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.     

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.     

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.     

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.     

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.     

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).     

Microtacticity and hydrodynamic behaviour of poly(trityl methacrylate) prepared in hexamethylphosphoric triamide

Trityl methacrylate was polymerized with 2,2′-azodiisobutyronitrile at 60°C in a homogeneous hexamethylphosphoric triamide (HMPT) solution. The isotactic microstrucutre found by NMR spectroscopy was less important for this polymer than for poly(trityl methacrylate) prepared in benzene, a precipitating medium. Some aspects of the hydrodynamic behaviour of poly(trityl methacrylate) were examined in HMPT at 25°C. Relations between the intrinsic viscosity, the root-mean-square end-to-end dimension, and the weight average molecular weight were established. The unperturbed dimension 〈r 〉^1/2 was determined from viscosity and light scattering measurements using the well known extrapolation methods of Kurata-Stockmayer, Stockmayer-Fixman, Cowie, Inagaki-Kurata, and Baumann. Poly(trityl methacrylate) adopts a moderately expanded conformation in HMPT at 25°C. The correlation of the chain rigidity with the molar volume of the side group of polymethacrylic esters shows that poly(trityl methacrylate) has a higher chain rigidity than other polymethacrylates on account of the steric hindrance of the trityl group and of the strong interactions between the aromatic rings.     

The behaviour of poly(methacrylic acid) and poly(2-hydroxyethyl methacrylate) in water/2-chloroethanol mixtures

The viscosimetric behaviour and the preferential solvation of poly(methacrylic acid), (PMA, poly(1-carboxy-1-methylethylene)) and poly(2-hydroxyethyl methacrylate), (PHEMA, poly[1-(2-hydroxyethoxycarbonyl)-1-methylethylene]) in water/2-chloroethanol mixtures were studied. The system PHEMA/water/2-chloroethanol is a typical polymer/solvent/precipitant system in which 2-chloroethanol is preferentially solvated in the whole range of solubility. On the contrary, the system PMA/water/2-chloroethanol is a typical cosolvent system which exhibits the so-called inverse adsorption. This difference is attributed to the more hydrophilic character of the carbonyl group in PMA.     

Viscosity/temperature relationships for dilute solutions of poly(2,4,5-trichlorophenyl methacrylate)

The actual viscosity η of six fractions of poly(2,4,5-trichlorophenyl methacrylate) (PTCPh) with weight-average molecular weight M?_w, ranging from 9,11 · 10⁴ to 94,8 · 10⁴, was determined in benzene at a number of temperatures from 22 to 60°C. The variation of the pre-exponential term A and the apparent activation energy of viscous flow Q, with molecular weight and concentration was studied. Moore's equations are valid for PTCPh. The temperature coefficient of the unperturbed dimensions dln 〈r²₀〉/dT estimated from the intrinsic viscosity data by using the Burchard-Stockmayer-Fixman relation, is ?3 . 10^-3 (from 22 to 40°C) and ?0,87 . 10^-3 (from 40 to 60°C). These negative values indicate that extended configurations of PTCPh in benzene must be associated with lower energies.     

The effect of stereochemical structure on the viscoelastic behaviour of poly(ethyl methacrylate)

The low-frequency viscoelastic behaviour of three stereoregular samples of poly(ethyl methacrylate) (PEMA) in the main transition region was investigated. The main effect of tacticity in the transition from the syndiotactic sample to the isotactic one consists in a shift of the main transition region (or of the glass transition temperatures, T_g) to lower temperatures by ≈ 70 K. The temperature dependence of the shift factor of all samples could not be adequately described by the single Williams-Landel-Ferry (WLF) equation within the whole range of temperatures; in the range T>T_g+60K, isotactic PEMA exhibited the largest departures from the WLF equation. In all cases, departures from the WLF equation could be quantitatively described in terms of the temperature dependence of the Andreade coefficient β. The temperature dependence of the Andreade compliance, J_A, was also most pronounced for the isotactic sample. Vertical correction of the complex modulus G*, with WLF horizontal shifts preserved, led to the lowest activation energy ΔH for the isotactic sample, which means the highest magnitude of secondary relaxation mechanism in this sample. The birefringence measurement showed that the molecular nature of the deformational birefringence is independent of the tacticity of the sample and does not vary in the range T_g+25K<T<T_g+100K. In all the characteristics mentioned here, parameters of a conventional sample obtained by radical polymerization approached those of the syndiotactic sample.     

