Isotactic polystyrenes studies

Although the aromatic C-l carbon resonance of polystyrene is very complex, relatively simple aromatic C-l carbon resonance spectra are observed for partially epimerized isotactic polystyrenes. Studies on such "model polystyrenes" provide the information needed to interpret the spectrum of polystyrene itself. Based on assign-... 

Xu H, Cebe P. Transitions from solid to liquid in isotactic polystyrene studied by thermal analysis and X-ray scattering. Polymer 2005 46(20) 8734-8744. 

Among the uncommon stmctures of stereoregular polymers determined in recent times, is that of isotactic polystyrene first observed by Keller and coworkers in crystalline gels (185) and later studied by Corradini et al. (186). In this case too, a highly stretched helix [ (6/1)] is observed, with unit height h = 5.1 A and imit twist t = 60°. The repeating unit contains two independent monomer units with rotation angles close to 180°. 

Braun and Kern (25) believed that the production of isotactic polystyrene with alkalimetalalkyls takes place with the propagating anion on the carbon alpha to the aromatic ring. Smid and Szwarc (26) studied the copolymerization of styrene with various substituted styrenes... 

The polymerization of styrene with less anionic butyllithium has been studied by several workers (31, 32, 33). The results of Tobolsky and Boudreau (34) showed that the butyllithium polymerization of styrene follows the electronic behavior of an anionic reaction. Electron releasing groups on the aromatic ring decreased the reactivity of the monomer. Braun and co-workers and Worsfold and Bywater (35) have studied the production of isotactic polystyrene by butyllithium catalysis. Worsfold and Bywater found that water plays an important role in the isotactic polymerization and concluded that the production of lithium hydroxide in situ is important for the isotactic steric control. Added lithium butoxide, lithium methoxide or lithium carbonate were not effective. They concluded the associated forms of butyllithium do not produce isotactic steric control but require association with lithium hydroxide. 

The structure of isotactic polystyrene has been studied by means of x-ray diffraction [Natta and Corradini (152,153)]. It is found that the chain configuration is helical, with three monomer units per repeat exactly as in polypropylene. The only difference is that the chain repeat of 6.65 A in polystyrene implies an opening of the CCC bond angles in the chain to 116.5°. The orientation of the benzene ring is apparently not settled. In the above structure, if the axis of the benzene ring were perpendicular to the helix axis, then the plane of the benzene ring would be almost exactly perpendicular to the helix axis. In a variation of this structure proposed on the basis of stereochemical considerations [Bunn and Howells (30)], and shown in Fig. 16, the plane of the benzene ring... 

As an independent approach Fourier transform infrared studies of isotactic polystyrene gels favours isotactic sequences in an ordered conformation different from the Natta type three-fold helix (38). 

After having studied in our laboratory, polymer blends of amorphous polymers poly-c-caprolactone and poly (vinyl chloride) (1,2) (PCL/ PVC), blends with a crystalline component PCL/PVC (3,4), poly(2,6-dimethyl phenylene oxide) (PPO) with isotactic polystyrene (i-PS) (5) and atactic polystyrene (a-PS) with i-PS (6), we have now become involved in the study of a blend in which both polymers crystallize. The system chosen is the poly(1,4-butylene terephthalate)/poly(ethylene terephthalate) (PBT/PET) blend. The crystallization behavior of PBT has been studied extensively in our laboratory (7,8) this polymer has a... 

Boon (1966/1968) investigated the kinetics of crystallisation of isotactic polystyrene. This polymer is extremely interesting as a model substance for crystallisation work. Its rate of growth is so low that the crystallisation can be studied in the whole region from Tg to Tm. Due to the low growth rate the fundamental processes of nucleation and growth can be studied almost separately. 

As described earlier (Sect. 2.3) Guenet s study of thermally-induced conversion of isotactic polystyrene solutions to rigid gels led to his observation that the ratio, a, of residual adsorbed solvent molecules per phenyl group of polymer, after all of the non-adsorbed liquid has been removed by evaporation in vacuum, is characteristic of the liquid [79-82, 181]. This end-point was established by correlating the heat of fusion of the liquid in the system with the amount of residual sorbed liquid. The composition extrapolated to AH = 0 was taken to be a. He later reported [181] that his thermodynamic protocol is also applicable for the determination of adsorbed liquid by atactic polystyrene. 

Boon, J., G. Chalea, and P. H. Hermans Study of molten isotactic polystyrene. I. The relationship between melt viscosity and average molecular weight. Makromol. Chem. 74, 129 (1964). 

PEC, PPO, and PS are amorphous materials as normally melt processed, a fact which prevents the use of melting point depression analyses for experimentally determining AHnix or B for the blends with PS. Isotactic polystyrene, i-PS, is able to crystallize, is miscible with PPO, and has been successfully used to determine the parameters related to AHaix (7,12.18). This study shows that i-PS is also miscible with PEC copolymers which contain up to 20 moleX trimethyl comonomer. This fact permits the use of i-PS melting point depression analysis to determine the effect of comonomer content on AHaix with i-PS. 

Smmmmmm can be measured from the chemical shift of isotactic polystyrene or from that of the largest signal in polymers epimerized to low extents and is 146.40 ppm for the conditions employed in the present study. Accordingly, the chemical shift of any heptad can be calculated by the following general formulas and specific examples. 

As for the effect of chirality in the vicinity of the chain terminals, a detailed study was performed for iso tactic polystyrene prepared using an optically active Ti(IV) catalyst. From the relation between optical activity of highly isotactic polystyrenes and their molecular weight, it was concluded that the chain terminal effect becomes negligible in the range >5000. ... 

Materials studied include c/s-1,4-poly butadiene [27-44], ethylene-propylene copolymers [28], PS [30-39, 44], isotactic polystyrene [40], styrene-butadiene copolymers [41-43,... 

In addition to the studies mentioned above, there has been a number of reports on GPC of specific polymers amongst these are studies of short-chain polyethylene, polyethylenes, isotactic polystyrene, cellulose nitrate, and polysiloxanes. Slagowski et have reported GPC of poly(tetramethylene terephthalate) in hexafluoroisopropanol and Paschle et show that a mixture of small amounts of nitrobenzene with tetrachlorethane is a useful solvent for GPC of poly(ethyIene terephthalate). 

Of course, other crystaUizable polymers have been studied (114-119).These include polypropylene (114-117), poly(ethylene oxide) (118), and isotactic polystyrene (119). Wignall et al. (113) have summarized the values of in both the melt and crystalline states (see Table 6.8). Most interestingly, the dimensions in the crystalline state and in the melt state are virtually identical for all these polymers. None of these data show a decrease in Rg on crystallization. That the Rg values in the melt and in the crystallized material are the same all but rules out regular folding. In fact, the data for poly(ethylene oxide) (118) shows a slight increase, if anything. By way of summarizing the above... 

Devise an NMR experiment to study chain folding in (a) cellulose triacetate, (b) isotactic polystyrene, and (c) transpolyisoprene (Gutta percha). [Hint What chemical modifications, if any, are required ]... 

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