Okay, yeah, last time we talked about the bunch of synthetic rubbers that the humans

developed next to the still most important rubber, which is the natural rubber. If you're

speaking mass-wise or volume-wise, we talked about the butadiene rubber, which is the chemically

most simple rubber because it's just butadiene polymerized, simplest D you can get. And then

we talked about the first relief feasible synthetic elastomer, which was the styrene

butadiene rubber, so it's a copolymer. However, with the technique they had at the beginning of

this development of synthetic rubbers, it was way more feasible to first do that one. So it was

really the first synthetic rubber that had acceptable rubber properties. Last time we also

talked about the emulsion polymerization because as we are dealing with synthetic rubbers right now,

we have to create or polymerize our own polymers because nature is not doing that for us. So that's

why we always have to look a bit on the polymerization technique we are using to

first get the polymer and then later the crosslinking. Okay, so for the styrene butadiene

rubber, as for many rubbers, there are many techniques. However, for this one, it's particularly

important that you get the hang of it because the solution-based styrene butadiene rubber is

now catching up greatly. So the emulsion styrene butadiene rubber is becoming less and less important.

I think five, six years ago, or ten years maybe already, it was that the emulsion-based one was

twice as much as the solution-based one. However, because you can tailor the chemical composition of

it so nicely with adding solvents or monomers, you can tailor it directly to your final application.

And that's always a selling point for the chemists, for the application engineers. So this material

fits your application better. You would get this in this benefit, however, if it costs that much.

And that and that much more. So they're making the business case. And that increased, so now it's

almost 50-50. And the solution-based one is still increasing. Okay, so last time we talked about the

basic variant, but now we're talking a bit more about the chemically advanced one.

So the chemical basis for that one is still the living polymerization with the butyl lithium

catalyst. So it's the living polymerization technique. As you can see here, we have an alkyl

residue and we have this metal ion positively charged. And that one will then induce dipole in

the double bond, which will then continue to polymerize. It doesn't matter if it's like this

from the basic mechanism, it can work as well with the butadiene as well with the styrene.

Both have a double bond here. Just the substituent here is changing. The X will be a hydrogen for

the hydrogen, but a C2 body with also double bond here. And for the styrene, this will be,

of course, the benzene ring. Living polymerization, quick recap from last time maybe,

it's called that because there's no termination reaction. For radical polymerization, you can

have a combination of the radicals, so they're terminated. It does not work with the living or

anionic polymerization because if you have an anion like that one here, it won't react with

another one. This will not recombine with another cation here. For the polymerization, I think we

talked about that already a bit for the butadiene rubber, that the molecular weight distribution

changes depending on your catalyst technique. We have this emulsion butadiene rubber, which was

very broad. Then we have this living polymerization butadiene rubber, which was quite narrow from the

molecular weight distribution. I think the polydispersity index was between one and two.

And then we have this Siegler-Natta, this highly stereoselective catalyst, where we had a

polydispersity index between two, two point five maybe, so medium to narrow width. Here we're using

again this living polymerization, so we also get this narrow molecular weight distribution.

This gives us some advantages because we can quite nicely tailor the molecular weight that we want to

achieve in the end. Speaking of maybe some numbers maybe, we can adjust it between 150

and 500 kilograms per mole. So that's a medium to high molecular weight that we can achieve. However,

the width of this distribution is rather limited. It's quite narrow. As you know, if you have the

conversion rate and the polymerization degree, the living polymerization just yields a straight line.

That was the chain growth. Then we had the step growth. And then again, we had the living

polymerization, which gave this nice linear correlation in that plot. If you want to have

some nicer properties or some more deliberate properties, we can introduce chain branching.