Studies of micro-brownian motion of a polymer chain by the fluorescence polarization method. I. Fluorescent conjugates of polyacrylamide

Polyacrylamide having a fluorescent residue at the chain end was prepared by polymerization of acrylamide in the presence of a fluorescent dye. The segmental motion of the chain end in dilute solution was studied by the fluorescence polarization method on the fluorescent polyacrylamide conjugates thus obtained. The linear relation between 1/p and T/η₀ held for every sample studied in aqueous media, where p is the degree of polarization of the fluorescence, T is the absolute temperature, and η₀ is the viscosity of the medium. The mean relaxation time 〈ρ〉 of the conjugate was evaluated from these data as a function of the molecular weight of the conjugate. The value of 〈ρ〉 increased slightly with molecular weight, varying from 3.3 × 10^?9 to 7 × 10^?9 sec. The absolute values of 〈ρ〉 and its molecular weight dependence suggest that 〈ρ〉 represents the mean rotational relaxation time for the cooperative motion of about ten monomeric units at the chain end. The effect of the mean extension of polymer chain on the segmental motion was found to be negligible.     

Study of polymer complexes by size exclusion chromatography coupled with light scattering in combination with fluorescence spectroscopy

Poly(methyl methacrylate) stereocomplexes prepared at different concentration in dilute tetrahydrofuran solutions were studied by size exclusion chromatography coupled with refractive and light scattering detectors in combination with fluorescence spectroscopy. A considerable increase in segment density due to complexation compared with free poly(methyl methacrylate) chain was only slightly affected by the polymer concentration in solution where stereocomplexes were formed. At polymer concentrations up to 3×10⁻³ g cm⁻³, an increase in non‐uniformity of polymer complex molecular weight and size and a shift to higher values of both were observed. In semidilute solutions (at c > 3×10⁻³ g cm⁻³) stereocomplexes virtually did not become heavier and larger.     

Effects of polymer chain disentanglement on NMR properties. II. 13C magnetic relaxation in polystyrene

The transverse magnetic relaxation of ¹³C_α nuclei has been studied in concentrated solutions of polystyrene. The magnetic relaxation rate was measured as a function of molecular weight at several temperatures (313,318, and 323 K) and at several concentrations (0.53, 0.43, and 0.34 g/cm³). The spin-system response of these nuclei in natural abundance exhibits a characteristic evolution from pseudosolid properties to liquidlike one, induced by decreasing the molecular weight of polymer molecules. This evolution is analogous to that already observed in protons attached to polyisobutylene or polydimethylsiloxane chains; it is assumed to be induced by an increase of the disentanglement rate of polymer chains. The spin-system response may be considered as reflecting single-chain magnetic properties, because of the low concentration of ¹³CC_α nuclei, although all chains are in dynamic interaction with one another. The NMR disentanglement transition is interpreted in terms of a two-step motional averaging effect involving submolecules. A numerical analysis of NMR properties is given using a model of polymer chain relaxation based on a multiple-mode relaxation process, characterized by (i)a terminal relaxation time τ^v₁ depending upon M³, the molecular weight, and approximately proportional to the polymer concentration C (like the reptation time); (ii)a relaxation-time spectrum analogous to a Rouse spectrum; (iii)a terminal relaxation time τ^v₁ = 2.5 × 10^?2s for M = 2.5 × 10⁵, C = 0.53 g/cm³ in carbon tetrachloride at 313 K.     

Swelling of polyacrylamide gels in polyacrylamide solutions

Swelling behavior of polyacrylamide (PAAm) and polyacrylamide-co-polyacrylic acid (PAAm-co-PAAc) gels was investigated in aqueous solutions of monodisperse PAAms with molecular weights (M_w) ranging from 1.5 × 10³ to 5 × 10⁶ g/mol. The volume of the gels decreases as the PAAm concentration in the external solution increases. This decrease becomes more pronounced as the molecular weight of PAAm increases. The classical Flory–Huggins (FH) theory correctly predicts the swelling behavior of nonionic PAAm gels in PAAm solutions. The polymer–polymer interaction parameter χ₂₃ was found to decrease as the molecular weight of PAAm increases. The swelling behavior of PAAm-co-PAAc gels in PAAm solutions deviates from the predictions of the FH theory. This is probably due to the change of the ionization degree of AAc units depending on the polymer concentration in the external solution. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 1313–1320, 1998     

Dependence of viscosity of polystyrene solutions on molecular weight and concentration

Viscosities of solutions of polystyrene in toluene were measured for concentrations up to 400 kg m^?3 at 298 K. Polymers of molecular weights ranging from 8.7 × 10³ to 2.4 × 10⁶ were used. It is observed that viscosity of the polymer solution increases with increasing concentration and molecular weight; the rate of increase is greater at higher values of the two parameters. A master curve for the system is constructed by using the experimental data for viscosity, concentration and molecular weight of the polymer. Regions of various polymer interactions in solution are identified.     

