Reaction rate enhancement during swollen-state polymerization of poly(ethylene terephthalate)

Abstract

Experimental data are obtained for the extent of swelling and progress of the step-growth swollen-state polymerization (SwSP ) of polyethylene terephthalate (PET). The SwSP is carried out in biphenyl and diphenyl ether mixture (26 : 74 w/ w) solvent under appropriate conditions designed to understand the factors responsible for enhanced reaction rates. The kinetics rate constants, evaluated in terms of simple model, are found to be 2.5-5 times higher for SwSP as compared to the solid-state polymerization (SSP). As the diffusional/mass transfer effects are eliminated in our experiments, this increase in rate constants can be attributed to increased mobility of reactive chain ends. Polymerization rate is found to be further enhanced by addition of a polycondensation catalyst (Sb 2 O 3 ) to the solvent during SwSP.

The Solid State Postcondensation of PET, 1

“…Another means of obtaining high molecular weight polyesters is to polycondense fibres or granulated powders in a solvent, or mixture of solvents that can swell the polymer 30,33–38. The rate of polycondensation remains high since the presence of a swelling agent in the polymer matrix facilitates the diffusion of small molecules like EG, and thus improves the rate of mass transfer from the polymer phase.…”

“…It should be clear from the above discussion that, regardless of which process we choose for SSP, some of the more important issues that need to be addressed from a reaction engineering point of view will include: the influence of the continuous medium and temperature on the rate of polycondensation, the role played by an eventual catalyst, the solidification (and thus crystallisation) of the polymer melt, its dispersion in a continuous gas or liquid phase,30,33–39 the removal of EG and reaction by‐products and influence of reaction conditions, solid phase morphology,31,36,37 influence of particle morphology on kinetics and mass transfer, the choice of inert gas to use in the reactor, and optimising the rate of reaction via correct choice of starting conditions 3,32,40–42…”

Kinetics and chemical reactions of acetaldehyde stripping and 2‐methyl‐1,3‐dioxolane generation in poly(ethylene terephthalate)

“…Table 8 shows reaction rate constants for PET polycondensation and esterification reactions obtained by Duh [18] and Parashar et al [19] from experimental solid‐stating studies at different temperatures. In their research, the rate constants k 1 and k 2 were determined by neglecting the diffusion resistance of the byproducts in their calculations because of the small particle size or thickness of the chips.…”

Broadening of molecular-weight distribution in solid-state polymerization resulting from condensate diffusion

“…In addition, raising the temperature may be counterproductive if K decreases or k f increases more rapidly than D. A more elegant method of raising the condensate diffusivity is to introduce a plasticizing agent, which will effectively increase the free volume of the polymer and consequently enhance molecular mobility and increase the diffusion coefficient. 6,13,16,17 Of particular interest are nontoxic penetrants such as supercritical carbon dioxide, which plasticize the polymer without contaminating it or generating difficult-to-recycle waste streams. 5,6 Figure 6(a,b) shows the effect of particle size on average molecular weight and polydispersity for a phenol diffusion coefficient of 10 Ϫ7 cm 2 /s.…”

“…Other aspects of the SSP of PET have also been examined, such as the effect of particle size, 9,[11][12][13][14] the type of purge gas, 15 the flow rate of purge gas, [12][13][14] and the use of plasticizers to increase the rate of polycondensation. 6,13,16,17 Models for the SSP of nylon-6 3 and nylon-6,6 10 have also been developed. Solid-state polymerization in multiple particles and the effect of reactor type and conditions on the final product have also been examined for several different polymers.…”