Postcondensation, solid state

For very high melting polymers (Tm > 300°C), a solution polymerization is normally employed. If this is started from the reactive acid chloride, the reaction temperature can be low. Polymers from acid chlorides can also be prepared by the interfacial method. Semicrystalline PA can be postcondensed in the solid state to higher molecular weights. To do this, the polymer powder/particles are heated for many hours below their melting temperature in an inert atmosphere. 

The precondensation can be earned out continuously with the use of a tubular reactor at a temperature of 290-310°C.56 The tubular reactor is a 4-m-long coiled pipe with a diameter of 4 mm which is heated at 300°C. At the end of the pipe is a valve which is regulated so that the pressure is 1.5 bar. The residence time in the pipe is only seconds. The prepolymer obtained can be postcondensed in the solid state to a high molecular weight. 

If polymers with a molecular weight over 15,000 are required, then a postcondensation step is needed. The postcondensation step is carried out at low water concentrations in the melt or in die solid state. The typical solid-state postcondensation conditions for PA-6 are given below. 

If a very high viscosity is required, die granulated polymer can be postcondensed in die solid state at 160-190° C for 4-24 h. The postcondensation step can be done batchwise in large revolving reactors or can be carried out in a continuous manner using tall moving-bed reactors. Surprisingly, die water concentration is not critical to the rate of postcondensation. The method employed for PA-6 is similar to tiiat for PA-6,6 (Example lc). As a result of a postcondensation step for 24 h at 190°C, the i/inh in 85% formic acid is increased from 0.8 to 1.35 (Afn = 18,000-35,000). 

This polymer is postcondensed in the solid state. For this, 5 g of material is placed in a glass flask which has been flushed with a stream of nitrogen. The flask is placed in a tube oven at 290° C and kept at that temperature for 1 h. The resultant polymer now has an r]i h of 1.52. The polymer is highly crystalline and has a melting temperature of 475° C. 

Solid-state polymerization, 159 Solid-state postcondensation, 170 PA-6, 177... 

Figure 5.7 Degree of polycondensation as a function of retention time and temperature [12b]. From Weger, F., Solid-state postcondensation of polyesters and polyamides, presentation given at the FrankI and Thomas Polymer Seminar, 16 June, 1994, Greenville, SC, USA, and reproduced with permission of EMS Inventa-Fischer, GmbH Co. KG...

The drying unit can be extended to a solid-state postcondensation, i.e., drying and solid-state postcondensation occurs in one process stage. Thus, high viscosity chips for industrial yarns, films and extrusion molded parts can be produced. 

Application New process for directly producing polyesters from all the polyalkylene terephthalate family for bottle-grade resins, based on terephthalic acid (PTA) or dimethyl terephthalate (DMT) and diols using the DIF proprietary two-reactor (2R) process consisting of the tower reactor ESPREE and DISCAGE finisher without a solid-stating postcondensation. 

Super clean PET recycling, i.e., conventional PET recycling with an additional deep cleansing process, for example, solid state postcondensation. The resulting material can be expected to be suitable for direct food contact applications [12]. 

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