Eur. Phys. J. E (2011) 34: 134
https://doi.org/10.1140/epje/i2011-11134-4

Dielectric and molecular dynamics study of the secondary relaxations of poly(styrene-co-methylmethacrylate) copolymers: Influence of the molecular architecture

¹ Departamento de Química Física I, Facultad de Química, Universidad Complutense, 28040, Madrid, Spain
² Departamento de Materiales e Ingeniería Aeroespacial, ETSI Aeronáuticos, Universidad Politécnica, 28040, Madrid, Spain
³ Departamento de Ciencias y Técnicas Fisicoquímicas, Facultad de Ciencias, Universidad Nacional de Educación a Distancia, 28040, Madrid, Spain

^* e-mail: rgrubio@quim.ucm.es

Received: 2 August 2011
Revised: 7 November 2011
Accepted: 9 November 2011
Published online: 28 December 2011

Abstract

The effect of the structure of copolymers (random, alternate or diblock) on their dynamics has been studied by dielectric spectroscopy. Six copolymers of styrene and methyl methacrylate (three diblocks, one alternate and two random) have been studied. The results show that the sub- T _g transitions of the diblock samples can be described by one asymmetric Havriliak-Negami (HN) function, while two are necessary for the rest of the copolymers (β and γ relaxations). The characteristic times of the sub- T _g relaxations show an Arrhenius temperature dependence and there is a strong coupling of the α and β relaxations at high temperatures. The deconvolution of the merging relaxations has been made in the framework of the Williams Ansatz set out in terms of Havriliak-Negami distributions. Because the 2D ²H-NMR results excluded any significant contribution from the rotation of the methoxy group of the methacrylate group around the C-OCH₃ bond, the γ relaxation may be assigned to the rotation of the methyl methacrylate group in a styrene-rich environment. The Molecular Dynamics simulations of a poly(methyl methacrylate) homopolymer and of the alternate copolymer are in qualitative agreement with the experimental results, although they predict smaller values for the activation energy of the sub- T _g relaxations.