Catalysis in olefin polymerization: A Ziegler–Natta catalyst system of the type AlR3–AlCl3 (representative of organoaluminum/metal halide systems) is classically used to polymerize which monomer to a stereoregular polymer?

Introduction / Context:
Ziegler–Natta catalysts revolutionized polyolefins by enabling stereoregular (isotactic or syndiotactic) polymers at moderate conditions. Recognizing the monomers most associated with these catalysts is a key concept in polymer reaction engineering and materials selection.

Given Data / Assumptions:

• The catalyst described is representative of Ziegler–Natta systems (organoaluminum + transition metal halide).
• We look for monomers that yield tactic, crystalline polyolefins under such catalysis.
• Industrial hallmark product: isotactic polypropylene (iPP).

Concept / Approach:
Ziegler–Natta catalysts (e.g., TiCl4/MgCl2 with AlR3 cocatalyst) polymerize alpha-olefins like propylene to highly stereoregular polymers. While other monomers can be polymerized with different catalysts, the archetypal success story is propylene → isotactic polypropylene with high crystallinity and excellent mechanical properties.

Step-by-Step Solution:

Verification / Alternative check:
Process flowsheets and catalyst literature document Ziegler–Natta catalyzed propylene polymerization as a foundational polyolefin technology.

Why Other Options Are Wrong:

• Vinyl chloride, styrene, vinyl acetate: Commonly polymerized by radical routes; Ziegler–Natta is not the standard industrial path.

Common Pitfalls:
Confusing organoaluminum co-catalysts with the full catalyst system; the key is stereospecific coordination-insertion polymerization of alpha-olefins.

Final Answer:
propylene