Amorphous state transitions in butadiene–acrylonitrile copolymers

Differential thermal analysis, creep measurements, and gas permeation rates are used to confirm the existence of a transition zone in three butadiene acrylonitrile copolymers in a temperature region that starts at roughly 15° to 25°C above the main glass transition temperatures of the copolymers and extends over a broad temperature range. The change appears to be slightly endothermic and softens the copolymers upon heating. It is speculated that the copolymers are in a mesomorphic state above their main glass temperature in which there is either a degree of ordering or a low-grade crystallinity of polybutadiene units along the copolymer chains. It is not until the copolymers are 50° to 75°C above their main glass temperature that they become truly amorphous.     

Thermal behavior of p-acryloyloxy-tri-n-butyltin benzoate–acrylonitrile copolymers

The copolymerization of p-acryloyloxy-tri-n-butyltin benzoate (ABTB) with acrylonitrile (AN) has been investigated in dimethylformamide (DMF), using azobisisobutyronitrile (AIBN) as an initiator. The prepared homopolymer of (ABTB), as well as the copolymers, were characterized by a variety of analytical, spectral, and thermal methods. Thermogravimetry (TG) and differential thermal analysis (DTA) data showed a little improvement in the thermal behavior of the investigated copolymer. A mechanism for the initiation of ABTB units in the nitrile oligomerization in the copolymer was also proposed. © 1994 John Wiley & Sons, Inc.     

Thermal behavior of pentachlorophenyl methacrylate–acrylonitrile copolymers

Acrylonitrile was copolymerized with pentachlorophenyl methacrylate (PCPMA)in dimethyl formamide using azobisisobutyronitrile as initiator. The composition of the copolymers was determined by nitrogen analysis and the monomer reactivity ratios (r₁ and r₂) were calculated. Both the homopolymer and the copolymers were characterized by a variety of spectral and thermal methods. Thermogravimetry and differential thermal analysis data showed that the comonomer (PCPMA) initiates the nitrile oligomerization reaction in the copolymer upon heating. A mechanism for the initiation of (PCPMA) units in the nitrile copolymers was also proposed. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 296–302, 2004     

Vibration damping and electrical conductivity of styrene–butyl acrylate random copolymers filled with carbon black

Emulsion‐polymerized poly(styrene‐rand‐butyl acrylate) (St–BA) copolymers exhibit damping capabilities over a wide temperature range with changes in the monomer ratio. Blending copolymers of different compositions results in a multidamping peak, further widening the effective damping temperature range. Adding carbon black (CB) reduces the peak damping intensity but enhances damping at higher temperatures. The addition of dodecyl benzene sulfonic acid to an St–BA/CB aqueous dispersion improves the dispersion of CB in the polymer, reducing the percolation threshold and improving the conductivity while slightly affecting the mechanical behavior. The electrical properties of the St–BA/CB system are affected by the copolymer composition, influencing the polymer surface tension. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Modification of butadiene–acrylonitrile and styrene–acrylonitrile copolymerizations in emulsion systems

Modification of acrylonitrile in copolymerizations with butadiene and with styrene in hot and cold emulsion recipes has been studied. Series of primary, secondary, and tertiary mercaptans in addition to several miscellaneous modifiers were tested. Kinetically the rate data for the monomer pairs containing acrylonitrile better fit first-order plots than the curves obtained for an ideal emulsion polymerization. In this study all modifier depletions in nitrile systems were plotted as log mercaptan versus log conversion and the slope of the curve was taken as the transfer constant. Normal mercaptans were inefficient modifiers in nitrile systems as determined in polymerization and depletion experiments. Secondary mercaptans, 2-nonyl, 2-decyl, and mixtures in this molecular weight range, were promising modifiers for low temperature (5°C.) nitrile systems. 2-Nonyl mercaptan gave enhanced modification by incremental addition of the modifier indicating this procedure could be used to advantage in preparing nitrile rubbers. The series of tertiary mercaptans from C₁₃ to C₇ showed an improvement in modification of low temperature nitrile systems as the molecular weight decreased. A plot of the data on a molar basis shows that the optimum modifier falls in the C₉–C₈ range. The optimum transfer constant for the most efficient modification of 70/30 and of 80/20 butadiene–acrylonitrile polymerizations at 5°C. terminated at 60% conversion is 2. Depletion data show that the transfer constant for a mercaptan decreases as the nitrile content in mixtures with butadiene increases. The properties of the vulcanizates of the 70/30 and 80/20 butadiene–acrylonitrile polymers prepared in the presence of low molecular weight mercaptans were equivalent to or better than those of the controls. These data show that nitrile polymers could be modified with a lower molecule weight mercaptan with no loss of properties but with a considerable saving in amount of modifier. Mercaptans are essential for the initiation of butadiene–acrylonitrile in the presence of persulfate at 50°C. For the hot nitrile rubber preparations, the series of mercaptan from t-C₁₀ to t-C₇ are efficient modifiers. However, the heptyl and octyl mercaptans are retarders, and the t-C₉ and t-C₁₀ are the preferred modifiers for efficiency and unretarded polymerization. The modification with a series of mercaptans ranging from t-C_13.2 to t-C₈ of 75/25 styreneacrylonitrile at 50°C. in presence of persulfate–bisulfite showed a consistent behavior. The transfer constant decreased in a regular manner as the molecular weight of the mercaptan increased, and for the series of tertiary modifiers the t-C₁₀ mercaptan was the most efficient as judged by a melt flow test.     

