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Nanophase Separation of Poly(N‑alkyl acrylamides): The Dependence of the Formation of Lamellar Structures on Their Alkyl Side Chains
journal contribution
posted on 2019-12-13, 20:05 authored by Kazuki Ebata, Yuki Hashimoto, Shunsuke Yamamoto, Masaya Mitsuishi, Shusaku Nagano, Jun MatsuiIn this study, poly(N-alkyl acrylamides)
[(pAlkylAms)],
which contain alkyl side chains that differ with respect to the chain
length (n; n = 4–18), were
synthesized and the formation of lamellar structures via nanophase
separation was examined. Differential scanning calorimetry (DSC) measurements
indicated that p(AlkylAms) (n = 4–15) powders
are amorphous at 20 °C, whereas p(AlkylAms) (n ≥ 16) contain partially crystalized side chains. The X-ray
diffraction (XRD) patterns of the spin-coated films of p(AlkylAms)
(n = 4–15) exhibited broad diffraction peaks
that correspond to the nanosegregated alkyl side chain domains (qnd), while the spectra of the polymer films
of p(AlkylAms) (n ≥ 16) exhibited both qnd and diffraction corresponding to crystalized
side chains (qca). The spin-coated films
were annealed in water (water annealing) for 12 h to induce nanophase
separation and then characterized using XRD. The XRD results for the
water-annealed films were categorized into three groups. The first
group comprised of p(AlkylAms) (n = 4–7),
which showed XRD patterns similar to those of the pristine films.
The second group contained p(AlkylAms) (n = 8–14),
which exhibited strong Bragg diffraction peaks that correspond to
lamellar structures (qlm). The last group
was composed of p(AlkylAms) (n ≥ 15), which
exhibited not only qlm but also qca. The results indicate that in p(AlkylAms)
(n ≥ 8), the nanosegregation force between
the hydrophilic main chain and the hydrophobic side chains is sufficient
to produce an amorphous film with a lamellar structure. Furthermore,
based on a comparison of the lamellar structure of p(AlkylAms) (n = 18) prepared by conventional thermal annealing with
the structure obtained using water annealing, we concluded that nanosegregation
competes with side-chain crystallization.