Facile Method to Determine the Molecular Weight of Polymer Grafts Grown from Cellulose Nanocrystals

Abstract

One of the main challenges associated with the modification of cellulose nanocrystals (CNCs) with polymers by surface-initiated polymerization is the characterization of the resulting products, notably the molecular weight of the grafts. The solid nature of the (modified) CNC nanoparticles limits the possibility to apply solution-based characterization techniques, and the cleavage of the macromolecules from the surface of the CNCs to enable their characterization using solution-based techniques is intricate. Here, we report that 1H NMR spectroscopy of the supernatant of the heterogeneous reaction mixture can be used to approximate the molecular weight of poly­(hexyl methacrylate) grafts grown from the surface of CNCs via surface-initiated atom transfer radical polymerization. This was achieved using 1H NMR spectra to determine the monomer conversion from the change of the relative ratio of monomer and solvent signals in the 1H NMR spectra, which in turn allowed determining the weight of PHMA produced. The number-average molecular weight of the grafted polymer was then estimated by assuming that standard atom transfer radical polymerization kinetics are at play and using the initiator concentration on the CNC surface determined by elemental analysis. The method was validated by comparing the results with the gravimetric data and the data of free polymers that were synthesized with a sacrificial initiator.

Alteration of the cellulose nanocrystal surface chemistry for guided formation of polymer brushes

“…Characterizing and determining the molecular weight of the polymeric brushes grafted on the surface of CNC is very challenging. 33 A commonly used approach to determine the polymer length on the CNC surface is adding a sacrificial initiator (EBiB). When working with surfaces containing a low number of initiating groups (DS), the use of a sacrificial initiator allows tailoring the length of the polymer by changing the initial ratio of [monomer]/[EBiB] and polymerization conversion (the number of initiating sites on the CNC being negligible compared to the amount of sacrificial initiator).…”

“…However, all these approaches have several limitations. 16,26,33 In this study, we synthesized various "free" PtBA polymers with varying M n and used their thermal stability (T onset ) to approximate the molecular weight of the CNC-grafted PtBA systems. 34 The "free" PtBA polymers were synthesized by polymerization with EBiB, and the molecular weight and dispersity of the "free" synthesized polymers were obtained via SEC.…”

A Review on the Modification of Cellulose and Its Applications

“…AMIMCl/DMF with 2-bromoisobutyryl groups were initially added to the cellulose backbone as a solvent. Copolymerizing MMA with the resulting macroinitiators yielded the final copolymer products [ 115 ]. The copolymers had similar transparency to linear PMMA films, and significantly increased tensile toughness.…”

One-Component Nanocomposites Made from Diblock Copolymer Grafted Cellulose Nanocrystals

“…To achieve a high grafting density, we targeted a grafting-from approach based on surface-initiated atom transfer radical polymerization (SI-ATRP) from initiator-modified CNCs . This general methodology has recently been used to decorate CNCs with a variety of polymers, including poly­(styrene), poly­(methyl acrylate), poly­(methyl methacrylate), , and poly­( N -isopropyl­acrylamide) . Applying the same framework to diblock copolymers is challenging because only highly polar organic solvents can disperse the CNCs. , Yet, the solvent must also dissolve both polymers and support the ATRP mechanism, and the polymerization must remain living once the first block has formed.…”