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Increasing the Molecular Weight of Polycondensates Disclosure Number: IPCOM000019621D
Publication Date: 2003-Sep-23

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It has been discovered that the co-use of certain sterically hindered hydroxyphenylalkylphosphonic monoesters and polyfunctional compounds is very effective towards increasing the molecular weight of polycondensates. Increasing the molecular weight of polycondensates is disclosed for example in U.S. Pat. No. 5,807,932. Polycondensates are for example polyamides, polyesters, polycarbonates, and copolymers and blends of these polymers. Copolymers and blends are for example PBT/PS, PBT/ASA, PBT/ABS, PBT/PC, PET/ABS, PET/PC, PBT/PET/PC, PBT/PET, PA/PP, PA/PE and PA/ABS. The hydroxyphenylalkylphosphonic monoesters are disclosed in U.S. Pat. No. 5,807,932. The monoester is for example calcium bis(ethyl 3,5-di-tert-butyl-4-hydroxybenzylphosphonate), CAS#65140-91-2. The polyfunctional compounds are for example epoxides, anhydrides, polyols (more than difunctional alcohols), carbodiimides and esters. The hydroxyphenylalkylphosphonic monoester/polyfunctional compound combination is employed for post-condensation in the solid phase, or likewise is employed during the synthesis of the polycondensates. For example (PET): at least one difunctional alcohol, at least one dicarboxylic acid, a more than difunctional alcohol, an organic phosphonate) and antimony trioxide are mixed within a metal container. The mixture is transferred into a 10 L reactor (stainless steel) fitted with stirrer, refluxing unit and an outlet-die at the bottom of the reactor. The reactor can be either pressurized with nitrogen up to 6 bars or operated under vacuum down to 1 mbar. The monomer mixture is heated from room temperature to 250°C within 30 mins. During heating phase pressure is increased up to 4 bars. A water/ethylene glycol mixture is distilled off for 3.5 h. Temperature is increased consecutively to 280°C. Within next 5 h pressure is continuously reduced to further distill off water and ethylene glycol. The polyester product is extruded through the bottom die, cooled to room temperature in a water bath and pelletized to yield clear PET granules. The polycondensation in the melt (above) is followed by a solid state polycondensation (SSP) for further increasing the molecular weight as monitored by measuring the intrinsic viscosity. Furthermore, this process decreases content of acetaldehyde.