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

Abstract

We demonstrated, using grazing incidence wide-angle X-ray diffraction (GI-WAXD), sum frequency generational spectroscopy (SFG), and atomic force microscopy (AFM), that the aggregation state and molecular ordering of polymer brushes with crystalline side groups (i.e., poly(n-octadecyl methacrylate)) can be well controlled by their grafting densities (σ p ). The long-range ordered structure, which is the lamellar structure formed by rodlike noctadecyl (C18) side groups, sequentially changes with increasing grafting density from the standard lamellae with a periodicity (d lam ) of 3.0 nm at low σ p , to shrinking lamellae with d lam = 2.6 nm, and then to a structure lacking lamellar ordering. This regulation is ascribed to the restricted conformation and suppressed lateral mobility of the densely grafted chains and most importantly to a particular spatial confinement imposed by the limited end-to-end distance of the tethered chains, which hinders the long-range ordered organization of the bulky side groups. Meanwhile, we also showed that such a confinement effect occurring in densely tethering chains can be mitigated by introducing a soft grafting substrate.

Enhanced Dynamics of PMMA Brushes Induced by the Chain Ends of a Flexible Polymer Chain

“…The water contact angles increased from 67 to 111° when the PODMA block was connected to the PMMA brush surface, as shown in Figure f,g. This finding was identical to that in a previous report . In addition, the water contact angle increased from 67 to 87 ° (Figure f,h) when the PBMA block was connected to the PMMA brush surface, which was similar to the reported value of PBMA brushes .…”

“…We prepared PMMA homopolymer brushes by initiating ATRP from the substrate surface-anchored initiators. The grafting densities of PMMA brushes (σ p ) were obtained by the quantitative relationship among σ p , the thicknesses ( h p , PMMA ) and the molecular weight ( M n ) of PMMA brushes in which the M n of PMMA brushes was determined by gel permeation chromatography (GPC), and the brushes were detached from the substrates by cleaving the Si–O bond using TBAF. , The grafting density (σ p ) of the PMMA brushes was calculated to be approximately 0.64 nm –2 . The PODMA chains and PBMA chains were grafted from high-density PMMA brushes with an ATRP initiator at their chain ends to fabricate PMMA- b -PODMA and PMMA- b -PBMA brushes, respectively.…”

“…Then, PODMA or PBMA was synthesized by the C–Br initiator that existed on the ends of PMMA brushes through a second SI-ATRP process. The same procedure was used for the preparation of PMA- b -PODMA brushes . The common procedure for synthesizing PMMA homopolymer brushes was as follows.…”

“…The same procedure was used for the preparation of PMA-b-PODMA brushes. 45 The common procedure for synthesizing PMMA homopolymer brushes was as follows. The initiator-functionalized silicon substrates were added to 10 mL of a degassed anhydrous toluene solution containing CuBr (0.425 g), PMDETA (2 mL), and MMA monomers (5 mL) in a flask under stirring and with a nitrogen gas purge.…”

Microstructure Induced Rigidity of Polysiloxane Yielding Hierarchical Self‐Assembly of Alkyl Side Chains

“…The comb-like polymers with a long alkyl side chain have attracted much of a scientific attention owing to their fascinating crystallization and self-assembly properties. [1][2][3][4] These polymers are typically composed of two kinds of macromolecular units one being the backbone and the others are alkyl side chains. The impact of alkyl side chains on the crystallization of these polymers is quite well established in the literature.…”