Flexible aliphatic poly(isocyanurate–oxazolidone) resins based on poly(ethylene glycol) diglycidyl ether and 4,4′‐methylene dicyclohexyl diisocyanate

New flexible aliphatic oxazolidone‐isocyanurate networks (AISOX) are obtained by reacting a low molecular weight diisocyanate (4,4′‐methylene dicyclohexyl diisocyanate, H₁₂MDI) and a macro‐diepoxyde (poly(ethylene glycol) diglycidyl ether, M_n = 526, PEGDGE) in different molar ratio. The curing reaction, carried out from 25 °C to 200 °C, is studied by using DSC and FTIR. The effect of the molar ratio of the two monomers on thermal and mechanical properties of AISOX resins is investigated by DSC, thermogravimetric analysis, stress?strain measurements and optical microscopy. Independently from the feed composition, it is observed that the reaction steps are: (i) partial hydrolysis of isocyanate caused by water traces, (ii) incomplete trimerization of isocyanate to give isocyanurate, and (iii) formation of oxazolidone and complete conversion of isocyanate. At the highest concentration of the soft macrodiepoxyde (PEGDGE), the AISOX resin is in the rubbery state at room temperature and shows an elastomeric behavior. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43404.     

Percolation and catalysis effect of bamboo‐based active carbon on the thermal and flame retardancy properties of ethylene vinyl‐acetate rubber

The effect of percolation and catalysis of bamboo‐based active carbon (BAC) on the thermal degradation and flame retardancy of ethylene vinyl‐acetate rubber (EVM) composites with intumescent flame retardants (IFR) consisting of ammonium polyphosphate (APP) and dipentaerythritol (DPER) has been investigated. The vulcanization characteristics were analyzed by a moving die rheometer. Thermogravimetric analysis (TGA) and fire behavior tests such as limiting oxygen index (LOI), vertical burning (UL 94), and cone calorimetry were used to evaluate the thermal properties and flame retardancy of EVM composites. Scanning electron microscopy (SEM) was used to study the morphology of residues of EVM composites. The addition of BAC significantly increased the maximum torque (M_H) of EVM composites and EVM matrices. The combination of IFR with BAC can improve the thermal stability of EVM composites. Moreover, BAC can enhance char residue and promote the formation of a network for IFR. The current EVM/37IFR/3BAC composite achieved an LOI of 33.6% and a UL 94 V‐0 rating. The PHRR, total heat release (THR), and total smoke release (TSR) for EVM/IFR/BAC were greatly reduced as compared to EVM/40IFR. Also, the mechanical properties of the EVMIFR/BAC composites increased with increasing BAC contents. The physical percolation effect between BAC and EVM before and after thermal degradation, and the chemical catalysis effect between BAC and IFR during thermal degradation are responsible for the improved flame retardancy of EVM composites. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42414.     

Fluorinated Polyphosphazenes: A Survey

A general survey of fluorinated phosphazene polymers starting from their synthesis in 1965 to recent times is presented. Various types of fluorinated phosphazenes are described depending on the way fluorine atoms are connected to the polyphosphazene skeleton. The characterization, properties and practical utilization of these compounds in different domains are critically discussed.     

Enhanced properties of poly(styrene–b–ethylene–co–butylene–b–styrene) nanocomposites with in situ construction of interconnected graphene network

In this work, such elastomeric nanocomposites were fabricated with graphene (GE) sheets selectively distributing between polymer matrices and forming three-dimensional networks. The solvent evaporation process was first introduced to produce poly(styrene–ethylene–co–butadiene–b–styrene) (SEBS) microspheres and then reduced GE oxide attached to the surface of SEBS microspheres via electrostatic interaction and sonication-assisted reduction. The microstructure of nanocomposites, prepared by compression molding using SEBS/GE microspheres, was investigated using scanning electron microscopy and transmission electron microscopy. The results showed that interconnected GE networks formed in heat-pressing composite and was destroyed after twin-roll mixing. The SEBS/GE nanocomposites showed enhanced electrical, thermal, and mechanical properties. The electrical resistivity of nanocomposites obtained via heat-pressing reached to 1.1 × 10³ Ω m at a 2.5 wt % (1.07 vol %) content of GE. The thermal and mechanical properties were also characterized. It was found that the initial degradation temperature increased by nearly 40 °C and the mechanical properties continued to rise with GE content below 0.5 wt %. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47118.     

Effect of the compatibilizer,on the engineering properties of TPV based on Hypalon® and PP prepared by dynamic vulcanization

Elastomeric Chlorosulfonated polyethylene (Hypalon^®) and thermoplastic Polypropylene (PP) based thermoplastic vulcanizates (TPVs) were prepared in presence of different doses of compatibilizer, maleic anhydride grafted PP (PP‐g‐MA) by employing dynamic vulcanization technique. The effect of incorporation in different proportions of compatibilizer on mechanical, spectral, morphological, thermal, and rheological properties of such TPVs was studied and the same were compared to that of virgin PP and amongst themselves. The mechanical analysis of the prepared TPVs exhibited significant improvements in stress at 25% modulus, ultimate tensile strength (UTS), and hardness values. FTIR studies revealed that a chemical interaction had taken place between Hypalon^® and functionalized compatibilizer during the process of dynamic vulcanization which led to an enhancement of interfacial adhesion between them. The two‐phase morphologies were clearly observed by scanning electron microscopic studies. The T_g values of Hypalon^® was modified in the TPVs as exhibited by differential scanning calorimetric studies. TGA studies indicated the increase in thermal stability of all TPVs with respect to the elastomeric Hypalon^®. Rheological properties showed that the compatibilizer reduces the melt viscosity of TPVs and thus facilitates the processibility of such TPVs. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40312.     

