ma8b00719_si_001.pdf (6.43 MB)
Bottlebrush Copolymer Additives for Immiscible Polymer Blends
journal contribution
posted on 2018-07-20, 17:40 authored by Adeline
Huizhen Mah, Pantea Afzali, Luqing Qi, Stacy Pesek, Rafael Verduzco, Gila E. SteinThin films of immiscible polymer
blends will undergo phase separation
into large domains, but this behavior can be suppressed with additives
that accumulate and adhere at the polymer/polymer interface. Herein,
we describe the phase behavior of polystyrene/poly(methyl methacrylate)
(PS/PMMA) blends with 20 vol % of a bottlebrush additive, where the
bottlebrush has poly(styrene-r-methyl methacrylate)
side chains with 61 mol % styrene. All blends are cast into films
and thermally annealed above the glass transition temperature. The
phase-separated structures are measured as a function of time with
atomic force microscopy and optical microscopy. We demonstrate that
subtle changes in bottlebrush architecture and homopolymer chain lengths
can have a large impact on phase behavior, domain coarsening, and
domain continuity. The bottlebrush additives are miscible with PS
under a broad range of conditions. However, these additives are only
miscible with PMMA when the bottlebrush backbones are short or when
the PMMA chains are similar in length to the bottlebrush side chains.
Otherwise, the limited bottlebrush/PMMA miscibility drives the formation
of a bottlebrush-rich interphase that encapsulates the PMMA-rich domains,
stabilizing the blend against further coarsening at elevated temperatures.
The encapsulated domains are aggregated in short chains or larger
networks, depending on the blend composition. Interestingly, the network
structures can provide continuity in the minor phases.