An experimental study of adsorption of polymers on activated carbon: Butadiene—styrene polymers and poly(methyl methacrylate)

An experimental study of the extents and rates of adsorption of several polymers from various solvents onto activated carbon has been carried out. The polymers studied included polystyrene, polybutadiene, butadiene–styrene copolymers and poly(methyl methacrylate). The solvents included toluene, cumene, decalin, 2-pentanone, and methyl ethyl ketone (MEK). Polystyrene is adsorbed from the different solvents in the order MEK, 2-pentanone, cumene, toluene, decalin. The adsorption from toluene, decalin, and cumene is in the order polystyrene, polybutadiene butadiene—styrene copolymer. The fact that the copolymer is adsorbed less than either homopolymer is striking. The variation of molecular weight distribution with extent of adsorption has been studied. It was found that low molecular weight polymer was preferentially adsorbed in the early stages of the experiment, but high molecular weight polymer was adsorbed at longer times. The apparent adsorption rate constants have been evaluated for the various systems and resolved into external mass transfer, internal (intraparticle) mass transfer, and adsorption rate constants. The experimental data have been applied to the prediction of the elution of the polymers from chromatographic columns packed with activated carbon.     

Phase separation in polymer blends comprising copolymers: 7. Statistical theory of block copolymer-homopolymer systems

The miscibility of a homopolymer in corresponding domains of a copolymer predicted by Meier's theory is far less than found experimentally. In this paper, a density gradient model is suggested for describing the segment distribution of the bound and free chains in block copolymer-homopolymer systems. Using this model, Helfand's theory, which has been successful in explaining microphase separation of block copolymers, is extended to polymer blends of homopolymer and corresponding block copolymer with lamellar structure. The calculated free energy of mixing of the system shows that the predicted miscibility is much larger than that obtained by Meier's theory and is in good agreement with the main known experimental results. In particular, on the basis of the present theory, homopolymer can be expected to be solubilized by corresponding blocks in the whole composition range provided that the molecular weight of the former is less than that of the latter.     

Investigation of polyacrylonitrile solution inhomogeneity by dynamic light scattering

Dynamic light scattering (DLS) has been used to quantify nanoscale heterogeneity in the industrially significant polyacrylonitrile (PAN) polymer solution. The heterogeneity in polymer solution, traced by the ratio of amplitudes of the slow to fast mode, is observed to be related to various parameters, such as molecular weight of the polymer, the type of co‐monomer, processing time, concentration of the solution, and the choice of the solvents. It has been identified that low molecular weight PAN homopolymer have the least heterogeneity issues. Amongst the chosen co‐polymers for this study, similar degree of heterogeneity was observed at concentration slightly above the critical concentration at which the polymer chains begin to overlap. Whereas, at higher concentration, PAN‐methacrylic acid (4 wt%) copolymer showed the least heterogeneity issue. The aggregate diffusion coefficient of PAN‐methacrylic acid (4 wt%) copolymer solution in dimethylformamide (DMF) and N,N‐dimethylacetamide (DMAc) are respectively determined to be ～1.6 × 10^?12 cm²/s and ～1.6 × 10^?13 cm²/s, which results in an estimated aggregate size of 9 nm and 90 nm. POLYM. ENG. SCI., 55:1403–1407, 2015. © 2015 Society of Plastics Engineers     

The influence of the solvent upon the low shear viscosity of styrene–acrylonitrile copolymer solutions

