Jean Herz

Effect of crosslinking density on the orientational order generated in strained networks: A deuterium magnetic resonance study

Abstract The orientational order generated in uniaxially strained rubbers is investigated as a function of crosslinking density. This study was carried out on two sets of rubbers; on randomly crosslinked diene networks and on model end-linked silicone rubbers. The degree of orientational order was measured by means of the deuterium n.m.r. technique; the experiments were carried out either on dissolved deuterobenzene as an n.m.r. probe (dienes) or directly on labelled polymeric chains (silicones). The induced order increases with the crosslinking density as predicted by the kinetic description of rubber elasticity. Data are related to the thermodynamics of the networks rather than to their chemical mesh size which does not accurately describe the topological structure of interest. For both sets of samples, the degree of order varies linearly with the corresponding volume fraction of polymer at swelling equilibrium.

Synthesis and characterization of multiblock copolymers containing poly(dimethyl siloxane) blocks

Abstract Multiblock copolymers of polystyrene and poly(dimethyl siloxane) were obtained by a hydrosilylation reaction between a,w dihydrogeno poly(dimethyl siloxane) and a,w -di(vinyl silane) polystyrene. Under well chosen experimental conditions the polycondensation is free of site reactions and the macromolecules formed are linear with up to 10 blocks, which corresponds to reaction of 90% of the functions initially present. The block copolymers obtained have been characterized by g.p.c. viscosimetry and light scattering.

Unidirectional compression measurements on swollen polydimethylsiloxane networks

Abstract Polydimethylsiloxane model-networks were prepared by the endlinking reaction of α, ω-functional polydimethylsiloxane precursor polymers with 3, 4 and 6 functional compounds. The elastic behaviour of these networks, swollen at equilibrium in toluene, has been studied by unidirectional compression measurements. The influence of the structural characteristics of the networks (average length of the elastic chains and functionality of the crosslinkages) on the elastic modulus has been determined. The experimental results indicate that the way in which the elastic chains are connected depends on the functionality of the crosslinkages. For low functionalities, the network chains mainly connect crosslinkages which are nearest neighbours, whereas for higher functionalities more distant branch-points may also be connected by the elastic chains.

New crosslinking processes

Synthesis of model-networks characterized by the quasi-constant length of the linear chain elements between two successive branch points has been carried out by anionic block copolymerization of two monomers, one being bifunctional. The influence of various parameters (concentration, temperature, number of molecules of bifunctional monomer added per active chain end) on the behaviour of the gels is discussed. This method can be applied to several systems.Another method was successfully used to synthesize networks: reaction of α, ω-difunctional linear polymer chains with tri- or tetrafunctional molecules, in stoichiometric amount was shown to lead to gels in which both the length of the linear chain elements and the functionality of the branch points are controlled. Reactions of terminal carbon metal bonds with electrophilic groupings of various kinds were used, as well as reaction of silane end groups with allylic double bonds. The gels obtained were characterized by their swelling behaviour, in relation to the molecular weight of the chain elements and the functionality of the branch points.

Experimental evidence for an isotropic distribution of cross-linkages in polystyrene model-networks

Abstract Polystyrene model-networks containing ferrocene labelled cross-linkages have been synthesized by anionic block copolymerization. A study by low-angle X-ray diffraction confirms the isotropic distribution of cross-linkages and the isotropic deformation of the network on swelling.

Hydrophilic non-ionic polymer networks. Synthesis and application to size exclusion chromatography in aqueous media

Abstract Polystyrene networks with elastic chains of known length and containing pendant poly(ethylene oxide) chains selectively attached to the crosslinks were obtained by anionic block-copolymerization. Such networks can exhibit a residual swelling-degree in water that allows easy access to the network-pores. One network with known characteristics was used as a column filling in S.E.C. with water as eluent. Even under high driving pressures, the mechanical strength of this material appears to be satisfactory. In the present example, the domain of selectivity extends from approx. 100–5000.

Investigations on metallation and grafting of styrene-vinylnaphthalene copolymers

Abstract Random copolymers of styrene and vinylnaphthalene, prepared in solution, have been metallated in THF with Na, K and Cs. It has been shown that in this case no chain scission occurred during the metallation process. The metallated sites are able to initiate polymerization of cyclic monomers; graft copolymers with polyethylene oxide graftings have thus been obtained.

Etude de la reaction du carbanion styryle avec le dibromo-1,3 dibromethyl-2,2 propane

Resume Des quatre atomes de brome contenus dans le dibromo-1,3 dibromomethyl-2,2 propane (DDP), trois seulement entrent en reaction avec le carbanion polystyryle. On observe la formation de produits couples de masse moleculaire double de celle du polymere initial et de composes non couples contenant du brome. Ces resultats sont independants de la nature du solvant et du cation. La reaction du DDP sur les potassio-1 phenyl-1 ethane, modele micromoleculaire du carbanion polystyryle, confirme ces observations.

Specific volume of polystyrene networks

Abstract We have described a method for the measurement of the specific volume of polymer networks at different degrees of swelling. We have observed a very small difference between the apparent specific volume of polystyrene in the swollen gel state and in solution in the same solvent and at the same polymer concentration. This indicates a small variation in the chain expansion with the degree of swelling. Moreover, our precise measurements of the swelling parameters confirm the interdispersion phenomenon as the main process for the swelling in a ‘theta’ solvent.