Effects of composition on the solution properties of styrene–acrylonitrile copolymers

Short-range interactions between chain units of random copolymers in solution may be influenced by the composition or precisely by the distribution of sequence lengths of the same monomer units. Steric factors were derived for random copolymers of styrene and acrylonitrile with different compositions from the relation between the limiting viscosity number and the molecular weight. Mark-Houwink relations were obtained in methyl ethyl ketone (MEK) or in N,N′-dimethylformamide (DMF) at 30°C. for random copolymers containing 0.383 (Co-1) and 0.626 (Co-2) mole fraction of acrylonitrile, the expressions are: [η] = 3.6 X 10^?4 M _w^0.62, for Co-1 in MEK; [η] = 5.3 X 10^?4 M _w^0.61, for Co-2 in MEK; [η] = 1.2 × 10^?4M _w^0.77 for Co-2 in DMF. With the Stockmayer-Fixman expression, these correlations become, respectively: [η]/M^1/2 = 1.24 × 10^?3 + 8.0 × 10^?7 M^1/2; and [η]/M^1/2 = 1.70 × 10^?3 + 6.3 × 10^?7 M^1/2; and [η]/M^1/2 = 1.68 × 10^?3 + 31.3 × 10^?7 M^1/2. From the unperturbed mean-square end-to-end distances, 〈L²〉₀, determined from the first terms of the latter expressions, together with 〈L²〉_0f calculated by assuming the completely free rotation, gives the steric factor σ = (〈L²〉₀/〈L²〉_0f)^1/2 as 2.25 ± 0.05 for Co-1, and 2.31 ± 0.10 for Co-2. These values of σ are close to those for polystyrene (σ = 2.22 ± 0.05) and for polyacrylonitrile (σ = 2.20 ± 0.05). Therefore, it is concluded that the dimensions of random copolymers of styrene and acrylonitrile in solution are not significantly influenced by the composition. In other words, the unperturbed dimensions are not affected by a change in the alternation tendency between styrene units with phenyl side groups having a large molar volume and acrylonitrile units with nitrile groups responsible for the electrostatic interactions. On the other hand, the long-range interactions reflect the effect of sequence length. The Huggins constant and the second virial coefficient obtained from the light-scattering measurements have optimum values at about 0.5 mole fraction of acrylonitrile, where the greatest tendency for alternation seems to exist.     

Determination of composition of ethylene–propylene copolymers by intrinsic viscosity

Intrinsic viscosities have been measured at 25° on five ethylene–propylene copolymer samples ranging in composition from 33 to 75 mole-% ethylene. The solvents used were n-C₈ and n-C₁₆ linear alkanes and two branched alkanes, 2,2,4-trimethylpentane and 2,2,4,4,6,8,8-heptamethylnonane (br-C₁₆). This choice was based on the supposition that the branched solvent would prefer the propylene segments and the linear solvent the ethylene segments, due to similarity in shape and possibly in orientational order. It was found that [η]_n ? [η]_br ≡ Δ[η] is indeed negative for propylene-rich copolymers, zero for a 56% ethylene copolymer, and positive for ethylene-rich copolymers. The Stockmayer–Fixman relation was used to obtain from Δ[η] a molecular-weight independent function of composition. The quantities (Δ[η]/[η])(1 + aM^?1/2) and Δ[η]/M are linear with the mole percent ethylene in the range investigated with 200 ≤ a ≤ 2000. The possibility of using these results for composition determination in ethylene–propylene copolymers is discussed. Intrinsic viscosities in the same solvents are reported for two samples of a terpolymer with ethylidene norbornene.     

Comparison of semicrystalline ethylene–styrene and ethylene–octene copolymers based on comonomer content

The structure and properties of homogeneous copolymers of ethylene and styrene (ES) and ethylene and octene (EO) were compared. Semicrystalline copolymers presented a broad spectrum of solid‐state structures from highly crystalline, lamellar morphologies to the granular, fringed micellar morphology of low‐crystallinity copolymers. The combined observations from density, thermal behavior, and morphology with primarily atomic force microscopy revealed that the crystalline phase depended on the amount of comonomer but was not strongly affected by whether the comonomer was styrene or octene. This was consistent with the exclusion of both comonomers from the crystal. However, ES and EO showed strong differences in the amorphous phase. ES had a much higher β‐relaxation temperature than EO, which was attributed to restrictions on chain mobility imposed by the bulky phenyl side group. The deformation behavior of ES and EO exhibited the same trends with comonomer content, from necking and cold drawing typical of a semicrystalline thermoplastic to uniform drawing and high recovery characteristic of an elastomer. Aspects of deformation behavior that depended on crystallinity, such as yielding and cold drawing, were determined primarily by comonomer content. However, the difference in the β‐relaxation temperature resulted in much higher strain hardening of ES than EO. This was particularly evident with low‐crystallinity, elastomeric copolymers. A classification scheme for semicrystalline copolymers based on comonomer content, previously developed for EO, was remarkably applicable to ES. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 1578–1593, 2001     

