Synthesis and characterization of poly(aminobismaleimide)s obtained from solvent‐free mixtures

A series of eight poly(aminobismaleimide)s containing aromatic units have been synthesized from a one‐step nucleophilic addition reaction between diamine and bismaleimide, without exogeneous solvent, to provide encapsulant withstanding high temperature suitable for power electronics. To have a homogeneous medium at room temperature, the solid aromatic diamines are first mixed with different liquid aliphatic ones, and then mixed with bismaleimide. The syntheses were then carried out at 175 °C for 15 min. Thus, according to their composition, these obtained thermosetting resins are characterized by a relaxation temperature between 98 and 190 °C and a coefficient of thermal expansion between 20 and 150 ppm/K. All material surfaces are hydrophobic and their moisture uptake is lower than 2–3 wt %. Finally, as expected, the substitution of a part of the aliphatic diamine by an aromatic one improves the thermal stability under air atmosphere of the resulting materials (T_d = 280–300 °C increased to T_d = 315–340 °C). Their use as power module encapsulant can therefore be considered. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46105.     

Crosslinking of high‐density polyethylene in the presence of organic peroxides

The crosslinking efficiency of various commercially available organic peroxides (dicumyl peroxide, O,O‐t‐butyl O‐2‐ethylhexylperoxycarbonate, t‐butyl peroxybenzoate, t‐butyl 3,5,5‐trimethylperoxyhexanoate, and t‐butyl 2‐ethylperoxyhexanoate) was tested on high‐density polyethylene (HDPE) in its molten state. The variations of the concentrations of the peroxides versus the crosslinking extent were plotted for these peroxides, and the values were compared. Dicumyl peroxide was found to be the best crosslinking agent for HDPE. The efficiency of the HDPE crosslinking with each peroxy derivative was analyzed on the basis of the behavior of the radicals generated from it. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 75–81, 2004     

Characterization of the viscoelastic and mechanical properties of tightly cross‐linked polythiourethane networks

Both viscoelastic behavior and plastic deformation in compression were investigated on new polythiourethane networks based on diisocyanates and tri‐ or tetra‐thiols. Dynamic mechanical analysis was used to characterize the mechanically‐active α and β relaxations as a function of crosslink density and nature of the diisocyanate. Data molecular analysis on these novel materials led to conclusions in good agreement with earlier statements on the well‐known epoxy‐amine networks. Besides, consideration of the relaxational behavior, and especially in the β relaxation region, allowed one to interpret the plastic deformation properties of the systems under study and to predict their poor resistance to fracture. By the way, analysis of the energy required to yield permitted determination of a new characteristic temperature, T_y, which can be compared to the thermomechanical main transition temperature, T_α, and to the glass transition temperature, T_g. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Trimethylsilyl permodified cyclodextrins: Hydrolysis at the air-water interface

The behavior at the air-water interface of amphiphilic α, β and γ trimethylsilyl per-modified cyclodextrin (pTMS-CD) monolayers is reported, as a first step towards the building up of a Langmuir-Blodgett assembly with potential gas sensor properties. The pTMS-CDs form stable monolayers with unusually high collapse pressure. It is shown that this peculiar behavior arises from a partial hydrolysis of TMS groups at the air-water interface. This hydrolysis reaction was confirmed by infrared spectroscopy and the departure of TMS groups was evidenced by weight loss measurements through quartz crystal microbalance carried out on the pTMS-CD monolayers deposited through the Langmuir-Blodgett technique.     

Raman spectroscopic investigations on the kinetics of gelation and densification of Cd- and Pb-doped silica glasses under basic conditions

In the present work, the evolution of the gelation of undoped and Cd²⁺-and Pb²⁺-doped silica sols has been studied. Tetramethyl orthosilicate and cadmium and lead nitrates were selected as suitable precursors for the synthesis of nanoporous undoped and doped silica systems. Raman spectroscopy was used both to follow the different species formed and the structural changes occurring at various stages of the sol-gel transformation. The combination of information obtained from Raman spectra and from textural measurements using nitrogen adsorption-desorption served to investigate the effects of doping metal ion on the structure of both the gels and on the resulting nanoporous silica glasses. Results showed that doping silica materials with different concentrations of Cd²⁺ or Pb²⁺ makes it possible both to decrease the densification time and to control the porosity of the resulting gels and glasses.     

