P&P I dit a lot of natural rubber processing as a student and cutting lumps of natural rubber and then mixed with sulphur and other ingredients on a two roll mill then cured sheets for tear , resiliency and tensile testing  – so your vulcanite test sounds good. 

Polypropylene has a methyl side group that can be distributed either side of the chain – so when it is synthesized it can be produced as random, alternating or all on one side – which affects its crystallization and physical properties.  The tech terms are  atactic, syndiotactic and isotactic. Large use in ropes as it is very aliphatic and doesn’t get affected by water.