Chain Growth and Step Growth: Two Routes to a Polymer · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

Two ways to grow a chain

Science · Chemistry · ages 22-24
Name ______________________   Date ____________

  1. In step growth, when does molar mass climb?

    • Steadily from the first minute
    • It never climbs at all
    • Only at very high conversion

  2. In chain growth, when do full-length chains appear?

    • Only at the very end
    • From the start at active centres
    • Never, chains stay short

  3. A dispersity near one means nearly uniform chain lengths.

    Circle one:   True   False

  4. A step-growth batch uses a small excess of diol. What happens to chain length?

    • It is capped, since excess ends have nothing to meet
    • It doubles automatically
    • It stays exactly the same

  5. A polycondensation reaches 99 percent conversion. What is the average degree of polymerisation?

    Answer: ______________

  6. A sample reports dispersity 1.05. What does that imply about how it was made?

    • Classic step growth
    • Controlled chain growth
    • Random degradation

  7. A polycondensation stalls at 98 percent conversion with short chains. What is the sharpest diagnosis?

    • The reaction needs more time but conversion is irrelevant
    • The temperature display is wrong
    • Side reactions or imbalance froze conversion, and length depends on those last percent

  8. A student sees molar mass jump only past 95 percent conversion. Which route is it?

    • Step growth, by its flat-then-steep curve
    • Chain growth, by its early chains
    • Neither, the data must be wrong
LightMySky · lightmysky.comW1-mt_LADBgarlKs-s1

Answer key

For grown-ups. Fold this page away before handing over the rest.

Two ways to grow a chain W1-mt_LADBgarlKs-s1

  1. Only at very high conversion · Everything couples with everything, so length waits for near-full conversion.
  2. From the start at active centres · Active centres grow complete chains while monomer remains.
  3. True · Values near one report controlled, even growth.
  4. It is capped, since excess ends have nothing to meet · Unpaired end groups stop growth on every chain.
  5. 100 · One over one minus 0.99 is 100 units.
  6. Controlled chain growth · Near-one dispersity is the mark of controlled growth.
  7. Side reactions or imbalance froze conversion, and length depends on those last percent · At 98 percent the average is only 50 units, so anything capping conversion caps length.
  8. Step growth, by its flat-then-steep curve · Late climbing is the step-growth sketch.
Worksheet · LightMySky