Entanglement networks of 1,2-polybutadiene cross-linked in states of strain. V. Relaxation phenomena and calculations of entanglement trapping

Linear 1,2-polybutadiene is cross-linked near its glass transition temperature by γ-irradiation while strained in simple extension with a stretch ratio λ_o. After release, the sample retracts to a state of ease (λ_s). From λ_o, λ_s, and stress-strain measurements in extension from the state of ease, the concentrations of network strands terminated by trapped entanglements (v_N) and by cross-links (v_x) can be calculated. For v_x/v_N ≡ R′_o > 1, retraction to the state of ease is rapid. For R ? 0.3 or less, retraction is slow and extends over many logarithmic decades of time scale. When an eased sample is stretched to λ_o where the cross-links do not contribute to stress, the subsequent stress relaxation of the entanglement network toward equilibrium is also very slow if R′_o is small. The slow timedependent processes are attributed to a high proportion of untrapped entanglements on dangling branched structures. The concentration of trapped entanglement strands, v_N, can also be calculated from the equilibrium stress at λ_o. The fraction of trapped entanglements agrees rather well with the predictions of the theory of Langley.     

Correlation of swelling and crosslinking density with the composition of the reacting mixture employed in radical crosslinking copolymerization

This article reports the scaling laws relating the synthesis conditions with the crosslinking density (ν_e) and swelling degree (S) of poly(N‐vinylimidazole) hydrogels (PVI) prepared by radical crosslinking copolymerization in aqueous solution, with N,N′‐methylene bisacrylamide (BA) as crosslinker. Multiple linear regression of ν_e versus BA concentration ([BA]) and total comonomers concentration (C_T) in double log scale render the scaling law ν_e ～ C × [BA]^1.04 as comparable to that predicted by the model of polymer network with pendant vinyl groups (ν_e ～ C_T × [BA]), and showing inverse dependence on C_T to that expected, following from stoichiometry, for an ideal network (ν_e ～ 2[BA]/C_T). S scales with ν_e through a solvent‐dependent exponent ranging from ?0.46 to ?0.54, only slightly over the value predicted by the Flory–Rehner theory (?0.6) or the blob's model by de Gennes (?0.5 to ?0.8). Finally, the scaling law of S with the composition of the reacting mixture is also solvent‐dependent and it seems to result not only from the dependence of ν_e on C_T and [BA] but also from that of v_2r, the polymer volume fraction in the reference state, and χ, the polymer–solvent interaction parameter. Models used seem to overestimate the contribution of entanglements to the effective crosslinking density of PVI. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 263–269, 2007     

Characterization of polyisobutylene-based model urethane networks

Polyisobutylene-based model urethane networks have been prepared by crosslinking liquid α, ω-di(hydroxyl)polyisobutylenes, i.e., PIB-diols carrying exactly two ? CH₂OH functions, F _n = 2.0 ± 0.1, and rather narrow molecular weight distributions, M _w/M _n = 1.5?1.6, with tritriphenylmethyl isocyanate \documentclass{article}\pagestyle{empty}\begin{document}$$\rm{HC}\ (\hskip-6pt\hbox{---}p\rm{C}_6\rm{H}_4\hbox{---}\rm{NCO})_3$$\end{document}. Networks prepared with M _n = 1400 and 7500 PIB-diols, and with 90/10 and 80/20 mixtures of these PIB-diols (bimodal networks), have been characterized by extraction, by the Flory–Rehner swelling method, and by the Mooney–Rivlin equilibrium modulus method, and tested by stress–strain measurements. M _c values of the M _n = 1400 PIB-diol network obtained by swelling (1550) and by equilibrium modulus studies (1500) were in excellent agreement with the M _n of the prepolymer. Also the C₂ parameter was negligible in comparison to C₁, suggesting the absence of interchain entanglements. This is the first hydrocarbon-based polyurethane network that exhibits a negligible C₂ value by stress–strain measurements of unswollen samples. The M _c values of the M _n = 7500 PIB-diol were also in good agreement with the M _n of the prepolymer; however, C₂ was larger than C₁, indicating interchain entanglements. Evidence for strain-induced toughening was observed with both networks prepared with the M _n = 1400 and 7500 PIB-diols. The ultimate properties of the two bimodal networks did not show improvement over those of the individual constituents; however, the M _n's of the constituents were not very different.     

