Comprehensive Structural Assessment of Linear Block Polymers by NMR and SEC

Abstract

Block polymers are an important class of materials offering unique and useful properties different from random polymers. Because of their tailored structure, these materials present synthetic challenges. For this reason, it is necessary to provide a thorough structural analysis to drive the synthetic effort. We describe an analytical methodology that includes size exclusion chromatography (SEC), quantitative 13 C NMR, and 1 H pulsed gradient spin echo (PGSE) NMR coupled with direct exponential curve resolution algorithm (DECRA) data analysis. The combination of these complementary techniques provides a comprehensive assessment of the chemical structure of the final polymeric material, including the detection and quantification of homopolymer formation, compositional heterogeneity with molecular weight, and monomer sequencing. We present work on two different linear block polymers: poly(styrene-b-allyl methacrylate) and poly[styrene-b-(styrene-alt-maleic anhydride)].

Characterization of Polymer Molecular Weight Distribution by NMR Diffusometry: Experimental Criteria and Findings

“…The result illustrated in Figure a clearly contradicts such a consideration, demonstrating that solvent diffusion is inadequate for such a purpose. Even at a moderate M = 174k, D PMMA does not become invariant until C falls below 0.2 mg/mL, which is lower than most of the concentrations using NMR diffusion reported up to date − ,− and still not adequate for samples with higher M . C dilute * is determined with high confidence (SI) and plotted against M using the double logarithm mode to yield a linear regression in Figure b.…”

“…Easy sample preparation, flexible choice of solvent, and a broad range of operating temperature further strengthen the practicality of diffusion measurement on a routine basis. As research and development progresses, these advantages of NMR diffusometry have become overwhelmingly important when studying polymer systems with increased structural complexity, ,,, which often necessitates more detailed characterization. Under the dilute condition, polymer diffusion ( D ) is related to M based on the following equation α is the Mark–Houwink coefficient and k is a constant that depends on the polymer system.…”

“…In fact, a common problem associated with M /MWD characterization using D polymer stems from the selection of the aforementioned sufficiently dilute condition. A seemingly low concentration, typically between 0.5 and 4.5 mg/mL, has been used in the majority of polymer diffusion studies for M /MWD characterization, − ,− ,− yet solid justification is rarely provided. In some extreme cases, the polymer concentration is even up to ∼80 mg/mL .…”

New Hyperbranched Polysiloxanes Made by Thiol‐yne Click Reaction: Lanthanide Complexation and Applications in Bioimaging

“…[34][35][36] The thiol-yne "click" reaction includes two cyclic processes: the reaction of sulfhydryl with triple bonds (TYC) and the reaction of sulfhydryl with double bonds (TEC). [37][38][39][40]…”

Molar Mass Distribution and Chemical Composition Distribution of PS-b-PMMA Block Copolymers Determined by Diffusion Ordered Spectroscopy

“…In the case of homopolymers even the determination of the molar mass distribution could be performed with DOSY including the calculation of the weight-average molar mass M w and number-average molar mass M n , and PDI. − Most works deal with M w of polymers determined due to the relating calibration of the diffusion coefficient according to eq . Multiple methods like the gamma distribution model, ,, inverse Laplace transform, ,, CONTIN, , DECRA, , and many more were investigating molar mass distributions of polymers. Viéville et al successfully investigated the molar mass distribution of linear poly­(ethylene oxide)­s by using DOSY with inverse Laplace transform .…”