Effect of Block Copolymer Chain Architecture on Chromatographic Retention

Abstract

The chain architecture dependence of the retention behavior of block copolymers in the temperature gradient interaction chromatography (TGIC) and liquid chromatography at the critical condition (LCCC) was investigated. For the purpose, polystyrene (PS)/polybutadiene (PB) diblock (SB), SBS triblock, and BSB triblock copolymers were prepared by sequential anionic polymerization and further fractionated by reversed-phase TGIC to obtain a set of the block copolymers with high purity, narrow distribution, and matched block length. In the TGIC separation with C18 bonded silica stationary phase and a mixture of CH 2Cl2/CH3CN mobile phase, retention of the three block copolymers with matched molecular weight and composition shows a significant architecture effect: SBS elutes significantly earlier while BSB or SB elute later at similar retention volume. It indicates that the polymer-stationary phase interaction is less effective for the PB block located at the middle of the chain than the blocks located at the chain end. In LCCC separation at the critical condition for PB block, SBS is eluted early while SB and BSB were eluted later at the same retention time. Therefore, triblock copolymer with an invisible middle block behaves differently from those having invisible end block(s). This behavior is consistent with the theoretical prediction by Guttman et al.

Synthesis and characterization of 4-arm star-shaped amphiphilic block copolymers consisting of poly(ethylene oxide) and poly(ε-caprolactone)

“…At LCCC one block of block copolymers becomes 'chromatographically invisible' i.e., it does not contribute to retention. At this point, so-called chromatographic critical point, block copolymer is assumed to be eluted exclusively with respect to the functionality/end-group 20,21,24,25 or other block in block copolymer. [26][27][28][29][30][31][32][33][34] A fair estimation of non-critical block length and quantications of critical homopolymers is possible by appropriately applying LCCC. )…”

Characterization of Linear and 3‐Arm Star Block Copolymers by Liquid Chromatography at Critical Conditions

“…Recently, Chang et al reported that the polyA block in a diblock or triblock linear copolymer was not completely ''invisible'' at the LCCC analysis, and the elution behavior of the block copolymer was affected to some extent by the length and architecture of the ''invisible'' block. [34,35] These results were different from the theoretical assumption and the experimental results of Falkenhagen et al, who analyzed the diblock copolymer, poly(methyl methacrylate)-poly(tert-butyl methacrylate) (polyMMApolytBMA), under the LCCC for polyMMA and polytBMA separately and proved that the ''invisible'' block had no influence on the elution behavior of block copolymers. [43] In order to evaluate the ''invisibility'' of polyMA block during the LCCC analysis of polyMA-containing block copolymer, series of polySt-polyMA linear and 3-arm star copolymers were synthesized.…”

“…An interesting application of LCCC is the characterization of block copolymers [32][33][34][35][36] since it is important to evaluate the efficiency of initiation from the MI during the synthesis of block copolymers. A theoretical model shows that under the critical condition for polyA homopolymer, the elution behavior of polyA-polyB block copolymer (polyA is defined as MI) is entirely dependent on the length of polyB block; while under the critical condition for polyB homopolymer, the elution behavior of the block copolymer depends only on the length of polyA block.…”

“…However, the validity of this assumption is largely untested and even challenged in some reports. [24,34,35] In this paper, LCCC for poly(methyl acrylate) (polyMA) homopolymer was established and then applied to systematically study the structure of polyMA-polySt (St ¼ styrene) linear and 3-arm star block copolymers, in which the elution peak of polyMA-Br MI was completely separated from that of copolymer. The precision of this LCCC method on quantitative determination of the polySt ''visible'' block was evaluated by studying the influence of the molecular weight and architecture of the polyMA ''invisible'' block on the elution volume of the polySt-polyMA linear and star block copolymers.…”

Characterization of EO‐PO Block Copolymers by Liquid Chromatography Under Critical Conditions

“…Obviously, gradient elution cannot be used to solve this problem, regardless the nature of the gradient: mobile phase composition or temperature [23] : in both cases the critical conditions would be lost.…”