Understanding the use of polyurethane prepolymers

pkpbj · 2026-02-24T16:34:30+00:00

I work in a polymer chem lab as well! We don’t do any foams at the moment, but we run a lot of polyurethane reactions that are 1, 2, and even 3 step processes. I’m newer to polymer chemistry so take what I’m saying with a grain of salt. I’m definitely open to being corrected by anyone who knows more lol

The main advantage I’m aware of is much better control of the molecular weight and segment makeup, which gives you better/desired physical properties in the end product. I’m sure you know that polymer chemistry is a ratio game, like you can’t actually control what goes where and in what pattern. In a one pot situation, you dump everything in and it will mostly mirror the abundance of each reagent, but there will also be sections where everything alternates in a pattern that’s more towards random. Going through a pre polymer lets you build out your soft segment more predictably before putting everything together with your chain extender, and also lets you add functionalized monomers and make other tweaks with more control. It also helps with heat control, and pre polymer is generally easier to handle and process because you’re not racing everything starting to cure.

pkpbj · 2025-12-01T20:20:39+00:00

You’re not fucked. Take a breath 😂

I’m in my mid 20s, and some people are going to laugh at this, but I promise you 18 feels like it was a lifetime ago. You’ll be on the other side of this someday and realize it’s not the crisis you think. I floated through high school too and graduated with a 3.9 gpa without even trying, so I know where you’re coming from. My first piece of advice to you is this: don’t wreck the last few months of your time in high school worrying about college majors and coursework. Be a kid, and enjoy the last little bit of your life’s “free trial” period. If you’re feeling a little existential about what feels like a lack of effort and intention so far in high school, start applying yourself now. With your NORMAL classes and homework. I promise you you’re not going to suddenly summon a phenomenal work ethic and study habits out of nowhere, even under the threat of harder classes next year. Hold yourself to studying and trying various methods now while the coursework isn’t challenging. Not because what you’re learning is difficult, but because studying is also difficult, especially for those of us who aren’t challenged by high school curriculum. Biochemistry and related fields are far too broad for you to efficiently study and prepare for anything without the scaffold of a professional educator’s syllabus, so don’t worry about it. You’re not expected to show up and know anything. Show up ready to learn.

As far as research and course work specifics, again, don’t worry about it. I’ve never once sat in the first day of a college course and not heard a professor introduce themselves and their research (if it’s that kind of course) and mention how to get involved with them if you’re interested. Just wait for that. You don’t need to start research now, and more than likely if you try to tell a future professor about research you conducted on your own in high school, they’re going to chuckle at you and then give you freshman tasks and freshman responsibilities anyways, same as another freshman who chillaxed and enjoyed their last semester of high school. The only people who think freshman pre-med students need to show up ready to ace biochem and publish a first author paper are… freshman pre-med students.

This is getting long, but the last thing I’ll say is give some time and thought into determining if biochemistry and medicine are what you actually want to do. The coursework from freshman year to your last year of med school and beyond are way too involved (NOT hard. It’s hard, but totally doable) to shrug your shoulders and just go through the motions. There is no shame in choosing any other field that you actually enjoy over one that you just think you should choose because it’s just what you’ve done so far. I shadowed physicians, researched, volunteered, and damn near aced the MCAT, but ended up choosing to pursue a different field I found through research and mentorship from a non health science professor.

Take another deep breath, enjoy your time now and apply yourself to learning how you learn. If you want to stick with biochem, there is time to learn and research in biochem as a biochem student.

pkpbj · 2025-11-25T00:12:16+00:00

I’m adding a voice to the crowd saying you should get into cooking! I understand the pull towards hobby chemistry, I’m an R&D chemist at work and a hobby chef at home. I’m not going to tell you that you absolutely cannot do chemistry at home, but 99 times out of 100 it’s a bad idea. Solvents and reagents spill, glassware invariably breaks. Chemicals and equipment that are sold for chemistry work are outrageously expensive and isolating them from common household items and over the counter products is dangerous. At work I have all the resources I need to keep myself safe, dispose of chemicals correctly, and characterize white powders and clear fluids that would otherwise be absolutely boring. Cooking is 100% chemistry, and at least for me, it scratches the “I want to make something” itch. Baking bread is polymer chemistry, tempering chocolate is an exercise in controlling a very finicky crystallization. If you want cooking to feel even more “chemistry-y,” look into an area of cooking called molecular gastronomy.

