Elution Behavior of Polypropylene with Different Tacticity – An Overview

Abstract

High-temperature liquid chromatography (HT-HPLC) using solvent gradients enables to separate polypropylene (PP) according to tacticity. Varying the combination of adsorption and desorption promoting solvent the three stereochemical variants iPP, aPP and sPP can be selectively retained in a Hypercarb TM column. Two new desorption promoting solvents, namely 1-chloronaphtalene and 2-chlorotoluene, were tested. Among these 2-chlorotoluene was found to improve the selectivity of the separation of the atactic variant from the syndiotactic one. Linear polyethylene (PE) was retained in the column in the majority of the tested solvent/sorbent systems. Thus, several HPLC systems described in this paper enable the separation of blends consisting of PE and PP, as well as the realization of selective HPLC separations of polypropylene according to its tacticity.

Solvent and Polymer Stereochemistry Play Key Roles in Deuterium Exchange and Partial Racemization of Polypropylenes

“…13,15,16 This sequence of reaction susceptibility mirrors the behavior of these polymers in interaction chromatography, a group of polymer separation techniques based on adsorption to graphite that is widely used in the plastics industry. 36,37 For example, in solvent gradient interaction chromatography (SGIC), polymers are exposed to the graphite surface while dissolved in a poor solvent. The solvent quality is then gradually raised (via the introduction of a second, better solvent) at constant temperature, and elution of polymer is monitored during this gradient.…”

Solvent Selection for Liquid Adsorption Chromatography of Ethylene–Propylene–Diene Terpolymers by Combining Structure–Retention Relationships and Hansen Solubility Parameters

“…26−28 Several research groups have comprehensively explored various solvents to realize their effect on the separation of polyolefins. Macko et al 29 demonstrated that polypropylene (PP) with varying tacticities substantially differs in its retention on PGC, and it was concluded that the tested solvent systems would enhance the ability to resolve these stereoisomers. Similarly, in a recent study by Arndt et al, 25 it was found that the choice of the desorption-promoting solvent (desorli) influenced the elution volumes more strongly than the choice of an adsorption-promoting solvent (adsorli).…”

“…However, no indication of shoulder was found with n-decane as the adsorli, suggesting a poorer separation resolution. 29 Mekap et al explored a range of binary solvent mixtures as the mobile phase with the aim to increase the resolution in TGIC of E/O copolymers. 37 In essence, these studies highlight the impact of different solvent gradients when it comes to improving the resolution and thus a more accurate evaluation of CCD.…”

“…Several research groups have comprehensively explored various solvents to realize their effect on the separation of polyolefins. Macko et al . demonstrated that polypropylene (PP) with varying tacticities substantially differs in its retention on PGC, and it was concluded that the tested solvent systems would enhance the ability to resolve these stereoisomers.…”

“…In a study by Arndt et al on the separation of E/O copolymers, a pronounced main peak with a weaker shoulder was observed for the gradient 1-decanol to 1,2,4-trichloro benzene (TCB), indicative of a broad, asymmetric CCD. However, no indication of shoulder was found with n -decane as the adsorli, suggesting a poorer separation resolution . Mekap et al explored a range of binary solvent mixtures as the mobile phase with the aim to increase the resolution in TGIC of E/O copolymers .…”