Syndiotactic polystyrene crystal form

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... 

Stacking faults in syndiotactic polystyrene (s-PS) P-form crystals [3, 29-34]... 

The mutual repulsion between substituents may cause some displacement. As a result, the plane of symmetry is bent in the form of a helix. This occurs also in biopolymers (double-helix of deoxyribonucleic acid (DNA)). Different stereoisomers have different mechanical and thermal properties. For example, atactic polystyrene is an amorphous polymer whereas syndiotactic polystyrene is a crystalline substance. The chemical design of macromolecules determines their properties as extent of crystallization, melting point, softening (glass transition temperature), and chain flexibility which in turn strongly influence mechanical properties of the materials. 

Syndiotactic polystyrene (s-PS) can be crystallized into two polymorphs [26], forms I and II. The alUtrans, planar zigzag conformation is adopted by the chains in form I crystals, while in form II crystals the s-PS chains adopt the same 4i-helical,.., ttggttgg... conformation found for the prevalent form of crystalline s-PP. Notice the CH2 carbon resonances [26] in form II... 

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

De Rosa C (1996) Crystal Stmcture of the Trigonal Modification (a Form) of Syndiotactic Polystyrene. Macromolecules 29 8460-8465... 

Depending on the ciystallization conditions, sPS chains can ciystalUze into at least four ciystalline modifications (a, p, y, and 8 forms). The mechanical strength of sPS samples depends on the crystalline modification and the degree of ciystalUnity. Graphene nanosheets acted as P-nucleating agent for syndiotactic polystyrene. Carbon nanotubes increase peak crystallization temperature by 14°C. ... 

Finally, a few comments about the uniqueness of polymer crystal structures and phase space localization are warranted. Almost all crystallizable polymers exhibit polymorphism, the ability to form different crystal structures as a result of changes in thermodynamic conditions (e.g., temperature or pressure) or process history (e.g., crystallization conditions) [12]. Two or more polymorphs of a given polymer result when their crystal structures are nearly iso-energetic, such that small changes in thermodynamic conditions or kinetic factors cause one or another, or both, to form. Polymorphism may arise as a result of competitive conformations of the chain, as in the case of syndiotactic polystyrene, or as a result of competitive packing modes of molecules with similar conformations, as in the case of isotactic polypropylene. In some instances, the conformational change may be quite subtle isotactic polybutene, for example, exhibits... 

Not aU polymers can crystallize. Polyethylene does, but atactic polystyrene (the common form) does not. Though the speciahzed syndiotactic and the more common isotactic forms do, albeit into completely different crystal forms (de Rosa and Auriemma 2013). Isotactic polypropylene and many nylons commonly crystallize into more than one crystal type, and polyethylene terephthalate (PET), a polyester, is commonly found in a glassy form in soft drinks bottles but crystallizes readily on appropriate thermal treatment. 

As an example, syndiotactic polystyrene (s-PS) [76] can be crystallized in two conformationally distinct polymorphs, form I, with all-trans, planar zig-zag chains, and form II, where the chains adopt the helical... ttggttgg... conformation, very similar to that observed [77] in syndiotactic polypropylene (s-PP) crystals. CPMAS/DD NMR spectra of both s-PS polymorphs are shown in... 

Thermal and spectral properties of annealed cast syndiotactic polystyrene (SPS) films were investigated. The sample annealed at lower temperature e bited an ordered conformation but a lack of crystal regularity. This result indicated the presence of a mesophase. CO2 sorption properties of these films were also examined and dual-mode sorption parameters were obtained. In particular, the hole saturation constant for Langmuir sorption (Ch ) reflected the fine structure of the annealed SPS and exhibited a different annealing time dependence when annealed at different tenq)eratures. From these results, we propose that the samples annealed at lower temperature contain many nanovoids, which form as a result of solvent desorption. 

Syndiotactic polystyrene can crystallize in many crystal forms as well nonequilibrium structures depending on the thermo-mechanical processing conditions... 

Chatani, Y, Shunane, Y, Ijitsn, T., Yukinari, T. Structnral stndy on syndiotactic polystyrene 3. Crystal stmctnre of planar form I. Polymer, 34(8), 1625-1629 (1993). 

Vittoria, V, Ruvolo Filho, A., De Candia, F. Structural organization of syndiotactic polystyrene films crystallized in the P form. J. Macrom. Sci. Phys., 31(2), 133-148 (1992). 

De Rosa, C., Rapacciuolo, M., Gnerra, G., Petraccone, V., Corradini, P. On the crystal structure of the orthorhombic form of syndiotactic polystyrene. Polymer,... 

De Rosa, C, Rizzo, P, de Ballesteros, O. R., Petraccone, V, Guerra, G. Crystal structure of the clathrate delta form of syndiotactic polystyrene containing 1,2-dichloroethane. Polymer, 40, 2103-2107 (1999). 

Tarallo, O., Petraccone, V. On the crystal structure of the clathrate forms of syndiotactic polystyrene containing carbon disulfide and iodine. Macromol. Chem. Phys., 205(10), 1351-1360 (2004). 

Tosaka, M., Tsnji, M., Kohjiya, S., Cartier, L., Lotz, B. Crystallization of syndiotactic polystyrene in P-form. 4. Crystal stmctnre of melt-grown modification. Macromolecules, 32(15), 4905-4911 (1999). 

Hamada, N., Tosaka, M., Tsnji, M., Kohjiya, S., Katayama, K. Crystallization of syndiotactic polystyrene in P-form. 2. Qnantification of stacking faults in the solution-grown single crystals. Macromolecules, 30(22), 6888-6892 (1997). Napolitano, R., Pirozzi, B. Models of adjacent re-entry folds in the beta form of syndiotactic polystyrene. Conformational and packing analysis by molecular mechanics. Macromol. Theor Simul., 11(5), 472-480 (2002). 

Wang, C., Chen, C-C., Hung, C-H., Lin, K-S. Lamellar morphologies and crystal stability of syndiotactic polystyrene in a-crystalline form. Polymer, 45,6681-6689 (2004). 

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