Limits of the dilute regime for the solution viscosity of PMMA in good and in poor solvents

The concentration (c′) marking the first deviation from linearity in the Huggins plot of specific viscosity η_sp/c vs c) has been determined for PMMA in chloroform, benzene (good solvents), acetonitrile, chlorobutane (poor solvents) and acetonitrile/chlorobutane mixtures (cosolvent). The dependence of c′ on polymer chain length and on solvent quality is given. The results are analysed in terms of the influence on c′ of incipient coil overlap, peripheral entanglements and other interactions, such as polymer association.     

Dilute solution studies of pyrrone prepolymers

Data on dilute solutions of a pyrrone “prepolymer” are presented and the tendency of this polymer to aggregate in certain solvents commonly used in dilute solution studies is discussed. It is concluded that reliable molecular weights can be determined if solvents that interact with the prepolymer through hydrogen bonding are used.     

Dilute solution studies of nitrogen-substituted polyurethanes

A high molecular weight linear polyurethane was prepared by the polyaddition of equimolar amounts of ethylene glycol and methylene bis(4-phenyl isocyanate). Varying amounts of the labile carbamate protons of the polyurethane backbone were substituted by a number of groups of varying length and composition. The resultant grafted or nitrogen-substituted polyurethanes were then studied viscometrically in both polymer solvent and in a polymer solvent—nonsolvent mixture. The configuration of the nitrogen-substituted polyurethane was found to be dependent upon the number and length of pendent branches.     

Thermoplastic urethane elastomers. VI. Dilute solution properties in various solvents

A thermoplastic urethane elastomer prepared from a polycaprolactone diol, 4,4′-diphenylmethane diisocyanate, and 1,5-pentanediol was fractionated and the solution properties of the fractions were characterized in terms of viscosity and sedimentation. Mark-Houwink relations were established for data obtained at 30° in various solvents: In dimethylacetamide, tetramethylurea, and N-methyl pyrrolidone, the value of K_θ increased systematically in the range (1.7 to 2.0) × 10^?3. Lower values of K_θ were obtained in dimethylformamide (0.8 × 10^?3) and meta-cresol (0.9 × 10^?3). The molecular expansion coefficients in the various solvents were approximated from the experimental viscosity data. Short-range interactions between the solvent molecules and polymer chains are suggested as possible causes for differences in the hydrodynamic parameters.     

Polymerization of pyromellitic dianhydride with 3,3′-diaminobenzidine in aprotic solvents II. Dilute solution studies

Solution properties were determined for the poly(amide acid amine) obtained from the room-temperature polymerization of pyromellitic dianhydride with 3,3,-diaminobenzidine in aprotic solvents. Membrane osmometry data, viscosity studies, solution aging studies, and pH–viscosity relationships were given. Anomalous upswings in viscosity–concentration plots were attributed to absorption or capillary wall effects and not to polyelectrolyte effects, such as were induced by addition of strong bases. Similar absorption effects were found with polyamic acid solutions, in contrast to earlier reports that these polyimide precursors were polyelectrolytes. Unfavorable storage characteristics of the polymer solutions were explained by aging studies which showed that at 25°C dilute solutions exhibited a rapid drop in viscosity; in concentrated solution a slow increase to gelation was observed.     

Dilute solution properties of a polybenzimidazole

Light scattering and viscometric studies have been carried out on dilute solutions of a polybenzimidazole in N,N-dimethylacetamide. The data, which span the molecular weight range 2.9 ≦ 10^?4M_w ≦ 23.3, and the temperature range 290 ≦ T/K ≦343, yield the dependence of the mean-square radius of gyration 〈s²〉_LS, the second virial coefficient A₂, and the intrinsic viscosity [η] on molecular weight M_w and temperature. The unperturbed mean-square radius 〈s〉_LS was calculated using experimental values of 〈s²〉_LS and A₂. It was found that excluded volume effects on 〈s²〉_LS are very small. The unperturbed hydrodynamic chain dimension 〈s〉_η was estimated by considering draining effects. A small value of the draining parameter was obtained. Analysis of the temperature dependence of A₂ and [eta;] leads to the conclusion that this system approaches a lower theta temperature with increasing temperature. The steric factor σ = 〈s〉/〈s〉f, based on the value of 〈s〉_f calculated for the polymer chain with free rotation, is nearly unity. Most of these properties can be interpreted in terms of long rotational units within the main chain.     

