Compositional dependence of free volume in PAN/LiCF3SO3 polymer‐in‐salt electrolytes and the effect on ionic conductivity

The free volume behaviour of the polyacrylonitrile/lithium triflate system is investigated over the composition range 0–75 wt % salt. The addition of salt, up to 45 wt %, to the PAN polymer substantially increases the free volume as measured by the orthopositronium pickoff lifetime, τ₃. Beyond this salt concentration (i.e., 45–70 wt %) the free volume remains approximately constant. This constant free volume region corresponds to a region of high ionic conductivity in the glassy state, making these materials polymer‐based fast ion conductors, that is, having a decoupling ratio R_τ ≫1. The high salt content in these fast ion conductors results in a high susceptibility to polar solvents such as water. For all compositions, water absorption results in a free volume increase attributed to plasticization; however, in the fast ion conducting region, a significantly larger free volume response due to plasticization is measured and may be connected to a percolation morphology in these samples. Salt addition is shown to lower the T_g, as measured by positron annihilation lifetime spectroscopy (PALS). T_g is 115°C for PAN and 85°C for 66 wt % lithium triflate. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 341–350, 2000     

DAMAGE OF SILICONE RUBBER INDUCED BY PROTON IRRADIATION

In this paper, the damage to methyl silicone rubber induced by irradiation with protons of 150 keV energy wasstudied. The surface morphology, tensile strength, Shore hardness, cross-linking density and glass transition temperaturewere examined. Positron annihilation lifetime spectrum analysis (PALS) was perfomed to reveal the damage mechanisms ofthe rubber. The results showed that tensile strength and Shore hardness of the rubber increased first and then decreased withincreasing irradiation fluence. The PALS characteristics τ_3 and I_3, as well as the free volume V_f, decreased with increasingirradiation fluence up to 10~(15) cm~(-2), and then increased slowly. It indicates that proton irradiation causes a decrease of freevolume in the methyl silicone rubber when the fluence is less than 10~(15)cm~(-2), while the free volume increases when thefluence is greater than 10~(15)cm~(-2). The results on cross-linking density indicate that the cross-linking induced by protonirradiation is dominant at smaller proton fluences, increasing the tensile strength and Shore hardness of the rubber, while thedegradation of rubber dominates at greater fluence, leading to a decrease of tensile strength and Shore hardness.     

Synthesis and characterization of chitosan‐modified polymethyl methacrylate latex particles

Stable chitosan‐modified polymethyl methacrylate (PMMA) latex particles were prepared by using 2,2′‐azobis(2‐amidinopropane) dihydrochloride (V‐50) as the cationic initiator. The polymerization rate (R_p) is controlled by the V‐50 concentration ([V‐50]) and R_p is less sensitive to the chitosan concentration ([C]) used in the synthesis work. The reaction system follows Smith–Ewart Case III kinetics due to the relatively large particles produced. The zeta potential data show that the isoelectric point (pI) of the latex particles is 10.7. The amounts of V‐50 (C_V‐50) and chitosan (C_c) ultimately incorporated into the particles correlate reasonably well with [V‐50] and [C], respectively. At pH 7, the quantity of the negatively charged bovine serum albumin (BSA, pI = 4.8) adsorbed on the positively charged chitosan‐free particles (Q) via the electrostatic interaction increases with increasing C_V‐50. However, Q is relatively insensitive to changes in C_c. This result implies that only the outermost region of the hairy chitosan‐modified particles is available for adsorption of the relatively large protein species. Colloidal stability shows a significant influence on the BSA adsorption process. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1489–1499, 1999     

