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Polymeric MDI (PAPI)

General Description

Synonyms:  MDI oligomer; PMDI; polymeric MDI; polymeric isocyanate; polymeric 4,4’-methylenediphenyl diisocyanate; polymethylenepolyphenol isocyanate; polyphenyl isocyanate

OSHA IMIS code: P125

CAS number(s): 9016-87-9

Chemical description and physical properties:

  • liquid
  • molecular weight: &~400
  • molecular formula: CH2(C6H4NCO)2
  • melting point: 200°C @760 mm Hg
  • flash point: 200°C

Health Factors

Carcinogenic classification:

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

Notes on other potential health effects and hazards:

  1. Although OSHA has a PEL for methylene bisphenyl diisocyanate (MDI) monomer (20 ppb ceiling), OSHA does not have a PEL for polymeric MDI (PAPI).
  2. 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.
  3. 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.
  4. 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.
  5. 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.
  6. 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).

Partial reference list:

  • 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 diisocyanateIARC Monogr. Eval. Carcinog. Risks Hum. 71(Pt. 3): 1049-1058, 1999.

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