Special topic: nonisocyanate routes to polyurethanes
GOVERNMENTAL REGULATION OF ISOCYANATES
The growth of commercial polyurethane building blocks and products is a testament to their efficacy and their efficiency. From the standpoint of both cost and processing, polyurethanes are attractive alternatives to many alternative thermoplastic and thermoset materials. The specificity of isocyanate reactivity with active hydrogen atoms, and the large number of available building blocks that have active hydrogen atoms, results in enormous potential for polymer innovation. However, this specific reactivity also makes isocyanate a potential hazard to living organisms ubiquitous with active hydrogen in living tissues and water [1-3]. Industrial consumers of isocyanates have adapted to the challenges associated with handling isocyanates by protecting workers from inhalation and skin contact. This is usually achieved by installing necessary and commonsense safeguards for worker protection . However, the recent appearance of consumer products with unreacted isocyanates means that consumers, unregulated contractors, and also unknowing bystanders have the potential for unintentional primary exposure or incidental secondary exposure to isocyanates with the potential for harm. Occupational exposure has been documented to result in dermal and inhalation sensitization (rashes and asthma-like symptoms). Chronic exposure to isocyanates can additionally cause permanent harm to lungs, while of course acute exposure can in most severe cases be fatal .
In 2011, the U.S. Environmental Protection Agency (EPA) produced an action plan (RIN 2070-ZA15, April 20, 2011) for possible future regulation of methylene diphenyl diisocyanate (MDI) and related compounds (4,4', 2,4', 2,2' isomers, polymeric MDI, and MDI dimers and trimers). The conclusion of the review resulted in the following action plan:
EPA intends to:
1. Issue a data call-in for uncured MDI under TSCA section 8(c) to determine if there are allegations of significant adverse effects and initiate a TSCA section 8(d) rulemaking for one-time reporting of relevant unpublished health and safety studies for uncured MDI.
2. Consider initiating a TSCA section 4 test rule to require exposure monitoring studies on uncured MDI and its related polyisocyanates in consumer products and exposure monitoring studies in representative locations where commercial products with uncured MDI and its related polyisocyanates would be used.
3. Consider initiating rulemaking under TSCA section 6 for
a. Consumer products containing uncured MDI, and
b. Commercial uses of uncured MDI products in locations where the general population could be exposed.
4. Consider identifying additional diisocyanates and their related polyisocyanates that may be present in an uncured form in consumer products that should be evaluated for regulatory and/or voluntary action.
The U.S. Occupational Health and Safety Administration (OSHA) has issued Directive Number CPL 03-00-017 (June 30, 2013) to initiate a National Emphasis Program "to identify or eliminate the incidence of adverse health effects associated with occupational exposure to isocyanates." As mentioned earlier, occupational exposure to isocyanates in the developed economies, including the United States, is not previously a prominent issue, but the growing use of uncured isocyanate products may create a problem. OSHA "targets" for particular scrutiny are listed: general industry, construction, and maritime industries "where exposure to isocyanates are known or are likely to occur."
Lastly, the State of California's Department of Toxic Substances Control listed (March 25,2014) spray polyurethane systems containing unreacted polyurethane (along with fire retardant tris(l,3-dichloro-2-propyl)phosphate and surface cleaners containing methylene chloride) as a priority product under the Green Chemistry Law of 2008. The covered materials for review include all isomers and mixtures of MDI (presumably including polymeric that contains MDI monomer), all isomers and mixtures of TDI, and hexameth-ylene diisocyanates (HDI). Other isocyanates or isocyanate trimers are specifically not included. While being listed as a priority product is not itself a ban, it is a step in the state process toward regulation. Promulgation of legal code could occur in 2016.
This activity follows the original activity of the European Commission (No. 552/2009 June 22, 2009) (and updated on May 25, 2011, to specify isomers) that MDI shall not be placed on the market after 27, December 2010, as a constituent of mixtures in concentrations equal to or greater than 0.1% by weight of MDI for supply to the general market, unless suppliers shall ensure before the placing on the market that the packaging: (a) contains protective gloves which comply with the requirements of Council directive 89/686/EEC; (b) is marked visibly, legibly and indelibly as follows and without prejudice to other Community legislation concerning the classification, packaging and labeling of substances and mixtures "Persons already sensitized to diisocyanates may develop allergic reactions when using this product. Persons suffering from asthma, eczema or skin problems should avoid contact, including dermal contact with this product....
With the governmental regulatory environment and the general European goal of using industrial solutions employing the least toxic effective components available, there has been increasing industrial and academic emphasis on obtaining urethane properties from systems that do not employ isocyanates. This chapter covers nonisocyanate chemistries that are actively explored for their potential to functionally substitute in polyurethane applications, regardless of economic barriers. The increased activity can be illustrated by analysis of the number of publications since 1990 on an emblematic nonisocyanate chemistry, reacting polycyclic carbonates and polyamines to make polyurethanes (Fig. 12.1). While the overall activity is relatively small, encompassing all publications academic and patent, the exponential increase is quite dramatic (Fig. 12.2).
Like many new areas where there is perceived to be an opening for acquiring intellectual assets, there have been numerous forays into patent space with concentrations particularly in the area of inks and toners. However, many of the patents represent the attempt to stake out a particular product based on specific material rather than representing a concentrated strategy.
While the attention paid to cyclic carbonate transformations to polyurethanes is the area of most prolific publication and patenting, other areas have also been
FIGURE 12.1 Growth in public documents exploring or protecting the production of polycyclic carbonates, their polymerization to polyurethanes, or their uses. Total = 635 references.
FIGURE 12.2 Patent activity of top filers of polycyclic carbonate to polyurethane technology. Total = 282 patents from 2000 to 2014.
developed using completely unrelated raw material and building blocks. These will be taken separately.