What is the difference between Unhydrogenated Styrenic Block Copolymers (USBCs) and Hydrogenated Styrenic Block Copolymers (HSBCs)? And why does it matter?

The difference between USBCs and HSBCs lies primarily in their chemical composition and properties, which have significant implications for their applications:

Hydrogenation Process:

• • USBCs: Unhydrogenated styrenic block copolymers have not undergone a hydrogenation process. This means their polymeric backbone retains unsaturated (double) bonds in the rubber blocks (typically polybutadiene or polyisoprene).
  • HSBCs: Hydrogenated styrenic block copolymers have undergone hydrogenation, a chemical process that saturates the unsaturated bonds with hydrogen atoms. This results in fully saturated rubber blocks (polyethylene-co-butylene or polyethylene-co-propylene) within the copolymer structure.

Properties:

• USBCs: Due to the presence of unsaturated bonds in the rubber blocks, USBCs typically exhibit:
• • • Better elasticity and resilience compared to their hydrogenated counterparts.
    • Higher glass transition temperatures (Tg) for the rubber segments, which can lead to improved low-temperature properties.
    • Greater susceptibility to oxidation and degradation over time due to the presence of double bonds.
    • Residual olefin groups for crosslinking or selective functionalization in use.
• HSBCs: Due to the saturated mid-blocks, HSBCs typically exhibit:
• • • Improved thermal stability and resistance to oxidation because of the absence of double bonds.
    • Lower glass transition temperatures for the rubber blocks, which can enhance flexibility and processability.
    • Higher resistance to UV radiation and ozone, making them more suitable for outdoor applications.
    • Higher temperature resistance during processing due to inert mid-block improving suitability for compounding with high melt-flow polymers.

Applications:

• USBCs: They are often used in applications where elasticity and softness are critical, such as in adhesives, sealants, footwear, and certain types of flexible packaging.
• HSBCs: Their enhanced stability and mechanical properties make them suitable for applications requiring durability, such as in automotive components, durable goods, medical devices, and certain types of structural adhesives.

With their differing chemical structures, (presence or absence of hydrogenation) and the consequent differences in their physical properties, HSBCs and USBCs are applied to differing applications based on the needs of the end-use product. Each type has distinct advantages and is chosen based on specific performance requirements in various industries.