Two Dimensional Chromatographic Characterization of Block Copolymers of 2-Ethylhexyl Acrylate and Methyl Acrylate, P2EHA-b-PMA, produced via RAFT-Mediated Polymerization in Organic Dispersion

Abstract

For the precise characterization of block copolymers of 2-ethylhexyl acrylate (2EHA) and methyl acrylate (MA) produced via RAFT (reversible addition-fragmentation chain transfer)-mediated dispersion polymerization, novel liquid chromatographic separations have been developed. SEC showed multimodal molar mass distributions (MMD) and HPLC showed multimodal chemical composition distributions (CCD). The analyses of MMD and CCD of the reaction products indicated the formation of the expected block copolymer along with remaining P2EHA and PMA homopolymer fractions. Online coupling of SEC and gradient HPLC in a two-dimensional liquid chromatography (2D-LC) setup proved to be an efficient method to fractionate all polymer species present in the samples. Different kinds of copolymer molecules were identified in addition to the two homopolymers. The quantification of P2EHA using liquid chromatography at critical conditions (LC-CC) showed that the unreacted macro(RAFT agent) amount remained unchanged during at least the first 4 h of polymerization. LC-CC experiments also allowed the relative molar mass of the PMA blocks contained in the copolymers to be determined. The implementation of 2D-LC combining SEC and LC-CC allowed a more precise characterization of the different copolymer structures in particular in terms of block size. Finally, the results obtained by SEC/HPLC were confirmed by LC-1 H NMR (proton nuclear magnetic resonance) experiments. It was concluded that the dispersed state of the polymerization system was the important factor for the formation of broadly distributed, complex copolymers when using a dithiobenzoate-based reactive macromolecular stabilizer. The detailed characterization of the system highlighted the enhancement of irreversible termination at the interface of the dispersed particles.

Living Radical Polymerization by the RAFT Process – A Third Update

“…[557] This typically involves some combination of high-performance liquid chromatography (HPLC) to separate a polymer sample according to composition and size-exclusion chromatography (SEC) or gel permeation chromatography (GPC) to separate according to molecular weight. [558] Two dimensional HPLC/GPC methods have been applied to characterize poly(EHA)-b-poly(MA) formed by RAFT dispersion polymerization, [275] the block copolymers formed by hetero-Diels Alder coupling of RAFT-synthesized poly(iBoA) with ATRP-synthesized poly(MMA), [294] and the block and star-poly(St)-PCL formed by sequential RAFT and ringopening polymerization. [319] A combination of LC/MS and LC/FTIR was used to characterize poly(NVP) formed with an acid functional xanthate RAFT agent.…”

“…S S * DEAm [273] (VAc) [274] (NVP) [248] EHA-b-MA [275] 39 S S O OH * H A [240] (Continued ) [240] MMA/433 [276] MMA/434 [276] MMA/435 [276] MMA/436 [276] MMA/437 [276] DMAEMA/433 [276] DMAEMA/434 [276] DMAEMA/434 [276] DMAEMA/437 [276] HEMA/433 [276] HEMA/434 [276] HEMA/434 [276] HEMA/437 [276] MAA/PEGMA [277] St/CMS [278] 41…”

Polymerization-induced self-assembly of block copolymer nanoparticles via RAFT non-aqueous dispersion polymerization

“…Compared to RAFT alcoholic dispersion polymerization, there are relatively few reports of RAFT dispersion polymerization being conducted in non-polar solvents [92][93][94][95][96][97][98][99]. Charleux and co-workers [92][93][94] reported an all-acrylic RAFT non-polar dispersion polymerization formulation that produced poly(2-ethylhexyl acrylate)-poly(methyl acrylate) (PEHA-PMA) diblock copolymer nanoparticles in iso-dodecane.…”

“…Charleux and co-workers [92][93][94] reported an all-acrylic RAFT non-polar dispersion polymerization formulation that produced poly(2-ethylhexyl acrylate)-poly(methyl acrylate) (PEHA-PMA) diblock copolymer nanoparticles in iso-dodecane. However, it is emphasized that only spherical nanoparticles could be accessed in this study.…”

Block copolymer synthesis by controlled/living radical polymerisation in heterogeneous systems

“…87 In addition, 2-dimensional approaches coupling LC and GPC have been developed as methods of detecting different homopolymer and block copolymer species. 88 Each method has its own assumptions and drawbacks, 89 and although we report values obtained from the different techniques in this review, quantitative comparison between different studies should be treated with caution. It is widely accepted that there is an intrinsic trade-off between the 3 types of purity from a one-pot process, since reaching a higher conversion of monomer to increase block sequence purity leads to an increased propensity of the propagating radicals to undergo termination or chain transfer reactions that lead to an increase in dispersity, the loss of livingness, and a lowering of blocking efficiency.…”