Effect of water sorption on oxygen‐barrier properties of aromatic polyamides

Aromatic polyamides based on poly(m‐xylylene adipamide) (MXD‐based polyamides) and poly(hexamethylene isophthalamide) (HMD‐based polyamides) were examined. Insight into the excellent gas‐barrier properties was obtained by the characterization of the effect of water sorption on the thermal transitions, density, refractive index, free‐volume hole size, and oxygen‐transport properties. Reversing the carbonyl position with respect to the amide nitrogen substantially lowered the oxygen permeability of MXD‐based polyamides in comparison with that of HMD‐based polyamides by facilitating hydrogen‐bond formation. The resulting restriction of conformational changes and segmental motions reduced diffusivity. The primary effect of water sorption was a decrease in the glass‐transition temperature (T_g) attributed to plasticization by bound water. No evidence was found to support the idea that sorbed water filled holes of free volume. When the polymer was in the glassy state, the drop in T_g accounted for hydration‐dependent changes in the density, refractive index, and free‐volume hole size. The correlation of the oxygen solubility with T_g and density confirmed the concept of oxygen sorption as filling holes of excess free volume. In some cases, water sorption produced a glass‐to‐rubber transition. The onset of rubbery behavior was associated with a minimum in the oxygen permeability. The glass‐to‐rubber transition also facilitated the crystallization of MXD‐based polymers, which complicated the interpretation of oxygen‐transport behavior at higher relative humidity. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1365–1381, 2005     

Viscoelasticity of nanobubble‐inflated ultrathin polymer films: Justification by the coupling model

The nanobubble inflation method is the only experimental technique that can measure the viscoelastic creep compliance of unsupported ultrathin films of polymers over the glass–rubber transition zone as well as the dependence of the glass transition temperature (T_g) on film thickness. Sizeable reduction of T_g was observed in polystyrene (PS) and bisphenol A polycarbonate by the shift of the creep compliance to shorter times. The dependence of T_g on film thickness is consistent with the published data of free‐standing PS ultrathin films. However, accompanying the shift of the compliance to shorter times, a decrease in the rubbery plateau compliance is observed. The decrease becomes more dramatic in thinner films and at lower temperatures. This anomalous viscoelastic behavior was also observed in poly(vinyl acetate) and poly (n‐butyl methacrylate), but with large variation in the change of either the T_g or the plateau compliance. By now, well established in bulk polymers is the presence of three different viscoelastic mechanisms in the glass–rubber transition zone, namely, the Rouse modes, the sub‐Rouse modes, and the segmental α‐relaxation. Based on the thermorheological complexity of the three mechanisms, the viscoelastic anomaly observed in ultrathin polymer films and its dependence on chemical structure are explained in the framework of the Coupling Model. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013     

Comparison between theoretical and experimental values of the volume changes accompanying rubber extension

The molecular theory of rubber elasticity assumes the free energy to consist of two parts: a liquidlike free energy that is governed by intermolecular interactions and is independent of strain at constant volume and an intramolecular interaction free energy equal to the sum of the free energies of the chains making up the network. The volume increases of rubber samples as a function of their length were found to be considerably larger than predicted by the molecular theory. Therefore, contrary to common belief, the values of (?E/?L)_V,T might not be related solely to changes in intramolecular interactions with extension. Also, the usual procedure to obtain values of (?E/?L)_V,T from measurements of (?f/?T)_p,L with the aid of the molecular theory is not correct.     

New Trends for Utilization of Rubber Wastes

Summary: The scrape rubber is difficult to recycle, since it is not thermoplastic material. Consequently, it must be converted into a powder. The scrape rubber powder can be reused via different ways: a- Reclamation The reclamation process was studied. This process converts the rubber powder into elastic-plastic materials. The obtained reclaims were introduced into NR formulations. The obtained data reveal that, 10–30% reclaimed rubber can replace virgin NR without scarifying the basic properties of the rubber vulcanizates. In such way we can gain cost reduction. b- Reuse as filler-extender The rubber powder was treated with some oxidizing agents and namely HNO₃ and H₂O₂ to modify its surface. The result of such treatment creates some functional groups such as carbonyl groups. The treated rubber powder was used as filler-extender in NR formulations. The treated rubber powder improves the tensile strength of the vulcanizates to some extent (62%). On the other hand, the treated powder was used in combinations with the classical reinforcing carbon black (HAF). The obtained results showed that, 20–40% of HAF can be replaced by the treated powder in NR mixes. The obtained vulcanizates have good physico-mechanical properties. In such way the production cost can be reduced. c- Utilization of sulfonated rubber powder as ion exchanger The rubber powder was sulfonated with Sulfuric and chlorosulfonic acids. The sulfonated product was evaluated as ion exchange resin to clear the industrial wastewater from heavy metals. The data showed that the Sodium salt form is more efficient ion exchanger than the acid form. d- Utilization in pavement The rubber powder is mixed with asphalt used in road pavement. The performance of asphalt concrete greatly depends on the particle size of the rubber powder used. The fine powder greatly improves the mechanical performance of the road pavement. The rubber powder was chemically modified. It was found that such modification had greatly improved the performance road pavement.     

