Poly condensation melt-phase

The chemistry of the solid-state polycondensation process is the same as that of melt-phase poly condensation. Most important are the transesterification/glycolysis and esterification/hydrolysis reactions, particularly, if the polymer has a high water concentration. Due to the low content of hydroxyl end groups, only minor amounts of DEG are formed and the thermal degradation of polymer chains is insignificant at the low temperatures of the SSP process. 

PCT, PETG, PCTG and PCTAs can all be prepared readily via standard melt-phase poly condensation processes [34, 35], The diacid can be delivered via transesterification of the dimethyl esters or via direct esterification of the diacids. Numerous conventional catalyst and catalyst combinations can be employed. The use of a catalyst or catalyst combination is important for the manufacture of polyesters via the melt-phase process and has been well reported in the literature [36-41], Appropriate catalyst systems enable the production of polyesters with high processing rates and high molecular... 

Polymer plasticization and overcoming compatibility problems helps in synthesis of many polymers in the presence of supercritical carbon dioxide. Carbon dioxide has been fotmd to be inert towards free radicals and cations but dramatically decreases glass transition temperamre of polymer due to plasticization (e.g., polystyrene Tg is reduced by about 50°C). Plasticization is especially useful in melt phase poly condensation processes. 

Poly(ethylene terephthalate) (PET) is commonly prepared by melt-phase polycondensation reactions. Bis(hydroxyethyl) terephthalate (BHET) was converted to PET under a variable flow (2-10 mL/min) of CO2 at 20.7 MPa (207 bar) (95). Molecular weights were obtained over the range 3 x 10 to 6.3 x 10 g/mol and increased significantly with flow rate and/or reaction time. These values are low compared to normal molecular weights obtained in commercial processes (approx. 2 X 10 g/mol) and may be attributed to the decreased solubility of the ethylene glycol condensate in CO2 compared with phenol in the polycarbonate system. 

Luyk [251] has examined formation of poly-brominated dibenzo-/ -dioxins (PBDD) and diben-zofurans (PBDF) during thermal processing of polymers containing polybrominated diphenyl ethers. The formation of PBDDs and PBDFs is a result of thermal and mechanical stress in the melt phase or condensed phase. The yield depends on temperature... 

Main ehain liquid crystalline polymers can be constructed from rod-like (calamitic) and disc-like (discotic) units by a condensation process (see Chapter 8). Seen here in racemic form, polymer 11 is a poly ether with repeating mesogenic-like core units separated by flexible alternating hydrocarbon spacers. This typical architecture ensmes a sufficiently low melting point for liquid crystalline phases to be exhibited. Polymer 11 has a molecular weight of 17,000 and a polydispersity of 1.7. 

Polymers often crystallize into metastable phases when cooling from the melt This subject has been recently reviewed by Keller and Cheng.(l) Metastable phases are usually considered to be those which are stable either indefinitely or at least long enough to measure. A transient phase would be a metastable phase which remains for a limited time and may therefore not be readily observed. Clearly the distinction between the two depends on the measurement time required by the specific observation technique. Transient phases are intrinsically difficult to observe and have therefore been the subject of limited study in poly meric (1-3) and other condensed matter systems.(4-6) However, transient phases are intermediate forms which occur on the path to the final state, (7) and therefore study of these phases is key to understanding the process of crystallization. For example, the temperature at which... 

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