Marly Antonia Maldaner Jacobi

Polymers oxidation with VO(acac)2 complex

Abstract The introduction of epoxy groups in the polymer backbone is one of the most promising methods of modifying polydienes. In this work the performance of the classical catalytic system VO(acac) 2 / tert -butylhydroperoxide was evaluated for the epoxidation of polydienes. The polymers investigated were a hydroxylated poly(butadiene), two polybutadienes with high and with low 1,4-content, a poly(isoprene), and a styrene–butadiene copolymer. The epoxidized polymers were characterized by IR, 1 H and 13 C NMR and GPC techniques. The vanadium system was active for the epoxidation reaction and the reactivity decreases in the order HTPB>PI>1,4-PB>1,2-PB∼SBR. The occurrence of secondary reactions to low extension could be detected by the presence of hydroxyl, carbonyl and alcohol signals in the spectra of epoxidized polymers. Incomplete mass recovery (70–90%) was observed probably due to the chain degradation or modification of the polymer polarity.

Very efficient epoxidation of 1,4-polybutadiene with the biphasic system methyltrioxorhenium (MTO)-CH2Cl2/H2O2

The biphasic system methyltrioxorhenium (MTO)-H2O2/CH2Cl2 was studied in the epoxidation of polybutadiene and the results showed that this system presents a high selectivity and the extension of epoxidation (10–50%) can be modulated by the amount of oxidant added, without significant change in the molecular weight of the polymer.

Direct comparison of the segmental orientations of free oligomer and network chains in polybutadiene model networks

The segmental orientation in a semi-interpenetrating polymer network based on crosslinked polybutadiene swollen to different degrees by free butadiene oligomers (of molar masses below the entanglement limit) is studied as a function of uniaxial strain for both the oligomer chains and the network chains by using 2H nuclear magnetic resonance (n.m.r.) spectroscopy. While the second moment of the orientation distribution function, P2, is usually obtained from the quadrupolar splitting of the maxima of the spectra, herein we obtain the averaged P2 from the whole spectrum. For high volume fractions of the network chains (φ > 0.8) the untangled oligomer shows the same degree of orientation as the network, while for larger degrees of swelling the oligomer orientation is smaller than that of the network chains. Strain birefringence measurements performed on the same materials show a similar strain dependence as the orientation parameter obtained from 2H n.m.r. spectroscopy.

Dynamically Vulcanized PP/EPDM Blends: Effect of Composition and Curing Agents:

The comparative study between two curing agents, conventional peroxide (Peroximon) and bismaleimide/dicumyl peroxide combination (BMI/DCP), and the influence of composition in TPE-Vs based on polypropylene (PP) and ethylene—propylene—diene terpolymer (EPDM) were investigated. The materials were characterized by mechanical, hardness, swelling and morphological properties. The TPE-Vs obtained using Peroximon presented lower tensile strength, remarkable lower deformation and swelling degrees than those cured with BMI/DCP. Among all the investigated PP/EPDM compositions, the content of thermoplastic increases the tensile at break. The experimental swelling values are in agreement with the theoretical for the TPE-Vs obtained using BMI/DCP and for the obtained using Peroximon all compositions showed experimental swelling degree higher than the theoretical ones. The hardness is determined by the amount of PP. We also observed in the morphology studies that the rubber domains are smaller and better defined when the BMI/DCP is used.

Evaluation of the influence of the polymer-filler interaction on compounds based on epoxidized elastomeric matrix and precipitated silica

The introduction of epoxy groups into the main chain of elastomers has emerged as a promising alternative, considering the monitoring of polymer-filler interaction leading to changes in the properties of vulcanizates. The epoxidation reaction (in situ) was chosen to modify elastomers, such as polybutadiene (BR) and copolymer of styrene- butadiene-rubber (SBR), because it is a simple, easily controlled reaction, even considering the small epoxidation degree. The modification degree of the polymeric chain was studied with FT-IR and 1 H-NMR. The shift of the Tg to high temperatures with the increase of the epoxy group in the polymer chain was monitored through differential scanning calorimetry (DSC). An analysis of the dynamic modulus of the material in relation to its dependence on the amplitude and temperature was carried out. The interaction between epoxidized elastomeric matrix and silica as filler was extremely improved, even in the presence of very low content of epoxy groups into the polymer chain.

