Gérard Beinert

Core-shell latex particles containing a fluorinated polymer in the shell.I. Film formation studied by fluorescence nonradiative energy transfer

The core-shell morphology of polyacrylate latex particles containing a fluoropolymer in the shell was characterized via the fluorescent nonradiative energy transfer (NRET) technique. This technique enables one to follow the extent of mixing of fluorescently labeled latex particles during film formation. The comparison between the film formation behavior of fully labeled core-shell particles and partially labeled (no probe in the shell) core-shell particles showed evidence of the core-shell morphology of our particles.

Synthesis and characterization of monofunctional polydimethylsiloxanes with a narrow molecular weight distribution

Polydimethylsiloxanes (PDMSs) with a narrow molecular weight distribution and fitted at one chain end with a hydrogenodimethylsilyl or a dimethylvinylsilyl function were prepared by the anionic ring-opening reaction of hexamethylcyclotrisiloxane in a 50 vol % benzene-tetrahydrofuran solution, followed by endcapping with chlorodimethylsilane or chlorodimethylvinylsilane. The experimental conditions were chosen on the basis of preliminary experiments in order to minimize the contribution of reshuffling reactions and it was checked that the possible formation of difunctional species was negligible. The functionalization was quantitative. The functional polymers were characterized by i.r. spectroscopy and by s.e.c. α-Hydrogenodimethylsilyl and α-dimethylvinylsilyl PDMS were prepared in the molecular mass range between 2500 and 40000 g mol−1.

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.

Contribution to a better knowledge of the crosslinking reaction of polydimethylsiloxane (PDMS) by end-linking : the formation of star-branched PDMS by the hydrosilylation reaction

Monofunctional polydimethylsiloxanes with a dimethylsilyl or a dimethylsilylvinyl end-group were reacted with respectively 1,3,5,7-tetramethyltetravinylcyclotetrasiloxane and 1,3,5,7-tetramethylcycloterasiloxane. The hydrosilylation reaction, carried out in bulk and in the toluene solution, were followed by FTi.r. spectrometry and the star-branched samples formed analysed by SEC-LS. In the second case, for PDMS silylvinylic function at the chain-end, the reaction is noticeably faster and the final conversions reached are higher than in the first case. The principal parameter which limits the maximum conversion is the concentration of functional groups in the medium.

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.

Radical polymerization of styrene initiated by benzopinacolates: kinetics and comments concerning the reaction mechanism

Abstract The present paper reports an investigation on the “pseudo-living” radical chain propagation process in the case of the styrene polymerization initiated by benzopinacolates. Two steps were observed, as in earlier reported investigations. Oligomers were formed first at low monomer conversions, due to the rapid chain-termination by the primary radicals present at a high concentration. Polymerization takes place only after consumption of the major part of these radicals. Experiments carried out on model molecules representative of the oligomer chain-ends yielded evidence that these species are unactive, they do not undergo further thermal cleavage. The in the literature reported insertion process was not confirmed for the styrene polymerization.

About “defects” in networks made by end-linking

Abstract We studied polydimethylsiloxane networks prepared by end-linking in the bulk. Neutron scattering and scanning light-scattering experiments indicate that the networks swollen with a “good solvent” exhibit rather strong spatial fluctuations of polymer concentration, which are nearly frozen-in. We attribute this effect to the presence of “defects” in the network structure, which is consistent with the results of high frequency rheology measurements, performed on dry networks. The spectrum of static fluctuations appears to be more sensitive to a change in the length of the precusor chains than to the proportion of dangling chains. We propose to explain this result by describing some of the network non-uniformities as fluctuations in the size of the shortest closed circuits along the network.

Synthesis of poly(ethylene oxide) macroinitiators with a view to the preparation of block copolymers by radical polymerization

Abstract Poly(ethylene oxide) radical macroinitiators with built-in benzopinacolate groups were prepared by two different methods: the first one involves a hydrosilylation reaction between α, ω-difunctional polylethylene oxide (PEO) precursors and a difunctional benzopinacolate; due to the presence of a spacer group on the benzopinacolate compound the resulting segmented PEO is rather close to a block-copolymer. The second method is based on the general duplication reaction of benzophenone groups fitted at both chain ends of a PEO precursor.

Radical polymerization of styrene initiated by poly(ethylene oxide) macroinitiators

Abstract Segmented poly(ethylene oxide) macroinitiators containing bistrialkylbenzopinacolate groups were used to initiate radical polymerization of styrene. A polystyrene-PEO block copolymer is formed by the incorporation of the PEO macroinitiator. The PEO fraction in the copolymer decreases with increasing polymerization yields. Since the molecular weight of the macroinitiator is low, the incorporated PEO fraction is necessarily small in high molecular weight copolymers.

Crosslinking of OH-functional polystyrenes through urethane bridges : kinetics of the three-dimensional addition reaction between hydroxyethyl functions and isocyanate groups of crosslinker

Abstract We have reported in a previous paper the synthesis and features of two kinds of functional polystyrene precursors that lead through a gelation process to a three-dimensional network. This paper deals with an experimental kinetic study of the addition reaction between hydroxyl functions belonging to the polymer and isocyanate functions of the crosslinker. The reaction follows a simple second-order kinetics until an extent of reaction of 75%. The gel point is reached at the extent of 85%. Below the gel point a characteristic time τ is introduced for each reaction. It is found that all the gelling systems used in our studies exhibit the same rate constant.