Currently, there is only 1 synthetic rubber recipe and it has really poor yield compared to just smelting resin, and this mod seems to be the perfect place to make some suggestions.
Aside from styrene-butadiene rubbers, there are also butyl rubbers, which the production chain could go
butane --(isomerization)--> isobutane --(dehydrogenation)--> isobutylene --(polymerization)--> polyisobutylene + small amount of isoprene --(could be raw bio rubber or get it from cracking naphtha like butadiene)--> rubber
Isoprene itself can be polymerized to make rubber. Like mentioned above, it could be obtained by cracking naphtha and then have a polymerization recipe to make rubber. From what I understand, it is very similar to butadiene and is obtained by similar processes.
There is also neoprene (polychloroprene) which could have the following production chain:
butadiene --(chlorine added)--> 3,4-dichlorobut-1-ene + 1,4-dichlorobut-1-ene --(isomerization)--> 3,4-dichlorobut-1-ene + sodium hydroxide solution --(dehydrochlorination)--> chloroprene + hydrogen chloride -> rubber (polychloroprene)
I think Angel's rubber is woefully underutilized and kind of a pain to make, so these options might make it more interesting.