Estudo da modificação química de polidienos do tipo SBR e BR

:: :modification of polydiene has been studied as an alternative route to obtain modified polymers with improved final properties. This improvement is due to the introduction of different kinds of reactive groups into a polymer chain, and it can be done in solution as well as in bulk. The chemical modification can be carried out by different methods such as epoxidation, maleination, carboxylation, sulfonation etc. In this work we show that in the epoxidation of SBR and BR even a small degree of modification can change the final properties of the polymer, as it occurred for the glass transition temperature.

Polybutadiene model networks —synthesis, mechanical characterization and comparison with rubber elasticity models

Model networks of defined crosslink density are prepared via nonradical statistical crosslinking of polybutadiene in bulk and concentrated solution using a masked bistriazolinedione as crosslinker. The kinetics of crosslinking is monitored by FT-IR-spectroscopy. The reaction follows pseudo-1st-order reaction kinetics. The activation parameter of the crosslinking reaction is estimated from crosslinking at various temperatures. Networks of deuterated polybutadiene are prepared by this reaction in a wide range of crosslink densities. The stress strain behavior is analyzed according to the Junction Constraint-Theory of rubber elasticity (JCT) and to the approach introduced by Graessley accounting for trapped topological constraints. The analysis clearly demonstrates that trapped entanglements contribute to the mechanically effective cycle rank, i.e., to the modulus in this system in the small and large strain limit.

Epoxidação "in situ" aplicada ao látex de borracha natural

Natural rubber latex was submitted to epoxidation reaction to establish the best reaction conditions without the occurrence of side reactions, which promote coagulation of the latex and development of an agglomerate of rubber. Epoxy groups were produced by in situ epoxidation with formic acid and hydrogen peroxide. The samples were characterized qualitatively by Fourier Transform Infrared (FTIR) analysis and the degree of modification determined by Hydrogen Nuclear Magnetic Resonance Spectroscopy (1H-NMR) analysis. A linear increase in the glass transition temperature (Tg) was observed. The results show that the epoxidation of natural rubber latex is possible and depends on the reaction conditions.

Divergent genetic mechanisms lead to spiny hair in mammals

In humans, a single amino acid change (V370A) in the Ecdysoplasin A receptor (Edar) gene is associated with a unique hair phenotype in East Asian populations. Transgenic experiments in mouse show that this mutation enhances Edar signaling in vitro, which in turn alters multiple aspects of hair morphology. Here we tested whether this substitution contributes to the spiny hair observed in six families of rodents. We first measured hair traits, focusing on guard hairs and their physical properties, such as tension and deformation, and compared the morphology between spiny and non-spiny sister lineages. Two distinct hair morphologies were repeatedly observed in spiny rodent lineages: hairs with a grooved cross-section and a second near cylindrical form, which differ in their cross-section shape as well as their tensiometric properties. Next, we sequenced a portion of the Edar locus in these same species. Most species surveyed have the common amino acid valine at position 370, but the kangaroo rat and spiny pocket mouse have an isoleucine. We also found one additional amino acid variant: tree rats have a Leu422Val polymorphism. However, none of these variants are associated with changes in hair morphology. Together these data suggest that the specific Edar mutation associated with variation in human hair morphology does not play a role in modifying hairs in wild rodents, highlighting that different evolutionary pathways can produce similar spiny hair morphology.

Divergent genetic mechanism leads to spiny hair in rodents

Spines, or modified hairs, have evolved multiple times in mammals, particularly in rodents. In this study, we investigated the evolution of spines in six rodent families. We first measured and compared the morphology and physical properties of hairs between paired spiny and non-spiny sister lineages. We found two distinct hair morphologies had evolved repeatedly in spiny rodents: hairs with a grooved cross-section and a second near cylindrical form. Compared to the ancestral elliptical-shaped hairs, spiny hairs had higher tension and stiffness, and overall, hairs with similar morphology had similar functional properties. To examine the genetic basis of this convergent evolution, we tested whether a single amino acid change (V370A) in the Ectodysplasin A receptor (Edar) gene is associated with spiny hair, as this substitution causes thicker and straighter hair in East Asian human populations. We found that most mammals have the common amino acid valine at position 370, but two species, the kangaroo rat (non-spiny) and spiny pocket mouse (spiny), have an isoleucine. Importantly, none of the variants we identified are associated with differences in rodent hair morphology. Thus, the specific Edar mutation associated with variation in human hair does not seem to play a role in modifying hairs in wild rodents, suggesting that different mutations in Edar and/or other genes are responsible for variation in the spiny hair phenotypes we observed within rodents.