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.     

Pressure dependence of viscometric relaxation times measured with a new apparatus. Williams-Landel-Ferry behaviour of moderately concentrated solutions of poly(butyl methacrylate)s in 2-propanol

A new rotational viscometer is presented which can be operated up to 2 000 bar and a maximum shear stress of 420 Pa. It allows, for the first time, to investigate the non-Newtonian flow behaviour of moderately concentrated polymer solutions. Results of measurements with two representatives of the system 2-propanol/poly(butyl methacrylate) with weight-average molecular weights M?_w = 520 000 and M?_w = 2 050 000, and ratios of weight- to number-average molecular weights M?_w/M?_n = 1,08 and M?_w/M?_w = 1,23, resp. in the region of moderate polymer concentrations are reported. For a ca. 7 wt.-% solution of the higher-molecular-weight polymer one obtains viscometric relaxation times τ₀ varying from 1 to 100 ms in the region from 1 to 2 000 bar and from 40 to 75°C; at the lower temperature the application of p can raise τ₀ by one order of magnitude. The steady-state shear compliance (proportional to τ₀/η₀, where η₀ is the zero-shear viscosity), is independent of pressure of varies only slightly. For the present system, which gels thermoreversibly upon cooling, η₀ and τ₀ as a function of temperature and pressure can be well represented by the Williams-Landel-Ferry equation.     

Vapour-liquid equilibria of concentrated poly(styrene-co-butadiene) and poly(styrene-co-acrylonitrile) solutions

Isopiestic vapor sorption measurements were carried out for concentrated solutions of poly(styrene-co-butadiene) (SBR) and poly(styrene-co-acrylonitrile) (SAN) in a number of aromatic solvents in the temperature range of 343 to 398 K. Henry constants were determined by means of inverse gas-liquid chromatography in the temperature range of 373 K (SBR) or 423 K (SAN) to 473 K, to obtain additional data at infinite dilution for the solvents, and for two of the monomers, styrene and 1,3-butadiene, in SBR. The chain-of-rotators (COR) equation of state model was used to calculate the thermodynamic quantities applying a group-contribution approach. In general, good agreement is observed between experimental and calculated results.     

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.     

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(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.     

Controlled biological response on blends of a phosphorylcholine-based copolymer with poly(butyl methacrylate)

Phosphorylcholine (PC)-based polymers have been used in a variety of medical device applications to improve biocompatibility. Here, solutions containing poly(butyl methacrylate) (PBMA) and 2-methacryloyloxyethyl phosphorylcholine-co-lauryl methacrylate (MPC-co-LMA(2)) copolymer were spin-coated onto glass coverslips at various ratios ranging from 5:1 to 1:0 for each of the two components, respectively. The resulting blend coatings were shown to be phase-separated on the nanometre-scale by atomic force microscopy, the PC copolymer within the blend being preferentially expressed at the surface. The adsorption of two key blood proteins, fibrinogen and albumin were investigated using surface plasmon resonance as an indicator of biocompatibility. The adsorption of protein to a biomaterials' surface can then stimulate further biological responses. This study therefore, also investigates the materials ability to elicit an inflammatory response by studying the adhesion of human mononuclear cells to the material surface. The materials ability to support the adhesion and growth of other tissue cells was also evaluated, looking specifically at the adhesion and proliferation of rabbit corneal epithelial cells. Results suggest that the adsorption of proteins and the adhesion of both corneal epithelial cells and mononuclear cells are dependent on the composition of the PBMA:MPC-co-LMA(2) copolymer.     

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.     

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.     

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).     

Factors influencing the creep behavior of poly(methyl methacrylate) cements.

Room temperature compression creep and recovery tests have been performed using samples of pure poly(methyl methacrylate) (PMMA), three commercially available poly(methyl methacrylate) cements, and several experimental cements. From these tests the influence of density, mixing procedure, particle size, methyl methacrylate-styrene copolymer, barium sulfate, aquenous storage environments, residual monomer, molecular weight of the continuous phase, benzoyl peroxide, and N,N-dimethyl-paratoluidine, upon the creep behavior of PMMA cements has been determined. The important results is that lowering the porosity or residual monomer content, increasing the powder size, or adding an MMA-styrene copolymer tends to increase the creep resistance of PMMA cement.     

Solution properties of poly(octadecyl methacrylate) in butyl acetate, 2. Semidilute solution

Semidilute solutions of a fraction of poly(octadecyl methacrylate) (PODMA) obtained by radical-initiated polymerization were investigated in the theta-solvent butyl acetate (BuAc) with static and dynamic light scattering (SLS, DLS, resp.) at four different temperatures between 13°C (near theta-temperature Θ) and 70°C. The molar mass of the investigated sample (PODMA 4) was 3,2 · 10⁶ g · mol^?1. A concentration region from dilute to 8 c^* was covered, where c^* = 1/[η] was taken as the coil overlap concentration, [η] denoting intrinsic viscosity. Above c = 3c^* the DLS correlation function exhibited bimodal behaviour at all temperatures. At these concentrations one finds two “apparent” molar masses, radii of gyration and diffusion coefficients for each concentration. The smaller apparent molar masses, smaller radii of gyration and larger diffusion coefficients correspond to characteristics of the transient network. The larger apparent molar masses, larger radii of gyration and smaller diffusion coefficients may be attributed to the formation of inhomogeneities in the semidilute solution.     

Solution properties of poly(octadecyl methacrylate) in butyl acetate, 1. Dilute Solution

Dilute solutions of poly(octadecyl methacrylate) (PODMA) obtained by radical-initiated polymerization were inverstigated in the theta-solvent butyl acetate (BuAc) by static (SLS) and dynamic light scattering (DLS) and viscometry at six different temperatures between 11°C (near the theta-temperature Θ) and 30°C. The mass-average molar masses ranged from M?_w = 6,2 · 10⁵ g · mol^?1 to 3,2 · 10⁶ g · mol^?1. It was found that PODMA in BuAc behaves in general as expected for linear flexible Gaussian coils in a theta-solvent. The Kuhn length was determined to be 35 Å. At temperatures slightly above Θ = 10,5°C the exponents of the intrinsic viscosity, radius of gyration and hydrodynamic radius versus molar mass relationships lie significantly below 0,5, the expected value for flexible linear chains at theta-conditions. Qualitatively, these findings are explained by a coil contraction due to the different chemical nature of the main chain and the side chains and therefore different polymer-solvent interactions of different parts of the molecules.     

Phase separation by synthesis of semi-interpenetrating network on the basis of polystyrene and poly(butyl methacrylate) from homogeneous solution

Phase separation by semi-interpenetrating polymeric network formation based on the copolymer styrene-divinylbenzene (PS-DVB) and poly(butyl methacrylate) (PBMA) was investigated by light scattering. The time for phase separation was measured as a function of the rate of the copolymerization reaction and of the composition of the initial blend. The time until the outset of phase separation decreases with increasing content of PBMA in the blend. The change in concentration of DVB does not influence the process of phase separation.     

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.     

Phase behaviour and solvent diffusion in the system poly(methyl methacrylate)/methanol

The diffusion of methanol into atactic poly(methyl methacrylate) is controlled by the interference of the demixing curve with the concentration dependence of the glass transition. Below the temperature of intersection of the two curves, the sample is always in the glassy state and diffusion is of case II. Above this temperature, absorption of methanol brings the sample through the glassy state into the solution state. With increasing temperature, diffusion changes from case II into Fickian. The maximum degree of absorption is determined by the position of the demixing curve in the temperature‐concentration plane.     

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.