Overview
ISO 4504:2025 specifies laboratory methods for determining co‑monomer content in polyethylene (PE) using solution‑state 13C‑NMR spectrometry. It defines two validated NMR pulse‑program methods - Method A (inverse gated decoupling) and Method B (INEPT: insensitive nuclei enhanced by polarization transfer) - and gives procedural requirements, calculation formulae and reporting guidance for ethylene copolymers containing less than 50% (mass fraction) of a single 1‑olefin comonomer. The standard is explicit that it does not apply to ethylene homopolymers or copolymers with two or more different 1‑olefin comonomers.
Key topics and technical requirements
- Two measurement methods:
- Method A - single pulse with inverse gated proton decoupling (direct 13C excitation).
- Method B - refocused INEPT pulse program (proton→13C polarization transfer for enhanced sensitivity).
- Instrument and conditions:
- Minimum PFT‑NMR magnetic field: 7.05 T (≈75 MHz for 13C / 300 MHz proton equivalent).
- Measurement temperature capability: 120 °C ± 1 °C (samples dissolved in deuterated solvent).
- Sample tubes: 5 mm (≈30 mg sample) or 10 mm (≈120 mg sample) with recommended solvent volumes.
- Sample prep and reagents:
- Use deuterated solvents (o‑DCB‑d4, p‑DCB‑d4, or TCE‑d2) and optional relaxation reagents (e.g., Cr(III) acetylacetonate).
- Dissolution at 120–130 °C and equilibration before acquisition.
- Data quality and limits:
- Signal‑to‑noise (SNR) criteria and LOQ/LOD depend on branch CH‑carbon and methylene peak SNR (standard provides guidance and integration regions in annexes).
- Supporting material:
- Annexes include spectral integration limits, formulae, calculation examples for both methods, relaxation time references, chemical shift regions, precision data and pulse program descriptions.
Practical applications and users
ISO 4504:2025 is intended for:
- Quality control laboratories in polymer manufacturing to quantify comonomer incorporation in PE copolymers.
- R&D and analytical teams developing or characterizing polyethylene grades (e.g., LLDPE, VLDPE).
- Raw material suppliers and downstream compounders who need verified co‑monomer content for specification compliance.
- Regulatory, certification and testing labs requiring standardized 13C‑NMR methods for traceable results.
Benefits: robust, comparable results across labs; options for high‑sensitivity (INEPT) or direct‑quantitation (inverse gated) workflows; detailed annexes for method validation and reporting.
Related standards
- ISO 472 (Plastics - Vocabulary) - definitions referenced.
- ISO 648 (Laboratory glassware - Single‑volume pipettes) - pipette class requirements.
Keywords: ISO 4504, polyethylene (PE), 13C‑NMR, co‑monomer content, solution‑state NMR, INEPT, inverse gated decoupling, polymer analysis, copolymer quantification.