First Step Prepolymerization

This prepolymerization could be performed via transesterification or direct esterification 

The catalyst amount represents 0.05-0.5 % of the total mass of the reaction medium. Antimony oxide historically emerged as the catalyst of choice. Germanium oxide is also used but although it is a more active catalyst than antimony, the high cost of the germanium excludes its common used in commercial production of PET. During the reaction, methanol is formed and is collected by distillation in order to displace the equilibrium of the reaction. 

When distillation of methanol ceases, the reaction is completed and bis-(2-hydroxyethyl) terephthalate is obtained (2,3). 

In this case, the reaction medium is heterogeneous because terephthalic acid is hard to dissolve in ethylene glycol. However, the use of small monomer feed ratio and high reaction temperature are useful to enhance the solubility. Water formed during the reaction was collected to estimate the reaction conversion. Addition of a catalyst is not necessary since the acid group of terephthalic acid self-catalyze the reaction. But, when concentration of acid groups decrease, metal catalysts could be employed to maintain the reaction rate (2). 

---

In the first step of the polymerization process, a prepolymer is prepared as a slurry in water. Excess diamine is added to control the degree of polymerization, eg, degree of polymerization = 6-14 (158). This prepolymerization step is conducted at approximately 200°C under autogenous pressure for less than 90 min. 

The partially aromatic PAs are exclusively made of die diamine-diacid type and not die amine-acid type. The aromatic diamines, similar to phenylene diamines, color easily and dieir polymers are conjugated, having a golden brown color. The aromatic diacids used in the formation of partially aromatic PAs are mainly terephthalic and isophthalic acids. Starting with the diacids, the PA salt is made first and with this the salt prepolymers are prepared. The prepolymerization is usually carried out in an autoclave to prevent die sublimation of the reactants. In a laboratory synthesis it would be preferable to avoid this autoclave step as one is not always available. It is possible to start with the more reactive esters, such as diphenyl isophtiialate, or with the acid chlorides starting with the reactive isocyanates is, in principle, also possible. The terephthalic and isophthalic acids are also used to modify PA-6,6 and PA-4,6 to more dimensionally stable copolymers.6,18... 

Description Catalyst components are mixed and fed directly to prepolymerization (1) with a light inert hydrocarbon, where a first bulk polymerization occurs under mild controlled conditions. This step exploits the catalyst system potential in terms of morphology, mileage and complete reliability in the following gas-phase reaction sections. 

Graft Copolymers. In graft copolymerization, a preformed polymer with residual double bonds or active hydrogens is either dispersed or dissolved in the monomer in the absence or presence of a solvent. On this backbone, the monomer is grafted in free-radical reaction. Impact polystyrene is made commercially in three steps first, solid polybutadiene rubber is cut and dispersed as small particles in styrene monomer. Secondly, bulk prepolymerization and thirdly, completion of the polymerization in either bulk or aqueous suspension is made. During the prepolymerization step, styrene starts to polymerize by itself forming droplets of polystyrene with phase separation. When equal phase volumes are attained, phase inversion occurs. The droplets of polystyrene become the continuous phase in which the rubber particles are dispersed. R. L. Kruse has determined the solubility parameter for the phase equilibrium. 

---