Some studies on a polymer from urea

A polymer having the structure of guanidinopolyhydroxynitrile has been produced by heating an equimolar mixture of urea and anhydrous ZnCl₂ in nitrogen at 300°C and 27 atm. The structure has been established from elemental analysis, percentage of nitrogen as primary amine, and ultraviolet and infrared spectra of the polymer and its derivatives. A mechanism of the polymerization based on some experimental evidence has been suggested. Its physical properties have been attributed to its skeletal structure and ring closure by hydrogen bonding. Thermograms reveal that it is stable to 150°C, after which it decomposes slowly till a 75% weight residue is obtained at 575°C with a constant weight plateau extended to 680°C. In acid solvents, protonation occurs at the ? NH₂ group or the azomethine nitrogen atoms, producing polycations. The polyelectrolytic character in acids has been confirmed by viscometric and osmotic studies and the molecules tend to be both coiled up and associated in solutions. [n] in anhydrous formic acid is 0.3636 dl/g. The molecular weights of the polymer and its various fractions range between 39,500 and 25,900. Dielectric constants, dielectric losses, and conductivities of the polymer have also been measured as functions of frequency and temperature and it has been proved that the dispersion is due to dipole polarization. The average energy of the dipole is 1.73 × 10^?2 eV/°K, the intrinsic activation energy for conduction is 0.186 eV, the conductivities being of the order of 2 × 10^?6 to 7 × 10^?7 mho-cm^?1. The polymer is therefore a semiconductor. The number of charge carriers is 2.12 × 10¹⁶/cm², which agrees reasonably well with the value, 6.66 × 10¹⁶, obtained from spin-density calculations from ESR signals.     

Studies of the micro-brownian motion of a polymer chain by the fluorescence polarization method. III. Fluorescent conjugates of polyethyleneimine

Fluorescent conjugates of polyethyleneimine (PEI) were prepared by conjugation of fluorescent dyes, fluorescein isocyanate (FIC), and 1-dimethylaminonaphthalene-5-sulfonyl chloride (DNS), to PEI. The degree of polarization of the fluorescence was measured as a function of temperature and solvent viscosity on aqueous solutions of the conjugates and the data thus obtained were analyzed in terms of an equation of the Perrin type to calculate the mean relaxation time of the conjugate. The mean relaxation times obtained for the two types of the conjugates, which differ in the excited lifetime by a factor of about three, practically agree with one another and are about 2.5 X 10^?8 sec. The relaxation time of the DNS conjugate increases with increasing molecular weight of the conjugate from 2 X 10^?8 to 4 X 10^?8 sec. These values are much larger than those of the PAA conjugates reported in Part I of this series. The relaxation time of this order may correspond to that for the cooperative rotary motion of about ten monomeric residues on the PEI chain, that is, for the motion of an intermediate segment of the PEI molecule in solution. Finally, relaxation time–molecular weight relationships for various types of fluorescent conjugates are compared. It is suggested that these data may serve as a basis for elucidating the mode of motion of a given molecule in solution from the polarization data.     

Rotational diffusion of 9,10-diphenylanthracene in di-n-butyl phthalate solutions of polystyrenes by the fluorescence polarization method: Dependence on polymer concentration and molecular weight

