Main-Chain Stiffness of Cellulosic Bottlebrushes with Polystyrene Side Chains Introduced Regioselectively at the O-6 Position

Abstract

In this article, we describe the conformational characteristics of a cellulosic bottlebrush, i.e., a cellulose derivative of densely substituted side chains, in a dilute solution in order to clarify the effect of cellulosic main-chain stiffness and side-chain crowdedness. Novel cellulosic bottlebrushes 1 with polystyrene (PSt) side chains and methyl groups at the O-6 and O-2,3 positions, respectively, were highly regioselectively synthesized via a protecting group strategy in combination with a copper-catalyzed azide−alkyne coupling click reaction, yielding densely graft polymers where PS chains were introduced in every anhydroglucose repeating unit, i.e., at a "constant" distance of 0.5 nm along the cellulose backbone. Small-angle X-ray scattering measurements of 1 in dimethylformamide revealed that the cross-sectional radius of gyration depended on the degree of polymerization (DP) of the PSt side chains in accordance with the power law with an exponent of 0.50, indicating that the PSt side chains adopted extended conformation because of the inter-side-chain interaction, i.e., the excluded volume effect among the neighboring side chains. Size exclusion chromatography−multiangle light scattering experiments were conducted to determine the main-chain stiffness. Despite the use of a poor solvent for PSt, the stiffness parameter λ −1 was almost independent of the DP of the PSt side chains up to 60, even in the brush regime of side-chains with interchain interaction and hence somewhat stretched conformation. This behavior differs from those of previously reported bottlebrushes of flexible main chains and successfully demonstrated the cellulosic main chain intrinsically so stiff to form bottlebrushes of sufficiently long side chains with little effect on the main-chain conformation. This would expand the diversity in design of bottlebrushes along with the chirality of the cellulosic chain.

Characterization of the Local Volume Probed by the Side-Chain Ends of Poly(oligo(ethylene glycol) 1-Pyrenemethyl ether methacrylate) Bottle Brushes in Solution Using Pyrene Excimer Fluorescence

“…The good agreement obtained in Figure A between the ratio ⟨ k ⟩/ f diff and [Py] loc , assuming a Gaussian conformation for the side chains of the P­(PyEG y MA) samples, might appear surprising at first glance as larger scaling exponents ranging between 0.57 and 0.75 have been proposed for the relationship between R G,SC or r EE,SC and N S . − However, it must also be stated that some reports in the literature have found good agreement between experimental scattering data and theory, while assuming Gaussian side chains. − Furthermore, the PBBs typically studied in the literature have much longer side chains than those involved in the P­(PyEG y MA) samples. The short PyEG y side chains might explain why the assumption that they would adopt a Gaussian conformation yields reasonable trends in Figure A since shorter chains do not generate much excluded volume.…”

“…The present study illustrates how the same PEF-based methodology can be applied to predict the conformation of the side chains of another family of multi-ended macromolecules, namely, a series of polymeric bottle brushes (PBBs) belonging to the PEGMA type introduced by the Lutz group due to their interesting thermo-responsive properties. , In solution, PBBs adopt an extended conformation as the main chain becomes more crowded with increasing side chain length. , The topology of the PBBs generates two length scales, one related to the main chain, which is often described by its persistence length ( l p ), and another by the side chains (SC), which is described by their R G,SC or r EE,SC . − Since it is difficult to separate the scattering signal of the main and side chains, the determination of the parameters l p , R G,SC , and r EE,SC , which are typically extracted from scattering data, requires “dividing out” the contribution of the side chains from the overall scattering signal to isolate the signal pertaining to the main chain. In turn, this mathematical process involves making assumptions about the density profiles of the side chains .…”

“…Assuming that the pyrenyl terminal of each EG n side chain could probe a spherical volume, whose diameter was defined by the r EE,SC (= n 0.5 × l , with n being the number of chemical bonds of length l ) of the side chain, yielded a predicted value for [Py] loc which was found to correlate strongly with ⟨ k ⟩, as had been observed for the Py x -G­( N ) dendrons. , The strong correlation between ⟨ k ⟩ obtained from PEF measurements and [Py] loc suggests that PEF provides an experimental means to probe the internal density of macromolecules in general and the conformation adopted by the EG y side chains of PEG y MA samples in solution in particular. This application of PEF to probe the conformation of macromolecules and specific parts of a macromolecule in solution represents an important development in the use of PEF, which should nicely complement scattering experiments. ,,,− …”

Reinforcement of Microbial Thermoplastics by Grafting to Polystyrene with Propargyl-Terminated Poly(3-hydroxybutyrate-co-3-hydroxyhexanoate)

“…27 The propargyl group is one of the useful reactive groups, which can be used for copper-catalyzed azide−alkyne cycloaddition (CuAAC) reaction known as click chemistry. 28,29 This reaction is one of the powerful tools to prepare varied polymeric structures such as graft copolymers 30,31 and block polymers. 32,33 Furthermore, the change of polymer structure not only improves the mechanical properties of PHAs but also endows new physical properties for PHAs, including hydrophilicity, 3,34 electroconductivity, 35,36 thermoresponsibility, 37 and fluorescence property.…”

“…Propargyl-PHBH was found to be quantitatively introduced at the terminal moiety of PHAs by the addition of propargyl alcohol through the chemical treatment or the fermentation process . The propargyl group is one of the useful reactive groups, which can be used for copper-catalyzed azide–alkyne cycloaddition (CuAAC) reaction known as click chemistry. , This reaction is one of the powerful tools to prepare varied polymeric structures such as graft copolymers , and block polymers. , Furthermore, the change of polymer structure not only improves the mechanical properties of PHAs but also endows new physical properties for PHAs, including hydrophilicity, , electroconductivity, , thermoresponsibility, and fluorescence property . Thus, the synthesis of a graft copolymer can be supposed to improve the compatibility between PHBH and PSt, obtaining PHBH to comparable tensile properties and high transmittance.…”