Prepolymerization syrup

The network polymer obtained on complete conversion contains ester, ether, and carbon-chain linkages. The bulk polymerization proceeds in two steps, so that the actual casting of the final product starts with a prepolymerized syrup much as in the methyl methacrylate sheet process (see Section 5.2). The hard, abrasion-resistant, transparent character of the polymer, most popularly known as CR-39 (PPG Industries, Pittsburgh, PA), makes it suitable for optical applications such as cast lenses for eyeglasses [1]. 

Suspension Polymerization. Suspension polymerization probably remains the most widely practiced method of producing PS. It can also be used to produce HIPS. To improve quality of the latter, however, a batch-mass prepolymerization of the rubber syrup is normally carried out first the syrup is then suspension polymerized to completion. 

Many proprietary methods have been developed for casting and shaping DADQ especially for lenses. In one method DADC containing 3.5% diisopropyl percarbonate is prepolymerized by warming to a syrup of viscosity 40—60 mm /s (=cSt) (15). Polymerization is continued in a lens for 18 h at 90°C followed by annealing at 120°C. 

Example 10.2 Purified styrene monomer is charged along with initiators into an aluminum prepolymerization vessel. Polymerization is carried out at about 90°C to 30% conversion. The resulting syrup is then poured into molds where the reaction is completed. Comment on the probable molecular weight distribution of the product polymer. 

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