Tuesday, July 15, 2014

An Unlikely Combination: Thiol-Ene Chemistry and Isocyanate-Free Polyurethanes

Long-time readers of this blog may recall that I spent a good deal of time with my previous employer working with thiol-ene chemistry. I really loved working with that chemistry - it was very fast and versatile, although my wife never enjoyed the experience of handling my cloths at the end of the day. Upon changing jobs a year and a half ago, I've set those malodorous chemicals aside and moved on to other monomers. These new monomers are apparently lightly scented, but I always question why someone would be sniffing them at all. You see, I'm now working with isocyanates to make polyurethanes and polyurea coatings and those aren't chemicals you shouldn't be smelling as you are probably being exposed to too high a level of them.

Isocyanates present a unique hazard to the polymer chemist - sensitization of the skins and lungs to the chemicals. Akin to an allergic reaction, once you are sensitized, you respond to increasingly smaller levels of exposure [*]. While skin sensitization is (merely) a rash, lung sensitization can induce horrible breathing problems and in extreme cases, death. Contrast that with the diamines used to make polyureas. They are corrosive and burn your skin, eyes and whatever else they contact, but that is pretty much the end of the story. You can march back into the lab the next day and carry on (albeit being more careful than before). But get sensitized to isocyanates and you are done working with them for the rest of your life. That's a risk for me and anyone working for me that always leaves me wondering whether it is justified. Fortunately, good PPE exists now that allows us to manage those risks.

Another way to manage the risk is to eliminate the use of isocyanates altogether, typically by reacting a cyclic carbonate with an diol or diamine such as is seen here:
Preparing a whole range of bifunctional cyclic carbonates can be a hassle, but a newly published patent application, discussed by the Innovations in Polyurethanes blog may change all that and best of all it does so by using my old love, thiol-ene chemistry. As is seen below, by starting with a vinyl-substituted cyclic carbonate, a dithiol (or trithiol or tetrathiol...) can react with that moiety to quickly and easily produce a difunctional cyclic carbonate, ready for polymerization.
This is only an application - the patent has not issued yet, but in a case of uncanny timing, the journal Polymer Chemistry today published online some new research showing how cyclic carbonates can be made from unsaturated fatty acids and how they can be dimerized by...thiol-ene chemistry:
Time will tell whether the application will issue and what the claims will be, but this is a world I never thought I would find myself in, combining my lovely thiol-ene reactions with isocyanate-free polyurethanes. Wait until I tell my wife!


[*} But the analogy stops there. Sensitization is not an allergic reaction. An allergic reaction produces a flood of histamines in your body, hence the application of antihistamines. Those medicines are useless for combating isocyanate sensitization.


Previous Years
July 15, 2013 - Closing the Door after the Horse has Gone Tilting at Windmills

July 15, 2011 - A New Polymer Blog

July 15, 2010 - Blow Molding on a Small Scale

Monday, July 14, 2014

A Novel Adhesive

A couple of weeks ago, the highly esteemed Chemjobber brought to my attention this article in C & E News about a newly developed set of adhesives based on 1,1-disubstituted alkenes. It is an interesting story from both the business and technology perspectives[1]. The challenge is in effectively preparing the monomers, something that has long been sought. Even W. H. Perkin, Jr. worked on the problem [2] as was mentioned in the inventors' patent. And once the monomers have been prepared,
keeping them from polymerizing prematurely is always a challenge.

I do find it funny that the inventors refer to this new monomer as a malonate, while the C & E News article refers to them as 1, 1-disubstituted alkenes. Neither term is wrong, but it does give you an different perspective on the molecule. Polymers made from 1, 1-disubstituted alkenes, and in particular 1, 1-disubstituted ethylene are commercially available if you like halogenated polymers. The polymer is 1, 1-dichloroethylene is known as polyvinylidene chloride (PVDC) which was originally known as Saran, the clingy food wrap with the excellent barrier properties. Sadly, due to concerns over the chlorine in the plastic, Saran is now a polyethylene-based food wrap with vastly inferior barrier properties. The fluoro- analog of PVDC is PVDF, an unusual polymer in that it is piezoelectric.

