📚 Learning Guide
Polymer Glass Transition Temperature
hard

Which of the following scenarios best illustrates how variations in molecular weight and chemical composition can affect the glass transition temperature (Tg) and subsequently influence the manufacturing conditions for a polymer used in a medical device?

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Choose the Best Answer

A

A polymer with high molecular weight and a high degree of cross-linking, designed for implant applications, requiring higher processing temperatures.

B

A low-density polymer with rapid cooling during processing, resulting in a Tg below room temperature, suitable for packaging.

C

A polymer with low molecular weight and high crystallinity, processed at low temperatures to maintain flexibility for automotive parts.

D

A polymer with a high Tg that is blended with a plasticizer to lower its Tg for easier processing in consumer goods.

Understanding the Answer

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Answer

The best illustration is a polymer that is a copolymer of a low‑melting monomer and a high‑melting monomer, where the ratio of the two determines the Tg. If the high‑melting monomer is increased, the overall Tg rises because the heavier, more rigid units dominate the chain dynamics. A higher Tg means the polymer must be processed at a higher temperature to flow, which can degrade sensitive medical components. For example, a polyurethane used in an implantable catheter may shift from a Tg of 20 °C to 60 °C when the hard segment content is doubled, requiring the mold temperature to rise from 30 °C to 70 °C to achieve proper flow without damaging the device. Thus, changing molecular weight and composition directly alters Tg and forces adjustments in the manufacturing heat profile.

Detailed Explanation

When the polymer chain is long and many chains are linked together, the material behaves more rigidly. Other options are incorrect because Cooling quickly does not change Tg; Tg is set by the polymer’s makeup; A short chain lowers Tg, while crystals make the material more solid and increase Tg.

Key Concepts

Significance of Tg in Polymer Processing
Factors Affecting Tg
Relationship between Tg and Polymer Applications
Topic

Polymer Glass Transition Temperature

Difficulty

hard level question

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