Macromolecules in a blend of poor and amphiphilic solvents

The globular state of the homopolymer macromolecule in a blend composed of a poor solvent and an amphiphilic solvent (substrate), whose molecules tend to be aligned with the solvent concentration gradient in the inhomogeneity region, was theoretically studied. The size of a homogeneous globule and the substrate concentration in its volume were calculated in terms of a bulk approximation. After the transition of the macromolecule from the coil to the globule state, its volume first decreases with a decrease in temperature and then begins to grow due to substrate molecules penetrating the globule. The substrate concentration in the globule insignificantly exceeds that outside the globule at identical second virial coefficients of interaction between monomer units and between substrate molecules. The expression for the free energy functional depending on the volume fractions of the components and on the orientation of substrate molecules was examined in the ground-state approximation. The orientation effect leads to narrowing of the surface layer and to a decrease in the surface tension of the homogeneous globule, thereby increasing its stability with respect to the transition to the unfolded-coil state.     

Dilute solution behavior of polyelectrolytes. Intrinsic viscosity and light scattering studies

The conformational character of a random copolymer of ethyl acrylate and acrylic acid (mole ratio 3:1) has been examined by intrinsic viscosity and light scattering in organic and in aqueous media. The unperturbed dimensions of this copolymer in its un-ionized state in an organic theta solvent are 1.3 to 1.4 times those obtained for the fully ionized polymer in an aqueous theta solvent. The data also suggest that a change in conformation from a swollen random coil to a compact random coil occurs in aqueous media as a function of ionic strength. These results are interpreted in terms of the hydrophobic interaction of the ester groups on the chain. An application of the wormlike chain model shows that viscosity data can be used to predict the light scattering results well with in experimental error.     

Dilute solution behaviour of amylose tributyrate. Light scattering,viscosity and osmotic pressure measurements in non-ideal solvents

Amylose tributyrate has been prepared and fractionated; the dilute solution behaviour of the polymer has been studied in four solvents, ethyl acetate, methyl ethyl ketone, carbon tetrachloride and tetrahydrofuran. The Mark-Houwink relations have been established for each solvent and the exponent γ varies between 0·72 and 0·86, for different solvents. Perturbed dimensions have been measured for the polymer dissolved in two solvents and an estimate of the unperturbed dimensions has been made; the latter appear to be solvent dependent. Heterogeneity corrections were applied using data established by gel permeation chromatography measurements. Values of the effective bond length b of between 17 and 19·5 × 10^?8 cm and the Kuhn statistical segment A_m of 70 to 180 x 10^?8 cm, indicate that amylose tributyrate behaves like a moderately stiff coil in good solvents, with a chain stiffness intermediate between the vinyl and cellulosic polymers.     

Dilute solution characterization of a POLA polyester

Samples of poly(4,4′-isopropylidenediphenylene 1,1,3-trimethyl-3-phenylindan-4′,5- dicarboxylate) were fractionated by the column-elution, temperature-gradient technique. Selected fractions, covering a 10-fold range of molecular weight, were shown to have narrow molecular weight distributions by gel-permeation chromatography (GPC), i.e., M?_w/M?_n = 1.15 ± 0.10. The fractions were further characterized by viscometry, light scattering, and membrane osmometry. Characterization of the small samples (ca. 0.3 g) was facilitated by use of a low-volume light scattering cell. This allows measurements of refractive increment, light scattering, and viscosity to be performed on as little as 50 mg of sample. Molecular weights estimated by the GPC-viscometry technique were in good agreement with the values obtained by light scattering. Estimates of the perturbed coil dimensions (150–200 Å) were in satisfactory agreement with those observed experimentally. The polydispersities of the fractions, determined by osmometry and light scattering, were in fair agreement with GPC data; the latter are considered subject to less experimental uncertainty.     

