Tacticity of polystyrene

If this is true, then it is reasonable to expect the tacticity of polystyrene to be the same as that of... 

Table 6 Tacticity of polystyrenes obtained in THF with NaNH2 R0Na...

Polymers that incorporate steric centers into their backbones can display various types of tacticity. The three principal types of tacticity are isotactic, syndiotactic, and atactic, as illustrated in Fig. 1.8 for polypropylene. Other polymers that display tacticity include polystyrene and poly a-olefins,... 

In figure 1 we present the experimental and calculated mK values of the copolymer poly(styrene-co-p-bromostyrene). From this study (3) we were able to show unequivocally that the tacticity of this polystyrene sample is pr — 0.55, where pr is the probability of racemic dyad replication. 

The tacticity of anionically prepared polystyrenes has been the subject of extensive study by a number of groups of workers, mostly by means of 13C-NMR spectroscopy. From a study of the aromatic Cl resonances, Matsuzaki and coworkers found 234) that there is a tendency towards syndiotacticity when using -butyl-Iithium in toluene as initiator. From the sensitivity of the CMR spectrum to the nature of the solvent employed it was concluded that the polymerization did not conform to Bernoullian statistics. Randall examined the methylene resonances in the CMR spectrum and concluded that butyllithium initiated polystyrene is essentially atactic 235) and that propagation is Bernouillian. Uryu et al.236) examined polystyrene... 

This chapter discusses the dynamic mechanical properties of polystyrene, styrene copolymers, rubber-modified polystyrene and rubber-modified styrene copolymers. In polystyrene, the experimental relaxation spectrum and its probable molecular origins are reviewed further the effects on the relaxations caused by polymer structure (e.g. tacticity, molecular weight, substituents and crosslinking) and additives (e.g. plasticizers, antioxidants, UV stabilizers, flame retardants and colorants) are assessed. The main relaxation behaviour of styrene copolymers is presented and some of the effects of random copolymerization on secondary mechanical relaxation processes are illustrated on styrene-co-acrylonitrile and styrene-co-methacrylic acid. Finally, in rubber-modified polystyrene and styrene copolymers, it is shown how dynamic mechanical spectroscopy can help in the characterization of rubber phase morphology through the analysis of its main relaxation loss peak. 

The relative intensities of the tetramer and pentamer diastereoisomers can be used for the evaluation of the tacticity of common polystyrene [28]. The increase in the pyrolysis temperature diminishes the content of tetramer and pentamer in the pyrolysate, favoring smaller fragments. The errors in the estimation of small peak areas increase, and the procedure using these fragments for tacticity estimation is sometimes difficult. 

In specifying the tacticity of the polymer, the prefixes it and st are placed before the name or structure to indicate isotactic and syndiotactic structures, respectively. For example, it-polystyrene means that the polystyrene is isotactic. The absence of these terms denotes that the polymer has an atactic structure. 

Diene polymerization may involve either or both of the double bonds. Geometric and structural isomers of butadiene, for example, are indicated by using appropriate prefixes — cis or irons, 1,2 or 1,4 — before poly, as in cw-l,2-poly(l,3-butadiene). Tacticity of the polymer may be indicated by using the prefix i (isotactic), s (syndiotactic), or a (atactic) before poly, such as 5-polystyrene. Copolymers are identified by separating the monomers involved within parentheses by either alt (alternating), b (block), g (graft), or co (random), as in poly(styrene-g-butadiene). 

Other homopolytners that are investigated in terms of stereochemical configuration are, for example polystyrene (mainly by means of carbon-13 NMR) and polyfcr-methyl stymie) [125]. More recoidy, the tacticity of poly(n-butyl methacrylate) has beoi studied by high-resolution carbon-13 and proton NMR... 

The highly ordered planar stmctures, as obtained by stereospecific polymerization, were mentioned in Section 2.3. In contrast to the branched chains, we deal here with linear chains where side substitute groups appear regularly on the same side of the plane, or alternatively. These structures are named isotactic or syndiotactic, respectively, and the degree of order is termed "tacticity." In both cases, good conditions for crystallization exist, even when the polymer itself is known as difficult to crystallize (as in the case of polystyrene or polymethylmethacrylate). Any orderless structure is named atactic. 

Fritz D, Harmandaris VA, Kremer K, van der Vegt NFA (2009) Coarse-grained polymer melts based on isolated atomistic chains simulation of polystyrene of different tacticities. Macromolecules 42 7579-7588... 

Ti(0-n-Bu)4 systems, the tacticity of the obtained polystyrene strongly depends on the support material (i.e., the presence of Cl in the carrier). When MgCh-supported Ti(0-n-Bu)4 is activated with MAO, the soluble part of the catalyst in toluene can afford sPS, whereas the insoluble part of the catalyst gives iPS. This is also true for the Ti(0- -Bu)4/Mg(0H)Cl system when activated with MAO. For Ti(0-n-Bu)4/Mg(OH)2/MAO, which has no Cl in the carrier, the insoluble part gives syndiotactic polystyrene, and the soluble part is almost inactive for styrene polymerization. For the TiCls (AA)/MAO-system (AA = aluminum-activated), iPS (95% mmmm pentad, melting point 221 °C) and sPS are obtained from the insoluble and soluble part of the catalyst respectively. ... 

NMR s ability to characterize the tacticity, or stereoisomerism, of polymers, such as polypropylene, polystyrene, or poly(vinyl chloride), is also significant. The tacticity of these, or of any other stereoirregular polymer, is analyzed as sequences of stereo pairs, or dyads. Each pair is designated as either meso (m) or racemic (r), depending on the stereostructure. In isotactic... 

Using PALS, Dammert et al. (92) and Yu et al. (93) examined the hole volume of a series of polystyrenes of different tacticity. They arrived at a free-volume hole size distribution maximum of around 110 at room temperature see Rgure 8.24 (92). This corresponds to an effective spherical hole radius of approximately 3 A. While this radius is somewhat larger than the theoretical value of 1.5 A found above, if the holes are actually irregular in shape the values are seen to agree quite well. 

Bond DA, Smith PA (2006) Modeling the transport of low-molecular-weight penetrants within polymer matrix composites. Appl Mech Rev 59(5) 249-268 Dammert RM, Maunu SL, Maurer FHJ, Neelov IM, Niemela S, Sundholm F, Wastlund C (1999) Free volume and tacticity in polystyrenes. Macromolecules 32(6) 1930-1938... 

A simplified treatment of the conformation tactic polymers in solution can be made in the way, that we shall discuss for two extreme cas case of polypropylene and that of polystyrene, from the identification of the minimum interna conformations available for a piece of a chain kind ... 

Apart from the ion-pairing aspect, the view that the activity of sulphonic acid groups does not markedly depend on local structure is perhaps supported by the observation by Sakurada et al. that a change in tacticity of the resin - which is expected to affect the geometrical distance between polymer groups - did not alter the catalytic behaviour of sulphonated polystyrene resins [26]. 

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