Elastic and viscoelastic behavior of ethylene–propylene copolymers

The viscoelastic behavior of an ethylene–propylene copolymer is analyzed. Two different vulcanization procedures were followed; in the first a binary mixture of initiator-polymer was used, while in the second the polymer was diluted by a solvent. The networks thus obtained show a different viscoelastic behavior depending on the different vulcanization procedure used. Results, analyzed in terms of supramolecular organization being present in the amorphous material, give some important information about the molecular nature of the C₂ coefficient of the Mooney-Rivlin equation, and therefore about the well-known deviations from the Gaussian theory shown by all rubber-like networks.     

Synthesis,characterization, and properties of reactive liquid rubbers based on butadiene–acrylonitrile copolymers

Reactive liquid polymers (RLP), carboxyl-terminated butadiene–acrylonitrile copolymers (CTBN), epoxy-terminated butadiene–acrylonitrile copolymers (ETBN), amine-terminated butadiene–acrylonitrile copolymers (ATBN) of different molecular weights (from 2200 to 6500 g/mol), and a nonfunctional butadiene–acrylonitrile copolymer were synthesized and characterized. Selection of end groups of RLPs and the synthesis were discussed. Phase behaviors of CTBN, ETBN, and NFBN in the RLP/DGEBA system were investigated regarding to the molecular weight, molecular weight distribution, chain composition, and end groups with a light transmission method. These experimentally determined phase behaviors will be related to those of the RLPs in the systems to be modified. The effect of molecular weight of RLP on the viscosity was also studied. © 1994 John Wiley & Sons, Inc.     

Thermodynamic interactions of solvents with styrene–butadiene–styrene triblock copolymers

Fundamental thermodynamic interaction data for various solvents with two styrene–butadiene–styrene triblock copolymers (Kraton D-1101 and Kraton D-1300X) have been collected by the use of inverse gas chromatography at infinite dilution. Experimental results are presented for nine D-1101/solvent systems and nine D-1300X/solvent systems at 308, 328. and 348 K. Weight-fraction activity coefficients and Flory–Huggins χ interaction parameters have been calculated from the retention volumes. The χ parameter is used as a measure of the strength of interaction and therefore as a guide in the prediction of polymer–solvent compatibility. In addition, partial molar heats of mixing, ΔH_m^∞, and heats of solution, ΔH_s, were determined. The Hildebrand–Scatchard solubility theory was combined with the Flory theory in order to estimate the solubility parameter of the thermoplastic rubbers at the three different temperatures.     

Dynamic rheological behavior of high‐density polyethylene filled with carbon black

The dynamic rheological behavior of high‐density polyethylene (HDPE) composites filled with carbon black (CB) was studied by controlling periodic small shear strains at constant temperatures. The results shed light on the relationship between the behavior of dispersed fillers and polymeric matrix systems. At sufficiently high filler concentration a structural skeleton seems to appear, which significantly raises the modulus at the low frequency region. High structure, finer size acetylene black raises the modulus significantly more than does the low structure and larger size one (e.g., N550). Oxidized CB increases the modulus in the whole frequency region for the enhanced interaction between polymer matrix and CBs. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 3527–3531, 2002     

Mechanical and viscoelastic properties of butadiene–styrene thermoplastic and oxidized carbon fibre composites

The mechanical and dynamic properties of oxidized carbon fibre and butadiene–styrene thermoplastic elastomer (SBS) composites were studied as a function of the level of fibre oxidation and in comparison with the properties of composites reinforced with untreated commercial carbon fibre. As a general rule, fibre oxidation gives rise to materials with improved mechanical properties—greater tensile and tear strengths. The improvements accomplished depend on the degree of fibre oxidation. The effects of long exposure times to oxidizing agents were tested on the experimental samples, i.e. increase in the number of functional surface groups and loss in mechanical strength due to a decrease in the L/d ratio, properties which act in opposite directions in the composite. Storage modulus retention with increasing strain amplitude is directly proportional to the number of functional groups incorporated into the fibre surface, whereas at low strain amplitude it is proportional to fibre strength, measured in terms of the L/d ratio after processing. It is suggested that improved adhesion at the matrix–fibre interface is obtained through the functional groups of the oxidized fibre. As a consequence of fibre–matrix interface and at any frequency, the damping peak temperature is shifted towards higher ranges and at the same time the apparent activation energy of the relaxation process is observed to increase.     