Thermodynamic and conformational properties of polystyrene. III. Dilute solution studies on branched polymers

Light-scattering and viscometric measurements on dilute solutions of five branched polystyrene polymers are reported. The data include studies in decalin as a function of temperature, including the theta temperature, and in toluene. The results for the radius of gyration and the second virial coefficient are not in accord with the two parameter random-flight model. Possible causes of this descrepancy are considered. It is shown that the intrinsic viscosity of branched chains is not uniquely determined by the radius of gyration.     

Adsorption of polyethylene from thermodynamically good solvents on a zeolite stationary phase

Adsorption of linear polyethylene and isotactic polypropylene on columns packed with zeolites ZSM‐5, Y, and silicalite was studied using high‐temperature liquid phase chromatography. Linear polyethylene was fully retained on a column packed with ZSM‐5 zeolite from non‐polar solvents, such as 1,1,2,2‐tetrachloroethane and 1,3,5‐trimethylbenzene at a temperature of 140°C. Partial adsorption on ZSM‐5 zeolite was found for polyethylene in 1,2,4‐trichlorobenzene and on silicalite from 1,2,4‐trichlorobenzene and 1,3,5‐trimethylbenzene. On the other hand, adsorption of polyethylene was not found from polar liquids, such as 2‐ethylhexyl acetate, cyclohexyl acetate, and cyclohexanone. Isotactic polypropylene was not adsorbed on any tested sorbent.     

Isothermal and nonisothermal dielectric relaxation studies on polycarbonate

Dielectric relaxation measurements at very low frequency were carried out on polycarbonate. Two prominent peaks were resolved from the broad β-relaxation peak with activation energies of 0.28 and 0.52 eV, respectively. Thermally stimulated discharge current was also studied and compared to the results obtained from the dielectric relaxation measurements.     

Structural correlations in comb heteropolymers in good and backbone-selective solvents

Molecular dynamics (MD) simulations of coarse-grained regular comb heteropolymers have been performed to explore structural correlations at equilibrium in a nonselective solvent and during the transition from coil to micelle in a backbone-selective solvent. We primarily consider the static structure factor measured directly from the simulations. In the good solvent, we consider cases ranging from short to long side chains, with respect to the spacer length. Reasonable agreement with a previously published theoretical structure factor is observed for a limited subset of the comb architectures in a small wavevector range. When the side chains are much longer than the spacers, the side-chain structure factor approaches that of starlike polymers. Additionally, plateau values of the structure factor scale with the side-chain length to the power of 0.736 when the side chains are shorter than the spacers. The transition from an open coil to a collapsed micelle is examined in MD simulations with explicit-solvent particles. Upon a sudden quench the from nonselective solvent to the backbone-selective solvent, the coil-to-micelle transition occurs via a side-chain clusterization mechanism. The time-dependent structure factors measured during the collapse process have plateau values that scale with the average cluster size to the power of 0.9. The origin of these two scaling exponents is still unknown. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 983-993, 2005     

Aggregation of polymer-grafted nanoparticles in good solvents: a hierarchical modeling method

Brownian dynamics simulations are carried out to study the aggregation behavior of polymer-grafted nanoparticles (NPs) in good solvents by using the coarse-grained model derived from the all-atom force field, according to the hierarchical modeling strategy, and here PEG-grafted gold nanoparticles (GNPs) were taken as an example. Generally, grafting PEG to the surface of GNPs is to protect them from aggregation in the solution. However, our results reveal that PEG-grafted GNPs may also aggregate when concentration increases. Our simulations indicate that there exists a critical aggregating concentration (CAC), beyond which the PEG-grafted GNPs will aggregate. We further check the effects of grafting density and the length of grafted chains on the aggregation behavior of the grafted GNPs, and find that there exists an optimized length of grafted chain, at which the system has the maximal CAC. Furthermore, the aggregate size of self-assembled mesostructures formed by the grafted GNPs increases with the concentration. Interestingly, it is observed that the aggregation favors to form linear gold nanowires rather than compact gold nanoclusters, and the corresponding mechanism is also addressed. It is expected that this work would provide useful information for the fabrication of metal nanowires and the surface modification of metal nanoparticles.     