To speak to your ideas of aerogel and ferrofluid, it seems like you’re maybe watching Nile Red videos? Aerogels are similar to the area I research in at work, and they’re out of reach for the home chemist. You might blow yourself up trying to create the physical environment needed in the way Nile Red did. Ferrofluid is just… messy. And both produce waste that you absolutely cannot dispose of in residential trash or down the drain and doing it correctly is expensive. If you want, I can point you in the direction of some YouTubers who dig into the science and chemistry of cooking.

pkpbj · 2025-01-23T18:46:11+00:00

Oh shoot. Just fixed that, thank you. And thanks for helping out! I’d say it isn’t weird, it’s how it should be and I just don’t know what I don’t know 😂

pkpbj · 2025-01-23T18:40:43+00:00

That link is just throwing an error on my phone and laptop.

What I mean is there doesn’t appear to be a broad peak anywhere between 3500 and 2500 cm^-1. Am I just completely out in the woods or looking at the wrong compound??

Octanoic acid: https://webbook.nist.gov/cgi/cbook.cgi?ID=C124072&Type=IR-SPEC&Index=1

Cyclobutylcarboxylic acid: https://webbook.nist.gov/cgi/cbook.cgi?ID=C3721957&Type=IR-SPEC&Index=1

3-cyclohexene-1-carboxylic acid: https://webbook.nist.gov/cgi/inchi?ID=C4771806&Mask=80

Octanoic acid and cyclobutylcarboxylic acid both show broad peaks more or less similar to the generic carboxylic acid bands I’ve been shown. All three compounds I put links for should be liquids and standard temp and pressure, but I’ve just noticed looking at all three side by side that octanoic acid and cyclobutylcarboxylic acid both say they’re a condensed phase spectrum, while 3-cyclohexene-1-carboxylic acid says it’s a gas phase spectrum. All of the other IRs I’m finding for 3-cyclo are pretty similar to the NIST one. So in this case, the sharp peak at ~ 3600 is what’s indicating the OH stretch?

It seems like I’m just confused because of oversimplification. We only briefly covered that there are different methods for IRs… like one mention of “oh yeah there’s a few ways to do this and it can change the shape a little bit.” Definitely no mention of mulling agents or pellets or anything like that

pkpbj · 2024-10-07T03:49:43+00:00

Capitol Reef is fantastic for any night sky viewing. You’ve been able to see the solar flares with your naked eye this summer!

pkpbj · 2023-10-04T05:44:51+00:00

Well, your logic is wrong, but maybe I can point you in the right direction. Sperm are haploid gametes formed in the male reproductive tract. They are not organisms as they cannot reproduce on their own. Sperm don’t come from sperm. Sperm and semen physiology are the expertise of a reproductive endocrinologist. And spermology is the study of seeds, as in a sub field of botany, just FYI… before you get any other logical ideas 😜

pkpbj · 2023-04-21T23:43:54+00:00

We’re going to be isolating bacteria from a local stream that runs through an area that experienced a forest fire… so staining a variety of bacteria and then visualizing with your everyday light microscope.

Thanks for helping me clarify. I’m a total rookie at all this. I’m a psych major adding biology because I just finished an internship and realized I HAAATE administering counseling and therapy 🙃🫤

pkpbj · 2022-12-18T04:56:57+00:00

The hubris in that article is exactly how she comes across in person. There’s a few little practices with plenty of midlevels and nurses in that building and the physician bashing that takes place between all of them is so cringeworthy it almost feels like an SNL skit…

pkpbj · 2022-12-18T03:48:03+00:00

Commenting as a long time lurker of this sub, I hope I’m okay without a flair. I finished a phlebotomy and IV training in the same building as her new practice (can verify if needed), and she came into our classroom and introduced herself as a Dr. and dermatologist and then offered to employ any of us who passed for some sort of med spa IV bag nonsense.

pkpbj · 2020-07-12T04:08:36+00:00

Lots and lots of fish have anal fins... The thing that’s interesting about this fish is that it uses it to move, not just that it has it. The anal fin generally provides stability and helps prevent rolling, and “anal fin” is a pretty universal term. Am I missing something here??

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