Dielectric behavior of carbon black filled polymer composites

This paper reports results on the dielectric properties of carbon black filled crosslinked polyethylene composites. These systems are shown to follow percolative type models. The dielectric constant increases slowly, with carbon black concentration, up to roughly the percolation concentration and then increases rapidly over the whole concentration ranges studied. The dissipation factor-concentration curves are bell-shaped with maximum values at approximately the percolation concentration. The dielectric properties of these systems are discussed in terms of interfacial Maxwell-Wagner polarization effects.     

Conductive and viscoelastic behaviors of carbon black filled polystyrene during annealing

Aggregation of carbon black (CB) aggregates in polystyrene melt was traced by simultaneous measurement of resistance (R) and dynamic storage modulus (G′) as a function of annealing time. There existed a dynamic resistance percolation in the time evolution of R while G′ increased gradually during the whole experimental time scale. Dynamic resistance and modulus percolation models were used to model the time-dependent R and G′, respectively. Furthermore, the time evolution of G′ was explained with a combination of the kinetic cluster–cluster aggregation model and the first order kinetics aggregation model. It was found that the aggregation of CB aggregates in the molten polystyrene has a close relation with the terminal relaxation of polystyrene molecules. The results indicated that the interfacial tension between polystyrene molecules and CB plays a crucial role in driving CB to aggregate.     

Dynamic mechanical behavior of copolymers containing carbon black

The storage and loss moduli of random copolymers of styrene and butyl methacrylate containing carbon black of varied surface area were determined by dynamic mechanical analysis at several temperatures about 100°C above the glass-transition temperature, T_g. At low frequencies, the pure polymers exhibit linear double log plots of moduli against frequency, with slopes of unity and approaching two for G″ and G′, respectively. With the addition of carbon black filler, both G′ and G″ become independent of frequency and temperature at low frequencies, consistent with yield behavior arid the formation of a carbon black network. The limiting dynamic complex modulus exceeds the yield stress from steady shear rheology, perhaps indicating the extent of the carbon black network, which was highest for low-molecular-weight copolymer and polystyrene. The filled random copolymers behaved Theologically like similarly filled polystyrenes of comparable molecular weights. Plasticization effects observed in the steady shear rheology of filled copolymers containing small concentrations of carbon black were not observed in dynamic mechanical analysis, although dynamic moduli converge at high frequency.     

Viscoelastic relaxation of styrene–butadiene–styrene block copolymers with different topological structures

The viscoelastic relaxation of linear styrene–butadiene–styrene triblock copolymer (l‐SBS) and star styrene–butadiene–styrene triblock copolymer (s‐SBS) with four arms were investigated with differential scanning calorimetry and dynamic rheological measurements. Three characteristic viscoelastic responses of l‐SBS and s‐SBS in the plot of the loss tangent (tan δ) and temperature at different frequencies (ω's), which corresponded to the relaxation of the polybutadiene (PB) block (peak I), the glass transition of the polystyrene (PS) phase (peak II), and the mutual diffusion between the PB blocks and PS blocks (peak III), respectively, were observed in the experimental range. Although ω was 0.1 rad/s, a noticeable peak III was gained for both l‐SBS and s‐SBS. The dynamic storage modulus (G′) of l‐SBS showed two distinct types of behavior, depending on the temperature. At temperature (T) < T₂ (where T₂ is the temperature corresponding to peak II), G′ of l‐SBS displayed a very weak ω dependency. In contrast, at T > T₂, G′ decayed much more rapidly. However, G′ of s‐SBS displayed a very weak ω dependency at both T < T₂ and T > T₂. Only near T₂ did s‐SBS decay with ω a little sharply. These indicated, in contrast to l‐SBS, that s‐SBS still exhibited more elasticity even at T > T₂ because of its crosslinking point between the PB blocks (the star structure). In the lower ω range, l‐SBS exhibited a stronger peak III than s‐SBS despite the same styrene content for l‐SBS and s‐SBS. The high tan δ value of peak III for l‐SBS was considered to be related to the internal friction among the PB blocks or the whole l‐SBS chain, not the PS blocks. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Structure–physical property relationships in peroxide-cured butadiene–styrene copolymers

