Solid-state polycondensation reaction time

To increase the PET molecular weight beyond 20 000 g/mol (IV = 0.64 dL/g) for bottle applications, with minimum generation of acetaldehyde and yellowing, a further polycondensation is performed in the solid state at low reaction temperatures of between 220 and 235 °C. The chemistry of the solid-state polycondensation (SSP) process is the same as that for melt-phase polycondensation. Mass-transport limitation and a very low transesterification rate cause the necessary residence time to increase from 60-180 minutes in the melt phase to... 

Figure 5.24 Effect of reaction time on the solid-state polycondensation process for PET reaction conditions, 250°C initial Mn, 16500, with a particle size of 0.18-0.25 mm data obtained by gas chromatographic analysis, employing a column of dimensions 8ft x 0.7.5 in o.d., with a nitrogen gas flow rate of 350ml/min [5], Reproduced from Hsu, L.-C., J. Macromol. Sci., Phys., B1, 801 (1967), with permission from Marcel Dekker...

SOLID-STATE POLYCONDENSATION OF POLYESTER RESINS 4.3.7 Reaction Time... 

For a long period of time, too litde attention has been paid to the content and the role of oligomers in the spinning process. Due to the equilibrium conditions in the reaction mixture, PET contains about 1-2% of oligomers. In certain conditions, this amount can be reduced to values below 1 % by solid-state polycondensation (SSP) processes. Figure 13.8 shows the variation of the oligomer content as a function of temperature and time during SSP processes. 

Figure 1.5 Changes in M of sb-PLA as a function of the reaction time through the whole process involving the solid-state polycondensation conducted at 170 °C (Refs. 21,26, with permission).

The term solid state polycondensation (SSP) simply says that chain growth by condensation steps occur under conditions, where at least one reaction partner exists in the solid state. As discussed below, SSP encompasses a broad variety of condensation reactions and substrates. Seemingly, the first example of a SSP (but not recognized as such) was the synthesis of poly(4-hydroxybenzoic acid), poly(4-oxybenzoate) by dry distillation of 4-hydroxybenzoic acid (see Chap. 2, Refs. [64—66]). A more detailed discussion of syntheses of poly(4-hydroxybenzoic acid) will we presented in Sect. 14.3. The first section is dedicated to SSPs of peptide esters which were also described for the first time before World War 1. 

The polyether-ester polyamic acid imidization process in a solid state under microwave irradiation was studied by Yu et al. [73]. The prepolymer, polyether-ester polyamic acid, was prepared by the polycondensation of poly(tetramethylene ether)glycol di-p-aminobenzoate (Polyamine-650, Polaroid, Co.) and pyromellitic acid dianhydride (PMDA) at room temperature in DMF solution. Later, the prepolymer solution was cast on polytetrafiuoroethylene plates to form 200 pm thin films that were imidized under microwave irradiation in a household microwave oven at 60 °C. The temperature was measured by means of a thermocouple applied to the film surface immediately after the intervals of microwave turn off It was found that microwave irradiation reduced both the reaction temperature and time. For example, during the solid phase thermal polymerization 68.3% polyamic acid was converted to polyimide at 155 °C, while under microwave irradiation 65 % of polyamic acid was reacted at 60 °C within 3 h [73]. 

The thermal polycondensation of dihydroxy(metallo)phthalocyanines to cofacially stacked polymer in the solid state as example of a type III polymers [equation (7)] is topotactic and under topochemical control, which means that well-defined intermolecular distances and interactions in the lattice control the reaction [56]. Following a kinetic study the fraction of unreacted -OH end groups X over time does not obey a first order kinetics (X = exp(— 2 ), M = Si, Ge, Sn n = 50-200). 

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