Dilute solution properties of a polyurethane. I. Linear polymers

A linear polyurethane of high molecular weight was prepared in solution by the polyaddition of equimolar amounts of ethylene glycol and methylene bis(4-phenyl isocyanate). The polymer was fractionated by using a direct sequential extraction procedure, with a solvent–nonsolvent system consisting of N,N′-dimethylformamide (DMF) and acetone (A). The resulting fractions were characterized by viscosity and lightscattering measurements. The relationship between the intrinsic viscosity and molecular weight was found in DMF at 25°C. to be [η] = 3.64 × 10^?4M^0.71. The unperturbed polymer chain dimensions were determined from intrinsic viscosity measurements carried out under experimentally determined theta conditions.     

Morphological structures formed by grafted polymers in poor solvents

We study a system of grafted polymers in a poor solvent by self-consistent-field methods as well as Monte-Carlo simulation methods. We observe a number of different morphological structures including an inverted solvent micelle or hole in the polymer layer, a lamella-like micelle structure, and fused, spherical micelle structures. These structures can be obtained by either varying the grafting density or chain length. We also develop a scaling theory for the existence of these structures and find reasonable agreement between this theory and our numerical calculations.     

Molecular characterization of a hyperbranched polyester. I. Dilute solution properties

A hyperbranched polyester was fractionated by precipitation to produce 10 fractions with molecular weights between 20 × 10³ and 520 × 10³ g mol^?1. Each of these fractions was examined by size exclusion chromatography, dilute‐solution viscometry, intensity, and quasi‐elastic light scattering in chloroform solution at 298 K. High‐resolution solution‐state ¹³C NMR was used to determine the degree of branching; for all fractions this factor was 0.5 ± 0.1. Viscometric contraction factors, g′, decreased with increasing molecular weight, and the relation of this parameter to the configurational contraction factor, g, calculated from a theoretical relation suggested a very strong dependence on the universal viscosity constant, Φ, on the contraction factor. A modified Stockmayer–Fixman plot was used to determine the value of (〈r²〉_o/M_w)^1/2, which was much larger than the value for the analogous linear polymer. The scaling relations of the various characteristic radii (R_g, R_h, R_T, and R_η) with molecular weight all had exponents less than 0.5 that agreed with the theoretical predictions for hyperbranched polymers. The exponent for R_g was interpreted as fractal dimension and had a value of 2.38 ± 0.25, a value that is of the same order as that anticipated by theory for branched polymers in theta conditions and certainly not approaching the value of 3 that would be associated with the spherical morphology and uniform segment density distribution of dendrimers. Second virial coefficients from light scattering are positive, but the variation of the interpenetration function, ψ, with molecular weight and the friction coefficient, k_o, obtained from the concentration dependence of the diffusion coefficient suggests that chloroform is not a particularly good solvent for the hyperbranched polyester and that the molecules are soft and penetrable with little spherical nature. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1339–1351, 2003     

Dilute solution properties and phase separation of branched low-density polyethylene

Viscosity, light scattering, and precipitation temperature measurements on dilute solutions of high-density and low-density polyethylene fractions have been carried out and a theory by Flory for phase equilibrium of linear polymers has been extended to branched polymer. From the results, it is shown that the entropy parameter ψ, depends on branching; a method for the determination of long-chain branching in polymer fractions is proposed combining precipitation temperature and molecular weight measurements. The method has been applied to the evaluation of long-chain branching in low-density polyethylene.