Structure–physical property relationships in high-vinyl butadiene–styrene copolymers have been determined for samples cured with dicumyl peroxide under the same conditions. Three different structures, butadiene–styrene–butadiene (B–S–B) triblocks, butadiene–styrene (B–S) diblocks, and random butadiene–styrene copolymers, have been examined. Flexural modulus increases with increasing styrene content owing to the inherent stiffness of a polystyrene backbone. Swelling increases whereas hardness and heat distortion temperature decrease with increasing styrene content. This behavior is explained by the decrease in crosslink density with increasing styrene content in all structures. Heat distortion temperatures of the B–S–B and B–S networks are superior to the heat distortion properties of the random structures. The B–S–B structure is the most solvent resistant, followed by the random copolymers, with the B–S structures swelling to the greatest extent. Swelling differences between the B–S–B and random networks decrease with increasing styrene content, while swelling differences between the B–S–B and B–S networks increase with increasing styrene content. These results are explained by the nature of the crosslinking reaction and the number of loose ends present in each network.     

Morphology,thermal, and mechanical properties of acrylonitrile–butadiene–styrene/carbon black composites

Acrylonitrile–butadiene–styrene (ABS) polymers are susceptible to degradation that increases the yellowness of the polymer, distorts the surface glossy, and affects the mechanical properties. One way to protect ABS against degradation is the addition of carbon black (CB) that can act as a stabilizer. In this work, CB was dispersed in ABS through melt‐compounding. Electron microscopy was used to study the morphology of the filled‐ and unfilled‐ABS, and revealed that the CB particles/aggregates were distributed within the styrene–acrylonitrile (SAN) phase and around the PB phase. The results of the Fourier transform infrared spectroscopy showed that upon processing of ABS, crosslinking in the polybutadiene (PB) phase was the governing degradation mechanism. Increasing the CB content resulted in increasing the heat stability of the ABS/CB compounds, which was confirmed by thermogravimetric analysis. The DTA results showed that the PB degradation peak occurring at about 395°C was disappeared by addition of CB. Impact strength test was performed to study the effect of CB on the toughness of ABS. Impact strength was reduced with increasing CB loading. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Carboxyl‐terminated butadiene–acrylonitrile rubber modified cyanate ester resin

The carboxyl‐terminated butadiene‐a‐acrylonitrile rubber (CTBN) has been proved to be the most effective toughener for cyanate ester (CE) resin. This work mainly focuses on the different modification effects caused by the addition of CTBN with different acrylonitrile content. The phase separation, morphology of fracture surface, and physical properties of the blends are studied by scanning electron microscopy (SEM), transmission electron microscopy (TEM), dynamic mechanic analysis (DMA), and thermogravimetric analysis (TGA). It is testified that the compatibility and toughness between CE and CTBN had a positive correlation with the acrylonitrile content of CTBN. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Solution properties of methyl methacrylate–acrylonitrile copolymers

Characterization of methyl methacrylate-acrylonitrile copolymers is done through viscosity, swelling, and differential refractometric studies. Viscosities of the copolymers and homopolymers were determined at 30, 40, and 50°C. The activation parameters of viscous flow, voluminosity, and shape factor were also calculated. The average shape factor was observed to be 2.5 ± 0.005 for all copolymer systems. Viscosity molecular weights were calculated, and from intramolecular expansion factor (α), it was observed that copolymers are less flexible than are homopolymers. dn/dc values obtained from differential refractometry are in good agreement with those calculated theoretically. © 1993 John Wiley & Sons, Inc.     

Rheological characteristics and morphologies of styrene–butadiene–maleic anhydride block copolymers

Studies on the morphologies and rheological characteristics of two styrene–butadiene–maleic anhydride block copolymers (SBMa) have been performed. The transmission electron microscopy micrographs show that the morphologies of SBMa change from matrix–island structure to co‐continuous structure. Curves for dynamic modulus varied with frequency (ω) show obvious solid‐like behavior in the low ω region, which is typical for ordered block copolymers or networked materials. Van Gurp–Palmen plots have been used to exploit the thermorheological complexity of two copolymers. The master curves of two copolymers have been acquired through time–temperature superposition principle, and the plateau modulus (G) have been obtained from G′ at ω, where the loss tangent (tan δ) approaches a minimum. Meanwhile, Williams–Landel–Ferry equation has been used to evaluate the free volume parameters. The relaxation time spectra of two copolymers have been calculated and fitted with modified Baumgaertel–Schausberger–Winter model. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012