Rubber interpenetrating networks

Another area of recent interest is covulcanization in block copolymers, thermoplastic rubbers, and elasto-plastic blends by developing an interpenetrating network (IPN). A classical example for IPN formation is in polyurethane elastomer blended acrylic copolymers [7]. 

Blends of elastomers are routinely used to improve processability of unvulcanized rubbers and mechanical properties of vulcanizates like automobile tires. Thus, cis-1,4-polybutdiene improves the wear resistance of natural rubber or SBR tire treads. Such blends consist of micron-sized domains. Blending is facilitated if the elastomers have similar solubility parameters and viscosities. If the vulcanizing formulation cures all components at about the same rate the cross-linked networks will be interpenetrated. Many phenolic-based adhesives are blends with other polymers. The phenolic resins grow in molecular weight and cross-link, and may react with the other polymers if these have the appropriate functionalities. As a result, the cured adhesive is likely to contain interpenetrating networks. 

Much work has been reported on studying the structure of thermoset resins via SAXS, especially focussing on interpenetrating network polymers (IPNs), thermoset nanocomposites, rubber-modified thermosets and thermoset-thermoplastic blends. Most recently Guo et al, (2003) have examined the use of SAXS to monitor the nanostructure and crystalline phase structure of epoxy-poly(ethylene-ethylene oxide) thermoset-thermoplastic blends. This work proposes novel controlled crystallization due to nanoscale confinements. 

In the last years of the history shown in Table II we see the announcements of new commercial thermoplastic rubbers. Uniroyal TPR appeared in 1971. (This thermoplastic rubber many not be a block polymer. Presumably it is a blend that achieves its properties by virtue of interpenetrating networks between the plastic and rubber constituents. The exact structure has not been disclosed.) Du Pont s Hytrel, an (A-B) polyetherpolyester thermoplastic rubber, came out in 1972. Also in 1972, Shell announced a second generation block polymer, Kraton-G, which is a three-block S-EB-S thermoplastic rubber (EB represents an ethylene-butylene rubbery midblock). 

In those years, Edison had switched from the cylinder-type phonograph records to the platter type. The latter ones were made of the new phenol-formaldehyde material, just invented by Leo Baekeland. The problem with the new material was that it was extremely biitfle, hence the new platters needed to be very thick. Aylsworth s solution to the problem was to mix in natural rubber and sulfur, which on heating forms a network. Since the phenol-formaldehyde compositions are all densely crosslinked, the overall composition was a simultaneous interpenetrating network. 

This chapter on applications of PAB s focuses on polymer systems giving synergistic and generally high performance properties. Low performance PAB s of commodity plastics, rubber toughened plastics, copolymers, and interpenetrating networks are excluded. Some of the more common PAB s are described elsewhere in this book. 

A commercial grade of high-impact (notched Izod > 900 J/m) POM resin (Delrin 100 ST, DuPont) is believed to be a blend of POM with >30 wt% of a thermoplastic poly(ester-urethane) elastomer derived from poly(l, 4-butane adipate) diol and methylene-bis-(4,4 -diphenyl diisocyanate) (MDl) (Hexman 1989). This blend is reported to have a cocontinuous or semi-interpenetrating network of the elastomer in a matrix of the polyacetal (Flexman et al. 1990). The toughening effect in such a blend of IPN-type morphology was interpreted to occur partly through a rubber band mechanism by which the fracture energy is absorbed. The bands of rubbery domains were believed to span the crack and participate in the deformation process. 

Reinforcing resins or novolacs form an interpenetrating network and can interact with other polymers. Hexamethylenetetramine-resorcinol systems do not start to react until temperatures exceed 120 °C. At vulcanization temperatures of 160 °C they can significantly increase the stiffness of rubber compounds though in dynamic service conditions such as in a tire tread compound the stiffness imparted by such novolac resins may be degraded. 

G. P. Belonovskaya, J. D. Chernova, L. A. Korotneva, L. S. Andriarova, L. S. Andriarova, B. A. Dolgoplosk, S. K. Zakharov, Yu. N. Sazanov, K. K. Kalninsh, L. M. Kaljuzhnaya, and M. F. Lebedeva, Interpenetrating Polymer Networks Based on Diisocyanates and Polar Monomers, Eur. Polym. J. 12(11), 817-823 (1976). Rubber, synthetic poly(propylene sulfide)-poly(tolylene diisocyanate) compatible interpenetrating networks. Polyisocyanate network, tensile, strength. 

N. Devia, J. A. Manson, L. H. Sperling, and A. Conde, Simultaneous Interpenetrating Networks Based on Castor Oil Elastomers and Polystyrene. 2. Synthesis and Systems Characteristics, Macromolecules 12(3), 360 (1979). Synthesis and Processing of castor oil-polyester/PS SINs. Rubber-toughened plastics and reinforced elastomers. 

D. Klempner, H. K. Yoon, K. C. Frisch, and H. L. Frisch, Polyurethane-Polyacrylate Pseudo-Interpenetrating Networks Chemical Properties of Crosslinked Polymers, in Chemistry and Properties of Crosslinked Polymers, S. S. Labana, ed.. Academic, New York (1977). SINs of urethane rubbers. Morphological and mechanical properties. Glass temperature, transitions and polymer morphology of urethane rubber/acrylic copolymer SINs. 

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