Elastic Behaviour of Ternary Rubber-filled Vulcanizates

Near-equilibrium stress–strain measurements have been carried out on ternary rubber vulcanizates. The effect of variation of the butyl rubber content on the elastic behaviour of the ternary rubber vulcanizates has been studied. It has been found that butyl rubber (IIR) is less sensitive to the vulcanization system used than either natural rubber (NR) or styrene–butadiene rubber (SBR). One can obtain a partially crosslinked system with an IIR phase embedded in the crosslinked matrix of NR and SBR. The role played by carbon black during mixing of the ternary blend has been investigated. The Mooney–Rivlin relationship was used to describe the behaviour of the ternary rubber matrix. The constants 2C₁ and 2C₂ have been calculated by use of the strain-amplification factor and the total crosslink density of the ternary rubber–carbon black systems has been investigated. The data have been evaluated in terms of the molecular theories of rubber elasticity. The elastic behaviour was found to be intermediate between the affine and phantom limits of the theory. © of SCI.     

Antiinflammatory polymer-bound steroids for topical applications. I. Synthesis and characterization

Covalent binding of hydrocortisone and dexamethasone to hydrophylic biocompatible macromolecular carriers through hydrolizable carbonate linkage was investigated according to two complementary strategies. (a) Radical copolymerization of hydrocortisone-²¹C-vinylcarbonate with N-vinylpyrrolidone (NVP,60°C), or N-[tris(hydroxymethyl)methyl]acrylamide (THMMA, 50°C) in dimethylacetamide solution: In spite of a nearly zero reactivity ratio for the steroid monomer which behaves as a degradative transfer agent—C_T ～ 5.7 × 10^?2 and 6.8 × 10^?3 for NVP and THMMA, respectively–this process may afford fairly high molecular weight polymers (M?_w ? 10⁴–10⁵) with high enough hydrocortisone content (0.03–0.10 mole.fraction). (b) Condensation of the hydrocortisone or dexamethasone-²¹C-chloroformates onto poly(oxyethylene glycol) (M?_n = 6220) or hydroxypropylcellulose (HPC, M?_w = 1.35 × 10⁵) in tetrahydrofuran solution (30°C): This straightforward process is of low efficiency (yields >50%), and only HPC derivatives show good chemical homogeneity.     

The elastic property of polyvinyl alcohol gel with boric acid as a crosslinking agent

The elastomers of polyvinyl alcohol gel were made from the polyvinyl alcohol polymer, with boric acid added as a crosslinking agent, in the mixed solvent of dimethyl sulfoxide and water. From the experimental results, the viscosity of polyvinyl alcohol solution is found to increase not only with an increment of boric acid content, but also with the temperature in the range of 70°C ∼ 100°C, although the viscosity is decreased in the range of 30°C ∼ 70°C. Moreover, the molecular mass between junctions of polyvinyl alcohol gel is calculated from the rubber elastic theory and found to be decreased with the increment of boric acid content. We also evaluated the values of Young's modulus of polyvinyl alcohol gel, E, E*, and the elastic parameters C₁ and C₂ of the Mooney‐Rivlin equation, according to Hook's law and theory of rubber elasticity. Based on these, the polyvinyl alcohol gel behaves as a good rubberlike elastic property. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 3046–3052, 1999     

Formation of triphenylmethyl cation during the photolysis of phenylazotriphenyl methane: a laser flash photolysis study

