Three series of poly(imide siloxane) (PIS) copolymers were synthesized through straightforward simultaneous condensation reaction of pyromellitic dianhydride (PMDA), 2, 2 0 -bis [4-(3-aminophenoxy)phenyl] sulfone (m-BAPS) and three different number-average molecular weights (M n ¼ 859, 1152 and 1619 gÁmol À1 ) of , !-bis (3-aminopropyl) polydimethyl siloxane (APPS). The effects of hard segment, polyimide (PI), on the properties of PIS copolymers were investigated. The prepared PIS copolymers possess the properties of thermal plastic elastomers. Microphase separation, affected by formulation, was found to be important phenomenon that determined the physical properties of the PIS copolymer. Mechanical measurement with the Instron-type tensile meter showed that the copolymers have elongation at break of up to 324%. Two prepared samples (APPS M n ¼ 859, PI content of 15 and 20 wt %) were found to exhibit good rubber property of being able to retract to original length upon release of the stress applied, others were characterized as plastics. The softening temperatures of the PIS thermoplastic elastomers ranged from 109 to 265 C, and can easily be processed by extrusion or injection molding, and recycled.KEY WORDS: Polysiloxane / Poly(imide siloxane)(PIS) / Copolymer / Thermoplastic Elastomer (TPE) / Microphase Separation / In the field of rubber industry, thermoplastic elastomer (TPE) is a group of polymeric materials that exhibit elastomeric behavior at their service temperature and can be reprocessed by melting at elevated temperatures.1,2 Hence TPE is considered a recyclable material. Diminishing supply of materials and energy from nature has become increasingly severe. The urgency in the demand for recyclable and energy efficient materials has become increasingly high through the years. When comparing to conventional vulcanized rubber, TPE not only exhibits elasticity, but also provides energy saving processibility which is similar to injection moldable plastics. TPE can be recycled by simple melt mixing and extrusion and/or injection, and the process can be fully automated.Polysiloxane rubbers have polymeric Si-O-Si backbone, which renders the material distinctive properties, such as good electric property, thermal stability, anti-oxidative property, durability at low temperatures, as well as ozone, weathering and radiation resistance.3 Although polysiloxane rubber has wide applications in the electronic, tubing and baby care industries, especially in the manufacturing of keyboards, the TPE of polysiloxane system has not yet been widely commercialized.Mostly, the manufacture of polysiloxane rubber adopts one of the following processes. The first process is the widely used high temperature vulcanized process (HTV), in which the polysiloxane gum of high molecular weights were mixed and vulcanized with peroxide, reinforce filler and other additives prior to hot compress molding. The second was the twocomponent room temperature vulcanized process (RTV-2), in which a separately pre-measured amount of highly reactive...