Synthesis, elastomer emulsion polymerization

Castor oil has found application in the synthesis of interpenetrating polymer networks (IPNs). These materials can be defined as a combination of two polymer networks, at least one of which is synthesized and/or cross-linked in the immediate presence of the other. They are called semi-lPN if just one of the polymers is a network (Athawale et al, 2003). Early reports on castor oil IPNs appeared in 1977 by Yenwo and co-workers. The report discussed the synthesis possibilities via cross-linking of double bonds with sulfur, reaction of hydroxyl groups with diisocyanates, and emulsion polymerizations with saponified ricinoleic acids as emulsifier. Moreover, the IPNs from acrylic polymers, such as polymethyl methacrylate and poly-2-ethoxyethyl methacrylate, and castor oil-based polyurethanes were reported to contribute to the final properties of the material (Cunha et al., 2004 Sanmathi et al, 2004). Incorporation of acrylic moieties into the PU networks increased toughness and thermal properties. In contrast, IPN polyesters derived from castor oil and dibasic acids (e.g. malonic, succinic, glutaric, adipic, suberic, and sebacic acid) were obtained as soft and opaque elastomers (Suthar et al, 2003). 

In the 1960s, anionic polymerized solutron SBR (SSBR) began to challenge emulsion SBR in the automotive tire market. Organolithium compounds allow control of the butadiene microstructure, not possible with ESBR. Because this type of chain polymerization takes place without a termination step, an easy synthesis of block polymers is available, whereby glassy (polystyrene) and rubbery (polybutadicnc) segments can be combined in the same molecule. These thermoplastic elastomers (TPE) have found use ill nontire applications. 

As pointed out by Hajji et al. [32], polymer blend nanocomposite systems can be prepared by various synthesis routes because of their ability to combine in different ways to introduce each phase. The organic component can be introduced as (1) a precursor, which can be a monomer or an oligomer (2) a preformed linear polymer (in molten, solution, or emulsion states) or (3) a polymer network, physically (eg, semicrystalline linear polymer) or chemically (eg, thermosets, elastomers) cross-linked. The mineral part can be introduced as (1) a precursor (eg, tetraethyl orthosilicate) or (2) preformed nanoparticles. Organic or inorganic polymerization generally becomes necessary if at least one of the starting moieties is a precursor. 

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