The photolysis of phenylazotriphenyl methane (PAT) in dichloromethane and acetonitrile solution at λ_inc = 347nm and at 23°C results in the formation of triphenyl methyl (trityl) radicals and trityl ions. The quantum yields in dichloromethane solution are Φ(Ph₃C^•) = 0·060 and Φ(Ph₃C⁺) = 0·004. Trityl ions are assumed to be formed by electron transfer between radicals formed by the photodecomposition of PAT. The yield of trityl ions is significantly increased upon irradiation of PAT solutions containing also an onium salt (N-ethoxy-2-methyl pyridinium hexafluorophosphate; (EMP⁺PF₆^-). This is due to the oxidation of trityl radicals by EMP⁺ ions. Trityl ions generated in this way were found to be capable of initiating the cationic polymerization of cyclohexene oxide. © 1998 SCI.     

Semi- and fully interpenetrating polymer networks based on polyurethane–polyacrylate systems. I. The polyurethane networks

The polyurethane networks based on commerical prepolymer, Adiprene L-100, and trimethylol propane (system 1) and on toluene diisocyanate, polypropylene gylcol, and trimethylol propane (system 2) were prepared and characterized in a number of ways. The materials constitute the first formed networks in a series of interpenetrating polymer networks and semi-interpenetrating polymer networks to be reported in subsequent papers in this series. System 1 networks were characterized by swelling tests which showed the M _c values to be sensitive to the amount of polyurethane present in the polymerization solvent. Stress–strain, stress–relaxation, and dynamic mechanical analyses wer also conducted. For system 2, M _c was measured, by both the swelling and the Mooney–Rivlin techniques, for materials in which the diol-to-triol ratios had been altered. the latter showed C₁ increasing as M _c decreased while C₂ was small and changed onlyy slightly indicating approximately ideal behavior. These M _c values were about 13 % larger than predicted by swelling.     

Electrical characteristics of Al/polyindole Schottky barrier diodes. I. Temperature dependence

In this study, the forward and reverse bias current–voltage (I–V), capacitance–voltage (C–V), and conductance–voltage (G/ω–V) characteristics of Al/polyindole (Al/PIN) Schottky barrier diodes (SBDs) were studied over a wide temperature range of 140–400 K. Zero‐bias barrier height Φ_B0(I–V), ideality factor (n), ac electrical conductivity (σ_ac), and activation energy (E_a), determined by using thermionic emission (TE) theory, were shown fairly large temperature dispersion especially at lower temperatures due to surface states and series resistance of Al/PIN SBD. I–V characteristics of the Al/PIN SBDs showed an almost rectification behavior, but the reverse bias saturation current (I₀) and n were observed to be high. This high value of n has been attributed to the particular distribution of barrier heights due to barrier height inhomogeneities and interface states that present at the Al/PIN interface. The conductivity data obtained from G/ωV measurements over a wide temperature range were fitted to the Arrhenius and Mott equations and observed linear behaviors for σ_ac vs. 1/T and ln σ_ac vs. 1/T^1/4 graphs, respectively. The Mott parameters of T₀ and K₀ values were determined from the slope and intercept of the straight line as 3.8 × 10⁷ and 1.08 × 10⁷ Scm^?1K^1/2, respectively. Assuming a value of 6 × 10¹² s^?1 for ν₀, the decay length α^?1 and the density states at the Fermi energy level, N(E_F) are estimated to be 8.74 Å and 1.27 × 10²⁰ eV^?1cm^?3, respectively. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

IR/CR共混物网络结构评价

根据Ｍｏｏｎｅｙ－Ｒｉｖｌｉｎ和Ｆｌｏｒｙ－Ｒｅｈｎｅｒ方程考察了辐射交联和化学交联ＩＲ／ＣＲ共混物的网络结构特征。结果表明．化学交联生成了比较密实、均匀的网络结构，而辐射交联生成比较松散的网络结构。研究了常数２Ｃ＿１，２Ｃ＿２及溶胀体系中橡胶的体积分数γ＿ｋ与共混物组成的不同依赖性，评价了物理交联对网络总模量的贡献。     

