RESUMO
Amorphous polymers currently have a wide range of applications, including the production of amorphous solid dispersions in the pharmaceutical industry. This application requires knowledge of the kinetic parameters of the glass transition process, which are the key to the formation of the end product. In the present work, we have thoroughly investigated the glass transition in the biocompatible polymer polyvinylpyrrolidone as a function of the polymer molecular mass, using differential scanning calorimetry, fast scanning calorimetry, and broadband dielectric spectroscopy. We have determined the dependence of the difference between the isobaric specific heat capacities of the liquid and the glass on the dynamic glass transition temperature, volume, and number of particles included in the cooperatively rearranging regions. A linear dependence between the shift factor from the Frenkel-Kobeko-Reiner equation and the molecular mass of polyvinylpyrrolidone was established. The results of the present work help in choosing the optimal excipient for the development of solid dispersions based on amorphous polymers.
RESUMO
Controlling the permittivity of dielectric composites is critical for numerous applications dealing with matter/electromagnetic radiation interaction. In this study, we have prepared polymer composites, based on a silicone elastomer matrix and Tuball carbon nanotubes (CNT) via a simple preparation procedure. The as-prepared composites demonstrated record-high dielectric permittivity both in the low-frequency range (102−107 Hz) and in the X-band (8.2−12.4 GHz), significantly exceeding the literature data for such types of composite materials at similar CNT content. Thus, with the 2 wt% filler loading, the permittivity values reach 360 at 106 Hz and >26 in the entire X-band. In similar literature, even the use of conductive polymer hosts and various highly conductive additives had not resulted in such high permittivity values. We attribute this phenomenon to specific structural features of the used Tuball nanotubes, namely their length and ability to form in the polymer matrix percolating network in the form of neuron-shaped clusters. The low cost and large production volumes of Tuball nanotubes, as well as the ease of the composite preparation procedure open the doors for production of cost-efficient, low weight and flexible composites with superior high permittivity.
RESUMO
Polymers from norbornenes are of interest for applications in opto- and microelectronic (low dielectric materials, photoresists, OLEDs). Norbornenes with ester motifs are among the most readily available norbornene derivatives. However, little is known about dielectric properties and the gas-transport of polynorbornenes from such monomers. Herein, we synthesized a new metathesis polymer from exo-5-norbornenecarboxylic acid and 1,1'-bi-2-naphthol. The designed monomer was obtained via a two-step procedure in a good yield. This norbornene derivative with a rigid and a bulky binaphthyl group was successfully polymerized over the 1st generation Grubbs catalyst, affording high-molecular-weight products (Mw ≤ 1.5·106) in yields of 94-98%. The polymer is amorphous and glassy (Tg = 161 °C), and it shows good thermal stability. Unlike most, polyNBi is a classic low-permeable glassy polymer. The selectivity of polyNBi was higher than that of polyNB. Being less permeable than polyNB, polyNBi unexpectedly showed a lower value of dielectric permittivity (2.7 for polyNBi vs. 5.0 for polyNB). Therefore, the molecular design of polynorbornenes has great potential to obtain polymers with desired properties in a wide range of required characteristics. Further tuning of the gas separation efficiency can be achieved by attaching an appropriate substituent to the ester and aryl group.
