Impact of the α-Methyl Group (α-CH₃) on the Aggregation States and Interfacial Isotherms of Poly(acrylates) Monolayers at the Water Surface

Abstract

Polymer monolayers at liquid surfaces have attracted considerable attention as tools to construct molecular devices with unique properties. The aggregation states of chains within the monolayers must be understood as the first benchmark to establish molecular designs for the devices. It has been reported that large differences exist in surface pressure−area isotherms of polyacrylates and polymethacrylates at the water surface, although they differ chemically only by the absence of an alpha methyl group (α-CH 3 ) in the former. Herein, we carried out experiments using sum-frequency generation vibrational spectroscopy, atomic force microscopy and infrared reflection absorption spectroscopy to explore the changes of the aggregation state and interaction of four poly(acrylates) (i.e., poly(methyl acrylate), PMA; poly(ethyl acrylate), PEA; poly(methyl methacrylate), PMMA; poly-(ethyl methacrylate), PEMA) at the water surface during compression. In the case of PMA and PEA without α-CH 3 , the polymer chains adopt an expanded 2-D random-coil conformation. The methyl group in the ester side chain (s-CH 3 ), which is the origin of the surface pressure variation, is increasingly ordered with compressing of the surface, leading to the expanded-type isotherms. Nevertheless, since chains of PMMA and PEMA were collapsed into compact globules, the s-CH 3 orientation becomes invariant on compression, giving rise to more condensed isotherms with faster increase of surface pressure with compression. Weaker hydration effects and suppressed segmental mobility due to introduction of an α-CH 3 group was responsible for the condensed molecular conformation and reduced structural compressibility of the monolayers of PMMA and PEMA.

Mussel-Inspired Self-Healing Metallopolymers for Silicon Nanoparticle Anodes

“…Furthermore, the low T g values of PDBP and Fe−PDBP@pH10 which are lower than room temperature verified the critical role of the BA units in lowering the T g . 55,56 For reference, polydopamine methacrylamide (PDMA 100 ), comprised solely of DMA units, did not show any T g points in the range of −50 to +100 °C (Figure S3) because of its brittle character originating jointly from the α-methyl groups (−CH 3 ) located on the main-backbone, 57 amide group with rigid bond character, 54 and the polar dopamine group on the side chain (melting point of dopamine = ∼128 °C). 58 PDMA 100 is indeed solid powder at room temperature.…”

A Nanoconfinement Effect Imposed by the Limited End-to-End Distance of the Grafted Chains on a Molecular Aggregation of Polymer Brushes with Crystalline Side Groups

“…The sum frequency generation (SFG) vibrational spectra of the surfaces of the PODMA brushes were obtained using a custom-designed SFG spectrometer (EKSPLA, Lithuania), as described in previous papers. − Briefly, a 532 nm visible input beam was generated by frequency doubling the fundamental output from an EKSPLA Nd:YAG laser. The IR beam was obtained from an optical parametric generation/amplification/difference frequency generation system based on LBO and AgGaS 2 crystals.…”

Enhanced Thermal Stability of Polystyrene by Interfacial Noncovalent Interactions

“…SFG spectroscopy was performed using an EKSPLA system (EKSPLA Co., Lithuania) as previously described. − The incident angles of visible and IR beams were 60° and 53°, respectively. The visible beam with a wavelength of 532 nm was generated by frequency doubling of the fundamental output pulses from a Nd:YAG laser (PL2241).…”