Adhésifs nanostruturés en voie émulsion

Nous avons étudié les propriétés d adhésifs préparés à partir de particules de latex nanostructurées. Une méthodologie basée sur deux critères rhéologiques a été proposée pour optimiser les performances adhésives. Elle nous a permis d identifier des stratégies applicables dans le cas particulier de PSA préparés à partir de particules de latex ayant une morphologie cœur-écorce. Une stratégie intéressante est l activation d une réaction de réticulation interparticule pendant le séchage du latex. Nous avons montré l effet remarquable de cette réaction de réticulation sur les propriétés en grandes déformations. Ces propriétés sont assez bien décrites par un modèle non-linéaire combinant le modèle de Maxwell sur convecté et le modèle de Gent. Les meilleurs résultats d adhésion sont obtenus pour des PSA préparés à partir de particules de latex ayant une fine écorce réticulée et un cœur mou et caractérisés par un net ramollissement à déformations intermédiaires suivi d un rhéodurcissement. Dans un registre plus industriel, des performances adhésives prometteuses ont été obtenues avec des PSA préparés à partir de latex tackifiés in situ synthétisés par polymérisation en miniémulsion.PARIS-BIUSJ-Thèses (751052125) / SudocPARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF

Allyl-Terminated Polypropylene Macromonomers: A Route to Polyolefin Elastomers with Excellent Elastic Behavior

We report the design, synthesis, and physical/mechanical properties of graft copolymers containing semicrystalline polypropylene side chains and amorphous ethylene/α-olefin copolymer backbones. These materials, a new class of semicrystalline, polyolefin-based thermoplastic elastomers, are made in two steps. First, allyl-terminated syndiotactic or isotactic polypropylene macromonomers are synthesized with controlled microstructure and molecular weight using bis­(phenoxyimine)­titanium or chiral <i>ansa</i>-zirconocene catalysts, respectively. Second, a pyridyl-amido hafnium catalyst is used to copolymerize the macromonomer, ethylene, and an α-olefin with precise control of composition and side chain incorporation. With highly crystalline polypropylene side chains and amorphous backbones of low glass-transition temperatures (<−55 °C), the samples have strain-to-break values up to 1400% and elastic recovery above 85% at maximum strains up to 1000%. The synthetic method described herein does not require the use of a living polymerization catalyst; in addition, the mechanical properties of these graft copolymers exceed those of the best linear block polyolefins

Tough and Elastic Thermoplastic Organogels and Elastomers Made of Semicrystalline Polyolefin-Based Block Copolymers

Development of stereo- and regioselective living alkene polymerization catalysts has led to the capability to produce multiblock copolymers with semicrystalline syndiotactic polypropylene blocks and poly­(ethylene-<i>co</i>-propylene) rubbery blocks that have excellent elastomeric properties, both undiluted and as gels with as little as 8 wt % copolymer in mineral oil. During step cycle mechanical processing, the crystals can plastically deform and partially transform from lamellae into rod-like fibrils, which align along the tensile direction, giving rise to very large tangent moduli at large strains. The dimensions of these aligned fibrils can be established from small-angle X-ray scattering and used to construct models of the large strain elasticity, as well as its evolution with plastic strain, based on short fiber composite theory. Wide angle X-ray scattering experiments as well as FTIR measurements suggest that the oriented fibrils have the transplanar (form III) crystal structure. The large toughness of the dilute gels can be attributed to the plastic deformation of the crystalline component, which not only evens out the forces on the rubbery chains running from crystal to crystal but also provides a mechanical hysteresis that is effective in absorbing energy at the tip of a growing crack