Analytical Instrument Documents

MSTips No. 407

Poly (ethylene terephthalate) (PET) is a thermoplastic polyester obtained by polycondensation of ethylene glycol and terephthalic acid, and has excellent properties such as transparency, toughness, rigidity, and heat resistance (Figure 1). PET can be roughly divided into two types depending on processability: crystalline PET (C-PET) and amorphous PET (A-PET). C-PET has a high density due to the regular arrangement of the molecules in the crystallized part, and is characterized by high strength and heat resistance. A-PET is characterized by high impact strength and easy bending. However, due to long-term use or exposure to heat, the amorphous portion of A-PET slowly crystallizes, causing internal stress due to changes in density and breaking the polymer chains, resulting in poor flexibility, impact resistance, and strength. Therefore, a polymer was devised in which about 30-40% of the ethylene glycol in PET was replaced with cyclohexanedimethanol; this polymer is called glycol-modified PET (G-PET, PETG) (Figure 2). G-PET is treated as an amorphous resin because the polymer does not crystallize during molding. In a previous report [1], we performed structural analysis of two types of commercially available PET resins (PET film and PET plate) using reactive pyrolysis GC-TOFMS and NMR, and confirmed that the PET film was PET and the PET plate was G-PET. In this report, we analyzed the oligomer region of the same samples using a high-resolution MALDI-TOFMS JMS-S3000 "SpiralTOF™-plus 2.0" in combination with Kendrick Mass Defect (KMD) analysis.