SynopsisT h e kinetics of solid state polymerization of poly(ethy1ene terephthalate) (PET) have been investigated a t a variety of conditions. Equations have been developed to describe the relationships of time, temperature, and final molecular weight for PET precursors prepared from specified catalyst and monomer systems. These studies show effects of: time and temperature of solid stating, moisture concentration, oxygen exposure, and nitrogen purge flow rate. Measurements of inherent viscosity, carboxyl end group concentration, melting point, residual acetaldehyde, and acetaldehyde generated during melting are used to monitor molecular weight, purity, and thermal stability of these solid stated resins.

SYNOPSISThe environmental degradation of high-density polyethylene (HDPE ) has been studied, in addition to that of HDPE blends, containing various concentrations of ethylene carbon monoxide copolymer. Extruded sheets of each material were exposed to natural Arizona sunlight for times up to 6 months. Exposed samples were then analyzed with respect to molecular weight, density, thermal behavior, mechanical properties, and infrared absorption. Additional samples were exposed to laboratory weathering conditions, evaluated in terms of property changes, melted, reformed, and then reevaluated without further weathering exposure. Results indicate that sunlight exposure causes decreased elongation to break, increased embrittlement, decreased molecular weight, and increased crystallinity. Environmental oxidative degradation is elucidated by the measurement of specific infrared bands, sensitive to the formation of carbonyl and vinyl end groups. As environmental degradation causes reductions of molecular weight, polymer chain mobility increases, leading to a higher degree of crystallinity. This increased crystallinity, along with the decreased molecular weight, accounts for the loss of ductility, indicated by a sharp decrease in ultimate elongation. The presence of carbon monoxide copolymer in the blended samples accelerates the process of environmental degradation, however, the degradation mechanisms appear to be similar to those observed for nonblended HDPE.

ABSTRACT:The solid-state polymerization (SSP) reaction kinetics of poly(ethylene terephthalate) were investigated in connection with the initial precursor intrinsic viscosity (IV; molecular weight). Evaluations were performed with otherwise equivalent precursors melt-polymerized to IVs of 0.50, 0.56, and 0.64 dL/g. The changes in the molecular weight and other properties were monitored as functions of the reaction times at solid-state temperatures of 160 -230°C. Precursors with higher initial molecular weights exhibited higher rates of SSP than those with lower initial values, as discussed in connection with the levels of crystallinity and the carboxyl and hydroxyl end-group composition. Activation energies decreased at temperatures above 200°C, and this indicated a change in the SSP reaction mechanism. At temperatures of 200 -230°C, similar activation energies were required for the polymerization of all three precursors. Lower temperature polymerizations, from 160 to 200°C, required higher activation energies for all precursors, with the 0.50-IV material requirement almost twice as high as that calculated for the higher IV precursors.

Poly(ethylene terephthalate) (PET) is known to be a hygroscopic thermoplastic, which absorbs moisture from its environment at a rapid rate. The water absorption characteristics of PET as a function of relative humidity, exposure time, temperature, thickness, and molecular weight are reported here. Results indicate that absorbed moisture has significant influences on the physical properties of PET, leading to large decreases in the glass transition temperature, crystallization temperature, and degree of molecular orientation.

The kinetics of thermal and thermal‐oxidative degradation of polyethylene terephthalate (PET) have been investigated as a function of melt temperature, melt residence time, melt environment, and drying environment. Rates of thermal and thermal‐oxidative degradation were measured in terms of: weight loss of volatile degradation products, decreasing inherent viscosity, and increasing carboxyl end group concentration. Thermal‐oxidative degradation was also investigated by Differential Scanning Calorimetry. Calorimetric results show that thermal‐oxidative degradation of PET is an exothermic reaction, with an apparent activation energy of 117 kJ/mol. Melt temperature, melt residence time, melt environment, and drying environment have all been found to affect the degradation of PET. Analysis of inherent‐viscosity kinetic data has been carried out, utilizing existing theories based on a random chain scission mechanism. Activation energies of 117 and 159 kJ/mol have been calculated for air‐dried and vacuum dried samples respectively.