Past exam of the chemistry course of the year 4 of the natural sciences course of the University of Cambridge / 2022 / Paper 2 / Section A / 18 / c

A sufficiently phase-separated block copolymer can show two glass transitions, associated approximately with its two microdomains. Simultaneous feeding instead tends to distribute the monomers along each chain, giving a statistical copolymer and usually one composition-dependent glass transition. Different monomer reactivities could produce a gradient rather than a perfectly random sequence.

For a homogeneous mixture an approximate interpolation is the Fox equation, $T_g^{-1}=w_1/T_{g1}+w_2/T_{g2}$, with temperatures in kelvin. Two transitions are not guaranteed merely by block architecture: short blocks, miscibility or insufficient experimental resolution can give one broad transition. The contrast is between domain-specific segmental environments and a more uniform mixed environment.