Characterization of Polystyrene-b-polyisoprene Diblock Copolymers by Liquid Chromatography at the Chromatographic Critical Condition

Abstract

In the chromatographic separation of macromolecules with a porous stationary phase, the retention is determined by both size exclusion and interaction mechanisms. At the chromatographic critical condition, the effects due to the two separation mechanisms compensate each other, and the retention of homopolymer molecules becomes independent of molecular weight. Liquid chromatography at the critical condition has attracted much interest for the characterization of block copolymers since it might permit the characterization of individual blocks of a block copolymer by making one block chromatographically "invisible". In this study, we critically examine this method using two sets of styrene-isoprene block copolymers designed to have one block length constant while varying the other block length. For these block copolymer systems we found that a block cannot be made completely "invisible" at the critical condition of its homopolymer, and the retention of block copolymers is affected to some extent by the length of the "invisible" block under its chromatographic critical condition.

A review on the development of liquid chromatography systems for polyolefins

“…These simulation results confirmed the previous experimental observations [108,109]. Moreover, Wang's group also studied the retention behavior of star-shaped PS in LCCC of linear PS.…”

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.…”

Two‐Dimensional Chromatography of Complex Polymers, 7 – Detailed Study of Polystyrene‐block‐Polyisoprene Diblock Copolymers Prepared by Sequential Anionic Polymerization and Coupling Chemistry

“…In particular, Chang used LC-CC, solvent gradient HPLC and temperature gradient interaction chromatography (TGIC) for the separation with regard to chemical composition. [12,[34][35][36][37] In the present study, special attention is given to the proper analysis of the molar masses and polydispersities of the precursor blocks, the block copolymers, and the single blocks of the block copolymers. It is known, that living anionic polymerization produces polymers with narrow polydispersities, usually much less than 1.1 (M w =M n ).…”