Nonlinear viscoelastic modeling of soft polymers

A one‐dimensional phenomenological constitutive model, representing the nonlinear viscoelastic behavior of polymers is developed in this study. The proposed model is based on a modification of the well‐known three element standard solid model. The linear dashpot is replaced by an Eyring type one, while the nonlinearity is enhanced by a nonlinear, strain dependent spring constant. The new constitutive model was proved to be capable of capturing the main aspects of nonlinear viscoelastic response, namely, monotonic and cyclic loading, creep and stress relaxation, with the same parameter values. Model validation was tested on the experimental results at various modes of deformation for two elastomeric type materials, performed elsewhere. A very good agreement between model simulations and experimental data was obtained in all cases. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42141.     

Synthesis and characterization of novel citric acid-based polyester elastomers

In this paper we report successful simple synthesis of unique elastic polyesters by carrying out catalyst-free polyesterification of multifunctional non-toxic monomers: 1,8-octanediol (OD), citric acid (CA) and sebacic acid (SA). The chemical, physical, and surface chemical properties of the resulting copolyester polyoctanediol citrate/sebacate [p(OCS)] have been investigated. This new material was characterized by matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-ToF-MS), nuclear magnetic resonance spectroscopy (NMR), thermal analysis (TA), mechanical tests, photo-acoustic Fourier-transform infrared spectroscopy (PA-FTIR), X-ray photoelectron spectroscopy (XPS) and swelling experiments. We demonstrate that the chemical structure, morphology, physical integrity and surface chemistry of the synthesized co-polymer can be controlled by simply varying the initial acid concentration (CA/SA) in the pre-polymer. This novel p(OCS) polymer exhibits versatility in mechanical properties, hydration and hydrolytic degradation as determined by the chemical structure of the polyester elastomer.     

Tetramethylammonium 3-aminopropyl dimethylsilanolate—aminopropyl dimethylsilanolate—a new catalyst for the synthesis of high purity,high molecular weight α,ω-bis(aminopropyl) polydimethylsiloxanes

Tetramethylammonium 3-aminopropyl dimethylsilanolate, readily prepared from bis(3-aminopropyl) tetramethyldisiloxane and tetramethyl-ammonium hydroxide pentahydrate, has been found to serve as a highly effective catalyst for the ring opening polymerization of cyclic siloxanes with an end blocker such as bis(3-aminopropyl) tetramethyldisiloxane to give aminopropyl terminated linear polydimethylsiloxanes. By following a novel two stage procedure, even high molecular weight (5,000–55,000 g/mol) silicone diamines were able to be prepared in a high state of purity; chain extension reactions of these diamines with diisocyanates gave a series of high molecular weight silicone polyureas with good elastomeric properties.     

Photomechanical degradation of thermoplastic elastomers

The photodegradation of thermoplastic elastomers designed for outdoor applications was studied with laboratory ultraviolet (UV) exposure in the unstrained state and under tensile strain (25 and 50%). Strained exposure caused a reduction of the strain to failure in subsequent tensile tests. For some combinations of material and exposure conditions, some recovery of extensibility occurred between 2 and 4 weeks. Microscopic examination revealed that this was probably due to embrittlement of the surface region that was sufficiently severe that surface cracks did not propagate into the interior and that the observed recovery did not correspond to repair or improvement of the material. Shielding the sample surface from UV irradiation reduced the formation of surface cracking very significantly, and it was deduced that the principal cause of degradation was photooxidation rather than ozone attack. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 150–161, 2006     

Structure of syndiotactic propylene-ethylene copolymers: Effect of the presence of ethylene units on the structural transitions during plastic deformation and annealing of syndiotactic polypropylene

Syndiotactic propylene-ethylene copolymers have been synthesized with a single-center C_s-symmetric syndiospecific metallocene catalyst. A study of the effect of the presence of ethylene comonomeric units on the polymorphic behavior of syndiotactic polypropylene (sPP) and on the structural transitions occurring during stretching is reported. For copolymer samples with low ethylene contents, in the range 2-7 mol%, crystals of the helical form I, present in the melt-crystallized samples, transform into the trans-planar form III by stretching at high deformation. Form III transforms in part into the helical form II by releasing the tension, as it occurs for sPP. Samples with ethylene contents in the range 8-10 mol% are crystallized from the melt as a mixture of crystals of helical form I and form II. Both helical forms transform by stretching at low values of deformation (lower than 300%) into the trans-planar mesomorphic form, which transforms into the trans-planar form III by further stretching at higher deformations (higher than 500%). For these samples form III transforms back into the mesomorphic form, rather than into the helical forms, by releasing the tension. Unoriented samples of copolymers with ethylene content in the range 13-18 mol% are mainly crystallized in the helical form II, which transforms into the trans-planar mesomorphic form by stretching. Upon releasing the tension the mesomorphic form remains stable and no polymorphic transition is observed. The presence of ethylene comonomeric units stabilizes the trans-planar forms in fibers of the copolymer samples. This has been confirmed by the result that for high ethylene contents the trans-planar form III and the mesomorphic form do not transform in helical forms by annealing of fibers stretched at high deformations.