Syndiotactic polystyrene crystalization rate

Small amounts of iso tactic polystyrene have been synthesized in the laboratory using noncommercial polymerization techniques. These polymers are capable of partially crystallizing, albeit at a very slow rate. Syndiotactic polystyrene was available commercially for several years, but its continued production proved unprofitable. 

Syndiotactic polystyrene is a new polymeric material150 152 of industrial relevance since it shows a high melting point (270°C) and high crystallization rates.153 Syndiotactic polystyrene is a highly stereoregular polymer which can be obtained by using several soluble titanium and, to a less extent, zirconium compounds. 

Syndiotactic polystyrene (sPS) represents an important achievement in olefin polymerization catalysis. Syndiotactic PS is an industrially relevant thermoplastic material produced by Dow Chemical and Idemitsu Kosan Co. under the tradenames Questra and Xarec , respectively. Industrial interest on sPS originates from the remarkable properties exhibited by this highly crystalline polymer. The high melting temperature, 270 °C, the relatively fast crystallization rate (at least much faster than that of iPS), the high heat resistance, the low dielectric constant, the high elastic modulus, and an excellent resistance to chemicals explain the industrial interest for this material. Syndiotactic PS was considered as an innovative new resin option for the automotive, electrical, and electronic markets, appliances such as... 

Above the the rate of polymer chain relaxation is faster than the diffusion of CO2, and hence Fickian diffusion is to be expected. The diffusion of CO2 is believed to occur within the amorphous domains of the polymer matrix, and for this reason the diffusion in semi-crystalline polymers may be more complex than it in the case for glassy polymers. In the case of semi-crystalline polymers, CO2 is not soluble in the crystalline domains, and therefore the degree of crys-taUinity and hence the amorphous fraction available for CO2 molecules may influence the diffusion characteristics. Furthermore, C02-induced crystallization is likely to lead to an increase in the tortuosity factor, and thus the diffusion path length may increase as a function of time. Syndiotactic polystyrene and poly(4-methyl-l-pentene) [45] are semi-crystalline polymers which have crystalline phases (helical in the case of sPS) with lower densities than that of the amorphous phase and are exceptions, as CO2 access is not restricted to the amorphous domains, in fact CO2 diffuses faster in the helical sPS than in the amorphous polymer [46]. 

Ishihara et al. reported in 1986 that syndiotactic polystyrene can be prepared with the aid of organic or inorganic titanium compounds activated with methylaluminoxane [177]. There is much greater incentive to commercialize syndiotactic polystyrene than the isotactic one. This is because isotactic polystyrene crystallizes at a slow rate. That makes it impractical for many industrial applications. Syndiotactic polystyrene, on the other hand, crystallizes at a fast rate, has a melting point of 275°C, compared to 240°C for the isotactic one, and is suitable for use as a strong structural material. 

Syndiotactic polystyrene (sPS) is a relatively new material discovery in semicrystalline pol5nners with a high melting point and rapid crystallization rate, which makes it possible to injection mold the material. The stereospecific polymerization was made possible by the combination of a transition metal catalyst with weakly coordinating cocatalysts, such as methylaluminoxane. The excellent balance of mechanical, electrical, solvent resistance, and dimensional stability properties combined with a relatively low price (based on styrene monomer) have made this material a competitor to existing engineering plastics. The products also have excellent heat performance and are finding application in antomotive (under the hood), electrical, and electronic connector systems. 

Although they have high stereoregularity in the polymer backbone, isotactic polystyrene and syndi-otactic polystyrene are still not perfect from a material applications point of view. The rather slow crystallization rate of iPS prevents its commercial application whereas the high syndiotacticity of... 

Polystyrene (PS) now on the market is atactic PS (APS), but there is a problem of low heat resistance. Isotactic PS (IPS) is also known, but there is a problem of low crystallization rate. A homogeneous Ti/metal-locene and MAO system is an effective catalyst for syndiotactic polystyrene (SPS). Advantages of SPS are heat resistance 7 110°C) and chemical resistance like engineering plastics, which are derived from its high crystallinity compared with APS produced by radical polymerization. Furthermore, the crystallization rate of SPS is faster than that of APS or IPS. 

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