RESUMO
Up to now, rubber materials have been used in a wide range of applications, from automotive parts to special-design engineering pieces, as well as in the pharmaceutical, food, electronics, and military industries, among others. Since the discovery of the vulcanization of natural rubber (NR) in 1838, the continuous demand for this material has intensified the quest for a synthetic substitute with similar properties. In this regard, synthetic polyisoprene rubber (IR) emerged as an attractive alternative. However, despite the efforts made, some properties of natural rubber have been difficult to match (i.e., superior mechanical properties) due not only to its high content of cis-1,4-polyisoprene but also because its structure is considered a naturally occurring nanocomposite. In this sense, cutting-edge research has proposed the synthesis of nanocomposites with synthetic rubber, obtaining the same properties as natural rubber. This review focuses on the synthesis, structure, and properties of natural and synthetic rubber, with a special interest in the synthesis of IR nanocomposites, giving the reader a comprehensive reference on how to achieve a mimic of NR.
RESUMO
Unsaturated copolyesters are of great interest in polymer science due to their broad potential applications and sustainability. Copolyesters were synthesized from the ring-opening metathesis copolymerization of ω-6-hexadecenlactone (HDL) and norbornene (NB) using ruthenium-alkylidene [Ru(Cl2)(=CHPh)(1,3-bis(2,4,6-trimethylphenyl)-2-imidazolidinylidene)(PCy3)] (Ru1), [Ru(Cl)2(=CHPh)(PCy3)2] (Ru2), and ruthenium-vinylidene [RuCl2(=C=CH(p-C6H4CF3))(PCy3)2] (Ru3) catalysts, respectively, yielding HDL-NB copolymers with different ratios of the monomer HDL in the feed. The activity of N-heterocyclic-carbene (NHC) (Ru1) and phosphine (Ru2 and Ru3) ligands containing ruthenium-carbene catalysts were evaluated in the synthesis of copolymer HDL-NB. The catalysts Ru1 with an NHC ligand showed superior activity and stability over catalysts Ru2 and Ru3 bearing PCy3 ligands. The incorporation of the monomers in the copolymers determined by 1H-NMR spectroscopy was similar to that of the HDL-NB values in the feed. Experiments, at distinct monomer molar ratios, were carried out using the catalysts Ru1-Ru3 to determine the copolymerization reactivity constants by applying the Mayo-Lewis and Fineman-Ross methods. The copolymer distribution under equilibrium conditions was studied by the 13C NMR spectra, indicating that the copolymer HDL-NB is a gradient copolymer. The main factor determining the decrease in melting temperature is the inclusion of norbornene units, indicating that the PNB units permeate trough the HDL chains. The copolymers with different molar ratios [HDL]/[NB] have good thermal stability up to 411 °C in comparison with the homopolymer PHDL (384 °C). Further, the stress-strain measurements in tension for these copolymers depicted the appreciable increment in stress values as the NB content increases.