A versatile double-beam polarization fluorimeter has been constructed for measuring the polarization of fluorescence from polymer solutions, melts, and glasses. Polarizations can be determined over a range of temperatures from ?20 to +80°C in a controlled atmosphere with a precision of ±0.001 to ±0.005 for the studies reported herein. Data collected at different temperatures for 1.5 × 10^?5M solutions of 9,10-diphenylanthracene (PA) in di-n-butyl phthalate (BP) fit a relation of the Perrin type, 1/P = (1/P₀) + (ST/_η1), where P is the polarization, T is the absolute temperature, and _η1 is the solvent viscosity. The constants P₀ and S were 0.400 ± 0.005 and (7.4 ± 0.3) × 10^?3 P/°K, respectively. Polarizations were also determined at 25.0 ± 0.1°C for BP solutions containing 1.5 × 10^?5M PA and polystyrenes at various weight fractions w₂ and molecular weights M. Rotational friction coefficients ζ_r deduced from these data showed no dependence on M from 5.1 × 10⁴ to 8.6 × 10⁵ g/mole, and a gradual increase as w₂ was varied from 0 to 0.1. It is concluded from these results that PA is an especially attractive emitter for rotational diffusion studies in nonaqueous systems, and that the abrupt changes in ζ_r with w₂ and M observed for some other emitter–polymer systems and attributed to onset of coil overlap are not universal characteristics of such systems.     

Intrinsic viscosity and axial extension ratio of random-coiling macromolecules in a hydrodynamic shear field

The shear dependence of the intrinsic viscosity and the conformation of high molecular weight polyisobutylene in dilute solutions of decahydronaphthalene under shear were determined simultaneously. Experimental variables investigated were the shear rate (0 to 2 × 10³ sec^?1), the molecular weight (1.0 × 10⁷ to 1.7 × 10⁷) and the polymer concentration (1.8 × 10^?4 to 8.4 × 10^?4 g/cc). Correlations allowing concentration and shear rate normalization for any one sample are described. Conformational extention ratios along the orientation direction of the deformed molecule to 1.42 and intrinsic viscosity ratios (sheared to zero shear) to 0.5 were observed.     

Light scattering study of an aromatic polyamide-hydrazide polymer

The aromatic Polyamide-hydrazide, Monsanto X-500, has been studied by light scattering in dimethyl sulfoxide, a thermodynamically good solvent. The unperturbed dimensions, (〈r〉_av/M)^1/2 = 1.93 × 10^?8 at 25°C., indicate a rather highly extended chain. The persistence length falls in the range 35–63 Å, which corresponds to a length of between two and four formula units. This is considerably smaller than the values which have been reported for the aromatic polyamides, poly(p-benzamide) and poly(p-phenylene terephthalamide). X-500 appears to approximate coil-like behavior at a molecular weight of 45,000. Theoretical predictions, based upon the 〈r〉_av/bL ratio, are compared with the observation that no evidence for an anisotropic phase has been found in X-500 solutions in dimethyl sulfoxide at polymer volume ranging from 0.12 to 0.19 (depending upon the concentration of added LiCl).     

Molecular dimensions and melt rheology of an all‐aromatic liquid crystalline polymer

The molecular dimensions and melt rheology of a thermotropic all‐aromatic liquid crystalline polyester (TLCP) composed of p‐hydroxy benzoic acid, hydroquinone, terephthalic acid, and 2,4‐naphthalenedicarboxylic acid is examined. The Mark–Houwink exponent (α) of 0.95 is estimated for the TLCP. The persistence length estimated from molecular weight (M) and intrinsic viscosity ([η]) data using the Bohdanecky–Bushin equation is about 95 Å, whereas that estimated from light scattering data is 117 Å. These persistence lengths and the observed α value, both higher than those for flexible polymers, suggest that the present TLCP is a semirigid polymer. The zero shear melt viscosity (η₀) varies with approximately M⁶ for molecular weight M > 3 × 10⁴ g/mol; below this molecular weight, η₀ varies almost linearly with M. Widely different entanglement molecular weights (M_e) are predicted, depending on the method used; the plateau modulus estimates M_e of about 8 × 10⁵ g/mol, whereas the ratio of mean square end‐to‐end distance and molecular weight (〈R²〉₀/M) predicts M_e's either too small (0.33 g/mol) or too large (2.5 × 10⁶ g/mol), depending on the theory used. Although the change in the molecular weight dependency of melt viscosity appears to be associated with the onset of entanglement coupling of the semirigid molecules, its origin needs further investigation. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2378–2389, 2001     

Emulsifier-free emulsion polymerization of tetrafluoroethylene by radiation. I. Effects of reaction conditions on the polymerization rate and polymer molecular weight