Tailored Silica Macrocellular Foams: Combining Limited Coalescence‐Based Pickering Emulsion and Sol–Gel Process

Solid‐sate monolithic macrocellular foams are synthesized by mineralizing the continuous phase of oil‐in‐water Pickering emulsions, used as templates, with the sol–gel process. For the first time, taking advantage of the limited coalescence phenomenon occurring in emulsions stabilized by solid particles, concentrated emulsions with calibrated drop size are produced, leading to the synthesis of monolithic foams with nearly monodisperse macroscopic voids. Such a strategy allows independent tuning of the macrocellular void diameters from 20 to 800 μm and the diameter of the windows connecting adjacent cells. The obtained macrocellular foams also bear micro‐ and mesoporosity, leading to Brunauer, Emmet and Teller (BET) surface area values between 700 and 900 m² g^?1 with a good mesopores monodispersity.     

Lignin/Carbohydrate Complex Isolated from Posidonia oceanica Sea Balls (Egagropili): Characterization and Antioxidant Reinforcement of Protein-Based Films

A lignin fraction (LF) was extracted from the sea balls of Posidonia oceanica (egagropili) and extensively dialyzed and characterized by FT-IR and NMR analyses. LF resulted water soluble and exhibited a brownish-to-black color with the highest absorbance in the range of 250–400 nm, attributed to the chromophore functional groups present in the phenylpropane-based polymer. LF high-performance size exclusion chromatography analysis showed a highly represented (98.77%) species of 34.75 kDa molecular weight with a polydispersity index of 1.10 and an intrinsic viscosity of 0.15. Quantitative analysis of carbohydrates indicated that they represented 28.3% of the dry weight of the untreated egagropili fibers and 72.5% of that of LF. In particular, eight different monosaccharides were detected (fucose, arabinose, rhamnose, galactose, glucose, xylose, glucosamine and glucuronic acid), glucuronic acid (46.6%) and rhamnose (29.6%) being the most present monosaccharides in the LF. Almost all the phenol content of LF (113.85 ± 5.87 mg gallic acid eq/g of extract) was water soluble, whereas around 22% of it consisted of flavonoids and only 10% of the flavonoids consisted of anthocyanins. Therefore, LF isolated from egagropili lignocellulosic material could be defined as a water-soluble lignin/carbohydrate complex (LCC) formed by a phenol polymeric chain covalently bound to hemicellulose fragments. LCC exhibited a remarkable antioxidant activity that remained quite stable during 6 months and could be easily incorporated into a protein-based film and released from the latter overtime. These findings suggest egagropili LCC as a suitable candidate as an antioxidant additive for the reinforcement of packaging of foods with high susceptibility to be deteriorated in aerobic conditions.     

Co-continuous morphology and stress relaxation behaviour of unfilled and silica filled PP/EPDM blends

These researches aimed at bringing significant and useful information regarding the morphologies and relaxation behaviour of PP/EPDM blends as detailed morphological studies of such uncrosslinked blends are still lacking in the literature. This work allowed a fruitful study of the correlation between their morphology and final mechanical properties, especially concerning their relaxation behaviour. In particular, among all the expected morphologies, the co-continuity is virtually undescribed in the literature whereas it is surely one of the most interesting one regarding the confinement effect of two continuous phases having such a low interfacial tension. The experimental conditions leading to such an atypical morphology have been thoroughly described, and its final properties have shown amazing results especially regarding the relaxation and strain recovery behaviours encountered during compression set experiments. As a matter of fact, these experiments highlighted interesting industrial properties related to such a particular morphology: uncrosslinked co-continuous blends reveal a final strain recovery of nearly 40% after a 25% strain applied for 10 h at 100 °C which could be discussed on the basis of several physical and rheological considerations. Additionally, the study of the stabilization of such a morphology has also brought interesting results. Finally, we have also studied the influence of hydrophilic and hydrophobic silica nanoparticles on such a specific morphology and its correlated compression set properties.