Morphology and strength of elastic films of structured latices

Thermoplastic elastomers (TPEs) are conventionally made of block copolymers or partly cross-linked polymer blends. Alternatively, TPEs can be prepared from structured latices, too. Hard-soft latex particles with a thermoplast ic core and an elastomeric shell yield highly extendable elastic films, the strength of which depends sensitively on the relative core size and the pa rticle architecture. Core-shell particles were prepared, by two-step emulsi on polymerization, with the thermoplastic polystyrene (PS) in the core and the elastomer polyethylacrylate (PEA) in the shell. PEA particles were synt hesized first. The PS cores were then incorporated in them in the second st ep. This method permits the design of monocore, as well as multicore, parti cles. These PS-PEA particles were not cross-linked in the core or in the sh ell. They can be classified as microblends. Compression-molded films of the m exhibited, therefore, a coarsened microphase morphology that was, however , still much finer than that of simple melt-mixed blends PS/PEA. The film m orphologies of monocore and multicore particles were different as far as th e former yielded spherical PS domains, while the latter yielded extended PS clusters. This was strongly reflected by the stress-strain behavior: Films from multicore particles responded in a viscoelastic, rubbery manner, whil e films from monocore particles behaved like viscous Liquids.