• Top library match: Polyester resin #156522

• Low‑wavenumber bands at 452, 529, and 665 cm-1 are not characteristic of the polyester backbone; literature attributes these to metal‑oxygen [5] and silicon‑oxygen [9] vibrations, indicating the possible presence of inorganic fillers or additives.
• A phosphate assignment at 1011 cm-1 obtained from the literature [2] is not typical for a polyester resin and may reflect an impurity or additive rather than a structural polymer feature.
• The library match is of moderate confidence (0.748) and the exact polyester composition (e.g., whether the diol is ethylene glycol or 1,4‑butanediol, or whether the acid is terephthalic acid alone or mixed with isophthalic acid) cannot be reliably distinguished from infrared data alone.
• Low‑frequency peaks at 452, 529, 665, and 1011 cm-1 remain unassigned to a specific polyester component and may indicate minor inorganic or organic additives whose identity could not be confirmed from the available evidence.

Recommended next steps: Confirm the polymer composition by differential scanning calorimetry (DSC) to determine melting point and crystallinity, which can distinguish PET from PBT. Perform thermogravimetric analysis (TGA) to quantify the inorganic filler content and identify the nature of any low‑wavenumber absorptions. If further specificity is required, complementary techniques such as NMR or pyrolysis‑GC/MS can provide detailed information on the diol and diacid monomers.