Structural Peculiarities of Triblock Copolymers Containing Poly(Ethylene Oxide) and Polyacrylamide

Abstract

The morphology of the triblock copolymers (TBC) containing chemically complementary poly(ethylene oxide) (M _vPEO = 3 · 10³ ÷ 1 · 10⁵) and polyacrylamide (M _PAAm = 4.5 · 10⁴ ÷ 9.07 · 10⁵) of different chain lengths is studied. The loss of the PEO ability to crystallize in TBC at M _vPEO ≤ 4 · 10⁴ is established. At the same time, PEO blocks with M _v  = 1 · 10⁵ form small crystalline domains in the TBC structure, but their crystallinity degree turns out to be by 2.8 times less than that in individual poly(ethylene oxide). A microphase separation in amorphous regions of the TBC structure at high values of M _PAAm is revealed. It is shown that the main reason for the effects observed is the formation of a complex between PEO and PAAm blocks by hydrogen bonds.

Keywords:

• intramolecular polycomplex
• poly(ethylene oxide)
• polyacrylamide
• structure
• triblock copolymer

Notes

^a The weight part of PEO in the copolymers.

^b The ratio between units of PAA and PEO blocks in the copolymers, base-mole_PAA/base-mole_PEO.

^a The glass transition temperature.

^b The temperature interval of a structural transition.

^c The heat capacity jump.

^d The glass transition temperature of compatible blends of PEG + PAA calculated by Couchman-Karasz equation.

^e The melting temperature.

^f The melting enthalpy.

^g The crystallinity degree: for pure PEG X _c  = ΔH _m /Δ, where ΔH is the melting enthalpy for 100% crystalline polymer (196.8 J · g⁻¹) [11]; for TBC X _c  = ΔH _m /(ΔH  · w _PEO)[12], where w _PEO is the mass fraction of PEO in TBC.