Probing into Homopolymer
Self-Assembly: How Does Hydrogen
Bonding Influence Morphology?
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Abstract
Self-assembly of amphiphilic homopolymers composed of
both hydrophilic
and hydrophobic components in each repeating unit is burgeoning in
recent years due to their facile synthesis compared to block copolymers.
However, ordered homopolymer nanostructures are very limited, and
solid TEM evidence for the formation of vesicles and other complex
morphologies is necessary to address the mechanistic insights of homopolymer
self-assembly. Presented in this article are the studies on the morphological
transition, the structure analysis, and the formation mechanism of
homopolymer self-assembly. First, a series of amphiphilic homopolymers,
poly(2-hydroxy-3-phenoxypropyl acrylate) (PHPPA) with various molecular
weights (MWs) have been designed and synthesized by the reversible
addition–fragmentation chain transfer (RAFT) process. Second,
upon simply changing the homopolymer’s chain length or cosolvents
during self-assembly, a wide range of new homopolymer-based nanostructures
can be obtained, such as large compound micelles (LCMs), simple vesicles,
large compound vesicles (LCVs), and hydrated large compound micelles
(HLCMs) as a result of different intensity of inter/intra-polymer
hydrogen bonding in the homopolymer self-assemblies. Moreover, micrometer-sized
branched cylinders are formed by premixing PHPPA<sub>36</sub> and
PHPPA<sub>103</sub> homopolymers, which is not observed by self-assembly
of PHPPA<sub>36</sub> and PHPPA<sub>103</sub> individually. Third,
we claim that the structures of homopolymer self-assemblies are much
different from their block copolymer analogues due to homopolymer’s
fuzzy hydrophobic and hydrophilic domains compared to block copolymer’s
distinct ones. We confirm that the structure of micelle core or vesicle
membrane (alike to each other in nature) consists of both hydrophilic
and hydrophobic moieties, which is different from block copolymer
micelles or vesicles with hydrophobic cores or membranes. Also, a
dye encapsulation experiment is employed to identify and distinguish
a new nanostructure, HLCMs, from LCMs. Our study has provided a new
perspective on homopolymer self-assembly