Polymerization melt polycondensation

Synthetic Fiber and Plastics Industries. In the synthetic fibers and plastics industries, the substrate itself serves as the solvent, and the whitener is not appHed from solutions as in textiles. Table 6 Hsts the types of FWAs used in the synthetic fibers and plastic industries. In the case of synthetic fibers, such as polyamide and polyester produced by the melt-spinning process, FWAs can be added at the start or during the course of polymerization or polycondensation. However, FWAs can also be powdered onto the polymer chips prior to spinning. The above types of appHcation place severe thermal and chemical demands on FWAs. They must not interfere with the polymerization reaction and must remain stable under spinning conditions. 

We examined several approaches for synthesizing polyanhydrides, including melt polycondensation, dehydrochlorination, and dehydrative coupling. Extensive details of these new polymer synthesis techniques and numerous polymerization conditions for a wide variety of polyanhydrides were previously described (1). 

In an attempt to avoid the polymerization/depolymerization equilibrium that occurs during melt polycondensation, Albertsson and Lundmark (1988) also studied the irreversible reaction of adipic anhydride with ketene. However, they reported very little difference in molecular weights when two ketene syntheses were compared to melt polycondensation and ringopening polymerization using a zinc catalyst (Albertsson and Lundmark, 1988). 

Polyanhydrides based on unsaturated and fatty acid-derived monomers are shown in Table III. Poly(fumaric acid) (PFA) was fist synthesized by Domb et al. (1991) by both melt polycondensation and solution polymerization. The copolymer of fumaric acid and sebacic acid (P(FA-SA)) has been synthesized and characterized (Domb et al., 1991 Mathiowitz et al., 1990b). The mucoadhesive properties of this polymer... 

Stevenson [99] conducted the first polycondensation experiments with thin polymer melt films of 0.07-5 mm thickness. The experiments were performed on metal surfaces at temperatures between 265 and 285 °C under vacuum. He varied the kind of metal and observed that the behaviour of the polycondensation rate with decreasing film thickness depended on the metal being used. He concluded that the reaction rate increased only on metals soluble in the polymerizing melts... 

High-molecular-weight polyesters cannot be made by polymerization in the molten state alone - instead, post-polymerization (or polycondensation) is performed in the solid state as chips (usually under vacuum or inert gas) at temperatures somewhat less than the melting point. The solid-state polycondensation of polyesters is covered in detail in Chapters 4 and 5. 

In the manufacture of polyesters by melt polycondensation, the apparent polycondensation rate decreases with an increasing degree of polymerization, and the terminal carboxyls increase because of longer holdup time (3). Consequently, it is very difficult to obtain PET with an intrinsic viscosity above 0.9 and with carboxyls less than 15 eq/106 g polymer. 

The difference between these polymers and conventional Hytrel-type poly(ether-b-esters) is emphasized by the attempt to polymerize PPO 3000/50 by melt polycondensation, the method normally used for Hytrel (42). Complete phase separation occurred, showing that the incompatibility between PPO/3IGT is much greater than poly(oxytetramethyl-ene-b-oxytetramethylene oxyterephthaloyl). 

A4 the higher temperatures used in melt polycondensations it is necessary to remove the liberated hydrogen chloride by bubbling inert gas through the reaction medium. Side reactions are common, and this polymerization method is used only rarely. No major kinetic studies have been made. 

Polyamides. Many methods have been reported for laboratory synthesis of polyamides ( ). Commercial methods include melt polycondensation, ring opening of lactams, and low-temperature solution polymerization. 

Several approaches were examined for synthesizing polyanhydrides melt polycondensation, dehydrochlorination, and dehydrative coupling. A report of polyanhydride synthesis techniques and polymerization conditions for polyanhydrides appears in Leong et al. (22). 

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