The radiation-induced emulsifier-free emulsion polymerization of tetrafluoroethylene was carried out at an initial pressure of 2–25 kg/cm², temperature of 30–110°C, and under a dose rate of 0.57 × 10⁴?3.0 × 10⁴ rad/hr. The rate of polymerization was shown to be proportional to 1.0 and 1.3 powers of the dose rate and initial pressure, respectively, and is maximal at about 70°C. The molecular weight of polytetrafluoroethylene (PTFE) lies in the range of 10⁵?10⁶, increases with reaction time in the early stage of polymerization, and is maximal at 70°C but is almost independent of the dose rate. An interesting discovery is that PTFE, a hydrophobic polymer, forms as a stable latex in the absence of emulsifier. When PTFE latex coagulates during polymerization under certain conditions, the polymerization rate decreases, probably because polymerization proceeds mainly on the polymer particle surface. The observed rate acceleration and successive increase in polymer molecular weight may be due to slow termination of propagating radicals in the rigid PTFE particles.     

Viscometric properties of dilute polystyrene/dioctyl phthalate solutions

We report viscometric data collected in a Couette rheometry on dilute, single‐solvent polystyrene (PS)/dioctyl phthalate (DOP) solutions over a variety of polymer molecular weights (5.5 × 10⁵ ≤ M_w ≤ 3.0 × 10⁶ Da) and system temperatures (288 K ≤ T ≤ 318 K). In view of the essential viscometric features, the current data may be classified into three categories: The first concerns all the investigated solutions at low shear rates, where the solution properties are found to agree excellently with the Zimm model predictions. The second includes all sample solutions, except for high‐molecular‐weight PS samples (M_w ≥ 2.0 × 10⁶ Da), where excellent time–temperature superposition is observed for the steady‐state polymer viscosity at constant polymer molecular weights. No similar superposition applies at a constant temperature but varied polymer molecular weights, however. The third appears to be characteristic of dilute high‐molecular‐weight polymer solutions, for which the effects of temperature on the viscosity curve are further complicated at high shear rates. The implications concerning the relative importance of hydrodynamic interactions, segmental interactions, and chain extensibility with increasing polymer molecular weight, system temperature, and shear rate are discussed. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 787–794, 2006     

Excluded-volume effects in dilute polymer solutions. IV. Polyisobutylene

Statistical radii of gyration, second virial coefficients, and intrinsic viscosities of sharp fractions (M?_w/M?_n ≈ 1.1) of polyisobutylene (PIB) covering a wide range of molecular weight (1.6 × 10⁵ to 4.7 × 10⁶) were determined in isoamyl isovalerate (IAIV) at a number of temperatures ranging from 20 to 60°C, in n-heptane at 25°C, and in cyclohexane at 25°C by light-scattering and viscosity measurements. It was found that IAIV at 22.1°C is a theta solvent for PIB. Analysis of the data by the methods described in preceding papers of this series indicated that, except for minor differences, the conclusions derived from similar studies with polychloroprene, polystyrene, and poly-p-methylstyrene hold equally for solutions of the typical linear polymer investigated here. In particular, no decisive evidence for the drainage effect was found.     

Morphology and thermodynamics of selenium-containing nanosystems: The effect of polymer stabilizers

Nanosystems based on zero-valent selenium and biocompatible polymer stabilizers (polyvinylpyrrolidone with molecular weight (MW) М _w = (10–55) × 10³, poly-N,N,N,N-trimethylacryloyloxyethylammonium methylsulfate with М _w = (30–250) × 10³ and polyethylene glycol with М _w = (1–40) × 10³) are studied by means of static and dynamic light scattering, and the resulting data are compared. Dense spherical multimolecular nanosystems are found to be formed. Morphological and thermodynamic characteristics of selenium-containing nanosystems, depending on the nature and MW of the polymer stabilizer, are determined. It is shown that the properties of nanosystems can be adjusted by varying the molecular weight of the polymer stabilizer.     

Fluorescence polarization studies of the conformation of soil fulvic acid

The conformation of soil fulvic acid was studied by fluorescence polarization as a function of pH, concentration, and ionic strength. Rotational relaxation times were measured from the slopes of plots of polarization vs. the ratio of temperature to viscosity. The rotational relaxation time did not change over the pH range 5–8 or over the concentration range 3.3 X 10^-5–3.3 × 10^-4 M fulvic acid. This suggests that fulvic acid does not aggregate or change conformation. Changes in ionic strength also do not cause a measurable change in rotational relaxation time. A net rotational relaxation of 2.0 ns was calculated for fulvic acid. This value is based on a fluorescence lifetime of 2.1 ns which is the best single exponential fit to the observed fluorescence decay. A molecular weight of 2400 was calculated for fulvic acid assuming that fulvic acid is spherical. The discrepancy between this value and the true number-average molecular weight of 990 suggests that fulvic acid exists in a flat extended conformation.     

