4 research outputs found
Long-Chain Hyperbranched Comb Block Copolymers: Synthesis, Microstructure, Rheology, and Thermal Behavior
Long-Chain Hyperbranched Comb Block Copolymers: Synthesis, Microstructure, Rheology, and Thermal Behavior
A series of poly颅(ethylene-<i>co</i>-acrylic acid)-<i>cb</i>-atactic polypropylene
(EAA-<i>cb</i>-aPP) comb block copolymers were synthesized
by grafting aPP-OH macromonomers onto a commercial EAA copolymer made
by the high-pressure free radical process. The starting EAA copolymer
contains 11 wt % of EAA units and has a significant amount of long
chain branches. Therefore, the EAA-<i>cb</i>-aPP copolymers
can be classified as hyperbranched. Room temperature atomic force
microscopy and X-ray scattering measurements reveal strong, finely
textured, phase segregation of the amorphous aPP and semicrystalline
EAA domains, which persists in the melt state. The amorphous aPP side
chains have an unexpected nucleating effect that facilitates crystallization
of the EAA backbone, as evidenced by an increase in crystallization temperature.
Moreover, phase segregation has a strong effect on both the linear
and nonlinear viscoelastic response of the copolymers. Increases in
both the branching density and branch chain length result in an improvement
of melt strength as well as an increase in the extensional strain
hardening (SH). We postulate that the SH enhancement may arise from
the interfacial anchoring of the aPP side chains in the aPP homopolymer
domains. This would produce additional resistance for the EAA backbone
to stretch under uniaxial load due to an energetically unfavorable
process of pulling the aPP arms into the EAA phase where they would
face strong repulsions