Fracture toughness of nylon‐6 blends with maleated rubbers

The fracture toughness of blends of nylon‐6 with maleated ethylene–propylene rubber and maleated styrene/hydrogenated butadiene/styrene triblock copolymer was investigated with a single‐edge‐notched three‐point‐bending instrumented Dynatup test. The blends for which the rubber particle size was less than 0.7 μm fractured in a ductile manner over the whole range of ligament lengths, whereas the blends with particles larger than 0.7 μm showed a ductile‐to‐brittle transition with the ligament length. In this regime, ductile fracture was observed for specimens with short ligaments, whereas brittle fracture was seen for those with long ligaments. The ductile fracture behavior was analyzed with the essential‐work‐of‐fracture model, whereas linear elastic fracture mechanics techniques were used to analyze the brittle fracture behavior. The fact that the ductile fracture energy was larger for the blends with the styrene/hydrogenated butadiene/styrene triblock copolymer than for those with ethylene–propylene rubber was due to the larger dissipative energy density of the blends based on the styrene/hydrogenated butadiene/styrene triblock copolymer. Both the critical strain energy release rate (G_IC) and the plane‐strain critical stress intensity factor (K_IC) increased as the rubber particle size decreased for both blend systems. The G_IC and K_IC parameters had similar values, regardless of the rubber type, when the rubber particle size was fixed. The transition ligament length was near the size criterion for plane‐strain conditions for both blend systems. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1739–1758, 2004     

Synthesis and characterization of poly (styrene-co-vinyl phosphonate) ionomers

Poly(styrene-co-diethyl vinylphosphonate) copolymers were synthesized by free radical copolymerization. The ester groups of the copolymers were hydrolyzed to phosphonic acid groups, and the sodium and zinc salts ionomers were obtained by neutralization. The structure and the thermal and viscoelastic properties of the copolymers and ionomers were characterized by nuclear magnetic resonance, Fourier transform infrared spectroscopy, differential scanning calorimetry, dynamic mechanical analysis, and small-angle X-ray scattering. The phosphonate ester lowered the glass transition temperature (T_g) of polystyrene. The free acid derivatives and metal phosphonates increased T_g and produced a rubbery plateau region in the viscoelastic properties due to the formation of a physical network. The acid and salt ionomers exhibited microphase-separated morphologies and were thermorheologically complex. The phosphonic acid derivatives absorbed relatively little water, even for materials with ion-exchange capacities greater than 1.0 mEq/g, and were not conductive, which made them unsuitable for application as proton exchange membranes. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3628–3641, 2004     

Curing of epoxidized natural rubber with p-phenylenediamine

The curing of epoxidized natural rubber with p-phenylenediamine catalyzed by bisphenol A was investigated. The curing reaction was found to be first order with respect to the amine and to have an activation energy of 67.5 kJ/mol. Vulcanizates of tensile strength 12.5–16.0 MPa were obtained at cure times of 30–75 min at 180°C. The amine-cured vulcanizate was observed to be more rigid than the sulfur-cured one at room temperature consistent with its relatively high T_g. Stress-strain analysis and dynamic mechanical properties indicated that the high T_g of the amine-cured vulcanizate could be attributed to the bulky amine crosslinks and hydrogen bonding effect of bisphenol A. © 1994 John Wiley & Sons, Inc.     

Surface-Initiated RAFT Polymerization of 2,3-Dimethyl-1,3-butadiene on Silica Nanoparticles for Matrix-free Methyl Rubber Nanocomposites

Reversible addition-fragmentation chain transfer (RAFT) polymerization of 2,3-dimethyl-1,3-butadiene (DMB) in solution and on the surface of silica nanoparticles was investigated and PDMB-grafted silica nanoparticles (PDMB-g-SiO₂ NPs) with different chain densities and molecular weights were prepared. The kinetic studies of DMB polymerization mediated by silica anchored RAFT agents at different graft densities were investigated and compared to the polymerization mediated by the corresponding free RAFT agent. The PDMB-g-SiO₂ NPs were cured to prepare rubbery films and obtain matrix-free nanocomposites, which exhibited a good dispersion of silica nanoparticles and improved mechanical properties compared to the unfilled crosslinked rubber. © 2020 Wiley Periodicals, Inc. J. Polym. Sci. 2020 , 58, 417–427     