Polymers from renewable sources. IV. Polyurethane elastomers based on myrcene polyols

Two hydroxy-functionalized liquid rubbers, one a commercially available polybutadiene (PB) and the other a specially synthesized polymyrcene (PM), have been converted into homopolyurethane elastomers by reaction with 4,&4prime;-diphenylmethane diisocyanate (MDI). Additionally, PB and PM, each in admixture with various amounts of 1,4-butane diol, were reacted with MDI to yield two series of segmented copolyurethanes having different hard-block contents (0–30% w/w). The physical properties of these elastomers have been compared by stress–strain, thermal, and dynamic mechanical analyses, and by swelling experiments. The two series of segmented copolyurethanes have similar morphologies being almost completely phaseseparated and variations in physical properties have been empirically related to hard block contents. The PM-based elastomers exhibited higher T_g values, ultimate elongations, and larger swelling ratios, but were softer and possessed lower tensile strenghts in comparison with elastomers based on PB. These differences have been related to solfraction contents, the nature and distribution of molecular species present in the parent liquid rubbers and hence to polyol functionalities (f?_n). Analysis of the stress–strain data from the homopolyurethanes using the Mooney–Rivlin expression enabled the relationship between f?_n and elastomer structure to be quantified in terms of the molar mass (M?_c) of the polyurethane network chains forming the soft blocks.     

Polyurethane elastomers studied by the Mooney–Rivlin equation for rubbers

A series of poly(ester–urethane) block copolymers were prepared via a two-step polymerization process. The prepolymer composition was kept constant in all the samples, while the NCO/OH ratio during extension was varied from 0.9 up to 1.2. By this way, chemical and physical cross-links were constructed into the materials. Equilibrium stress–strain measurements have been carried out for the examination of the elastomeric behavior of the materials tested. Calculation of an extra entropy term resulting from the network deformation is based on a first-principles derivation of the distribution function, taking into account a new type of network constraints. The process yields the Mooney–Rivlin equation and the constant C₂ as a function of physical cross-links.     

Mechanistic studies in tackified acrylic emulsion pressure sensitive adhesives

Twenty‐three wt % aqueous tackifier dispersion based on glycerol ester abietic acid (T_g = 64°C, M_w = 940) was added to emulsion polymer 50/32/15/3 poly(2‐ethyl hexyl acrylate‐co‐vinyl acetate‐co‐dioctyl maleate‐co‐acrylic acid) pressure sensitive adhesive (PSA). From these latices, 25 μm thick films were cast. The films were dried at 25°C for 24 h or at 121°C for 5 min. Dynamic mechanical analysis (DMA) of the films included measuring elastic modulus (G′) and damping factor (tan δ). Under the above drying conditions, the films did not produce significant differences in their DMA and PSA properties as measured by loop tack, peel, and shear holding power. DMA of the tackified acrylic film showed thermodynamic miscibility between the tackifier and polymer regardless of the drying conditions. Microgels formed during emulsion polymerization of the acrylic PSA brought inherent weakness to the tackified film properties. In the neat acrylic PSA film, these discrete networks entangled with the uncrosslinked chains while in the tackified film, these networks could not form entanglements due to the increased molecular weight between entanglements for the uncrosslinked chains. This lack of network entanglements caused shear holding power of the tackified acrylic PSA film to be 4× lower than that of the neat acrylic PSA film. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1965–1976, 2000     

Ferroelectric,dielectric and pyroelectric properties of Sr and Sn codoped BCZT lead free ceramics

