Solid-state Polymerization of PEN

When the full improved property potential of PEN compared to PET is not needed for an end-use application, copolyesters may be considered. Common available comonomers which may be used include terephthalic acid and isoph-thalic acid (IPA), DEG and cyclohexane dimethanol glycols. 

The modification of PET with low levels of naphthalate comonomer increases the Tg and enables optimally oriented articles (films, fibers, containers, etc.) to resist higher temperatures without shrinkage. Heat setting under tension may be applied to further extend thermal stability. In addition, when retention of optical transparency is required, such copolymers crystallize less readily than PET, and may readily be quenched from the melt to the transparent, amorphous state. Thus, 

---

In the solid state polymerization of crystalline PEN, the temperature employed ranges from 240°C to about 265°C. As the solid state polymerization of PEN prepolymer proceeds, its sticking temperature increases. Thus, the solid state polymerization temperature can be gradually increased in the course of the process. ... 

After the PEN prepolymer has been crystallized, it can be dried and solid state polymerized in a batch or continuous process.Solid stating or solid state polymerization is a technique to increase the molecular weight of polyesters. Higher molecular weight polyesters are commonly produced from lower molecular weight polyesters of the same composition by solid state polymerization. 

Suitable solid state polymerization temperatures can range from a temperature just above the threshold temperature of the polymerization reaction up to a temperature within a few degrees of the sticking temperature of the PEN prepolymer. 

The use of a foamed PEN prepolymer, combined with a devolatilization step prior to solid state polymerization, provides a particularly fast and productive solid state polymerization process for a PEN polymer. Us-... 

PET/PEN blends can be subjected to a solid state polymerization to increase the intrinsic viscosity or to reduce the acetaldehyde generation. In the course of the solid state polymerization, the extent of transesterification is increased. A low level of transesterification of the PEN/PET preform causes poor transparency, while a high level of transesterification prevents strain-induced crystallization and poor mechanical properties. 

It is possible to control both the rate of change of intrinsic viscosity (IV) and the rate of transesterification of a blend of PET and PEN during solid state polymerization. The method comprises providing PEN with a first IV and a PET with a second IV. The PEN and PET are reacted in the presence of an ethylene glycol compound in an amount sufficient to achieve a desired final IV and final level of transesterification in the copolymerized PEN/PET product. Due to the improved thermal resistance, the materials can be used for hot fill containers. 

A polyester composition having better gas barrier properties with less acetaldehyde ejection consists in a blend of prepolymers of PET and PEN, or a copol5uner. This blend is subjected to the solid state polymerization process. " ... 

---