Referring to the monomer as a 1, 1-disubstituted alkene implies a polymer of this sort:
but the issued patent also shows another polymer structure:
which I have a harder time swallowing. That quite a few electrons to be moving around. No worries though, as the patent is only for the synthesis of the monomer. The polymerization is not claimed.

I do pity the business however, for wanting to focus on the automotive industry. That is just a plain brutal business to be in and it will only cause pain and misery for them. But those volumes are so attractive! The company will need to invest a huge amount of capital needed to produce the large volumes that Detroit wants, only to find later find out that they really don't want the new adhesive all that much, or at least not a decent price. And the pressure on the pricing is only going to increase each year.

But I do wish them the best of luck. It's a neat adhesive that should be able to find a spot in the world, proving once again, that while the Big 6 polymers may dominate production, there is still plenty of interesting options in the long tail for us polymer chemists.




[1] Although I do think the 4th and 5th paragraphs should be swapped. As it is written, Sheppard is referred to without being previously introduced.

[2] Hey Chemjobber, ever been mentioned in the same paragraph as Perkin before? I'm sure it won't be the last time.

Previous Years
July 14, 2010 - Chemistry and Music

July 14, 2010 - No RDA on BPA in the EU

July 14, 2008 - Accelerated Aging - Getting Bad Data Even Faster - 1st in a Series

July 14, 2008 - Playing the Building

Friday, July 11, 2014

A House Fire due to Spontaneous Combustion of Polyurethanes? - Not so Fast

This is just a quick followup to a post from a few days ago in which I wrote about spontaneous combustion of polyurethanes leading to a house fire. You may recall that I was initially skeptical of concept in general, but have come around to accepting it.

But that might not be the case with the house fire that first came to my attention. The Urethane Blog is now reporting that investigators are looking at other causes for the fire. (The headline states that spontaneous combustion is ruled out as as a cause, but the article isn't so definitive.)

I seriously doubt that we will hear anything more about this fire unless there are judicial proceedings (criminal or civil) arising from this. Fires make for good news, especially when a large, 10,000 ft2 house is involved, but few reports or publishers have the interest in following up on the dry details of a fire department report.

Previous Years
July 11, 2012 - "What is Journal Access Like in an Industrial Setting?"

Cash Flow in Small Businesses

I was quite surprised this morning to see the local paper reporting that Obama wants companies to pay their suppliers faster, mostly because this doesn't strike me as anything that a president should be getting involved in.

Having worked for small companies for more than a decade, I highly appreciate the problems they have in getting paid and how that impacts their cash flow. In my last job, our standard contract was 30-days net, but we had many large clients that would routinely change that to 45-days or 60-days and there was little we could do about it. They had the power and we didn't, so they got their way.

It's pretty much the same way with us an individuals. Imagine if your employer were to start doing this with your paycheck, delaying payment of it by a couple of weeks or a month. There would be more than a few households that would be in pretty desperate straits, but what could you do about it? (And conversely, how well it would work if you decide to delay payment on your mortgage, taxes or credit card by a few weeks?) Small businesses are no different. It's difficult to budget and operate when you can't predict cash flow. And while it can be done, it's a time drain. That time really could and should be spent elsewhere, such is in efforts to increase sales, develop new and better products... - the activities for which people started up the business in the first place.

So while it is nice that these 26 companies decided make quicker payments, they only represent 5% of the companies in the Fortune 500, and the list of companies delaying payments could be extended to a goodly portion of the Fortune 10,000 (and more). It's a nice gesture, but it really isn't going to help the economy in any meaningful way.


Previous Years
July 11, 2012 - "What is Journal Access Like in an Industrial Setting?"

