Polycondensation, melt phase polyester

Key words In situ infrared spectroscopy, stable free radical polymerization, free radical alternating polymerization, living anionic polymerization, melt phase polyester polycondensation... 

Polycondensation of highly viscous polyesters in the melt phase is limited. The removal of the volatile by-products becomes more difficult due to diffusion inhibited by the increased viscosity of higher-IV polyesters. In addition, undesirable side reactions due to thermal degradation impede the growth of the molecular chains. As a consequence, the reaction rate decreases and decomposition reactions dominate, thus resulting in a decrease in the melt viscosity [2], As it is able to address these limitations, SSP has become the method of choice and is therefore so popular. 

More recently Dieterich and Reiff (166) have described the formation of aqueous urethane dispersions by the dispersion of ionomer melts with subsequent polycondensation in two-phase systems. The principle of this procedure consists of reacting molten ionic modified polyester or polyether prepolymers containing NCO groups with urea to yield bis(biuret), followed by methylolation by means of aqueous formaldehyde in a homogeneous phase, and the resulting plasticized melt of methylolated ionic urethane bis(biurets) dispersed in water at 50-130 °C. These steps can be represented schematically as follows ... 

Solution polycondensation is used in industry to produce polyurethanes, polycarbonates and certain types of polyamides and polyesters. Polycondensation in solution is most frequently used when it is difficult or impossible to keep the reactants in the same phase using bulk polymerization, or when the melting point of the resulting polymer is too high. Solution polycondensation takes place at lower temperatures than melt polymerization and enables efficient heat transfer to be maintained due to lower viscosity. However, solution polycondensation requires polymer separation from solution, recovery of solvent, and polymer washing and drying. 

Preparation of Amorphous PETGs and PCTGs. In general, amorphous PETG and PCTG polyesters can be made by standard melt-phase polycondensation processes, starting either with DMT or TPA. One significant difference... 

The most widely known aromatic homopolyester made of 1,4-CHDM is doubtless poly(l,4-cyclohexylenedimethylene tereph-thalate) (PCT) (Figure 6.5). This polyester, which was firstly developed in 1959 by Tennesee Eastman Co. for its utilization in the fiber industry with the trade name of Kodel, is nowdays produced by two-step melt phase polycondensation from DMT and 1,4-CHDM. When high molecular weight PCT is desired, the... 

This melt phase polycondensation method was also applied for the synthesis of a good number of aliphatic (24,27,28,32) and aromatic (11,46,47,50,55) polyesters and copolyesters derived from 1,4-CHDM. Depending on the polyester to be prepared, small variations in temperature or/and reaction time are introduced, and the catalyst is specifically chosen. The target is in most of cases to minimize undesirable side reactions giving rise to coloration of the final product. 

Ring opening polymerization (ROP) of cyclic oligoesters is an emerging method of polymerization that has some advantages compared to melt phase polycondensation (71). In this method, the polyester is prepared from low-viscosity precursors by an entropi-cally driven process that evolves without releasing of volatiles and emission of heat. 

The next development in liquid crystal polyesters was the preparation by polycondensation based on terephthalic acid (TPA) and hydroquinone (HQ) or p-hydroxybenzoic acid (HBA). The polyesters are insoluble with very high melting temperatures of 600 °C for poly (TPA/HQ) and 610 °C for poly (HBA), which are by far too high to obtain stable liquid crystalline phases for melt processing. In 1972, Economy and coworkers patented several copolyester compositions, and one of these are the copolymerization of poly (4-hydroxybenzoic acid) (PHB) with 4,4 -dihydroxybiphenyl (BP) and terephthalic acid (TPA) due to the need for lower melting, melt-processable polymers. Considerable synthetic efforts have been attempted in order to decrease the melting temperatures of aromatic LC polyesters while retaining LC properties. The copolyester structure was tailored by partial substitution of TPA with isophthalic acid to produce a melt-spinnable material. 

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