This paper describes the results of an experimental investigation concerning the effect of polymer–solvent thermodynamics on low-shear viscosity of copolymer soltions. Thermodynamic parameters and low-shear solution viscosities were measured for solutions of polystyrene homopolymer and styrene–acrylonitrile copolymers in four solvents: benzene, dioxane, methyl ethyl ketone, and dimethylformamide. The thermodynamic quality of a solvent for a polymer is characterized by free-energy-of-mixing parameters. These quantities are: the Flory-Huggins thermodynamic interaction parameter χ, the second virial coefficient (from light scattering), the intrinsic viscosity, and the polymer expansion factor. The thermodynamic interaction between a solvent and a polymer in solution influences the rheological behavior of the system. At low concentrations of polymer in solvent, the low-shear solution viscosity is larger in a good solvent than in a poor solvent. In solutions of higher concentration, the reverse may be true and the viscosity is often significantly larger in a poor solvent than in a good one. These results are not predicted quantitatively by existing theory. The parameters in existing viscosity correlation techniques are found to be solvent dependent. The so-called entanglement concentrations for polymer solutions are not unique for a particular polymer but are related to the free energy of mixing polymer with solvent.     

溶剂对低1,2—结构无规溶聚丁苯橡胶合成的影响

研究了不同溶剂对低１ ,２－ 结构含量无规溶聚丁苯橡胶合成的影响, 比较了在不同溶剂中溶聚丁苯橡胶的单体分布、微观结构、相对分子质量分布、共聚合速度和产物的物理机械性能。结果表明,在环己烷或环己烷／ 正己烷混合溶剂中制得的溶聚丁苯橡胶较在抽余油中制得的溶聚丁苯橡胶具有更好的物理机械性能     

Polyacrylate-N-vinyl lactam polymer or copolymer blends as pressure-sensitive adhesives

It has been previously shown that blends of a homopolymer or a copolymer of an N-vinyl lactam with an acrylate or a related copolymer containing a small proportion of acidic groups exhibit macroscale compatibility and a phase separated microstructure. This paper presents an application of this two-phase polymer system for the preparation of melt processable acrylic pressure-sensitive adhesives (PSA). 2-Ethylhexyl acrylate-acrylic acid copolymers, having molecular weights in the range of 50 000 to 115 000 were prepared by free-radical solution polymerization. These copolymers were tacky but possessed insufficient cohesive strength at ambient temperatures to be useful as PSAs. Blending such acrylate copolymers, having some acidic functionality, with minor proportions of a glassy homopolymer or a copolymer of an N-vinyl lactam resulted in materials having a balance of cohesive and adhesive characteristics required of a good PSA. Due to low molecular weights of the components of the polymer blend acrylic PSAs, they are amenable to hot melt processing. Some of the parameters affecting the pressure-sensitive adhesive properties of the polymer blend are: (a) fraction of the glassy polymer in the blend, (b) molecular weights of the polymeric components, (c) acidic functionality of the low molecular weight acrylate copolymer, and (d) N-vinyl lactam functionality of the glassy polymer.     

Styrene–isoprene block copolymers. II. Hydrogenation and solution properties

Styrene–isoprene block copolymers with a different degree of monomer distribution are hydrogenated with homogeneous catalysts. The products are characterized by means of IR and ¹H-NMR spectroscopy, GPC, viscometry, and light scattering. Hydrogenation proceeds without destruction and selectively for olefinic unsaturation. The hydrogenated copolymers are homogeneous in molecular weights and chain composition. The influence of the copolymer structure on the solution properties in selective solvents is established. In cyclohexane an equilibrium between micelle associates and individual polymer coils, monomolecular micelles, or micelle aggregates are observed, depending on the type of the copolymer. The micellization in base-lubricating oil leads to micelle fractions with a different degree of association.     

Refractive index increments of di-n-alkylitaconate polymers and copolymers

Refractive index increments of 11 poly(di-n-alkylitaconate) polymers were determined systematically in seven organic solvents, expected to be suitable for light scattering and other solution property measurements. Of 13 solvents tried, poly(dimethylitaconate) was soluble only in 6, however higher members of the polymer series exhibit better solubility. The measured dn/dc values in butanone and ethyl-and amylacetate are practically independent of an increase of the number of carbon atoms in the ester substituents of the monomer, however a decrease of the values for solvents with higher refractive indices can be observed. For statistical poly(styrene-co-di-n-alkylitaconate) samples the additive character of dn/dc in butanone and toluene was observed and verified from copolymer compositions determined by UV and elemental analysis.     

