Molecular Weight Distribution of Polystyrene Made by Anionic Polymerization

Abstract

A set of polystyrenes of varying molecular weights was synthesized by anionic polymerization under identical conditions, and their molecular weight distributions were critically examined. Polymerization of styrene was initiated with 2-butyllithium in cyclohexane at 45 °C. During the polymerization, seven aliquots of the reaction mixture were taken out at various reaction times using a cannula and terminated. The polymerization time varying molecular weights and molecular weight distributions of the polystyrenes were analyzed by temperature gradient interaction chromatography (TGIC) as well as size exclusion chromatography. The molecular weight distribution of the polystyrene approaches the Poisson distribution in the late stages of the polymerization, in accordance with the early prediction of Flory. We also confirmed that the molecular weight distribution of polystyrenes determined by TGIC is close to the true value.

A report on the certification of an absolute molecular mass distribution polymer standard:

“…For example, the observed MMD is often compared to predictions from kinetic or mechanistic models of the polymerization reaction itself 8,9 . Similarly, the tensile strength, melt flow rate, and many other physical properties are dependent on MMD.…”

Two‐dimensional chromatography as a tool for studying band broadening in size‐exclusion chromatography

“…UV detectors [3][4][5][6], refractive-index (RI) detectors [3,7], and evaporative light-scattering detectors (ELSD) [7] are commonly used for this purpose. In addition, SEC can yield information on the intrinsic viscosity [3,8] and the degree-of-branching by coupling it to viscometric (Vis) or light-scattering (LS) detectors [9][10][11]. SEC can also be combined (online or offline) with NMR or IR spectroscopy or with MS to yield information on the (average) chemical composition and functionality in each fraction of the effluent.…”

“…Manufacturers specify values for commercial standards, which are usually upper limits. Several research groups [9,10,18] have demonstrated that these specifications overestimate the true PDI values. Other authors [9,10,19] have claimed that the PDI obtained by SEC is also an upper limit, because it is significantly affected by band-broadening phenomena.…”

“…Several research groups [9,10,18] have demonstrated that these specifications overestimate the true PDI values. Other authors [9,10,19] have claimed that the PDI obtained by SEC is also an upper limit, because it is significantly affected by band-broadening phenomena. Temperaturegradient-interaction chromatography (TGIC) was found to give much narrower peaks than SEC [9,19].…”

“…Other authors [9,10,19] have claimed that the PDI obtained by SEC is also an upper limit, because it is significantly affected by band-broadening phenomena. Temperaturegradient-interaction chromatography (TGIC) was found to give much narrower peaks than SEC [9,19]. [13] and it requires a low sample PDI (PDI a 1.2 or preferably lower) [14,15,20].…”