Brillouin scattering from amorphous bisphenol-A polycarbonate

Brillouin scattering has been studied from amorphous bisphenol-A polycarbonate in the temperature interval 60–240°C. Both longitudinal and transverse Brillouin peaks are observed over the entire range. The behavior of both types of Brillouin splittings, Δω_l and Δω_t, in the region of the glass–rubber relaxation is typical of an amorphous polymer. Equilibrium values of Δω_l and Δω_t were obtained 20°C below the glass-transition temperature T_g determined at cooling rates of 20°C/hr. Comparison of the present results with previous ultrasonic data reveals a considerable dispersion in the longitudinal phonon velocity below T_g. The origin of the large transverse Brillouin intensities is related to the structure of polycarbonate.     

STUDY ON THE TOUGHENING MECHANISM OF RUBBER TOUGHENED EPOXY

The following factors affecting the rubber toughened epoxy resin system were studied: 1. kindsof curing agent used, 2. the M_c value of the matrix, 3. the bonding foce between the dispersed phaseand the matrix. Our experimental result indicates that the average chain length between crosslinks(M_c) is a much more important affecting factor. Chemical bonding between the dispersed phaseand the matrix is also important. A toughening mechanism of rubber toughened epoxy has beenproposed. In the material with relatively low crosslinking density, extensive fracture process stripis formed which is induced by the combined stress field near the rubber particles. The chemical bond-ing between the dispersed phase and the matrix may inerease the strength of the local stress field aboutthe rubber particles which is in favor of broading the fracture process area.     

Cryogenic tensile stress–strain properties of cis- and trans-polybutadienes,polyisoprenes, and related copolymers

The low-strain-rate tensile stress–strain properties of cis- and trans-polybutadienes and -polyisoprenes, polybutadiene (cis/trans/vinyl), butyl rubber, and two SBR copolymers have been investigated from 77°K to up to 25°K below the glass transition temperature T_g. The energy E_p dissipated in a stress–strain test in the region of previously reported secondary glass transitions is found to be a function of both the free volume f? at the T_g and the damping A from 4°K to T_g ?25°K. The complex relationship between the impact strength, the free volume and the damping is briefly discussed. The effect of quenching through the T_g with liquid nitrogen was found to increase the value of E_p for all materials. In a number of cases this increase was associated with the presence of internal crazes. The surface-craze initiation stress is increased by the presence of surface residual compressive stresses caused by quenching. The internal tensile stresses balancing the surface compressive stresses together with the applied tensile stress cause internal dilatation and hence preferential initiation of internal crazing.     

Rouse–Bueche theory and the calculation of the monomeric friction coefficient in a filled system

Direct experimental access to the monomeric friction coefficient (ζ₀) relies on the availability of a suitable polymer dynamics model. Thus far, no method has been suggested that is applicable to filled systems, such as filled rubbers or microphase‐segregated A–B–A thermoplastic elastomers (TPEs) at T_g,B < T < T_g,A. Building upon the procedure proposed by Ferry for entangled and unfilled polymer melts, the Rouse–Bueche theory is applied to an undiluted triblock copolymer to extract ζ₀ from the linear behavior in the rubber‐glass transition region, and to estimate the size of Gaussian submolecules. When compared at constant T – T_g, the matrix monomeric friction factor is consistent with the corresponding value for the homopolymer melt. In addition, the characteristic Rouse dimensions are in good agreement with independent estimates based on the Kratky–Porod worm‐like chain model. These results seem to validate the proposed approach for estimating ζ₀ in filled systems. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1437–1442     

Nanocavitation around a crack tip in a soft nanocomposite: A scanning microbeam small angle X‐ray scattering study

We explore nanocavitation around the crack tip region in a styrene‐butadiene random copolymer filled with typical carbon black (CB) particles used in the rubber industry for toughening the rubber. Using quasistatic loading conditions and a highly collimated X‐ray microbeam scanned around the crack tip, we demonstrate the existence of a damage zone consisting of nanovoids in a filled elastomer matrix. The existence of voids near the crack tip is demonstrated by a significant increase of the scattering invariant Q/Q₀ in front of both fatigued and fresh cracks. The size of the zone where cavities are present critically depends on the macroscopic strain ε_m, the loading history, and the maximum energy release rate G applied to accommodate the crack. Our findings show that nanovoiding occurs before fracture in typical CB‐filled elastomers and that realistic crack propagation models for such elastomers should take into account a certain level of compressibility near the crack tip. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 422–429     

