Poly l,3-propylene 2,6-naphthalate

Poly( 1,3-propylene 2,6-naphthalate) (3GN) is synthesized from dimethyl-2,6-naphthalene dicarboxylate and 1,3-propanediol. The ingredients are reacted under atmospheric pressure under nitrogen in the presence of Ty-zorTM titanium tetraisopropoxide catalyst. The vessel is heated to 240°C over a period of about 330 min. At 188°C, methanol started to evolve. 

In the final stage, the pressure in the reaction vessel is reduced and the temperature is increased to about 280°C within 90 min and polymerization was allowed to proceed an additional 30 min. 

3GN has a unique combination of properties that provides a number of advantages over PEN when used in multilayers with PET. 3GN has a lower melting point of 181-213°C than PEN (264-267°C) and PET (250-256°C), but its glass transition temperature of 79°C for unstretched films and 94°C for fully oriented films is similar to that for PET (70°C for unstretched films and about 80°C for fully oriented films, respectively). 

The preferred orientation temperature for 3GN and 3GN-rich copolymers and blends is 90-135°C. The preferred orientation temperature for PET is 90-115°C, thus allowing 3GN to be biaxially oriented under optimum thermal stretching conditions for PET. 

On the other hand, PEN has a significantly higher glass transition temperature of 113-125°C for unstretched films, and 140°C for fully oriented films and requires higher orientation temperatures, of about 120-150°C. 

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