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Lab 12 Report for MATSE 473Hyfrolysis of Polyvinyl Acetate/ Crosslinking of Polyvinyl alcoholName: Mengfang LiGroup D Lab Partners: Michael Lorenzo, Peter Mcclure04/24/2012
Introduction: The main purpose of this laboratory experiment is to perform the metallocene polymerization of styrene. The two type of catalyst are used to produce syndiotactic polystyrene (PS). The stereospecific preparation of polystyrene is demonstrated in this lab. The resulting polymer is characterized by differential scanning calorimetry (DSC) in order to compare with the amorphous PS prepared in free radical polymerization. Polystyrene is widely used as commercial polymer that constitutes 8% of world market. Styrene can be polymerized by all known mechanism. For example, free radical accounts for 99% of production of atactic polystyrene. The methods can be anionic cationic and coordination-insertion polymerization. First highly syndiotactic polystyrene (s-PS) was synthesized in 1985, using homogeneous titanium half-sandwich catalysts. Because of the syndiotactic configuration of polymer back-bone, sPS is able to give a semi-crystalline material that form well-structured spherulitic morphologies hwne crystalized . As a result, the polymer presents a high melting temperature (Tm=270C) while maintaining glass transition temperature Tg= 100 C. The unique combination of chemical and heat resistance with good electrical properties (low electric constant and loss) along with low density (1.05g/cm3) makes sPS attractive for automotive and electrical applications. The first system developed for sPS synthesis were MAO-activated half-metallocene of type Cp’MXn (Cp=substituted, X= halogen, alkoxy or alkyl, n=2,3). Titanium-based catalysts showed higher activities compared with zirconium. Figure 1. Syndiotactic styrene polymerization by titanium half-sandwich complexesThe stereocontrol mechanism of polymerization process can be explained using
Bernoullian statistical model. The polymer structure is long sequences of racemic diads