Molecular-weight dependence of the formation of highly ordered lamellar structures of poly( N -dodecyl acrylamide) by humid annealing

• Published in: Polymer chemistry Vol. 10; no. 7; pp. 835 - 842
• Main Authors: Ebata, Kazuki, Hashimoto, Yuki, Ebara, Kohei, Tsukamoto, Mayu, Yamamoto, Shunsuke, Mitsuishi, Masaya, Nagano, Shusaku, Matsui, Jun
• Format: Journal Article
• Language: English
• Published: Cambridge Royal Society of Chemistry 21.02.2019
• Subjects: Acrylamide; Annealing; Chemical synthesis; Crystal structure; Crystallinity; Dependence; Diffraction patterns; Domains; Free radical polymerization; Free radicals; Lamellar structure; Molecular weight; Polymer chemistry; Polymers; Relative humidity; Self-assembly; Spin coating; Thin films; X-ray diffraction
• ISSN: 1759-9954; 1759-9962
• DOI: 10.1039/C8PY01660G

The molecular-weight dependence of the formation of highly ordered lamellar structures of poly( N -dodecylacrylamide) (pDDA) during humid annealing was studied. For this purpose, pDDA polymers with a number-average molecular weight ( M n ) ranging from 1200 to 52 000 were synthesized by free radical polymerization. Thin films of these polymers were prepared by spin-coating and their structures were examined by X-ray diffraction (XRD) and FT-IR measurements. The XRD patterns of the spin-coated films showed a broad halo at q = 2 nm −1 , which was attributed to scattering from nanosegregated alkyl domains in the case of pDDA with M n ≥ 3500 and to semi-crystalline lamellar domains in the case of pDDA with M n = 1200. Subsequently, the films were annealed at 60 °C and 95% relative humidity (humid annealing), which resulted in the formation of lamellar structures for pDDA films with M n ≥ 3500, whereby the long-range ordering of the films increased with the M n of the pDDA polymers. In contrast, pDDA with M n = 1200 afforded a semi-crystalline film even after 96 h of humid annealing. The higher M n polymers showed more disordered alkyl side chains and main chains in the lamellar film. Thus, it was concluded that the segregation between the alkyl side chains and main chains, which contain water-adsorbed amide groups, should be the driving force for the observed structural changes. Our results suggest that unique self-assembled structures can be obtained by humid annealing even from amorphous homopolymers.