PS, syndiotactic

Polypropylene and Polystyrene. As with PE, afm has yielded important structural details for the different grades of polypropylene (PP) and Polystyrene (PS). Syndiotactic polystyrene (sPS) was imaged (Fig. 12), showing a spherulitic... 

Poly(cyclohexyl acrylate) was shown to be miscible with PS with ucst behavior [720]. Random copolymers of cyclohexyl acrylate with n-butyl acrylate showed miscibility with PS above 50% cyclohexyl acrylate[721]. Poly(cyclohexyl methacrylate)/isotactic PS blends showed miscibility based on calorimetry and NMR studies [722]. The NMR results showed homogeneous behavior at a scale of 2.5-3.5 nm. Poly(4-trimethylsilyl styrene) miscibility with polyisoprene was observed with a lest behavior (critical temperature = 172 ° C at degree of polymerization of 370) [723]. The interaction parameter, showed the following relationship = 0.027—9.5/T. Isotactic and syndiotactic polystyrene both exhibit crystallinity, whereas atactic polystyrene is amorphous. Atactic PS/isotactic PS blends exhibited crystallization kinetics, which decreased linearly with atactic PS addition indicating miscibility [724]. The TgS of aPS and iPS are identical, thus Tg methods could not be employed to assess miscibility. Atactic PS/syndiotactic PS blends were also noted to be miscible with rejection of atactic PS in the interfibrillar region between the lamellar stacks of sPS [725]. 

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. 

It is typical, for instance, of syndiotactic polystyrene (s-PS) [7-9] and syndiotactic poly- p-methylstyrene (s-PPMS) [10] to present crystalline forms with a transplant conformation of the chains (shown for s-PS in Fig. 1) as well as crystalline forms with sequences of dihedral angles of the kind TTG+G+ (or the equivalent G G TT), corresponding to a s(2/l)2 helical symmetry of the chains (shown for s-PS in Fig. 1). 

As an example we report in this paper the conformational energy maps of two already cited stereoregular polymers, which have been obtained very recently, syndiotactic polystyrene s-PS and syndiotactic polybutene s-PB (Fig. 4 and 5, respectively). In fact, the energy map calculated for s-PS shows... 

A radical initiator based on the oxidation adduct of an alkyl-9-BBN (47) has been utilized to produce poly(methylmethacrylate) (48) (Fig. 31) from methylmethacrylate monomer by a living anionic polymerization route that does not require the mediation of a metal catalyst. The relatively broad molecular weight distribution (PDI = (MJM ) 2.5) compared with those in living anionic polymerization cases was attributed to the slow initiation of the polymerization.69 A similar radical polymerization route aided by 47 was utilized in the synthesis of functionalized syndiotactic polystyrene (PS) polymers by the copolymerization of styrene.70 The borane groups in the functionalized syndiotactic polystyrenes were transformed into free-radical initiators for the in situ free-radical graft polymerization to prepare s-PS-g-PMMA graft copolymers. 

Polystyrene (PS), 7 610t 23 326, 348, 358. See also Polystyrenes Styrene Styrene plastics biodegradation of, 23 376 brominated, 11 470-474 chain transfer to, 23 383 colloidal suspensions, 7 275 crystalline syndiotactic, 23 388 decomposition of, 14 109 effect of orientation on oxygen permeability, 3 393t... 

Stacking faults in syndiotactic polystyrene (s-PS) P-form crystals [3, 29-34]... 

Although PS is largely commercially produced using free radical polymerization, it can be produced by all four major techniques—anionic, cationic, free radical, and coordination-type systems. All of the tactic forms can be formed employing these systems. The most important of the tactic forms is syndiotactic polystyrene (sPS). Metallocene-produced sPS is a semicrystalline material with a of 270°C. It was initially produced by Dow in 1997 under the trade name Questra. It has good chemical and solvent resistance in contrast to regular PS that has generally poor chemical and solvent resistance because of the presence of voids that are exploited by the solvents and chemicals. 

The rate parameters for the model compounds of PS and P2 VN are given in Table 10. The values of M for isotactic, syndiotactic, and heterotactic triads of P2VN can be calculated as 0.035, 0.147, and 0.0565, respectively. For the same triads of PS, the values of M are 0.0097, 0.172, and 0.0184, respectively. If we assume that a typical atactic polymer has 50 % isotactic dyads, and if the dyads are independently distributed on the polymer, then there will be 25 % isotactic and 25 % syndiotactic triads. Thus, the value of M for a 50% isotactic P2VN sample in solution should be about 0.074 that for a 50% isotactic PS sample in solution should be 0.0545. 

