Determinants of polymer properties: which collective factors significantly affect bulk properties such as strength, toughness, and thermal response?

Introduction / Context:
Bulk polymer properties arise from molecular architecture and interactions. Chain length, secondary bonding, and network structure collectively control mechanical, thermal, and rheological behaviour. Recognising the combined influence of these factors is foundational for materials design.

Given Data / Assumptions:

• Higher molecular weight (chain length) generally raises strength and toughness up to a plateau.
• Intermolecular forces (hydrogen bonding, dipole interactions) strongly affect glass transition and modulus.
• Branching and crosslinking alter crystallinity, melt viscosity, elasticity, and heat resistance.

Concept / Approach:
Because all three listed factors are fundamental, the correct choice is the combined option. While tacticity also matters, the question specifically highlights chain length, intermolecular forces, and branching/crosslinking as the principal levers for tuning performance across commodity and engineering polymers.

Step-by-Step Solution:
Assess effect of chain length → increased entanglement and properties.Assess intermolecular forces → higher Tg and modulus with stronger attractions.Assess branching/crosslinking → modifies crystallinity and thermal stability.Conclude that all these factors together govern properties.

Verification / Alternative check:
Design of nylon (H-bonded), PET (polar), and PE (varying branching) demonstrates property changes tied to these variables.

Why Other Options Are Wrong:
Single-factor answers are incomplete.“Only tacticity” excludes equally important determinants listed.

Common Pitfalls:
Overemphasising one factor (e.g., molecular weight) while ignoring morphology and interactions.

Final Answer:
All (a), (b), and (c)