Isotactic styrene copolymers

The spectra of the methyl methacrylate-a-methylstyrene copolymers are similar to those of the methyl methacrylate-styrene copolymers and are not shown. The backbone methylene regions (8.1—8.6t) of the two comonomer units cannot be distinguished from each other. On the other hand, the methyl methacrylate a-methyl resonances are clearly multiple except at the two lowest values of f . In the spectrum of the 46 54 methyl methacrylate-a-methylstyrene copolymer, the shape of the methyl methacrylate a-methyl resonance is markedly altered from that observed at higher f , the peak at lower field (8.83r), which corresponds to isotactic triads in the homopolymers and is normally very small in free radical polymers, appears to be the most prominent. The a-methyl protons of the a-methylstyrene units appear at highest field, 9.6r—9.8t. Peak positions for the a-methylstyrene copolymers are... 

Metallocenes and methylalumoxanes can further be used to synthesize isotactic polypropylene [70, 71], syndiotactic polypropylene [38], other propylene polymers or oligomers [72], ethylene/cycloolefin copolymers [10-13], syndiotactic polystyrene [14, 61], and ethylene/styrene copolymers [64]. Cycloolefin copolymers are amorphous, with high glass transition temperatures [10-13]. The syndiotactic polystyrenes are semicrystalline polymers with a glass transition temperature around 100 °C and a melting point of 270 °C [14]. 

Another example of ionic graft copolymerization is a reaction carried out on pendant olefinic groups using Ziegler-Natta catalysts in a coordinated anionic-type polymerization. The procedure consists of two steps. In the first, diethylaluminum hydride is added across the double bonds. In the second the product is treated with a transition metal halide. This yields an active catalyst for polymerizations of a-olefms. By this method polyethylene and polypropylene can be grafted to butadiene styrene copolymers. Propylene monomer polymerization results in formations of isotactic polymeric branches ... 

Particular studies of the IR spectra of polymers include isotactic poly(l-pentane), poly(4-methyl-l-pentene), and atactic poly(4-methyl-pentene) [18], chlorinated PE [19], aromatic polymers including styrene, terephthalic acid, isophthalic acid [20], PS [21, 22], styrene-glycidyl-p-isopropenylphenyl ether copolymers [23], styrene-isobutylene copolymers [24], vinyl chloride-vinyl acetate-vinyl fluoride terpolymers [25], vinyl chloride-vinyl acetate copolymers [26], styrene copolymers [27], ethylene-vinyl acetate copolymers, graft copolymers, and butadiene-styrene [28] and acrylonitrile-styrene copolymers [29]. 

Fig. 5.14 Plot of melting temperatures of isotactic styrene-p-fluorostyrene copolymers as a function of mole fraction of p-fluorostyrene. (From Natta (102))...

Fig. 7a and b. Distribution of moncnner units in propylene-styraie copolyrtwrs 47). a) Distribution of styrene units. Experimental points are for the 565 cm band CalculaticHis are for n = 2, r, = 1 and 5. b) Comparisrm between the and Ag Ali ratios (the parameters of the distributicm of propylene units in long isotactic sequences, see Table 1) for prylene-styrene copolymers ( ) and ethylene-propylene copolymers (O)... 

Polypropylene block and graft copolymers are efficient blend compatibilizers. These materials allow the formation of alloys, for example, isotactic polypropylene with styrene-acrylonitrile polymer or polyamides, by enhancing the dispersion of incompatible polymers and improving their interfacial adhesion. Polyolefinic materials of such types afford property synergisms such as improved stiffness combined with greater toughness. 

Frounchi and Burford [37] studied the effect of styrene block copolymer as a compatibilizer in isotactic PP-ABS blends. It was found hat in PP-rich blends a marginal improvement in mechanical properties was obtained. However, in acrylo nitrile butadiene styrene (ABS) rich blends no improvement was obtained. The effects of four different block copolymers, SBS, SIS,... 

Polystyrene (PS) is the fourth big-volume thermoplastic. Styrene can be polymerized alone or copolymerized with other monomers. It can be polymerized by free radical initiators or using coordination catalysts. Recent work using group 4 metallocene combined with methylalumi-noxane produce stereoregular polymer. When homogeneous titanium catalyst is used, the polymer was predominantly syndiotactic. The heterogeneous titanium catalyst gave predominantly the isotactic. Copolymers with butadiene in a ratio of approximately 1 3 produces SBR, the most important synthetic rubber. 

Blend with Isotactic Polypropylene and Styrene-Ethylene-Butylene-Styrene Block Copolymer... 

Figure 2.20 Sequences of torsion angles in chains of syndiotactic and isotactic alternating styrene-CO copolymers, according to tc and s(M/N) symmetries, respectively.

Several reports have appeared in which the UV absorption spectrum of PS was found to be qualitatively similar to an alkyl benzene model compound. Vala and Rice15> demonstrated the similarity between atactic PS and ethyl benzene this was confirmed for atactic PS in cyclohexane by Hirayama 16) and in tetrahydrofuran by Abuin 17>. Bovey and co-workers20) found that absorbance spectra for isotactic PS, atactic PS, and styrene-methylmethacrylate copolymers in 1,2-dichloroethane were roughly similar to that of toluene. 

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