Mixtures of diastereomers of 2,4,6-trlphenylheptane are epimerized. The mole fractions olisotactic, heterotactic, and syndiotactic isomers at equilibrium at 343 K are 0.217, 0.499, and 0.284, respectively. There results are interpreted according to the theory of stereochemical equilibrium. The theory of equilibria between isomers and the associated theory of the conformer populations for each isomer provide a mutually consistent interpretation of the two kinds of results, the same arbitrary parameters being used for both. Stereochemical equilibria and conformer population calculated for PS for the same parameters differ considerably from those for the oligomers. 

The theory of strain birefringence is elaborated in terms of the RIS model as applied to vinyl polymer chains. Additivity of the polarizability tensors for constituent groups is assumed. Stress-birefringence coefficients are calculated for PP and for PS. Statistical weight parameters which affect the incidences of various rotational states are varied over ranges consistent with other evidence. The effects of these variations are explored in detail for isotactic and syndiotactic chains. 

FIGURE 14.2 X-band TREPR spectra of main-chain polymer radical la produced from 248 nm laser flash photolysis of atactic, isotactic, and syndiotactic PMMA in propylene carbonate at 0.8 ps delay time. The temperature for each spectrum is shown in °C, and the magnetic held sweep width is 150 G for aU spectra, which exhibit net E CIDEP in aU cases. Simulations of each fast motion spectrum (highest temperature) are shown at the bottom of each data set. Hyperflne values for each simulation are 3 anCCHs) = 22.9 G, 2aH(CH2)= 16.4 G, 2aH(CH2) = 11.7G for isotactic PMMA 3ah(CH3) = 22.9G, 2aH(CH2>= 16.2G,... 

Figure 1.12 shows the timeline of discovery of various styrenic polymers and copolymers. It would be naive to suggest that the rate of invention and innovation will level off in this century. Rather, the pace of discovery of new styrenic polymers will probably increase. Advances in new catalyst technology and controlled radical polymerisation technology will undoubtedly yield new styrenic polymers with well-defined architecture, as we have recently seen with the introduction of syndiotactic PS and ethylene-styrene interpolymers. 

Polystyrene (PS) in its atactic and syndiotactic forms is a brittle thermoplastic, even in an orientated state [4]. To improve the toughness of aPS, impact modification has been practised for a long time, either by polymerizing the styrene in the presence of a polybutadiene rubber leading to high-impact polystyrene, commonly called HIPS, or by blending the polystyrene with multi-block copolymers, mainly of the styrene-butadiene-styrene (S-B-S) type. 

PS, in either its atactic or syndiotactic form, is a polymer which shows no segmental mobility of chain segments below its glass transition temperature. Secondary relaxation processes which can be attributed to mobility in the main chain are missing. Therefore, these materials do not exhibit long-range energy... 

Figure 23.1 13C NMR spectra of (a) syndiotactic PCHE from hydrogenation of sPS, (b) atactic PCHE from hydrogenation of PS, (c) isotactic PCHE from Ziegler-Natta polymerization of vinylcyclohexane and (d) isotactic PCHE from hydrogenation of /PS (Ref. 18)...

Syndiotactic PCHE (sPCHE) has been prepared by the hydrogenation of syndiotactic PS [18,21]. The dynamic mechanical analysis of sPCHE with different degrees of hydrogenation has been reported. [21] The sub-Tg relaxation transitions observed in the atactic polymer were also observed in the... 

Tacticity of the PS chain seems to have an influence on the height and breadth of the 3 peak. A quenched isotactic PS shows essentially no (3 peak whereas an anionic PS (about a 1 1 ratio of syndiotactic to isotactic placements) shows a high, broad peak [10,11]. The fact that the (3 peak is suppressed by isotacticity implies sensitivity to the physical disposition of neighbouring phenyl groups along the chain. 

The a relaxation in both isotactic and syndiotactic PS is broader than that in atactic PS and the actual location of the peak is slightly shifted to higher temperature. The broadening effect was attributed to restrictions imposed by crystallites on the amorphous phases [12,24,25], Nakatani et al. [26] showed how the broadness of a syndiotactic PS sample can be represented by the overlapping of two glass relaxation processes arising from one purely amorphous component and the other amorphous component, which is under restrain owing to the proximity of crystallites. 

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