Styrene-propylene copolymer characterization

As shown in Figure 2, 13C-NMR analysis of the copolymer gave unambiguous signals of a block copolymer with two long sequences of essentially pure iPS and iPP (iPS-fc-iPP). Isotactic triads of each block were about 98%. Because of little measurable shift of peak locations, which might be interpreted in terms of the repeat unit interaction of a styrene-propylene sequence as compared with respective homopolymers, the copolymer characterized in this study is considered to be a simple mixture of the two homopolymers. But the results of successive fractionation, as discussed in the section Experimental Details, could eliminate the possibility of homopolymer mixtures. 

By sequential copolymerization of styrene and propylene using a modified Ziegler-Natta catalyst, MgCl2/TiCl4/NdClc(OR) //Al(iBu)3, which was developed in our laboratory, a styrene-propylene block copolymer is obtained. After fractionation by successive solvent extraction with suitable solvents, the copolymer was subjected to extensive molecular and morphological characterization using 13C-NMR, DSC, DMTA, and TEM. The results indicate that the copolymer is a crystalline diblock copolymer of iPS and iPP (iPS-fo-iPP). The diblock copolymer contains 40% iPS as determined by Fourier transform infrared spectroscopy and elemental analysis. 

A survey of chemistries used for spontaneously anchoring polymer thin films is shown in Fig. 3. Early work by Stouffer and McCarthy [27] in this area showed that styrene polymers bearing only one terminal thiol group or styrene-propylene sulfide block copolymers could both form stable films via attachment to gold surfaces. Since those initial studies, several different polymer chemistries and architectures have been characterized as chemisorbed monolayers on gold, extending this concept. 

Studies of ethylene-vinyl aromatic monomer polymerizations continue to be published. Chung and Lu reported the synthesis of copolymers of ethylene and P-methylstyrene [28] and the same group extended these studies to produce and characterize elastomeric terpolymers which further include propylene and 1-octene as the additional monomers [29,30]. Returning to the subject of alternative molecular architectures for copolymers, Hou et al. [31] has reported the ability of samarium (II) complexes to copolymerize ethylene and styrene into block copolymers. 

Pan, Q., et al. (1999). Synthesis and characterization of block-graft copolymers composed of poly(styrene-b-ethylene-co-propylene) and poly(ethyl methacrylate) by atom transfer radical pol5merization. J. Polym. ScL, Part A Polym. Chem., 57(15) 2699-2702. 

Similar crystallization behavior, where the ordered melt structure was destroyed upon crystallization and replaced by alternating lamellae with a spherulitic superstructure was also observed in diblock copolymers of poly(ethylene oxide-fe-(l,2-butylene oxide)) [109], poly(ethylene oxide-6-ethylethylene) [110],poly(ethylene oxide-6-isoprene) [111], poly(ethylene-6-(head-to-head propylene)) [112],poly(ethylene-6-ethylethylene) [113] and poly(ethylene-6-(ethylene-a/f-propylene)) [113], and a triblock copolymer of poly(ethylene oxide-6-styrene-6-ethylene oxide) [114]. In all instances, the solid-state morphology was characterized by a semicrystalline lamellar structure regardless of the initial melt morphology. 

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