Random styrene-ethyl acrylate copolymers

Figure 3, i.e., 50/50-styrene/ethyl acrylate copolymer made by uniform (random), staged, or power feed processes (24). Using the carbonyl carbon of the acrylate ester as a probe of the sequence distributions in a series of random styrene/ethyl acrylate copolymer, assignments were made for the three major resonance regions in terms of triad sequences. Figure 6 illustrates the differences observed. In the... 

Figure 3. HPLC-chromatogram of styrene-ethyl acrylate copolymers at different compositions and high conversion. Also shown is the styrene content obtained by HPLC calibration -) and on-line HPLC- H NMR experiments (o). (Reprinted from MacromolChem.Phys, Vol.201, LKramer, W.HiUer, H. On-line coupling of gradient-HPLC and NMR for the analysis of random poly[(styrene)-co-(ethyl acrylate)]s , 1662-1666, 2001, with permission from Wiley-VCH)...

Styrene/ethyl acrylate random copolymers were prepared with ethyl acrylate..contents of 10,25,50,75 and 90% by weight. Examination of the 3C NMR spectra of the copolymers reveals that the carbonyl carbon of the acrylate ester is a sensitive probe of the sequence distribution in these copolymers. Figure 2 shows the carbonyl carbon resonance region for a sample containing 50%... 

Coupled HPLC-NMR measurements performed at slow flow rates in fully deuterated solvents and at room temperature have been made in several studies to determine polymer MWD, to analyze the end-groups and the copolymer chemical composition distribution, and to assess the chemical structure and the degree of polymerization of all oligomer species [176-178]. Gradient HPLC-NMR was used in the analysis of the chemical composition distribution of random poly (styrene-co-ethyl acrylate) copolymers [179]. A major drawback in most of these studies is that the measurements could only be conducted at ambient or slightly elevated temperatures, which limits the method applicability, since many polymers, such as polyethylene, polypropylene, and polyolefin copolymers are soluble at high temperatures. 

Figure 9 shows the results obtained for a DSC study of the variation of the Tg and transition temperatures for a series of styrene-ethyl acrylate random copolymers. The reader is referred to the literature for details about the synthesis of this copolymer series. This study was the first of its kind to characterize both the Tg and Tn transitions for a series of random copolymers over the entire composition range. Both the glass transition and the Tn transition showed a linear temperature dependence with copolymer composition. The TulTg ratio, where the transition temperatures are expressed in degrees Kelvin, averaged 1.2 for the four intermediate random copolymers. 

Fig. 9. Effect of copolymer composition on the and Tn transitions for a series of styrene-ethyl acrylate random copolymers. The TulTg ratio averaged 1.2 over the entire composition range. After Kumler et al., ref. 28.

Problem 11.5 Devise a synthetic scheme, using TEiMPO-based SFRP, to obtain graft copolymers of controlled molecular weight and low polydispersity, in which random copolymers of styrene (St) and ethyl acrylate (EA) containing about 0.2 mole fraction of ELA are grafted onto polystyrene (PS) chains. 

Scheme Pll.5.1 Graft copolymer synthesis random copolymer of styrene and ethyl acrylate grafted onto polystyrene (Problem 11.5). (Drawn following the synthesis method of Hawker, 1995.)...

FIGURE 5.4 Chromatograms of poly (styrene—co ethyl acrylatels of different chemical composition. Source Reprinted from D. Braun, I. Kramer, H. Pasch, S. Mori, Phase separation in random copolymers from high conversion free radical polymerization. Part 2. Chemical heterogeneity analysis of poly(styrene-co-ethyl acrylate) by gradient HPLC., Macromolecular Chemistry and Physics, 200 (1999) 949, (1999), used with permission from Wiley-VCH (Ref [29]). 

For most of the IPN s ethyl acrylate served as m.onomer one and various admixtures of styrene and methyl methacrylate served as monomer mix two. The random copolymers of styrene and methyl methacrylate formed exhibit the striking property of having essentially the same glass transition temperature ca, lOO C, over the complete composition range. 

Samples tested were styrene copolymers of methacrylates, acrylates, vinyl acetate, and acrylonitrile, in addition to ethyl methacrylate-butyl methacrylate copolymers. These samples were dissolved in the initial mobile phase and the injection volume was 0.05-0.2 mL. These samples were prepared by solution polymerization at low conversion and have rather narrow CCD. These samples are random (statistical) copolymers. 

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