Siegfried Bantle

Studies of cyclic and linear poly(dimethyl siloxanes): 9. Quasi-elastic light scattering and concentration dependences of diffusion coefficients

Abstract The concentration dependences of the diffusion coefficients (D) of linear and cyclic poly(dimethyl siloxanes) (PDMS) in toluene at 298K are reported. Three cyclic/linear pairs of fractions with molar masses in the range 300 to 23 500 g mol−1 were used. The values of D obtained by quasielastic scattering were in good agreement with those measured by the classical boundary-spreading technique. Analysis of the concentration dependences in terms of the theory of Pyun and Fixman indicates that the solute molecules show a minimum of interpenetration in toluene at 298K.

Monte Carlo calculations in comparison to neutron scattering studies: 3. On the structure of 12-arm star molecules

Abstract The small-angle neutron scattering curves of polystyrene 12-arm star molecules exhibit deviations from the Gaussian star model according to Benoit. These deviations are comparable with those observed in the scattering curves of simulated polymethylene 12-arm star chains. They can be partially interpreted in terms of chain stiffness within the arms. If the simulated chains contain a specific star centre, their scattering curves, normalized by the radius of gyration, are in good agreement with the normalized experimental scattering curves. For very short arms the scattering curves of the simulated chains with a specific star centre approach the particle scattering factor of the rod-like star model.

Branching in epoxy resins: molecular weight as a function of the extent of reaction and critical behaviour

Abstract Series of linear and branched epoxy resins have been investigated. Molecular weights in the range Mw = 1500 to 30 000 have been determined by means of static and dynamic light scattering. The dependence of Mw and Mn on the extent of reaction are presented. The polydispersity M w M n shows a clear difference between the two series. Extrapolation to infinite Mw yields the gel point with the critical extent of reaction. A kinetic model of the reaction is tested with the experimental values of the extent of reaction. Branching can be described with a branching parameter that links the extents of reaction of the functional groups. The experimental results are compared with results from the cascade branching theory where good agreement is found. The exponent in the critical plot is found to support the classical treatment rather than the percolation theory.

Small-angle neutron scattering from branched epoxide resins

Abstract Small-angle neutron scattering experiments in the range of q2 from 0.01 to 25 nm−2 have been carried out on branched epoxide resins based on bisphenol-A at the Institute Laue—Langevin (I.L.L) in Grenoble ( q=( 4π λ ) sin ( θ 2 ) ). Measurements were made with six samples in the range of MW from 1500 to 19 000 and four concentrations between 1.3 and 10% (w/w) in deuterated diglyme. The results are as follows: (i) The mean square radius of gyration follows a relationship 〈S2〉z=4.69×10−4M1.20W (nm2). (ii) In all cases fairly large second virial coefficients A2 are obtained which, however, decrease strongly with molecular weight. Above MW=2500, the virial coefficient follows the relationship A2=1.6M−0.85W (mol cm3g−2). (ii) The reciprocal particle scattering factor as a function of q2 exhibits only a slight upturn and otherwise shows the behaviour of a randomly branched polycondensate. The slight upturn is discussed as being caused by the finite volume of the monomeric unit. Possible reasons for the high exponent in the 〈S2〉zversusMW dependence are briefly discussed.

Monte Carlo calculations in comparison to neutron scattering studies: 1. Linear chains

Abstract The structures of linear polystyrene chains as well as of generated rotational isomeric state backbone chains are discussed in the light of the worm-like chain model. The global dimensions of these linear chains are represented satisfactorily by the theory of Kratky and Porod, if the system is under ϑ conditions. The particle scattering factors of backbone chains, consisting of point scatterers, can be described well by the theory of Koyama up to a certain q range. In the crossover region of coiled to rod-like behaviour, significant deviations occur. The particle scattering factors of polystyrene chains are approximated well by the theory of Koyama in the low q range. The range of validity in q is enlarged by introducing an effective chain thickness correction. During the change of solvent from cyclohexane to toluene, the structure of polystyrene chains is modified by two independent effects (i) enhanced long-range interactions due to the excluded volume; (ii) a change in short-range interactions, which modifies the chain stiffness of polystyrene. The second effect may be explained by specific interactions between the benzene rings of styrene and toluene.

Monte Carlo calculations in comparison to neutron scattering studies: 2. Global dimensions of 12-arm stars

Abstract Light and neutron scattering studies were carried out on 12-arm star polystyrene molecules in toluene (a good solvent) and in cyclohexane (a ϑ-solvent). The polymers had a molecular weight range of 5 × 10 4 M w 6 . The global dimensions of all samples under ϑ conditions are larger than those predicted by the existing theories. Monte Carlo simulations of 12-arm star chains as a function of chain length were performed using Florys rotational isomeric state model. Two different types of star chains, a pure combinatorial star and a star with a specific centre were used. These aided the interpretation of the experimental results.