Solution properties of poly(fluorostyrene-co-chlorostyrene) copolymers. I. Light scattering,differential refractometry and viscometry

The weight-average molecular weights (M?_w) of nominally random, unfractionated copolymers of ortho- and para-fluorostyrene and ortho- and para-chlorostyrene were determined by light scattering measurements in tetrahydro-furan, toluene, carbon tetrachloride and chloroform. It was shown that there is no significant variation in measured M?_w in the various solvents, a finding indicating that the copolymers are not compositionally heterogeneous. Intrinsic viscosity measurements in the same solvents established a consistent relationship between [n] and M?_w despite the differences in copolymer compositions. It was not possible to establish a similar relationship between the second virial coefficient A₂ and M?_w. It was concluded that measurements of the specific refractive index increment could be used for determining copolymer composition if the measurements were performed in thermodynamically poorer solvents. The results established for the Mark-Houwink constant α, intrinsic viscosity, and A₂ values indicated that these solvated copolymer molecules are in a less expanded conformation than are polystyrene molecules of similar molecular weights in a given solvent.     

苯乙烯－丁二烯共聚物的表征──稀溶液性质的研究

用紫外／示差双检测器ＧＰＣ仪，小角激光光散射仪及红外光谱仪测定了苯乙烯（Ｓｔ）－丁二烯（Ｂｄ）共聚物（Ｋ树脂）的微观结构、分子量及其分布、组成分布及稀溶液特性。实验表明，Ｋ树脂是ＳＢＳ，ＳＢ和ＰＳ三段聚合物的混合物；在四氢呋喃，甲苯，氯仿和环己烷４种溶剂中，Ｋ树脂Ｍ＿Ｗ基本一致，但其特性粘数与溶剂有关，其大小按溶剂四氢呋喃、甲苯、氯仿、环己烷顺序递减。国产Ｋ树脂稀溶液的性质与国外试样基本相似。     

Flexibilität und thermodynamische Eigenschaften von Polyacrylaten,Polymethacrylaten und statistischen Acrylat/Methacrylat-Copolymeren 2. knäuelparameter

Flexibility and interaction parameters of the polymers have been calculated from the results of light-scattering and viscosity measurements with polyacrylates, polymethacrylates and random copolymers of methyl methacrylate with acrylates and n-butyl methacrylate. Only slight differences are found when the chain rigidity of polyacrylates is compared with that of polymethacrylates. There is however a clearcinfluence of the ester alkylgroup. With increasing size of the ester alcohol the polymer chain gets more rigid. In case of copolymers the chain flexibility does not result simply from the homopolymer values. The measured values don't reveal a systematic connection, moreover in case of copolymers there is a strong influence of solvents on the unperturbed dimensions. The repulsive powers occuring in the copolymer coil due to hetero-contacts have been characterized quantitatively. The graduaeion which was found coincides with compatibility tests of the corresponding homopolymers in a concentrated solution : the more intense the expansion of the copolymer coil caused by heterocontacts, the lower the concentration where a demixing of the homopolymers is observed.     

HDPE/LLDPE reactor blends with bimodal microstructures—part I: mechanical properties

