Viscosity and intrinsic viscosity/temperature relationships for dilute solutions of poly(2-biphenylyl methacrylate) and poly(4-biphenylyl methacrylate)

The actual viscosity η and the intrinsic viscosity [η] of six fractions of poly(2-biphenylyl methacrylate) {poly[1-(2-biphenylyloxycarbonyl)-1-methylethylene], (POB); weight average molecular weight M?_w: 4,0 · 10⁴ to 1,42 · 10⁶, polydispersity ratio M?_w/M?_n ≈ 1,4} and of three fractions of poly(4-biphenylyl methacrylate) {poly[1-(4-biphenylyloxycarbonyl)-1-methyl-ethylene], (PPB); M?_w : 8,1 · 10⁴ to 5,3 · 10⁵, M?_w/M?_n ～ 1,4} in benzene have been determined at different temperatures between 20 and 60°C. Values of the apparent activation energy of the viscous flow Q and the pre-exponential term A in the expression η = A · exp[Q/(RT)] have been obtained. Q varies with M?_w and concentration c according to Moore's equation: Q = Q₀ + K_e · M · c, where Q₀ refers to the solvent and K_e depends on polymer and solvent. The numerical value of K_e for POB and PPB is 1,6 · 10^?4 (6,7 · 10^?4) and -8,1 · 10^?4 cal · dl · g^?1 (-3,4 · 10^?3 J · dl · g^?1), resp. From all polymethacrylates studied POB is the only polymer with a positive K_e value. The positive value of K_e for POB may possibly be related to the more extended form of POB in benzene and also may be connected, at least partly, with its low flexibility. The temperature coefficient of the unperturbed dimensions dln〈r₀²〉/dT for POB estimated from the viscosity data using the Burchard-Stockmayer-Fixman relation, is 0,14 · 10^?3, much lower than for PPB (2,3 · 10^?3 between 22 and 40°C and 1,2 · 10^?3 between 40 and 60°C). The positive values of dln〈r₀²〉/dT indicate that extended conformations of these polymers in benzene must be associated with higher energies.     

The flexibility of poly(2,4,5-trichlorophenyl methacrylate)

Light scattering in benzene and intrinsic viscosities [η] in tetrahydrofuran, chloroform, 1,4-dioxane, and benzene of poly(2,4,5-trichlorophenyl methacrylate) (PTCPh) were measured in dilute solutions. Relations between [η], z-average root-mean-square end-to-end distance (r²_z )^1/2, and molecular weight M?_w were established. The unperturbed dimensions, calculated from viscometric and light scattering data by different methods, are in excellent agreement with one another. PTCPh has a lower flexibility factor (σ = 2,37) than poly(phenyl methacrylate) (σ = 2,5), in spite of the higher bulkiness of the side group of PTCPh. It seems, therefore, reasonable to suggest that the presence of the chlorine atoms hinders partly the interactions between the aromatic groups.     

Viscosities of dilute solutions of poly(tetrahydrofurfuryl methacrylate)

The intrinsic viscosities of seven fractions (from M?_n = 1,69.10⁵ to M?_n = 6,13.10⁵) of poly(tetrahydrofurfuryl methacrylate) in eleven solvents at temperatures between 30° and 50° show the following order: tetrachloroethane > dichloroethane > tetrahydrofuran > chloroform > benzene > bromobenzene > ethyl acetate > carbon tetrachloride > methyl pentyl ketone > acetone > 2-hydroxymethyltetrahydrofuran. Values of HUGGINS slope constants range between 0,34 to 0,48 for the unfractionated polymer and the magnitudes of a and k in the expression [η] = kM^a show little variations with temperature in case of good solvents whereas the opposite is observed in case of poor solvents. The theta temperature for 2-hydroxymethyltetrahydrofuran containing 20% methanol is 31,2 ± 0,3° and 3,49, 5,72, and 4,97 are the values for K₀.10⁴, (r /M)^1/2.10⁹ and (r /Z)^1/2.10⁸, respectively.     

Viscosities of dilute solutions of poly (methyl methacrylate) and poly (ethyl methacrylate) in organic solvents

Poly(methyl methacrylate) and poly(ethyl methacrylate) prepared by a benzoylperoxide catalysed polymerization process were fractionated. The variation of the intrinsic viscosity and HUGGINS ' constant with temperature, molecular weight and solvent was studied. From the viscosity data the thermodynamic interaction parameters χ, ψ, k etc., and the solubility parameter of the polymers were evaluated and discussed.     