Positron annihilation lifetime and differential scanning calorimetric study of immiscible NBR/PE blends

The temperature dependence of the mean size of nanoscale free‐volume holes, 〈V_h〉, in polymer blend system consisting of polar and nonpolar polymers has been investigated. The positron lifetime spectra were measured for a series of polymer blends between polyethylene (PE) and nitrile butadiene rubber (NBR) as a function of temperature from 100 to 300 K. The glass transition temperatures (T_g) for blends were determined from the ortho‐positronium (o‐Ps) lifetime τ₃ and the mean size of free‐volume holes 〈V_h〉 versus temperature as a function of wt % of NBR. The T_gs estimated from the PALS data agree very well with those estimated from DSC in view of different time scales involved in the two measurements. Both DSC and PALS results for the blends showed two clear T_gs of a two‐phase system. Furthermore, from the variation of thermal expansivity of the nanoscale free‐volume holes, the thermal expansion coefficients of glass and amorphous phases were estimated. Variations of the o‐Ps formation probability I₃ versus temperature for pure PE and blends with low wt % of NBR were interpreted on the basis of the spur reaction model of Ps formation with reference to the effects of localized electrons and trapping centers produced by positron irradiation. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 227–238, 2009     

The free energy–reaction coordinate profile for α-chymotryptic hydrolysis of a series of N-acetyl-α-L-amino acid methyl esters

The effect of added nucleophiles (methanol and 1,4-butanediol) on the steady-state kinetics of α-chymotryptic hydrolysis of a series of N-acetyl-L-amino acid methyl esters, R-CH(NHCOCH₃)C(O)OCH₃, has been studied. As a result, the rate and equilibrium constants of the ‘elementary’ steps of the enzyme process have been determined. It has also been demonstrated how the free energy–reaction coordinate profile changes if the structure (the size of the hydrocarbon chain) of the ‘chemically inert’ substrate fragment R is varied. The effects observed can be described by the following equation: where ΔG_s and ΔG_a are the free energies of formation of metastable intermediates, i.e., the enzyme–substrate complex and the acylenzyme, respectively, ΔG₂≠ and ΔG₃≠ are the free energies of activation for the chemical steps, i.e., enzyme acylation and acylenzyme hydrolysis, respectively; and ΔG_trans^(R) is the free energy of transfer of substrate group R from water into a nonaqueous solvent. To explain the results obtained, a mechanism for enzyme–substrate interaction is suggested according to which the potential free energy of sorption of substrate group R on the enzyme is 2 ΔG_trans^(R). Such a high gain in the free energy of hydrophobic interaction may only be realized if (a) in the free enzyme the sorption region has a thermodynamically unfavorable contact with the aqueous medium, and (b) water is forced out of the active center as a result of the hydrophobic interaction of substrate group R with the enzyme. Such a model is in agreement with the published x-ray data on the structure of the crystalline enzyme. The kinetic experiment has proved that not all the potential free energy of sorption is realized as binding force. Thus the true free energy of the binding of substrate group R with the protein does not exceed half the maximum value, both in the enzyme–substrate complex and acylenzyme.     

Statistical mechanical model of diffusion of complex penetrants in polymers. II. Applications

The theory of Part I is applied to the diffusion of several aromatic diffusants in two “smooth chained” polymers: poly(ethylene terephthalate) (PET) and natural rubber. Modifications of the theory necessary to accommodate vinyl polymers are discussed and applied to benzene in PMA and PEA. In all cases the theory agrees satisfactorily with the experimental D(0,T) and D(c,T)/D(0,T) data, and the values of the disposable r_g and Δ parameters are of the expected order. The limiting Arrhenius behavior of benzene in natural rubber appears to be correctly predicted. The cell model is definitely more appropriate than the free volume model for the calculation of enfolding chain effects in highly crystalline PET. For the three amorphous polymers the two models give comparable results, the cell model being somewhat superior for natural rubber and PMA.