Reactor blends of polyethylene/poly(ethylene-co-1-octene) resins with bimodal molecular weight and bimodal short chain branching distributions were synthesized in a two-step polymerization process. The compositions of these blends range from low molecular weight (LMW) homopolymer to high molecular weight (HMW) copolymer and, vice versa, HMW homopolymer to LMW copolymer. The physical properties of the blends were found to be consistent with the nature of the individual components. For the tensile properties, the stiffness decreases with increasing the fraction of the copolymer, regardless of the molecular weight of the homopolymer fraction. For these blends with bimodal microstructures, it was confirmed that the degree of crystallinity governs the stiffness of the polymer. However, the energy dampening properties of the polymers benefit from the presence of the copolymer. A balance of stiffness and toughness can be obtained by altering the composition of the blends. For some blends, the presence of HMW homopolymer can dominate the tensile properties, showing little variation in the stiffness with increased addition of copolymer. It was also demonstrated that the testing conditions and thermal treatment of the polymer greatly influence the resulting elastic and energy dampening properties. Depending on the desired application, annealing these polymers (especially very low density copolymers) not only increases the crystallinity and stiffness, but also changes the frequency response of the dynamic mechanical properties.     

Concentrated solutions of SBS block copolymers in solvent mixtures

The viscosities of 10% and 20% solutions of linear and non-linear SBS block copolymers were measured in various solvent pairs comprising ethyl acetate/toluene, ethyl acetate/cyclohexane, ethylacetate/carbon tetrachloride, ethyl acetate/n-hexane, ethyl acetate/cyclohexanone, methyl ethyl ketone/cyclohexanone and methyl ethyl ketone/n-hexane. Addition of the second solvents to 10% solutions of the polymers in ethyl acetate or methyl ethyl ketone gave rise to peaks around 10% to 14% added solvents. These peaks are caused by phase separation involving micelles and their occurrence depends on the interplay of composition of solvent mixtures, molecular weight and solution concentration and not on polymer architecture, styrene content or state of shear.     

Local polydispersity detection in size exclusion chromatography: Method assessment

Local polydispersity is the term describing the variety of molecules present at the same retention volume in size exclusion chromatography (SEC) analysis. In the analysis of a linear homopolymer, local polydispersity is generally attributed to the effect of axial dispersion: it can cause molecular size variety (i.e., imperfect resolution) at each retention volume and thus local polydispersity in the molecular weight. In the analysis of polymer blends (copolymers and branched polymers), it is possible to have local polydispersity, even when the resolution is perfect, because molecules of different compositions (or degrees of branching) can have the same molecular size in solution. Conventional SEC interpretation assumes no local polydispersity if the axial dispersion effects are negligible. Three methods are currently available for detecting local polydispersity by using a combination of differential refractive index, light scattering, and viscometer detectors: the chromatogram comparison method, the conventional calibration curve comparison method, and the universal calibration comparison method. Here we experimentally assess these three methods using polymer blends and emphasize the chromatogram comparison method. All three are shown to be useful for assessing triple detector systems, but they are capable of detecting local polydispersity due to molecular heterogeneity only for very large differences in specific refractive index increments in the blend components. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 370–383, 2001     

Miscibility in blends of linear and branched poly(ethylene oxide) with methacrylate derivative random copolymers and estimation of segmental χ parameters

Miscibility in the blends of poly(ethylene oxide) (PEO) with n-hexyl methacrylate-methyl methacrylate random copolymers (HMA-MMA) and 2-ethylhexyl methacrylate-MMA random copolymers (EHMA-MMA) was evaluated using glass transition and light scattering methods. EHMA-MMA was more miscible with PEO than HMA-MMA. Both blends of PEO with HMA-MMA and EHMA-MMA showed UCST-type miscibility although homopolymer blends PEO/PMMA were predicted to be of LCST-type. This was attributed to an increase in the exchange enthalpy with increasing HMA or EHMA composition in the random copolymer. From the copolymer composition dependence of miscibility the segmental χ parameters of HMA/MMA, EHMA/MMA, EO/HMA and EO/EHMA were estimated using the Flory-Huggins theory extended to random copolymer systems. Miscibility in the blends of branched PEO with HMA-MMA whose HMA copolymer composition was 0.16 was compared with that in the linear PEO blends. The former blends were more miscible with HMA-MMA than the latter one by about 35 °C at the maximum cloud point temperature.     