Preferential adsorption behaviour of poly(alkyl methacrylate)s in 1,4-dioxane/methanol

The preferential adsorption of dilute solutions of poly(methyl methacrylate) and some poly(alkyl methacrylate)s in 1,4-dioxane/methanol, at 298 K, was studied by laser light scattering. It was found that the inversion composition depends on the molar volume or the number of carbon atoms of the polymer side group. This result can be explained in terms of specific interactions between the carbonyl group of the esters and methanol.     

Heats of dilution of poly[styrene-ran-(butyl methacrylate)] solutions measured with an automatic flow microcalorimeter

In order to obtain information about the thermodynamic behaviour of copolymers in solution, we built an automatic flow microcalorimeter equipped with a computer that satisfies the requirements of accuracy, reliability, and rapidity for the measurement of heats of dilution of copolymer solutions. By using this apparatus, the heats of dilution of the random copolymer, poly[styrene-ran-(butyl methacrylate)] in ethyl methyl ketone solutions were measured at 298 K. Furthermore, light scattering of the copolymer and its constituent homopolymer solutions was measured at 298 K. From the combination of the heat of dilution and the light scattering results, thermodynamic and intramolecular interaction parameters of the copolymer chain were determined.     

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.     

Study on antithrombogenicity of poly[beta-(acetylsalicylyloxy)ethyl methacrylate] relative to poly(hydroxyethyl methacrylate)

The antithrombogenicity of a polymer made of aspirin bound to hydroxyethyl methacrylate (HEMA), abbreviated as ASA-polymer, was compared with that of poly(hydroxyethyl methacrylate) (PHEMA). Platelet from platelet rich plasma (PRP) incubated with ASA-polymer surface exhibited noticeable decreases in adhesion and aggregation as compared to platelets incubated with PHEMA. Low molecular weight components other than aspirin, which may be released from ASA-polymer during the incubation with PRP, or contact with ASA-polymer causing denaturation of platelets without morphological changes could be responsible for the decrease of adhesion and aggregation. Both PRP and PPP exposed to ASA-polymer-coated surfaces exhibited a much smaller partial thromboplastin time (PTT) than if exposed to PHEMA-coated surfaces; the PTT of ASA-polymer was similar to that of glass exposed plasma. With respect to the in vivo antithrombogenicity, the ASA-polymer surface led to thrombus formation. This may be due to the partial hydrolysis of the acetyl groups resulting in the formation of a negatively charged surface which in turn accelerates the coagulation cascade despite its inhibitory effects on platelet adhesion and aggregation. On the other hand, neointima formed around a thrombus layer on PHEMA-coated sutures after 14 days.     

Vapour-liquid equilibria and segment-molar excess gibbs free energies of concentrated poly(butyl methacrylate) solutions

Solvent activities were measured by an isopiestic sorption technique for solutions of poly(butyl methacrylate) and poly(tert-butyl methacrylate), respectively, in various solvents between 323 K and 373 K (or 403 K). The experimental data were reduced to segment-molar excess Gibbs free energies and to χ-functions. There is a clear difference in the thermodynamic behaviour of both polymers in their corresponding solutions due to the steric effect of the tert-butyl group. The chain-of-rotators equation-of-state model was used to calculate the thermodynamic quantities applying a group-contribution approach. In general, good agreement can be observed between experimental and calculated results.