Styrene usually polymerizes well under radical methods, but simple olefins do not - and 5-bromo-1-pentene as a monomer would expect to behave a lot like a simple olefin. It is actually surprising that you get 46% alkyl in the product. Toluene can be a poor solvent for these polymerizations - it can act as a chain transfer agent: abstraction from toluene methyl ends a chain, and the resulting benzyl radical can then start polymerization again. This generates low MW polymers that you might not isolate,

5-bromo-1-pentene with AIBN might also be cyclizing.

A better methodology might be a metallocene catalyzed polymerization - check doi.org/10.1016/j.eurpolymj.2004.12.003

Thank you for your answer. Yes the result from molar mass was from 16k to 25k so to little for my aplication. I don't have an access to such exotic ligands. Can you give me an example of the simpler this type of catalyst (I think it is family of Ziegler-Natta) or different more simpler polymerization method?

For science reason I can tell that without dropping monomers I got worse yield about 5% and alkyl content about 7%, so big difference.

I see potential issues with both anionic polymerization (SN2 reaction with the primary bromide) and the radical polymerization (possible cyclization after abstraction of the Br). Have you thought about cationic polymerization? You might need to modify the olefin to 5-bromo-2-methyl-1-pentene. This paper did block polymers of isobutylene and styrene, not sure if random copolymers work - didnt see any papers on it.

Macromol 2021, 1(4), 243-255; https://doi.org/10.3390/macromol1040017

Thank you for answer. I think it will be very applicable, but getting 5-bromo-2-methyl-1-pentene will be a problem. Do you have in mind some cheaper alternatives, (I think I can brominate terminal methyl further)?

I thought about using something different from typical olefin, what do you think about using some biobased alkenes like myrcene with styrene in radical? If not radical can I use cationic with TiCl4 and ethylene diamine ligands?

I have seen pinene with styrene by radical.

if you don't need the halogen and can switch to a solvent that doesn't chain transfer radical could be ok.

I cannot find it, but otherwise for me longer alkyl chain is the better. I Found myrcene can work and then will perform radical bromination.

DMF right or chlorobenzene ?

I curious about physical properties, I need to make membrane from this polymer so molar mass is best to be about 150-300 kDa. Also it need to be stable up to 120 Celsius degrees. Do you think is indeed a good a aproach? cause I find some 0.6:0.4 styrene to myrcene has Tg = 40C, so lot less.

chlorobenzene would be my choice - DMF can have degradation impurities (dimethylamine, water, etc) that might interfere

Thanks for detail answer. Do you think something will came from this aproach that can be further a very good polymer or this terpenes aproach is very bad and I shouldn't waste time on it?

Hard to say without knowing the details - why are you making this polymer? How much of it do you need? (mg, g, kg?)

if your goal is a copolymer of styrene and and an alpha olefin with an omega halogen...

one option would be to use a protected alcohol as the stand in for the halogen. So for example, styrene with t-BOC protected hex-5-en-1-ol to get the copolymer. (Copolymer shouldn't go to very high conversion - 50% max). Treat with acid to de protect to the alcohol, then convert the alcohol to bromide with carbon tetrabromide and triphenylphosphine. The triphenylphospine oxide side product can be hard to get rid of, but this would work if you are on a smaller scale (under 10 g).

now g scale, further scalling to bigger. As I said physical properties are import like high MW can be 80< kDa and 30% minimum amount of alkyl group with T >120 C of temperature stabillity.

I have an Idea to make styrene with some terpene then after purification dissolution in dmf and add a bit of aquous hbr to add -Br