Styrene copolymers ethanol content

Copolymerization reactions Copolymerization experiments with styrene and MMA employed molar fractions of 20, 40, 60, and 80% comonomers, which were reacted in ethanol 1,2-dichIorethane 60 40 (by volume) mixtures and benzoyl peroxide as catalyst. Polymerizations were carried out at 70°C. The reactions were quenched by the addition of methanol as non-solvent, and the copolymer was isolated by centrifugation. Copolymer analysis employed UV spectroscopy for copolymers with MMA, and methoxyl content determination according to a procedure by Hodges et al. (16) in the case of styrene copolymers. Reactivity ratios were determined in accordance with the method by Kelen-Tiidos (17) and that by Yezrielev-Brokhina-Roskin (YBR) (18). Experimental details and results are presented elsewhere (15). 

Methods of Separation. Elution Behavior. First, elution was performed by an isocratic elution mode. At a constant column temperature, the copolymers and homopolymers of polymethacrylates and polyacrylates were retained in the column with chloroform (and DCE) without ethanol. Only polystyrene could elute from the column. By adding ethanol to chloroform (and DCE), copolymers with a higher styrene content started to elute, and by increasing the ethanol content in the mobile phase, copolymers with less styrene were eluted. 

The copolymers tend to adsorb on the column at a higher column temperature, and copolymers with a higher methacrylate or acrylate component required a lower column temperature for elution. For example, a P(S-MMA) copolymer with 66.3% styrene eluted 100% from the column at column temperatures 10-30 °C with the mobile phase of chloroform-ethanol (99 1) and was retained in the column at 50 °C (Figure 2). The reason for the observation in Figure 2d was the same as that in Figure Ic. Lower column temperature (and/or a higher ethanol content in the mobile phase) was preferable for the elution of the copolymers having less styrene. 

Mechanisms of Retention and Elution. These results can be summarized as follows the copolymers tend to adsorb in the column at a higher column temperature and at a lower content of ethanol in the mobile phase and the copolymers with a lower styrene component require a lower column temperature or a higher content of ethanol in the mobile phase to elute from the column. The ethanol content in the mobile phase or a column temperature did not affect peak retention volume for the copolymers. All the copolymers eluted at the same retention volume. 

A 30-min 99/1->93/7 chloroform/ethanol gradient was used with a silica column (A = 254nm) to characterize styrene/methyl and ethyl methacrylate copolymers [755]. That the ethanol content was critical was shown through a series of chromatograms for a 50/50 styrene/methyl methacrylate co-polymer and a 35/65 styrene/ethyl methacrylate co-polymer. For 25 pL injections of 0.1% w/v samples, the 50/50 co-polymer completely eluted with a 97/3 chloroform/ethanol mobile phase but was completely adsorbed to the silica at 99/1. Similarly, the 35/65 copolymer eluted at 95/5 chloroform/ethanol and did not elute at 98/2. Temperature effects (40-70°C) on the level of ethanol needed for elution were tabulated for these co-polymers as well. 

---