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Many attempts to upgrade polystyrene have been made in the past. One of the last and most popular examples is the upgrading of polystyrene by stereo-controlled polymerization of styrene monomer, yielding a syndiotactic material. But the property profile of polystyrene can also be improved by stiffening the polymer chain with bulky groups. 1,1-Diphenylethylene (DPE) was selected as a monomer with such a bulky group and was copolymerized anionically with styrene to give an amorphous copolymer with a statistical chain structure which was called 'super-polystyrene'. In this paper the conditions of the anionic polymerization and the properties of the resulting materials are described. Depending on the DPE content, the glass transition temperature can be varied from 104 • C to 180 • C. Up to a DPE content of 15%, these styrene-DPE copolymers are miscible with GPPS as well as with syndiotactic polystyrene. Toughening of the transparent polymers was achieved with glass fibers and grafted rubber particles. Block copolymerization with minor amounts of butadiene yielded a tough and transparent polymer. Thermoplastic elastomers with an enhanced softening point having the block sequence S /DPE-b-Bu-b-S /DPE and S /DPE-b-EB-b-S /DPE were also prepared.

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Anionic block copolymerization of isoprene and 1,3-cyclohexadiene (1,3-CHD) was carried out in the presence of a dilithium initiator derived from 1,3-diisopropenylbenzene. A special seeding technique, namely multistep seeding with isoprene, was developed to promote the efficiency of the dilithium initiator. Triblock, PCHD-PI-PCHD, pentablock, PCHD-PS-PI-PS-PCHD, and heptablock copolymers, PCHD-PI-PS-PI-PS-PI-PCHD, were synthesized using multistep seeded dilithium initiators. Phase separation and mechanical properties of the resulting block copolymers were investigated by DSC, TEM, and tensile strength test.

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Styrenic polymers and copolymers are often impact modified with rubber particles. The efficiency of rubber toughening depends mainly on the size of the rubber particles and the degree of cross‐linking. The deformation rate, the temperature, the orientation of the polymer molecules and the efficiency of rubber grafting also influence rubber toughening. It is thought that on impact, cavitation inside the rubber particles occurs which reduces the detrimental dilatational stress in the bulk polymer without forming cracks in the brittle matrix or at the rubber‐matrix interface. Crazing and shearing are facilitated if the rubber particles can easily cavitate. This can be achieved by either avoiding too much cross‐linking or by adding oil (silicone oil in the case of ABS) into the rubber particles, which acts as nuclei for void formation. An electron spectroscopic imaging method is described which allows visualizing the location of the oil. Already after cooling silicone oil modified ABS samples down to liquid nitrogen temperature rubber cavitation is observed. This cavitation is caused by the thermal stress developing due to the differences in thermal expansion coefficient between the rubber phase and the SAN‐matrix and is facilitated by silicone oil. Voiding also leads to an increase of light scattering, which can be detected by an optical microscope using dark field illumination.

The efficiency of rubber toughening of PSAN depends on the size of the rubber particles, their agglomeration, the deformation rate, the temperature, and the orientation of the polymer molecules. Large particles are more effective than small particles. By a suitable choice of processing, however, small particles can agglomerate, forming large soft units and improving in this way impact toughness. At high deformation rates crazing or/and stretching of the matrix wall between the rubber particles must be activated for ductility, otherwise the material is brittle. The temperature at impact must be above the glass transition temperature of the rubbery phase for toughening. Increasing the orientation of the material decreases the tendency for craze formation with the consequence of embrittlement, if stretching is not activated.