Conformational transition in poly[4-(1,1,3,3-tetramethylbutyl)phenyl methacrylate] and poly(4-tert-butylphenyl methacrylate) in dilute solutions

Temperature dependence of viscosity data and refractive index increment was investigated on two polymers: poly[4-(1,1,3,3-tetramethylbutyl)phenyl methacrylate] ( 1a ) and poly(4-tert-butylphenyl methacrylate) ( 1b ) in dilute solution. A discontinuity in intrinsic viscosity was observed over a narrow temperature range. From this behaviour it was possible to visualize sharp changes of unperturbed dimensions (K_θ) and thermodynamic parameters (B). This phenomenon can be accounted for by assuming conformational changes of the chain in the chosen solvent in a specific temperature range. These changes can be also observed by discontinuities in refractive index increments dn/dc. In the case of 1b the conformational change disappears on addition of a polar solvent (CHCl₃).     

The behaviour of poly(2,3-epoxypropyl methacrylate) in dilute solution

Homopolymers of 2,3-epoxypropyl methacrylate with various molecular masses were prepared by solution polymerization with 2,2′-azoisobutyronitrile as initiator. The effect of polymerization conditions on the molecular parameters (weight- and number-average molecular masses M_W and M_n intrinsic viscosity [η]) and the tacticity of the resulting poly (2,3-epoxypropyl methacrylate)s was investigated. For unfractionated polymers, the constants of the Mark-Houwink equation for 1,4-dioxane and tetrahydrofuran were determined. Gel permeation chromatography was tested as a tool for the determination of the M_w and M_n values.     

Non-newtonian flow behaviour of poly(decyl methacrylate) solutions

The viscosity of solutions of poly(decyl methacrylate)s, PDMA, in 1-pentanol (thermodynamically poor solvent) and in toluence or isooctane (good solvents) was measured up to shear rates of 3 · 10⁴s^?1 by means of rotational viscosimeters. The observed pronounced shear thinning is for all solutions well described by the theory of Graessley, with the extension, introduced by Ito. Two parameters, resulting from the evaluation of the flow curves on the basis of the above theory, are discussed: τ₀, a characteristic relaxation time of the polymer chain, is found to be in the range of ms. η_fric, a frictional parameter, independent of shear rate, amounts upto 50% of the zero-shear viscosity for the measured solutions. Both, τ₀ and η_fric, increase with decreasing solvent quality, increasing molecular weight, and increasing concentration, in accord with theory. A comparatively sharp downward bend, separating two power-law regimes, shows up with moderately concentrated solutions, as the shear rate exceeds about 10³ to 10⁴ s^?1. This transition is tentatively interpreted as an orientation of the long side chains of PDMA.     

High temperature demixing of poly(decyl methacrylate) solutions in isooctane and its pressure dependence

Solutions of poly (decyl methacrylate) in isooctane (2,2, 4-trimethylpentane) show lower critical solution temperatures (LCST) that lie well below the thermal degradation of the polymer. The corresponding exothermal theta-temperature (from the Shultz-Flory plot) amounts to 210°C. The increase in solvent quality by pressure turns out to be very pronounced (d T_c/d_p ≈ +1 K/bar). With solutions of the polymer in motor oils, high temperature demixing is unlikely to occur below their boiling point. The theoretical evaluation of published experimental data for 11 different systems exhibiting LCSTs demonstrates the following: Under the equilibrium vapour pressure of the solution high temperature demixing is generally observed withing the temperature interval between T_b, the boiling point of the pure solvent (1 bar), and 1,5 T_b. As T_c - T_b increases, the heats of mixing and the pressure influence on T_c increase, too.     

Thermodynamics and high-pressure viscosity of dilute solutions of poly(decyl methacrylate) and how the free volume influences them

Light scattering and viscometric measurements were performed for the system isooctane/poly(decyl methacrylate) of weight-average molecular weight M?_w = 250 000 within the concentration regime of pair interaction between the macromolecules in the temperature range from 25°C to 100°C. In case of the intrinsic viscosities [η], the pressure was varied up to 3500 bar. Under isobaric conditions, the osmotic second virial coefficients A_2, the z-average radii of gyration r_z and [η] pass through a maximum, the Huggins coefficient k_H through a minimum, with variation of temperature. These extrema indicate a change in the heat of dilution from endothermal at low, to exothermal at high temperature T. The calculation of the temperature dependence of the intrinsic viscosity [η] (T) for isochoric conditions does not yield a maximum, provided the pressure at the lowest temperature is chosen close to atmospheric pressure; it can, therefore, be concluded that the change in the sign of the enthalpy is in this case only due to the free volume of the system which increases markedly with increasing T. For pressures larger than ≈700 bar, maxima are always observed, no matter whether the temperature is changed isobarically or isochorically. All parameters under investigation are closely interdependent: A one-to-one correspondence exists between [η] and A₂ at 1 bar, and k_H and [η] interrelate linearly for constant T.     

