Polymeric MDI (PAPI)
- Synonyms: MDI oligomer; PMDI; polymeric MDI; polymeric isocyanate; polymeric 4,4’-methylenediphenyl diisocyanate; polymethylenepolyphenol isocyanate; polyphenyl isocyanate
- OSHA IMIS Code Number: P125
- Chemical Abstracts Service (CAS) Registry Number: 9016-87-9
- Chemical Description and Physical Properties:
- molecular weight: ~400
- molecular formula: CH2(C6H4NCO)2
- melting point: 200°C @760 mm Hg
- flash point: 200°C
- U.S. Environmental Protection Agency (EPA) carcinogenic classification: Group D, not classifiable as to human carcinogenicity
- Potential Symptoms: Itchy eyes, rhinitis, cough, pulmonary secretions, chest tightness, dyspnea, wheezing, asthma
- Health Effects: Respiratory sensitization---Asthma, hypersensitivity pneumonitis (HE9); Irritation-Eye, Nose, Throat, Skin---Marked (HE14)
- Affected Organs: Respiratory system, skin, eyes
- Although OSHA has a PEL for methylene bisphenyl diisocyanate (MDI) monomer (20 ppb ceiling), OSHA does not have a PEL for polymeric MDI (PAPI).
- EPA's inhalation reference concentration (daily inhalational exposure likely to be without an appreciable risk of deleterious effects during a lifetime) is 0.0006 mg/m3.
- Because toxicity is likely related to the very reactive isocyanate (N=C=O) group and commercial preparations often contain both MDI monomer and PAPI, exposure limit determination based upon the mass concentration of the N=C=O groups in polyisocyanates has been suggested.
- The MDI metabolites, N'-acetyl-4,4'-methylenedianiline and 4,4-methylene dianiline (MDA), have been measured in urine samples from employees involved in the manufacture of polyurethanes.
- Acid hydrolysis to release MDA from plasma proteins was used to measure the half-lives of MDI-protein adducts in four employees exposed to thermal degradation products of MDI-based polyurethane. The half-lives of such adducts in plasma ranged from 10-22 days.
- Chronic inhalation studies in rats with MDI (including PAPI) in concentrations up to 6 mg/m3 reported increased lung weight, interstitial fibrosis, broncho-alveolar hyperplasia and adenomas, and in one high-dose rat, lung adenocarcinoma. In contrast, chronic oral administration of the MDI metabolite, MDA, caused carcinomas in the thyroid (rats and mice), liver (female rats) and adrenals (male mice).
- Literature Basis:
- US EPA Integrated Risk Information System: Methylene Diphenyl Diisocyanate (monomeric MDI) and polymeric MDI (PMDI) (CASRN 101-68-8, 9016-87-9).
- Baur, X.: Hypersensitivity pneumonitis (extrinsic allergic alveolitis) induced by isocyanates. J. Allergy Clin. Immunol. 95(5 Pt. 1): 1004-1010, 1995.
- Bello, D., et al.: Polyisocyanates in occupational environments: a critical review of exposure limits and metrics. Am. J. Ind. Med. 46(5): 480-491, 2004.
- Bonauto, D.K., Sumner, A.D., Curwick, C.C., Whittaker, S.G. and Lofgren, D.J.: Work-related asthma in the spray-on truck bed lining industry. J. Occup. Environ. Med. 47(5): 514-517, 2005.
- Dalene, M., Skarping, G. and Lind, P.: Workers exposed to thermal degradation products of TDI- and MDI-based polyurethane: biomonitoring of 2,4-TDA, 2,6-TDA, and 4,4'-MDA in hydrolyzed urine and plasma. Am. Ind. Hyg. Assoc. 58(8): 587-591, 1997.
- Feron, V.J., et al.: Chronic pulmonary effects of respirable methylene diphenyl diisocyanate (MDI) aerosol in rats: combination of findings from two bioassays. Arch. Toxicol. 75(3): 159-175, 2001.
- Lamb, J.C., Huff, J.E., Haseman, J.K., Murthy, A.S. and Lilja, H.: Carcinogenesis studies of 4,4'methylenedianiline dihydrochloride given in drinking water to F344/N rats and B6C3F1 mice. J. Toxicol. Environ. Health 18(3): 325-337, 1986.
- No authors listed: 4,4'-Methylenediphenyl diisocyanate and polymeric 4,4'-methylenediphenyl diisocyanate. IARC Monogr. Eval. Carcinog. Risks Hum. 71(Pt. 3): 1049-1058, 1999.
- Date Last Revised: 07/24/2006
Monitoring Methods used by OSHA
Laboratory Sampling/Analytical Method:
- coated glass fiber filter (37 mm open face) coated with 0.1 mg 1-(2-Pyridyl)piperazine
- maximum volume: 15 Liters
- maximum flow rate: 1.0 L/min
- current analytical method: High Performance Liquid Chromatography; HPLC/UV
- method reference: OSHA (In-House File)
- method classification: Not Validated
- note: Results may not reflect accurate exposures to the polymeric forms of isocyanates. Keep filters refrigerated until use.
Conditions: Column: TMS Chromegabond (C3); Mobile Phase: 45:55 Acetonitrile: Water that is 0.02 M Ammonium Acetate; Detector Wavelength: 242 EX: 370 EM (Fluor)
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