The 1?mol.-%Sr and 1?mol.-%Sn codoped (Ba_0·84Ca_0·15Sr_0·01)(Ti_0·90Zr_0·09Sn_0·01)O₃ (BCSTZS) ceramics were synthesised by the normal solid state sintering method. The electric field and temperature dependence of the ferroelectric properties of the BCSTZS ceramics were investigated. Their energy storage density depending on electric field and temperature was determined from the polarisation–electric field (P–E?) hysteresis loops. According to the dielectric analysis, the BCSTZS ceramics experience three-phase transitions upon cooling. At room temperature, the pyroelectric coefficient p calculated from the remnant polarisation–temperature (P_r–T?) curve is 1116·7?μC?K^??1?m^??2, and the figures of merit F_d is 18·1?μPa^??1/2, F_v is 0·013?m²?C^??1 and F_i is 479·3?pm?V^??1 respectively. The pyroelectric figures of merit exhibit high frequency stability over a wide range from 100 to 2000?Hz, whereas these values vary gradually with the increase in temperature, which deserves further research to improve their stability. The excellent pyroelectric property of the BCSTZS ceramics is considered as correlating with a polymorphic phase transition occurring around room temperature. The present study demonstrates that the lead free BCSTZS ceramics are promising candidate for replacing the lead zirconate titanate based ceramics.     

Thermal conductivity of a polymer composite filled with mixtures of particles

A new thermal conduction model is proposed for a polymer system filled with a mixture of several types of particles. Predicted values by the new model are compared with experimental data. The model is derived by extending a model that was previously proposed for a two-phase system. The following equation is derived from the new model: log λ = V · (X₂ · C₂ · log λ₂ + X₃ · C₃ · log λ₃ + (1 ? V) log (C₁ · λ₁. When the thermal conductivities of polymer and particles (λ₁, λ₂, λ₃, …) and a mixing ratio of particles (X₂, X₃, …) are known, thermal conductivity of the filled polymer (λ) with several types of particles can be estimated from the equation, with any volume content of particles (V). Furthermore, from each polymer–filler composite (two-phase system) data, the thermal conductivity of a composite filled with different filler particles can be estimated.     

Electrocoated Films of Poly(N-Methylpyrrole-co-2,2′-Bithitiophene-co-3-(Octylthiophene)), Characterizations,and Capacitor Study

N-Methylpyrrole (N-MPy), 2,2′-bithiophene (BTh), and 3-(Octylthiophene) (OTh) were electrocopolymerized in 0.2 M NaClO₄/CH₃CN on glassy carbon electrode (GCE). The resulting terpolymers of N-MPy, BTh and OTh in different initial monomer feed ratios such as [N-MPy]₀/[BTh]₀/[OTh]₀ = 1/1/1 and 1/2/5 were characterized by cyclic voltammetry (CV), Fourier-transform infrared attenuated total reflectance spectroscopy (FTIR-ATR), scanning electron microscopy (SEM), energy-dispersive X-ray analysis (EDX), and electrochemical impedance spectroscopy (EIS). The capacitive behaviors of the modified electrodes were defined via Nyquist, Bode-magnitude, Bode-phase, and Admittance plots. The equivalent circuit model of Rs(C _dl1 (R ₁ (QR ₂ )))(C _dl2 R ₃ ) was performed to fit the theoretical and experimental data. The low-frequency capacitance (C_LF) were obtained from initial monomer concentrations of 50 mM as C_LF = ～2.34 × 10^?4 mFcm^?2 for P(N-MPy), C_LF = 5.06 × 10^?4 mF cm^?2 for P(BTh), C_LF = 5.07 m F cm^?2 for P(OTh), and C_LF = ～3.78 m Fcm^?2 for terpolymer for [N-MPy]₀/[BTh]₀/[OTh]₀ = 1/1/1. The terpolymer may be used as energy storage devices.     

Elastic behavior of natural rubber filled vulcanizates

The reinforcement effect of carbon black and, the effect of accelerator-to-sulfur ratio variation on the elastic behavior of natural rubber vulcanizates have been studied. The Mooney–Rivlin relation was used to describe the behavior of the rubber matrix, and values of constants c₁ and c₂ have been evaluated with the use of the strain-amplification factor. The stress softening of the vulcanizates tested has also been examined.     

