Lubricious hydrophilic coating

I'm studying the formulation of a hydrophilic lubricious coating for a stainless steel substrate for use in an acidic aqueous environment.

From the patent literature I've seen polyurethane,

polyvinilpyrrolidone, PEG/PPG and silicone lubricious coatings. So my first question is: does hydrophilic lubricious coating = hydrogel ?

According to one patent 'a polymeric diisocyanate is grafted to the substrate surfece and is then placed into water creating a urea bond and thus activating the hydrogel' - this does not make sence to me, has anyone experience of 'activating a hydrogel using such a method' ?

If I can include enough of a hydrophilic polymer in a crosslinked hydrophobic polymer and then swell it in water do I get a lubricious coating ?

thanks in advance,

Bob

Reply to
hartmanbobby
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Like you, I can't prove it, but it certainly seems to be the case. At least if the lubriscousness is for a water based environment.

The water reacts with the isocyanate to produce an amine and CO2. The amine can then react with another isocyanate to produce a urea. The rest of the magic (i.e., the "activation") is just patent mubo-jumbo. Either the author doesn't know any better, the author doesn't want to commit (not a bad idea in fact, as if he is wrong, the validity of the patent can be questioned all because he/she wanted to be a theoretical showoff) or the author is attempting to mislead.

If you read enough patents, you start become very sensitive to the BS in them.

You'll have to clarify this situation for me. Are you looking at an interpentrating polymer network of some sort? How are you "including" the hydrophilic polymer? Details, I need details!

Also, the word "enough" can be made to mean an ocean of hydrophilic material, so in that sense, the answer is YES. But I'm not going to take the easy way out.

John Aspen Research, -

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"Turning Questions into Answers"

Opinions expressed herein are my own and may not represent those of my employer.

Reply to
john.spevacek

Hi John,

Thanks for your comments - just to put my questions into context, I don't have a specific application for this. What I am trying to do is sanity check my thinking as I learn about these systems.

With regard to the patent I mentioned - can you think of a specific reason why someone would want to introduce more urea into a isocyanate polymer to create a hydrophilic hydrogel ? from what I've read there are a number of different functional groups like urethane etc that can be produced from isocyanate reactions, is the urea more hydrophilic or something ?

Again, in relation to my comment about a hydrophilic polymer in a crosslinked hydrophobic polymer - this was just me thinking out loud in a sort of hypothetical way - no specific situation. To clarify what I was thinking 'tho: Lets just say I take a PEG that dissolves in water and somehow crosslink it via the end groups with a reactant that is insoluble in water, would I then have a hydrogel or just a jelly blob. My intuition tells me that in such a situation the material would need to have some mechanical stability and thus a hydrophobic or non-soluble polymer chain would be rquired in addition to the PEG. If this is the case how does one decide upon the balance between soluble and non-soluble components. In my mind I'm visualising a lubricious material as being like a disposable contact lens, ie: slippery and full of water but yet a solid.

Thanks,

Bob

Reply to
hartmanbobby

I've been told more than once that studying polymers is insane :)

Just to clarify, the urea that I mentioned are urea linkages,

-N(C=O)N-, which are similar to the urethane linkages -N(C=O)O-. From the little bit of the patent that you cited, it seems like they are using the water to initiate the urea reaction thereby increasing the molecular weight and possibly crosslinking it depending on the functionality of the isocyanate.

Are you familiar with Pluronics made by BASF? These are triblock copolymers of PPO (polypropylene oxide) and PEO, with the PEO being the middle block in most cases. The PPO is insoluble (less soluble would be a better descriptor) in water and so it phase separates and combines with other PPO blocks from other molecules forming physical crosslinks. BASF makes these materials with a variety of molecular weights for the blocks. It's been few years since I've played with them, so I'm not armed with the most up-to-date knowledge. The one that I remember most is the L64. For a 20% solution in water, you can get a nice soft gel. What is bizarre is that the crosslinks can be broken by COOLING the material. It's very disturbing to see a ice cold water like solution turn into a gel when it warms. Try explaining that one to high school students.

John Aspen Research, -

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"Turning Questions into Answers"

Opinions expressed herein are my own and may not represent those of my employer.

Reply to
john.spevacek

Does silicone really belong into this line of hydrophilic coatings?

Unlike John, I would not consider this patent mumbo-jumbo, but a description of what's really going on. I assume the surface has been pretreated to contain amine functions. Then you can easily graft an isocyanate via an urea linkage to the surface. But a good hydrogel has to be crosslinked (commercial break: take a look at

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your case this is done by adding water (John has given an account on the chemistry involved). But water is also an essential ingredient for the hydrogel, e.g. if the hydrogel is dried it will be of no use. So the swelling of the gel (which certainly takes some time) could be considered as an activation step.

Is the patent in english? Perhaps you could provide the patent number.

Regards, Oliver

Reply to
Oliver 'Ojo' Bedford

Because of the two -NH-'s the urea linkage is probably more hydrophilic than a urethane group. The question I cannot answer is whether this is also true for the polymer.

You could also increase the crosslink density of your PEG.

PEG is known to crystallize. Another difficulty to keep in mind.

Regards, Oliver

Reply to
Oliver 'Ojo' Bedford

I guess I should probably clarify the "mumbo-jumbo" comment (and prove that I can spell it right too!) The use of the phrase "activating the hydrogel" is not a phrase that I would expect to find in a published scientific paper, unless the invention is far greater than what I am imagining. "Activing the hydrogel" strikes me as something the filing lawyer came up with, hence the mumbo-jumbo comment.

I've already listed reason previously about why the technical details may be avoided, and there is some validity to these reasons but only from a legal point of view. Using patents as a basis for scientific learning is not something I would advise. There is no refereeing system, the "inventor is his own lexicographer", and at least in a strict legal sense, the invention cannot be duplicated since doing so would violate patent law!

John Aspen Research, -

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"Turning Questions into Answers"

Opinions expressed herein are my own and may not represent those of my employer.

Reply to
john.spevacek

Guys,

Thanks for all the input it is much appreciated. John and Oliver, both of your points are well made - I can see how the patent is attempting to explain the invention but I can also see how the use of some technical terms can be...questionable. In this case I think the patent was describing both crosslinking and swelling as 'activating' - but that's ok as the term does make sense.

John, I totaly agree that the patent literature is no substitute for peer reviewed material but I have found that in addition to peer reviewed articles the patents I have read give an interesting, practical perspective to certain technology.

thanks,

Bob

Reply to
hartmanbobby

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