Wednesday, July 09, 2014

"Plastic Debris in the Open Ocean"

The Proceedings of the National Academy of Sciences has early online report regarding ocean plastic and the results are not exactly supportive of what is commonly accepted. In particular, the research found a profound absence of very small plastic pieces and thereby a corresponding lack of total plastic in the open ocean.

Before I get to far into the details, let me review a few basics about ocean plastic.
  1. Plastic debris has no business being in the ocean. None. It should be disposed of properly on land - end of story. The fact that there may be less plastic in the oceans than previously thought is a nice way of saying "it's not so bad". It's still bad. There is still way too much plastic in the oceans that shouldn't be there.
  2. This is not what ocean plastic looks like:
    Ocean plastic doesn't look like this
    And it doesn't look like this:
    Ocean plastic doesn't look like this
    or even this:
    Ocean plastic doesn't look like this
    There are no islands of plastic the size of Texas (as supported by the complete lack of satellite pictures of such floating structures).
  3. This is what ocean plastic looks like:
    This is what ocean plastic really looks like
    A thin soup of small plastic pieces, very dilute. Sadly, that dilution makes it all the more challenging to enact an economical recovery of the plastic. And so it just sits there and we can do little about it except striving to not add to the problem.

This new report is based on a circumnavigation expedition that sampled around the world and also on previously published reports.
Particle size distributions for ocean plastic
To get to the heart of the matter, look at Figures 3A and B shown on the right (I had to throw in 3C as well just because the particle size scale is below 3C and I didn't feel like cutting and pasting that much.) 3A shows a particle size distribution (the bars are for nonscaled data, while the circles when the data has been normalized by width of the particles. In both cases, the distribution falls off rather quickly below about 1 mm, giving us a normal or normal-like distribution. While normal distributions are the rule across much of science, that is not what is expected here. Rather a log-normal distribution should be seen. Figure 3B shows with the blue circles the normalized abundance of the pieces, while the red circles show what should be expected if the particles break down in any sort of conventional scheme. That such a particle size distribution is expected is further supported by Figure 12S-B in the supplemental information, where for non-plastic pieces collected during the trip, there is not a falloff in the number of small particles.

The authors speculate on a number of causes for this falloff but more research is needed. The significance of the falloff however cannot be underestimated. While these particles are small in size, there should be a tremendous number of them. This surprising lack of small particles what then leads to the conclusion that there isn't as much plastic in the oceans as was previously thought. Although the Fourth of July is over, there will still be plenty of fireworks around as some environmentalists go on the attack and some conservatives use this paper as kindling for their torches.

Previous Years
July 9, 2010 - Non-stick Chewing Gum

July 9, 2008 - Don't drink the water

Tuesday, July 08, 2014

Spontaneous Combustion of Polyurethanes

The Polyurethane Blog has an account of a large house fire that is being blamed on spontaneous combustion of polyurethane foam insulation. My first reaction on reading this was to shout "Boy Scout" or more properly, the initials of "Boy Scout". Polyurethanes are stable polymers that don't catch on fire as any house having wood floors with a urethane finish will verify. Further, the fire had just been put out. Knowing the cause that quickly seems like something appropriate for a news reporter to mention in order to seem really sharp, but a full investigation can take days or even weeks at times.

But a little bit of investigation has forced me to rethink this. Polyurethane foams can indeed spontaneously combust, but only for a short while after they have been applied. The exotherm from the reaction can generate quite a bit of heat and if the insulation is thick enough, that heat can have a difficult time dissipating leading to a fire. Such a scenario has been blamed for 3 house fires in Massachusetts as well.

But it should be pretty clear that spontaneous combustion is only a plausible cause shortly after the polyurethane foam has been sprayed. To blame a fire on it after 24 hours or more would be nonsense. A reacted polyurethane is just that - reacted, and it will not react any further.



Previous Years
July 8, 2013 - Solvents and polymers

July 8, 2010 - New Pressure-Sensitive Adhesives from Tree Byproducts

July 8, 2010 - Metathesis and Polymers