Influence of the reaction medium on the composition and the microstructure of styrene–acrylic acid copolymers

Two series of acrylic acid-styrene copolymers of various composition have been prepared in benzene and dimethylformamide in order to study their sequence distribution by using ¹³C NMR spectroscopy. The reactivity ratios in benzene were r_A = 0.13, r_A = 0.30 and in dimethylformamide r_A = 0.05, r_S = 1.60. Copolymers with the same overall composition but prepared in different media display marked differences in sequence distribution, the copolymers obtained in dimethylformamide always having longer sequences. For the series of copolymers prepared in dimethylformamide, the experimental percentages of acrylic acid-centered triads (SAS, SAA, AAA) disagree with the values calculated from the monomer reactivity ratios.     

Effect of gamma irradiation on ethylene–octene copolymers

Two ethylene–octene copolymers (POE) were irradiated with ⁶⁰Co gamma radiation and influence of irradiation atmosphere, absorbed dose and heat treatment of samples on the crosslinking were studied. Thermal properties and crystalline morphology of non-irradiated and irradiated POE were determined by using differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXS), respectively. The Charlesby–Pinner equation was used to describe the relationship between absorbed dose and sol fraction. The gel fraction of irradiated POE was lower and decreased with the increase of octene content when irradiated in oxygen, compared to irradiation in nitrogen atmosphere. The gel fraction increased significantly with the increasing of absorbed dose for the two copolymers. Heat treatment of samples prohibited the crosslinking of irradiated POE. The DSC results indicated that a subtle change of thermal properties of POE was observed before and after gamma irradiation at low dose. No change was found from the WAXS spectra of non-irradiated and irradiated POE. For heat-treating samples, the Charlesby–Pinner equation can not fit perfectly with the relationship between the sol fraction and absorbed dose, but it fits well with the crosslinking reaction of POE pellets.     

Radiation effects on styrene–butadiene–ethylene–propylene diene monomer‐multiple walled carbon nanotube nanocomposites: vulcanization and characterization

Varying compositions of styrene–butadiene rubber (SBR) and ethylene–propylene diene monomer (EPDM) 50:50 blend containing multiple walled carbon nanotube (MWNT) as nanoparticulate filler (0.5–5%) were prepared and their efficacy for radiation vulcanization was analyzed by gel‐content, Charlesby‐Pinner parameter, and crosslinking density measurements. Radiation sensitivity of the nanocomposites increased with increase in the MWNT fraction and radiation dose in the dose range studied. The elastic modulus, tensile strength increased with the radiation dose, while elongation at break exhibited downward trend. The extent of reinforcement as assessed using Kraus equation suggested high reinforcement of blend on MWNT addition. The reinforcing mechanism of nanocomposites was studied by various micromechanics models which predicted higher modulus than the experimentally observed results, indicating agglomeration in the nanocomposites. The thermal stability of the composites increased with increase in MWNT loading has been attributed to the antioxidancy induced by nanotubes and higher crosslinking extent of the nanocomposites. Copyright © 2010 John Wiley & Sons, Ltd.     

The preparation of polysiloxane–vinyl monomer graft and block copolymers

In another paper the radical polymerization of styrene in the presence of various chlorosilanes was investigated, and polystyrenes having chlorosilyl groups as endgroups were obtained. In the present work attempts were made to obtain polysiloxane styrene graft and block copolymers from chlorosilyl polystyrenes. Block copolymers were obtained with dichlorosilane and graft copolymers with tri- and tetrachlorosilanes. In the latter case the insoluble fractions increased, if a suitable stopper, such as butanol or trimethylchlorosilane [(CH₃)₃SiCl], was not used in the condensation reaction. Methyldichlorosilane was used for the preparation of the graft copolymer, because the Si? H bond was more effective than the Si? Cl bond for the chain transfer reaction.     

