J. Pleštil

Dilute and semidilute solutions of ABA block copolymer in solvents selective for A or B blocks: 2. Light scattering and sedimentation study

Abstract Micellar solutions of a triblock copolymer polystyrene- block -poly(hydrogenated butadiene)- block -polystyrene, in heptane and in 1,4- dioxane 25 vol % heptane have been studied by light scattering and sedimentation velocity methods. In dilute solutions, micellar molar mass, hydrodynamic radius of micelles, average volume fraction of polymer segments in a micellar core and in the whole micelle, and the unimer/micelles ratio have been determined. While in semidilute mixed solvent solutions only one diffusion mode, corresponding to collective diffusion, has been determined, at least two modes, diffusion and relaxation ones, have been observed in spectra of decay times in semidilute heptane solutions. Micellar models have been proposed for both systems under study, accommodating satisfactorily all experimental results.

Network structure of bimodal epoxies—a small angle X-ray scattering study

Small angle X-ray scattering measurements were performed on epoxies to determine their network structure. To provide the necessary scattering contrast the epoxy monomer used was a partially brominated diglycidyl ether of bisphenol A and the cross-linking agents were linear, low polydispersity, amine terminated poly(propylene oxide)s. Samples with both single and bimodal molecular weight distributions of cross-linking agent were prepared. A pronounced scattering maximum was observed in all networks and it can be interpreted in terms of correlation holes. Networks cured with a mixture of two cross-linking agents with different molecular weights, i.e. bimodal networks, exhibited scattering maxima at significantly lower scattering vector (q) than was observed for any single amine networks. In model bimodal epoxy graft copolymers with nearly identical chemical structure as the networks the shift to low q was barely perceptible. Experimental results from both epoxies and model graft copolymers are compared to a model calculation in order to establish a methodology to reduce molecular structure information from X-ray results.

Dilute and semidilute solutions of ABA block copolymer in solvents selective for A or B blocks: 1. Small-angle X-ray scattering study

Abstract Solutions of a triblock copolymer, polystyrene- block -poly(hydrogenated butadiene)- block -polystyrene, in a selective solvent either for the aliphatic middle block (heptane) or for the polystyrene outer blocks (1,4-dioxane/25 vol% heptane) were studied by viscometry and small-angle X-ray scattering. In both systems, micelles were detected with uniform spherical cores formed by insoluble copolymer blocks. In semidilute solutions, in concentration regions above 0.01 g cm −3 in heptane and ∼0.1 g cm −3 in the mixed solvent, micelles were found to be space-correlated, the effect being accompanied by a steep increase in zero-shear viscosity. Aliphatic micellar cores in the mixed solvent are highly swollen due to the effect of selective sorption.

Equilibrium and non-equilibrium copolymer micelles : polystyrene-block-poly(ethylene-co-propylene) in decane and in diisopropylether

Abstract When selective solvents are used for the dissolution of block copolymers, their solid-state structure may be partly preserved in solution. At room temperature, polystyrene- block -poly(ethylene- co -propylene) dissolves in decane, a selective solvent for the aliphatic block, to form a solution of metastable micellar structures with polystyrene core. These convert to stable micelles at elevated temperature; the molar mass of the micelles is reduced several times after the heat treatment. The change of the structure is explained by the existence of a frozen state of the micellar core at room temperature. A possible connection with the glass transition of the core is discussed. Static and dynamic light scattering, small-angle X-ray scattering, differential scanning calorimetry and viscometry have been used to characterize equilibrium and non-equilibrium micelles. A pronounced mutual interaction of micelles has been observed by light scattering even at a concentration as low as 5 × 10 −4 g cm −3 . The concept of sticky chains is introduced to explain the association of the micellar shells. The behaviour of micelles in another selective solvent, diisopropylether, is simpler, both effects observed in decane being absent.

Small-angle scattering from polyelectrolyte solutions. A novel method for studying counterion condensation

Abstract A new method is proposed for the study of binding of a low-molar-mass compound to a polymer chain, based on the calculation of the excess scattering amplitude from small-angle scattering data. The procedure requires the measurement of the scattering curve on an absolute scale at two polymer concentrations. Both smeared and desmeared scattering data may be used. The method is applied to aqueous solutions of poly(methacrylic acid) neutralized with NaOH. The number of Na + counterions bound to the polyion has been determined as a function of the degree of neutralization.

Investigation of the structure of isotactic polypropylene—thermoplastic elastomer blends by means of X-ray scattering

Abstract Blends of semicrystalline isotactic polypropylene (iPP) with two types of elastomer, butadiene/styrene (BS) and hydrogenated isoprene/styrene (HIS), block copolymers were investigated by means of wide-angle and small-angle X-ray scattering. Except for the sample with a low concentration of BS (5 wt%), where the copolymer macromolecules are probably dispersed in the amorphous phase of iPP, the blends can be described as two-component systems (copolymer-iPP), in which the crystalline phase of iPP is only slightly influenced by the copolymer. X-ray results in the structural investigation of the blends correlate well with the mechanical properties of the blends.

Molecular-weight determination from small-angle scattering without absolute intensities: advantages and limitations

Surprisingly, molecular weight can be determined from small-angle scattering data without using absolute intensities and the contrast factor. The formula underlying this novel procedure is illustrated by model calculations. Several examples of the successful use of the procedure applied to polymer solutions together with those where the method has failed are given.

Small-angle neutron scattering and differential scanning calorimetry study of associative behaviour of branched poly(ethylene oxide)/poly(propylene oxide) copolymer in aqueous solution

Tetronic RED 9040, a reverse-type [poly(propylene oxide) as terminal blocks] octablock star copolymer with four poly(ethylene oxide)/poly(propylene oxide) arms attached to the ethylenediamine core was studied in D 2 O at concentrations between 1 and 60 g dL -1 in the temperature range from 283 to 353 K. Depending on concentration and temperature, various structures (unimers, random network, micelles, micellar aggregates, micellar networks) were indicated by small-angle neutron scattering (SANS). Some structure characteristics of unimers, micelles and micellar networks have been determined by fitting model scattering functions to the SANS data. A competition between the increasing association number and dehydration of the micelles is suggested as a possible explanation of the observed non-monotonic temperature dependence of the structure parameters of concentrated systems. A partial phase diagram was suggested on the basis of SANS and differential scanning calorimetry (DSC) data and visual inspection of the solutions.

Small-angle scattering by polyelectrolyte solutions: Intermolecular correlation function of poly(methacrylic acid) in salt-free semidilute solutions

Abstract Intermolecular correlations in salt-free solutions of poly(methacrylic acid) neutralized by NaOD were investigated as a function of the degree of neutralization, α. At α = 0, the relative concentration of monomer units belonging to foreign macromolecules at a distance r from a reference monomer unit, g(r) = N(r) N , is nearly equal to unity in the r range investigated. Already at α = 0.01, however, the values of g ( r ) are significantly smaller than unity near the origin. With increasing r , g ( r ) monotonically increases and reaches unity at r = 120–150 A . No oscillations indicating an ordered structure are observed. The shape of g ( r ) curves is in agreement with the correlation hole concept. The non-monotonic dependence of the radius of the correlation hole on α is explained by the overlap of macroions at higher degrees of neutralization.

Small-angle scattering by polyelectrolyte solutions: Interpretation of molecular weight dependence of the scattering peak position

Abstract The variation in small-angle scattering curves of aqueous solutions of sodium poly(styrene sulphonate) with molecular weight is, in contrast to the original paper by Ise et al., interpereted as the result of differences in the single-chain scattering factors. Structural models of polyelectrolyte solutions are briefly discussed.