Aggregation in solutions of poly(γ-benzyl-l-glutamate) monitored by static and dynamic light scattering

We have studied dilute and semidilute solutions of poly(γ-benzyl-l-glutamate) in 1,2-dichloroethane by static and dynamic light scattering. The aggregational behaviour of the semiflexible polymer is evidenced in both static and dynamic scattering, and is sensitive to the temperature and the polypeptide molecular weight. In particular, both the reciprocal specific scattering intensity and the effective decay rate of the dynamic correlations exhibit a minimum as a function of the concentration. The slope of effective diffusion coefficient versus the square of the scattering vector displays an anomalous maximum as a function of the concentration which can also be attributed to aggregation. The experimental evidence is compatible with head-to-tail dimerization of the polymer as the concentration increases.     

Copolymerization of ethylene with vinyl acetate. II. Effect of solvent on polymer yield and molecular weight

In the free-radical solution copolymerization of ethylene and vinyl acetate, polymer yield and molecular weight were found to vary considerably with the solvent used. Solvents were toluene, benzene, hexane, heptane, and cyclohexane. Molecular weights were highest in benzene and lowest in toluene and were readily explained by different solvent chain-transfer constants. Polymer yields were highest in aliphatic solvents and lowest in aromatic solvents including benzene. This was attributed to different types of interactions of the solvents with radical species. The saturated aliphatic solvents undergo hydrogen abstraction reactions, but these give reactive alkyl radicals which reinitiate polymer growth. Toluene also undergoes hydrogen abstraction reactions, but the resultant benzyl radical is resonance stabilized and does not readily reinitiate polymerization. Benzene does not undergo hydrogen abstraction reactions. The low yields are attributed to complex formation. A consideration of kinetic theory indicates that complex formation with both initiator and growing polymer radicals is involved. Differences in viscosity, ethylene solubility, and initiator half-life in the different solvents, as well as induced decomposition of the initiator, were not determining factors.     

A binary interaction model for miscibility of copolymers in blends

Miscibility windows often exist in polymer blend systems when the chemical structure of one of the components is systematically varied, e.g. a random copolymer may be miscible with another polymer when neither limiting homopolymer is. A binary interaction model is developed which explains such behaviour. From this prediction, the general notion is advanced that many cases exist where the net exothermic heat of mixing required for miscibility of high molecular weight polymer mixtures may result from appropriate considerations of both intermolecular and intramolecular interactions of component units without an exothermic interaction existing between any individual pair of units. However, it is shown that for a net exothermic mixing the individual interaction parameters for the pairs of units must differ from those predicted by solubility parameter theory. Moreover, the departures from the geometric mean assumption of the solubility parameter theory need not be large to achieve conditions for miscibility. Several examples of the use of such a model are given including one where the homologous series of aliphatic polyesters is treated as ‘copolymers’ by considering their CH_x and COO constituents as the ‘monomers’.     

环戊二烯阳离子聚合的研究--聚合反应条件对产物分子量的影响

随着石油化工和煤化工的迅速发展，环戊二烯的产量大幅度增加，其聚合物已用于聚丙烯等通用塑料的改性，赋予其热封性、气体阻隔性。本实验以TiCl4为引发剂，研究不同浓度、温度溶剂中引发环戊二烯的阳离子聚合。结果表明，溶剂对产物的分子量和分子量分布的影响最为显著，这与离子对的状态有密切的关系；并且用甲苯作溶剂时，^1HNMR结果表明甲苯作为聚合反应的链转移剂参与链转移反应。     

Specific refractive index increments of ethylene–vinyl acetate copolymers in trichlorobenzene solutions at 145°C

Specific refractive index increments of ethylene/vinyl acetate copolymers have been masured in trichlorobenzene at 145°C. A relationship between these values and copolymer composition has been determined for use in light scattering measurements of weight-average molecular weights of these materials. The data are also required for analysis of molecular weight distributions by size exclusion chromatography with light scattering detection.