SiO2 Reinforcement and Morphology of a Novel Poly(imide-siloxane)-Based Thermal Plastic Elastomer Composite

Abstract

Silica (SiO 2 ) was used for the reinforcement of the poly(imide-siloxane) (PIS)-based thermal plastic elastomer. Trimethylsilyl modified SiO 2 was incorporated in the copolymer matrix to obtain the PIS/SiO 2 composties. In preparing the PIS/SiO 2 composite, the modified MeOH/THF solvent system provided a homogeneous reaction environment by offering good solubilities for the reactants and the intermediates while facilitating the dispersion of SiO 2 . The trimethylsilyl group modified fume silica offered excellent interfacial compatibility and kept the microphase separation at desirable level. SEM studies showed that such surface modification improved the dispersion of SiO 2 in the copolymer matrix. Morphological and thermal studies revealed the likelihood of a spatial rearrangement of the long chain alternating pyromellitic dianhydride/ polydimethyl siloxane (PMDA/PDMS) soft segments leading to a macroscopically homogeneous composite. Such spatial rearrangement further stabilized the microphase separation which is necessary for exhibiting TPE characteristics. The obtained composites have better thermal and mechanical properties than bare PIS copolymer. An elongation at break of 989% was obtained for the PIS/SiO 2 composite at silica content of 3 wt %.KEY WORDS: PIS Copolymer / Composite / Thermal Plastic Elastomer / SiO 2 Reinforcement / Morphology / Thermoplastic elastomers (TPE) are a group of materials that possess elasticity. The elasticity of a TPE is comparable to that of covalent bond crosslinked rubbers, and its meltability allows for repeated processing from melt in a way analogous to common plastics (e.g., by extrusion or injection molding). The chemical constituent of a TPE is generally a tri-block (or multiblock) copolymer, which usually provides a soft segment in the center and the hard segments in the bi-terminal portions of the coplymer. Typical examples are SBS (styrene-butadienestyrene block copolymer), SEBS (styrene-ethylene-butadienestyrene block copolymer) and TPU (thermoplastic polyurethane).1,2 In the development of new types of TPE, the chemical ingredients of the soft and hard segment as well as their spatial arrangement are important design variables for the success of their potential applications.The hard segment is one of the key components of TPE, which provides the physical crosslink points by strong intermolecular attraction when used at working temperature, but such intermolecular attraction can be reversibly dislodged by melting at high temperature. To function as the hard segment, the component polymer (or inorganic physical crosslinkers) should be easily solidified or crystallized, and at the same time, being limitedly compatible with the soft segment to maintain, at desirable level, the necessary microphase separation during copolymerization with the soft segments. Polyimides (PI) is a group of polymers and some members of PI possess such property, and have been identified as a good choice for the hard segment of TPEs. 3,4 Kricheldorf et al.3 synthesized poly(ether-ester-imides...

Influence of crystalline polyimide hard block on the properties of poly(imide siloxane) copolymers

“…Ghosh et al indicated the polysiloxane grafted PIS had much higher T g of the polyimide hard block than PIS with the polysiloxane moiety in the main chain [22]. SiO 2 and TiO 2 were also used for the reinforcement of PISs, and the obtained composites had higher thermal stability than bare PISs [23,24]. In addition, crosslinking could increase the thermal stability of PISs at high temperature [25,26].…”