Polybutylene terephthalate is a semicrystalline aromatic polyester produced from 1,4-butanediol and either terephthalic acid or dimethyl terephthalate. The polymer is identified commercially by CAS 26062-94-2; its principal backbone monomers are 1,4-butanediol (CAS 110-63-4, EC 203-786-5), terephthalic acid (CAS 100-21-0, EC 204-291-7) and dimethyl terephthalate (CAS 120-61-6, EC 204-311-5). Under Regulation (EC) No 1907/2006, polymers are excluded from registration and evaluation because of their polymeric status, but that exclusion does not remove the registration duties for the monomers chemically bound within the polymer chain. The critical trigger is both compositional and volumetric: where the polymer consists of ≥2% w/w of a monomeric unit and the total quantity of that monomer in the polymer placed on the EU market reaches ≥1 t/a, the monomer must be registered unless an upstream actor has already registered that use. For polybutylene terephthalate, this shifts the regulatory file away from the polymer as such and onto 1,4-butanediol, terephthalic acid and dimethyl terephthalate. The acronym PBT also has a parallel REACH meaning as persistent, bioaccumulative and toxic, but polybutylene terephthalate is not automatically classified as a PBT/vPvB substance under Article 57 classification criteria.

Does the polymer itself require a registration dossier?

No registration dossier is filed for polybutylene terephthalate as a polymer under Article 6 of REACH. The European manufacturer or importer of PBT resin instead calculates the bound monomer tonnage and verifies each monomer registration in the supply chain. The calculation under Article 6(3) uses the total mass of the monomeric unit as polymerised, not the residual free monomer content after compounding. If a PBT producer operates lines using terephthalic acid at one site and dimethyl terephthalate at another, each monomer is assessed separately against the ≥2% w/w and ≥1 t/a conditions. A monomer already registered by an upstream supplier for the same substance and use may be relied upon after the registration number and tonnage band are confirmed. A non-EU supplier of PBT does not register the polymer itself; instead, an only representative appointed under Article 8(1) may register the relevant monomers for the imported tonnage.

Under Article 10 of REACH, the monomer registration dossier is compiled in IUCLID and includes substance identity, classification and labelling under CLP, manufacture and use information, and robust study summaries. For hazardous monomers registered above 10 t/a, Article 14(1) requires a Chemical Safety Report. Polybutylene terephthalate producers frequently rely on existing joint registrations for 1,4-butanediol and terephthalic acid, but the use descriptor covering polymer production must appear in the exposure scenario. Production-scale continuous melt polycondensation lines operate with excess 1,4-butanediol that is removed by vacuum finishing; process control in the range 245–260°C and vacuum between 10–30 mbar reduces residual free 1,4-butanediol and tetrahydrofuran in the pellet, but the Article 6(3) tonnage calculation is not based on those residual values. The paperwork therefore separates polymer-exempt status from monomer dossiers with different exposure scenarios and data requirements.

Monomer registration dossiers and the joint submission packaging

For the three PBT backbone monomers, the registration dossier is structured around a lead registrant under Article 11(1). Co-registrants obtain a letter of access or participate in the joint submission after data sharing within the substance information exchange forum. The technical dossier must identify the registered uses of the monomer in polymer production; continuous polycondensation, batch reactors and solid-state finishing operations may require separate exposure-scenario coverage. A downstream user of PBT resin is not required to register the monomer, but must verify that its use is covered by the relevant exposure scenario when the monomer SDS includes an exposure scenario annex. If the use is not covered, Article 37 may require a downstream user chemical safety report unless an exemption applies.

The Safety Data Sheet for a PBT compound may list monomer registration numbers in Section 3.2 or Section 1.1, but the polymer itself has no registration number. For mixtures in which PBT is compounded with glass fibre, heat stabilisers, nucleating agents or flame retardants, the SDS must separately address the registration status of the added substances. Batch-to-batch verification of compound formulation against the SDS is essential because additive changes alter Section 3.2 and may activate distinct regulatory obligations. The registration paperwork for the monomer therefore remains a core supply-chain document even though the PBT polymer is not itself a registrable substance.

