Syndiotactic polystyrene structure

Since the last edition several new materials have been aimounced. Many of these are based on metallocene catalyst technology. Besides the more obvious materials such as metallocene-catalysed polyethylene and polypropylene these also include syndiotactic polystyrenes, ethylene-styrene copolymers and cycloolefin polymers. Developments also continue with condensation polymers with several new polyester-type materials of interest for bottle-blowing and/or degradable plastics. New phenolic-type resins have also been announced. As with previous editions I have tried to explain the properties of these new materials in terms of their structure and morphology involving the principles laid down in the earlier chapters. 

De Rosa, C. Guerra, G. Petraccone, V. Pirozzi, B., Crystal structure of emptied clathrate form (8e form) of syndiotactic polystyrene, Macromolecules 1997, 30, 4147 4152... 

Draw the structures of isotactic poly(acrylonitrile) and syndiotactic polystyrene. 

Metallocenes are very versatile catalysts for the production of polyolefins, polystyrene and copolymers. Some polymers such as syndiotaetic polypropene, syndiotactic polystyrene, cycloolefin copolymers, optically active oligomers, and polymethylenecycloalkenes can be produced only by metallocene catalysts. It is possible to tailor the microstructure of polymers by changing the ligand structure of the metallocene. The effect and influence of the ligands can more and more be predicted and understood by molecular modeling and other calculations. 

Titanium compounds with MAO or borate as co-catalysts effectively produce syndiotactic polystyrene from styrene monomer. The design of high-performance catalyst systems is now well demonstrated. The basic structure of the active site, the mechanism of coordination and insertion and the kinetics are also now well understood for this new polymerization. 

Syndiotactic polystyrene is produced by well stereo-controlled coordination polymerization by titanium compounds. The polymer has a high percentage of mr pentad structure. The 13C NMR chemical shift for the phenyl-1 carbon and backbone methylene carbon are approximately 145.3 and 44.9 ppm, respectively [1]. In general, these polymers are found to be >99% pure in syndiotactic structure as defined by NMR. The most stereoselective catalysts produce a >99.6% pure syndiotactic structure (Figure 18.2)... 

Polystyrene (PS), CAS 9003-53-6, is typically found in atactic and amorphous form. Isotactic and syndiotactic polystyrenes can be synthesized, but they are not used in practice since there are few advantages in properties compared to the atactic form. The reticulation of the carbon chains in polystyrene is frequently done using in the polymerization process a certain proportion of 1,4-divinyibenzene or less often of 1,3-divinylbenzene. The resulting polymer in the case of crosslinking with 1,4-divinylbenzene has the idealized structure shown below ... 

Kobayashi, M. Yoshioka, T Imai, M. Iton, Y. Structural ordering on physical gelation of syndiotactic polystyrene dispersed in chloroform studied by time-resolved measurements of small angle neutron scattering (SANS) and infrared spectroscopy. Mactvmolecules, 1995,28(22), 7376-7385. 

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. 

Whereas most of the early work on crystallization, etc., were concerned with predominantly isotactic chains, the recent developments in synthetic methodologies have enabled the preparation of highly syndiotactic polymers [13,14]. Since the high stereoregularity of these syndiotactic polymers facilitates their crystallization, several papers have been published on the x-ray crystal structure and polymorphism of syndiotactic polystyrene [15-18]. The chain conformation in the crystalline state has also been analyzed using NMR [19]. Similarly, the crystal structure of syndiotactic polypropylene has also been studied by a number of authors [20-22]. 

Thus, also in this case an increase in the quantity and quaUty of the available experimental data can help to remove ambiguity and aid to understand the polymer solidification in more detail. Interesting examples of the complex morphology that can be achieved in a transformation process come from the structural analysis of injection molded samples in Syndiotactic Polystyrene [22-25]. 

Kobayashi M, Nakaoki T, Ishihara N (1989) Polymorphic Structures and Molecular Vibrations of Syndiotactic Polystyrene. Macromolecules 22 4377-4382... 

De Rosa C, Guerra G, Petraccone V, Corradini P (1991) Crystal Structure of the a-Form of Syndiotactic Polystyrene. Polymer Journal 23 1435-1442... 

Cartier L, Okihara T, Lotz B (1998) The a Superstmcture of Syndiotactic Polystyrene A Fmstrated Structure. Macromolecules 31 3303-3310. 

Mahesh K P O, Sivakumar M, Yamamoto Y, Tsujita Y, Yoshimizu FI, Okamoto S (2004) Structure and properties of the mesophase of syndiotactic polyst3n-ene. Vin. Solvent sorption behavior of syndiotactic polystyrene/p-chlorotoluene mesophase membranes. J. Polym. Sci. Part B Polym. Phys. 42 3439-3446... 

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