On the Precise Determination of Molar Mass and Dispersity in Controlled Chain-Growth Polymerization: A Distribution Function-Based Strategy

Abstract

Accurate information for the molar mass of polymers is a critical item in polymerization kinetic investigation and precision polymer synthesis. Size exclusion chromatography (SEC) is an irreplaceable technique to determine molar mass averages based on conventional calibration, which may nonetheless lead to inaccurate results due to the dissimilarity between the sample and the standard polymer. Herein, a facile distribution function-based strategy was proposed for the precise determination of molar mass average properties, aiming at rectifying the deviation of the standard-equivalent results from the true values. The number-average molar mass (M n) can be recalculated involving the contribution of each molar mass component beyond the fundamental Mark–Houwink–Sakurada relation. In addition, the as-developed strategy is capable of converting the dispersity from the apparent to the true value, thereby re-estimating the uniformity of the rectified molar mass distribution. The strategy was successfully applied to the linear polymers with medium and low dispersities obtained by two well-controlled chain-growth polymerizations: reversible addition-fragmentation chain transfer polymerization and ring-opening metathesis polymerization, respectively. The rectified M n closely match the benchmarks (i.e., absolute/theoretical M n), showing a much higher accuracy than those conventionally calibrated SEC results. Attributing to the consideration of dispersity, the errors of the rectified results can be as low as zero. This work reduces the risk of experimental bias caused by conventionally calibrated SEC analysis to acquire precise mechanism insight and realistic polymerization process details.

The synthesis of polymers with ultra‐high molecular weight by combining ROMP and acyclic metathesis reaction

“…The acyclic metathesis reaction could be suppressed by adding extra ligand with stronger coordination than 3-bromopyridine. 21 According to the above studies, we speculated that the acyclic metathesis reaction could be promoted by weakening the coordination between 3-bromopyridine and ruthenium. Hence, acid was added to react with 3-bromopyridine, and the ruthenium at the end of polymer chain could react with the double bond on the polymer.…”

“…13,14 Among those cyclic alkenes, norbornene derivatives are one of the most polpular monomers because of the high activity, easy preparation, and easy functionalization. Numerous studies have been done around norbornene derivatives, such as polymerization mechanism, 15,16 the effect of monomer stereochemistry and composition on the ROMP polymerization, [15][16][17][18] the optimization of polymerization conditions, [19][20][21][22][23] the preparation and application of functional polymers based on polynorbornene derivatives. 5,6,[11][12][13][14][24][25][26][27][28][29][30][31] However, linear polymers with ultra-high molecular weight (UHMW) (>10 6 g mol À1 ) were difficulty prepared by ROMP directly owing to the restrictions of monomer stereochemistry, composition, purity, and polymerization conditions.…”

“…The control of ROMP could be enhanced by lowering temperature, enlarging steric hindrance, and adding extra ligand to suppress the acyclic metathesis reaction, and prepare polymers with narrow distribution. 21,37 However, the molecular weight has not improved by those methods. So far, the synthesis of UHMW polymers by using acyclic metathesis reaction has rarely been reported.…”