Ionic Liquid with Silyl Substituted Cation: Thermophysical and CO2/N2 Permeation Properties

Novel functionalized ionic liquid (IL) combining an imidazolium‐based cation with branched alkyl chain bearing silyl group, 1‐methyl‐3‐(2‐methyl‐3‐(trimethylsilyl)propyl)imidazolium ([Si?C₁?C₃‐mim]⁺), and bis(trifluoromethylsulfonyl)imide ([NTf₂]^?) anion was synthesized and its thermophysical properties (density, viscosity, surface tension, surface entropy and enthalpy, thermal stability) were studied in a wide temperature range and compared with those of ILs having linear alkyl ([C_n‐mim][NTf₂]) and siloxane ([(SiOSi)C₁mim][NTf₂]) side chains. It was found that at 25 °C [Si?C₁?C₃‐mim][NTf₂] is a liquid with dynamic viscosity of 224 cP (224 mPa s) and density of 1.32 g cm^?3. The presence of side branched alkyl chain with trimethylsilyl end‐group prevents crystallization of IL and leads to higher viscosities and lower densities in comparison with commonly known [C_n‐mim][NTf₂] (n=2–4). As surface excess enthalpy was found to be in the lower end of the usual range of values for ILs, the interactions between silyl‐functionalized cation and [NTf₂] anion can be considered as relatively weak. Finally, [Si?C₁?C₃‐mim][NTf₂] was used for the preparation of polymer supported ionic liquid membranes (SILMs) and their CO₂ and N₂ permeation properties at 20 °C and 100 kPa were determined: permeability PCO₂=311, PN₂=12 Barrer, diffusivity DCO₂=115×10¹², DN₂=227×10¹² m² s^?1 and CO₂/N₂ permselectivity αCO₂/N₂=25.3.     

Synthesis,Characterization and Properties of <Emphasis Type="Italic">N</Emphasis>-Alkyl-<Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>-di(2-hydroxyethyl) Amine Oxides

N‐Dodecyl‐N,N‐di(2‐hydroxyethyl) amine oxide (C₁₂DHEAO) and N‐stearyl‐N,N‐di(2‐hydroxyethyl) amine oxide (C₁₈DHEAO) were synthesized with N‐alkyl‐diethanolamine and hydrogen peroxide. Their chemical structures were confirmed using ¹H‐NMR spectra, mass spectral fragmentation and FTIR spectroscopic analysis. It was found that C₁₂DHEAO and C₁₈DHEAO reduced the surface tension of water to a minimum value of approximately 28.75 mN m^?1 at concentration of 2.48 × 10^?3 mol L^?1 and 32.45 mN m^?1 at concentration of 5.21 × 10^?5 mol L^?1, respectively. The minimum interfacial tension (IFT_min) and the dynamic interfacial tension (DIT) of oil–water system were measured. When C₁₈DHEAO concentration was in the range of 0.1–0.5%, the IFT_min between liquid paraffin and C₁₈DHEAO solutions all reached the ultra‐low interfacial tension. Furthermore, their foam properties were investigated by Ross‐Miles method, and the height of foam of C₁₂DHEAO was 183 mm. It was also found that they showed strong emulsifying power.     

Degradation of the mechanical properties of composite vulcanizates loaded with paraffin wax

A composite of Styrene Butadiene Rubber (SBR) and Natural Rubber (NR) loaded with 40 phr of High Abrasion Furnace (HAF) carbon black is loaded with different concentrations of paraffin wax. From the stress–strain curves, Young's modulus was found to decrease with increasing the amount of added paraffin wax. The modified Mooney-Revlin equation was used to calculate the parameters C₁ and C₂. A plot between the true tensile stress as a function of (λ² − λ⁻¹) was used to calculate two parameters σ₀ and G, and then both the average molecular weight between crosslinks and the number of effective plastic chains per unit volume were also calculated. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 2265–2270, 2001