Acrylonitrile–4-vinylpyridine copolymers effect of comonomer sequence distribution on properties

Acrylonitrile–,4-vinylpyridine copolymers were prepared in chloroform solution at 60°C with AIBN as initiator. Copolymer compositions were determined from their 15.01-MHz ¹³C-NMR spectra. Reactivity ratios of r_AN = 0.093 and r_4VP = 0.32 were calculated by the Kelen and Tudos method. The run number, number-average sequence lengths, and monomer sequence distributions were also calculated. The T_g values of the copolymers, their dye uptake, and degree of alkaline hydrolysis were influenced by the overall copolymer composition but particularly by the monomer sequence distribution in the copolymers.     

Properties of ethylene–propylene–vinyl chloride graft copolymers. II. Viscoelasticity and composition of graft copolymer and composite

The viscoelasticity and volume expansion of the raw polymerizate of ethylene–propylene copolymer with vinyl chloride grafts, and of the individual components has been studied. The raw polymerizate (composite) and the pure ethylene–propylene–vinyl chloride graft copolymer were found to consist of two phases. The pure graft copolymer has an ethylene–propylene matrix containing some fraction of poly(vinyl chloride) (PVC) grafts and a microphase with the remainder of the PVC grafts. The raw polymerizate consists of a PVC matrix plasticized with ethylene–propylene chains and a microphase of the ethylene–propylene copolymer. An attempt has been made to calculate the participation of components in microphases and the minimum dimension of the PVC microphase aggregates.     

Dilute solution properties of styrene–acrylonitrile and styrene–methyl methacrylate copolymers. I. Intrinsic viscosity–molecular weight relations

Styrene–acrylonitrile (St–AN) copolymers of three compositions—27.4 mole-% (SA₁); 38.5 mole-% (SA₂); and 47.5 mole-% (SA₃) acrylonitrile—and styrene–methyl methacrylate (St–MMA) copolymer (SM) of 46.5 mole-% methyl methacrylate were prepared by bulk polymerization at 60°C with benzoyl peroxide as the initiator, and were then fractionated. The molecular weights of unfractionated and fractionated samples were determined by light scattering in a number of solvents. The [η] versus M?_w relations at 30°C were established for SA₁, SA₂, SM, and polystyrene (PSt) in ethyl acetate (EAc), dimethyl formamide (DMF), and γ-butyrolactone (γ-BL), and for SA₃ in methyl ethyl ketone (MEK), DMF, and γ-BL. Second virial coefficients A₂ and the Huggins constant were determined. From values of A₂ and the exponent a of the Mark–Houwink relation it is seen that the solvent power for samples SA₁, SA₂, and PSt is in the order EAc < γ-BL < DMF, while for sample SA₃ the solvent power is in the order MEK < γ-BL < DMF. The solvent power decreases with an increase in AN content. The solvent power of the three solvents used for SM copolymer sample is practically the same within experimental errors. From the a values it is concluded that in a given solvent the copolymer chains are more extended than the corresponding homopolymers.     

Annealing‐induced increase of permeability and amorphous‐phase mobility in an ethylene–vinylacetate copolymer

The 50% increased permeability after annealing of semicrystalline poly(ethylene/vinylacetate) containing 3 mol % vinylacetate is linked to increased mobility in the amorphous phase, as identified by line‐narrowing of ¹H wideline nuclear magnetic resonance (NMR) spectra and by reduced cross‐polarization efficiency in ¹³C NMR. Other morphological parameters, such as crystallinity, measured as 30 to 35% by differential scanning calorimetry (DSC) and NMR, are hardly changed by annealing. Small‐angle X‐ray scattering and NMR studies, using spin diffusion as well as T_1ρ and T₁ relaxation, detected only a small increase in crystallite thickness. The annealing‐induced enhancement in segmental mobility in the amorphous regions corresponds to a temperature shift of about 10 K, from which an increase of the motional rate by a factor of 2 is estimated, and which can account for the enhancement in the permeability. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2774–2780, 2001     

Application of pyrolysis—gas chromatoghaphy in the analysis of diad sequence distribution in styrene—glycidyl methacrylate copolymers

A procedure has been suggested for the characterization of the distribution of diad sequences for copolymers of the vinyl type prepared to high degrees of conversation pyrolysis—gas chromatography. The procedure has been verified for styrene—glycidyl methacrylate copolymers.     

Ordered structures of styrene–butadiene block copolymers in the solid state

Several narrow molecular weight distribution block copolymers were prepared by a two-stage anionic polymerization technique. Films cast from these solutions were studied by electron microscopy. Replicas showed that the film surfaces were composed of layered structures with various orientations. Micrographs of ultrathin sections of stained films demonstrate that layered structure occur throughout the film. The widths of the copolymer layer spacings increase with increasing molecular weight and agree quite well with the calculated values.     