Viscosity of aqueous and alkaline solutions of poly(ethylene oxide)

Viscosity measurements over a wide range of temperature were made on aqueous solutions of poly(ethylene oxide) samples of different molar mass and of low polydispersity. Above ca. 308 K the Mark-Houwink exponent decreases and tends to a value of 0,50 at a lower critical solution temperature of 376 ± 2 K. The same value for this θ-temperature is derived also as that at which the slope of Stockmayer-Fixman plots tends to zero. At 298 K the unperturbed dimensions [〈r²〉₀/M]^1/2 = 0,089 nm · g^?1/2 · mol^1/2 and their temperature coefficient d ln 〈r²〉₀/dT ≈ ? 1,5 (±0,5) · 10^?3 K^?1. In aq. KOH the intrinsic viscosity [η] is virtually uninfluenced by pH at low-medium pH, but at high pH, [η] falls sharply. Viscosity and phase separation measurements yield θ-conditions in 1,24 M aq. KOH at 298 K. The derived polymer-water interaction parameters χ increase from 0,449 at 276 K to 0,493 at 358 K, but the enthaplic component χ_H is incapable of yielding a meaningful value for the solubility parameter δ₂ of the polymer in such a hydrogen-bonding system. The calculated value of χ₂ was 18,9 (kJ · dm^?3)^1/2.     

Properties of dilute solutions of poly(2-methyl-5-vinyl pyridine)

Poly(2-methyl-5-vinyl pyridine) was prepared by mass polymerization and elution fractionated. Cyclohexanone/n-heptane was used as solvent/nonsolvent pair. Fractions of various molecular weights were analyzed by viscosimetry and light scattering. The following intrinsic viscosity-molecular weight relation was obtained at 25°C. in methylethyl ketone by light scattering measurements on fractions with molecular weights ranging from ca. 6·10⁴ to 10⁶. [η]-M relations were also obtained in methanol and in three Θ-solvents, i.e. n-butyl acetate at 21.8°C., methylicobutyl ketone at 37.4°C., and n-amyl acetate at 48.2°C. The FLORY constant determined from the Θ-measurements was found to be constant with the temperature in the range considered. Its value is 83·10^?3·cm³·g^?1·(g.mole^?1)^?1/2. The same value was obtained by treating the viscosity and light scattering results in methylethyl ketone according to the KURATA and STOCKMAYER theory. The flexibility of the chains of poly(2-methyl-5-vinyl pyridine) was found to be similar to that of polymers of similar molecular structure such as polystyrene, substituted polystyrenes or poly(4-vinyl pyridine). The thermodynamic interaction parameters Θ and Ψ were determined in methylethyl ketone by viscosimetry. The experimental dependence of the second virial coefficient on molecular weight for the latter solvent was compared in detail with that calculated according to existing theoretical treatments.     

The temperature coefficient of the unperturbed dimensions of poly(pentachlorophenyl methacrylate)

Values of the temperature coefficient of the mean square unperturbed dimensions dln(r /dT) for poly(pentachlorophenyl methacrylate) are obtained from viscosity vs. temperature data under two different conditions: (a) viscosity determinations in several different solvents each at its Θ-temperature and (b) viscosity determinations in a thermodynamically good solvent with a similar chemical structure as compared to the repeating unit. An anomalous temperature dependence of the viscosity was observed in o-dichlorobenzene for this polymer. The results obtained from both conditions are compared and their limitations and interpretations are discussed.     

Unique morphologies found in freeze-dried poly(ethylene oxide) prepared from dilute solutions

Freeze-dried particles of poly(ethylene oxide) (PEO) were prepared from sublimation of a 1 × 10⁻² wt.-% solution of PEO in benzene in an ice-salt bath. After isothermal crystallization at 318.2 ± 0.1 K for 2 h, an unusual planar zigzag form of PEO was found. A variety of unique spherulite-like morphologies were also observed, and their formation is discussed on the basis of the interaction between solvent molecules and segment of the polymer chains.     

Temperature dependence of the viscosity of dilute poly(N-vinylcarbazole) solutions in 1,4-dioxane

The dependence of the viscosity of dilute solutions of poly(N-vinylcarbazole) in 1,4-dioxane on the temperature is studied by Moore's treatment. The numerical values of the constants from this treatment K_e, K_β, and β indicate that this polymer in 1,4-dioxane assumes the characteristic behaviour of flexible polymers. The numerical values of the parameters K_Θ and B from the Stockmayer-Fixman plot and the Mark-Houwink constants K and a are determined and the temperature coefficient of the unperturbed dimensions is evaluated for this system.     

