Effect of the Dipole−Dipole Interactions in the Molecular Dynamics of Poly(vinylpyrrolidone)-Based Copolymers B. Redondo-Foj, † M. Carsí, † P. Ortiz-Serna, † and M. J. Sanchis †, * † Instituto Tecnoló gico de la Energía, Departamento de Termodina ́ mica Aplicada, Universitat Polite ̀ cnica de Valè ncia, Camí de Vera s/n, 46022, Valencia, Spain S. Vallejos, ‡ F. García, ‡ and J. M. García ‡ ‡ Departamento de Quı ́ mica, Facultad de Ciencias, Universidad de Burgos, Plaza Misael Bañ uelos s/n, 09001 Burgos, Spain ABSTRACT: Poly(vinylpyrrolidone-co-butyl acrylate) samples with different proportions of monomers were prepared as tractable and hydrophilic materials. An analysis of the intermolecular interactions between the polymer groups was carried out by FTIR. The dependence of the CO bands (lactam and pendant butyl ester) with the composition suggests a strong interaction between the lactam groups. They exert an important influence in the molecular mobility, which was studied by DSC and DRS. A single narrow glass transition temperature (T g ) is observed in each random copolymer, consistent with a single phase of low compositional nanoheterogeneity. The dependence of the T g with the composition suggests significant interactions between polymer components. The dielectric spectra show γ, β, and α relaxations in increasing order of temperature, followed by conductive contributions. The apparent activation energies for secondary relaxations have similar values for all the samples. The γ-process is related to the local motions of the butyl units and the β-process is a Johari−Golstein secondary relaxation that is related to the local motions of the pyrrolidone group together with the motion of polymer backbone segments. 1. INTRODUCTION N-Vinyl-2-pyrrolidone (VP) is a cheap and widely available chemical, prepared industrially from acetylene and form- aldehyde following the Reppe’s procedure. 1,2 VP is a high boiling point liquid (92−95 °C at 1.3 kPa), highly miscible in water and in organic solvents, and with other vinyl or acrylic monomers. VP linear polymerization, either in bulk, in solution or in suspension, gives rise to linear polyvinylpirrolidone (PVP). PVP is also known as Povidone, an amphiphilic polymer soluble in water and in polar organic solvents but insoluble in esters, ethers, ketones and hydrocarbons. 3 It cannot be melt processed due to its low decomposition temperature. Its T g reaches a constant value (approximately 175 °C) when its average molecular weight is 100 000 g·mol −1 . 4 The films prepared from PVP solution are brittle, clear, and glossy. Its popcorn polymerization, i.e., proliferous polymerization, gives rise to highly cross-linked PVP, called Crospovidone, completely insoluble, and of the great industrial importance. Both, linear and cross-linked PVP have a wide range of applications. Because of its biocompatibility, PVP is used in pharmacological and biomedical applications. Furthermore, it is also utilized in numerous industrial fields like adhesives, ceramic, coatings, food, etc. 2,3 The relation between the structure of polymers and their properties has been widely studied in the literature. In this way, the copolymerization is presented as an effective method to prepare macromolecules with specific chemical structures and to control some properties such as hydrophilic/hydrophobic balances, solubility, polarity, etc. 5 Hence, copolymers have attracted a great attention because they can be frequently used to tune the properties of a material between those of the corresponding homopolymers. Copolymers comprised of VP and acrylic or vinyl comonomers are commercially produced to modify, to improve and to adapt the properties of PVP to specific applications. In the same way, the water affinity of the PVP, or even the water solubility, which can be too high for certain applications, has been reduced by copolymerizing with vinyl acetate or vinyl propionate. 3,6 Thus, acrylic chemicals are among the most versatile and inexpensive comonomers to prepare materials with specific properties. The dynamic mechanical and dielectrical properties are intrinsically correlated and they are associated with a structural polymer feature. 7−12 The dynamic relaxation properties of cross-linked polymer networks are highly sensitive to network composition and polymer chain architecture. The cooperative segmental motions (T g ) and the more localized processes observed below T g , can be dramatically affected by (i) changes in the backbone structure, (ii) cross-link density, or (iii) the introduction of pendant groups or branches. One of the most powerful and versatile methods for the study of molecular Received: April 16, 2014 Revised: July 8, 2014 Published: July 18, 2014 Article pubs.acs.org/Macromolecules © 2014 American Chemical Society 5334 dx.doi.org/10.1021/ma500800a | Macromolecules 2014, 47, 5334−5346