SVHC status is composition-dependent, not polymer-intrinsic

Polybutylene terephthalate is not placed on the REACH Candidate List for authorisation, and it is not listed in Annex XIV. The polymer also has no harmonised classification in Annex VI to CLP. Its SVHC condition is therefore controlled by species present in the residual or compounded fraction. Diantimony trioxide (CAS 1309-64-4, EC 215-175-0) is used as a polycondensation catalyst in some PBT production routes and is subject to Candidate List inclusion because of its CLP carcinogenicity classification. When residual diantimony trioxide remains in a PBT article above 0.1% w/w of the article mass, Article 33(1) communication applies. The same logic covers brominated flame retardant packages, cadmium-based pigments, and other compounding additives that may be identified as SVHCs. These SVHC thresholds are separate from monomer registration tonnage thresholds; they activate paperwork on the article maker or importer, not on the resin producer.

A PBT pellet or PBT compound supplied as a substance or mixture is not subject to Article 33 SVHC communication unless the material has been shaped, formed, or otherwise transformed into an article whose special shape, surface or design determines its function to a greater degree than its chemical composition. For the injection moulder or extrusion processor, the duty arises only after the PBT has been converted into a component such as a connector, sensor housing or mechanical latch. Under Article 33(1), the supplier of that article communicates the SVHC name, concentration and sufficient safe-use information. For consumer requests, Article 33(2) requires a response within 45 days and without charge. The SCIP database under Waste Framework Directive 2008/98/EC Article 9(1)(i) then requires a separate notification to ECHA with article category, material composition and SVHC concentration band. Article 7(2) notification may also arise for Candidate List SVHCs in articles above 0.1% w/w and 1 t/a unless the substance has already been registered for that use or exposure can be excluded.

Safety data sheet Section 15.1 and the recordkeeping boundaries

The Safety Data Sheet for PBT compound is prepared under Article 31 and REACH Annex II as amended by Regulation (EU) 2020/878. Section 1.1 must provide the product identifier; Section 3.2 must state whether the product is a mixture and list relevant components and registration numbers. Section 15.1 must report whether the product or its components are subject to SVHC candidate-list obligations, authorisation or restriction. For PBT resin, 1,4-butanediol and terephthalic acid are not Candidate List SVHCs, but Section 15.1 may still report diantimony trioxide where the compound contains a relevant residual fraction. Section 11 toxicological data and Section 12 ecological data are generally shorter for high-molecular-weight PBT than for its monomers because the polymer is non-volatile and poorly water-soluble. Records supporting registration dossiers, exposure scenario compliance, Article 33 communications and SCIP submissions should be retained for at least 10 years after the last manufacture, import, supply or use, consistent with Article 36 of REACH and the internal recordkeeping expectations of downstream chemical safety management.

Laboratory verification of monomer content for Article 6(3) purposes is commonly performed by ¹H NMR after depolymerisation or by chromatographic profiling of the monomeric units in the polymer. Elemental antimony residues in PBT articles can be quantified by acid digestion and ICP-OES according to ISO 11885:2007 when diantimony trioxide SVHC concentration must be checked. Gel permeation chromatography with polystyrene calibration provides molecular weight distribution data but does not resolve SVHC status. Published data for very low residual diantimony trioxide distributions in specific commercial PBT grades is limited; processors should therefore not rely on a nominal catalyst addition rate when determining whether the 0.1% w/w article threshold has been exceeded.

When the only representative files under Article 8, the EU importer is not the registrant but retains downstream-use documentation duties

An importer buying PBT resin from a non-EU supplier may rely on an only representative appointed by the non-EU manufacturer under Article 8(1). The only representative registration must cover the full imported tonnage of each monomer at the ≥2% w/w and ≥1 t/a thresholds. The EU importer is then a downstream user and must verify that the uses of the PBT compound fall within the boundaries of the registered exposure scenario. If the importer modifies PBT by adding colour concentrates, glass fibre or flame retardant packages, the resulting compound is a mixture for which the importer must check whether the additive substances themselves require registration or notification. The only representative paperwork includes a signed appointment with the non-EU manufacturer, a registration number for each monomer, and a documented mapping of tonnage and use coverage. Without this trail, the EU importer becomes responsible for monomer registration. No corresponding only representative mechanism exists for the Article 33 SVHC communication duty in finished PBT articles.