Gamma-oxidation of linear low density polyethylenes: Ethylene–butene and ethylene–hexene copolymers

Different linear low density polyethylenes (LLDPEs) based on hexene and butene comonomer were irradiated with γ-rays under air. The oxidation products have been quantified using NO and SF₄ treatments by IR spectroscopy. An FTIR examination displayed unexpected products such as free hydroperoxides and trans-vinylenes. It was found that the type of α-olefin used to process LLDPE films may influence the mechanism of oxidation. Parameters such as the melt index and the density seem to affect the γ-oxidation rate. © 1993 John Wiley & Sons, Inc.     

Temperature and concentration dependence of diffusion coefficients in ethylene–propylene-diene copolymers

Self-diffusion and partition coefficients were measured for two commercial ethylene–propylene-diene copolymers (EPDM) and five solvents at infinite dilution using inverse gas chromatography. Mutual diffusion coefficients for solvents in EPDM also were measured for finite concentration using gravimetric sorption for three of the solvents. From the inverse gas chromatography experimental values for self-diffusion coefficients were obtained. Free-volume parameters were obtained through regression of the self-diffusion coefficient as a function of temperature. Mutual diffusion coefficients as a function of concentration were predicted using free volume theory and compared with experimental data obtained using gravimetric sorption. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 1713–1719, 1998     

Carbon-13 nuclear magnetic resonance of ethylene–propylene copolymer and the determination of sequence distribution of monomeric units

The ¹³C-NMR spectra of ethylene–propylene copolymers and their model compounds were measured at 15.1 MHz. Assignments of the signals were carried out by using the equation of Grant and Paul and also by comparing the spectra with those of squalane, hydrogenated natural rubber, polyethylene, and atactic polypropylene. The accuracy and the precision of intensity measurements, that is, the deviation from the theoretical values and the scatter of the measurements, respectively, were checked for the spectra of squalane and hydrogenated natural rubber and were shown to be at most 12% for each of the signals. On the basis of these results the mole fractions of the four types of the dyad sequences, that is, the propylene–propylene (head-to-tail and head-to-head), the ethylene–propylene, and the ethylene–ethylene sequences, were determined together with the average sequence lengths of both monomer units.     

Dilute solution properties of styrene–acrylonitrile and styrene–methyl methacrylate copolymers. II. Short-range and long-range interactions from intrinsic viscosity data

Experimental data on styrene–acrylonitrile (St–AN), and styrene–methyl methacrylate (St–MMA) copolymers reported in Part I of this series are tested by “two-parameter” theoretical relations. The Fox–Flory (F–F) parameter K is estimated using the F–F, Stockmayer–Fixman (S–F), and Inagaki–Ptitsyn (I–P) equations. In general, the K values obtained by the F–F equation are low for the three St–AN copolymer samples in the systems studied while the values obtained from S–F and I–P equations agree within the limits of experimental error. Values of K obtained from Kurata–Stockmayer (K–S) equation for sample SA₁ agree with values obtained by the S–F and I–P equations. The specific solvent effect on the K values is discussed. Values of the unperturbed dimension r?0²/M?_w, calculated from the K values estimated from the S–F equation and from the homopolymer data are compared. Except in one case, the calculated r?0²/M?_w values from homopolymer data are low in comparison with the values obtained from experimental data, which shows that the presence of the repulsive interactions between unlike monomer units brings about an expansion of copolymer molecule. The effect of composition on the steric factor σ values is discussed. The long-range interaction parameter B, the excess interaction parameters ΔB_AB, and χAB are calculated. The effects of composition and solvent on these parameters are discussed.     

Crystallization of branched polymers. I. Ethylene–vinyl acetate and ethylene–acrylic acid copolymers

The following quantities were measured on a number of ethylene–vinyl acetate (EVA) and ethylene–acrylic acid (EAA) copolymers: (1) the small-angle x-ray scattering invariant, (2) the overall density, and (3) the crystallinity. Assuming a two-phase structure, the separate values of the densities of the crystalline and amorphous regions can be calculated from these data. Of these, the crystalline density is compared with the value obtained from the lattice constants. A systematic difference is observed which is ascribed to the presence of comonomeric side groups in the crystalline regions. For the EVA and EAA samples, their concentration is at least 0.3 and 0.5 times the overall concentration, respectively. The amorphous densities are found to be higher than the values calculated from completely amorphous copolymers by extrapolation procedures.