CRITICAL CONCENTRATIONS OF α(1→3)-D-GLUCAN FROM LENTINUS EDODES IN NaOH AQUEOUS SOLUTION

Critical concentrations of α-(1→3)-D-glucan L-FV-Ⅱ from Lentinus edodes were studied by viscometry andfluorescence probe techniques. The dependence of the reduced viscosity on concentration of the glucan in 0.5 mol/L NaOHaqueous solutions with or without urea showed two turning points corresponding to the dynamic contact concentration c_s andthe overlap concentration c~* of the polymer. The values of c_s and c~* were found to be 1×10~(-3) g cm~(-3) and 1.1×10~(-2) g cm~(-3),respectively, for L-FV-Ⅱ in 0.5 mol/L NaOH aqueous solutions. The two critical concentrations of L-FV-Ⅱ in 0.5 mol/LNaOH aqueous solutions were also found to be 1.2×10~(-3) g cm~(-3) fbr c_s and 9.2×10~(-3) g cm~(-3) for c~* from the concentrationdependence of phenanthrene fluorescence intensities. The overlap concentration c~* of L-FV-Ⅱ in 0.5 mol/L NaOH aqueoussolutions was lower than that of polystyrene with same molecular weight in benzene, owing to the fact that polysaccharidetends to undergo aggregation caused by intermolecular hydrogen bonding. A normal viscosity behavior of L-FV-Ⅱ in 0.5 mol/L urea/0.5 mol/L NaOH aqueous solutions can still be observed in an extremely low concentration range at 25℃.     

Mobility-sensitive fluorescence probes for quantitative monitoring of water sorption and diffusion in polymer coatings

The fluorescent molecular rotor probes 4-tricyanovinyl-[N-(2-hydroxyethyl)-N-ethyl]-aniline, tricyano-4-(dimethylamino) benzylidene, and tricyanovinyljulolidene have been used as extrinsic fluorescence probes for quantitative monitoring of water uptake in polymeric coatings. The presence of water causes plasticization of the polymer, which results in increased local mobility within the film. The nonradiative decay pathways of the rotor probes are increased as local mobility increases, and the resulting decrease in fluorescence intensity of the probes is directly proportional to the amount of water sorbed. Beyond allowing for the characterization of sorbent content, this fluorescence technique can be used to determine the diffusion coefficient of water in a polymer film. The relative change in fluorescence fits well to a Fickian diffusion model, yielding a diffusion coefficient for water of 3 × 10^-8 cm²/s in poly(vinyl acetate), and a value of 6 × 10^-9 cm²/s in a room-temperature cured epoxypolyamide, in excellent agreement with diffusion coefficient values determined from gravimetric analysis. Preliminary studies also demonstrate the utility of molecular rotor probes to monitor water uptake in individual layers of multilayered polymer systems. © 1995 John Wiley & Sons, Inc.     

Solution properties of high molecular weight polystyrene

A series of polystyrenes with weight-average molecular weight M?_w up to 1.3 × 10⁷ was prepared by anionic polymerization in tetrahydrofuran (THF). Each sample was characterized by gel-permeation chromatography, light scattering, and viscometry. It was found that each sample had an almost symmetrical and very narrow molecular weight distribution (M?_w/M?_n < 1.07). The mean-square unperturbed radius of gyration 〈S²〉₀ was determined in trans-decalin at 20.4°C as 〈S²〉₀ = 7.8₆ × 10^?18M?_w (cm²). The particle scattering factor was well represented by the Debye equation irrespective of solvent in the range of M?_w < 4 × 10⁶, and only a small deviation was observed in benzene at higher molecular weights. The penetration function Ψ ≡ A₂M²/4π^3/2N_A〈S〉^23/2 was found to approach a relatively low asymptotic value of 0.21–0.23 at molecular weights above 2 × 10⁶ in benzene at 30°C, where A₂ is the second virial coefficient and N_A is Avogrado's number. It was also found that the theta temperature in trans-decalin was affected by the nature of polymer samples. A difference of about 3°C in the theta temperature was observed between two series of anionic polystyrenes, one prepared in THF and the other in benzene, but there was practically no difference in unperturbed chain dimension.