly(vinyl chloride) by phosphorescence decay Effect of the chemical structure and the concentration of luminescent probes Gilbert Teyssedre b , Helmut Reinecke a , Teresa Corrales a , Rodrigo Navarro a , Nuria Garc´ ıa a , Pilar Tiemblo a,∗ a Instituto de Ciencia y Tecnolog´ ıa de Pol´ ımeros, Consejo Superior de Investigaciones Cient´ ıficas (CSIC), Juan de la Cierva 3, 28006 Madrid, Spain b Laboratoire de G´ enie Electrique, Universit´ e Paul Sabatier, 118 route de Narbonne, 31062 Toulouse, France Received 24 July 2006; received in revised form 10 October 2006; accepted 12 October 2006 Available online 1 November 2006 Abstract The phosphorescence emission of both naphthalene and pyridine can be used to detect the secondary () relaxation of PVC, as this relaxation manifests by a decrease in the emission from the grafted probe at the temperatures at which the local motion at the backbone begins. In this work, an extensive study of the kinetic and spectral features of the phosphorescence of 4-mercaptopyridine, 4-methoxybenzenethiol and 4-mercaptophenol groups as a function of temperature is presented. These three luminescent probes have been grafted onto PVC, with modification levels ranging from 3% up to 46%. The phosphorescence decay from -130 ◦ C up to 30 ◦ C has been followed and both the intensity of the emission and the spectral features have been studied as a function of temperature. The interaction between probes as the concentration increases leads in all cases to the emission from aggregates or excimers, which have features different to those of the isolated probe. Side reactions occur when grafting the hydroxyl containing probe, what also leads to surprising phosphorescence spectral and decay rate features. © 2006 Elsevier B.V. All rights reserved. Keywords: Poly(vinyl chloride); Phosphorescence; Secondary relaxation; Grafting 1. Introduction One of the main difficulties in the understanding of the structure of substances without long range order and out-of- equilibrium thermodynamics is the impossibility to infer local structure from macroscopic properties. This is the case of glassy solids and in particular of polymers below their glass transi- tion temperature. Properties such as mechanical and dielectric characteristics and behaviours such as physical aging depend dramatically on this point, what makes the relevance of this circumstance both academic and practical. The search for characterization tools able to probe the local structure of glassy polymers is thus of great importance. Among ∗ Corresponding author. Tel.: +34 915622900. E-mail address: ptiemblo@ictp.csic.es (P. Tiemblo). the candidates for such studies, the marking techniques 13 C NMR or neutron scattering using labelled and unlabelled chains are well known [1,2]. The inclusion, either by impregnation or by grafting, of luminescent probes has also being explored in the last decade, and several authors have studied secondary relax- ations of homopolymers, copolymers and blends by means of luminescent probes, which were incorporated, free or covalently attached, to the polymer matrix [3–6]. One of many attractive characteristics of luminescence is the large number of available probes with a wide variety of shapes, sizes, and photophysical properties that depend on the nature of the environment in which they are incorporated and the range of temperatures studied. The emission of the luminescent guest is sensitive to the relaxation processes related to the polymer matrix, since the emission of the molecular luminescent probe depends on both its intrinsic photophysical properties and the interactions developed with the surrounding polymer matrix. In general, a decrease in lumines- 1010-6030/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.jphotochem.2006.10.021