Solution properties of poly(methyl methacrylate) in methyl methacrylate, 1. Viscosities from the dilute to the concentrated solution regime

The viscosities of samples of poly(methyl methacrylate), PMMA, with narrow molecular weight distributions and with molecular weights in the range 1,75·10⁴ < M?_w < 1,60.10⁶ were measured in methyl methacrylate, MMA, as solvent at 20, 40, and 60°C in the dilute and in the semi-dilute concentration regime. By extrapolation to zero polymer concentration the limiting viscosity numbers and therefrom the Mark-Houwink-Kuhn-Sakurada parameters for PMMA in MMA were obtained. In addition, unperturbed dimensions were determined from dilute solution viscosity data. Together with some published results for more concentrated solutions of PMMA in MMA the viscosities of the semi-dilute systems were analysed in terms of scaling theories. It was found that irrespective of temperature, polymer concentration, and molecular weight all data could be quite well fitted by a single master curve when the relative viscosity η/η₀ was plotted as a function of the product of the intrinsic viscosity and mass concentration [η]·c. No sharp transitions between different concentration regimes were observed, however, and the scaling law exponents for the entangled solution are significantly higher than predicted by theory.     

Comparison of ethanolamine/ethylenediamine-functionalized poly(glycidyl methacrylate) for efficient gene delivery

Cationic polymers with low cytotoxicity and high transfection efficiency have attracted considerable attention as non-viral carriers for gene delivery. Recently we reported that ethanolamine (EA)-functionalized poly(glycidyl methacrylate) (PGMA) (termed PGEA) vectors can have excellent transfection efficiency, while exhibiting very low toxicity. Herein different EA- and ethylenediamine (ED)-functionalized PGMA (termed PGEAED) vectors, as well as ED-functionalized PGMA (termed PGED) vectors, are proposed and compared for efficient gene delivery. In addition to the cationic pendant secondary amine and hydroxyl groups of PGEA, PGEAED, and PGED also contain flanking primary amine groups. PGEAED and PGED exhibited a substantially enhanced ability to condense pDNA into complex nanoparticles at the 100 nm level with positive zeta potentials of about 30 mV at nitrogen/phosphate (N/P) ratios of 10 or higher. More interestingly, no obvious change in the cytotoxicity of PGEAED was observed with a substantial increase in ED content. Moreover, the flanking primary amine groups induced by ED could be readily functionalized by glycyrrhetinic acid or cholic acid to improve the biophysical properties of the gene vectors.     

Solution properties and unperturbed dimensions of poly(5-p-methyl methacrylate) and poly(2-tert-butylphenyl methacrylate)

The solution properties of poly(5-p-menthyl methacrylate) and poly(2-tert-butylphenyl methacrylate) are determined by several methods in good and ideal solvents. The flexibilities σ calculated on the basis of the unperturbed dimensions are 3,1 and 2,6, resp. These values are compared with those found for other polymethacrylates with bulky substituents. The influence of a large group in ortho position at the cyclohexyl and the phenyl rings is discussed in terms of steric hindrance and specific interactions.     

Notes on light scattering from dilute poly(vinyl chloride) solutions in a binary theta-solvent,tetrahydrofuran/water

Tetrahydrofuran (THF) with 8–9 vol.-% of water (depending on the polymer tacticity) is at 25°C a Θ-solvent for poly(vinyl chloride). The refractive index increment (dn/dc)_μ (i.e. measured after dialysis) for this system is 0.108₅ and 0.112 ml/g for λ₀ = 546 and 436 nm, respectively. The light scattering measurements yield correct molecular weights of the polymer. The measurements, however, require special care. Evaporation of THF and polymer aggregation in solvents with even slightly negative second virial coefficients are the major source of error.     

Viscosity-molecular weight relationships for low molecular weight polymers. II. Poly(vinyl acetate) and poly(methyl methacrylate)

[η]/M?_n relationships at 25°C. have been found for low molecular weight fractions of poly(vinyl acetate) (PV Ac) in chlorobenzene and poly(methyl methacrylate) (PMMA) in toluene. The PMMA used contains about 75% of syndiotactic form. Due to the difficulties of PMMA fractionation, the constants in the equation [η] = K M? refer to an average degree of polydispersity equal to M?_w/M?_n = 1.2. For both PVAc and PMMA there is a range of molecular weight where a = 0.5; in these ranges [η] is practically indistinguishable from [η]Θ.