Propylene oxide crystalline fractions

In 1955, Pruitt and Baggett (4,5) reported the polymerization of propylene oxide catalyzed by the reaction product of ferric chloride and propylene oxide, i.e., Pruitt-Baggett catalyst . Polypropylene oxide obtained from DL-monomer could be fractionated into two parts, one rubbery and another resinous. The latter fraction gave a discrete crystalline X-ray diffraction pattern. 

Polymerization of propylene oxide-a-d was carried out by the EtZnNBu ZnEt catalyst in benzene solution in the presence of varying amounts of added water at 70° C, and was terminated after 7 days. The microstructure of the crude polymer was determined by the 1H-NMR method and the yields of amorphous and crystalline polymers were determined by a fractionation method (Fig. 16). When the amount of added water was increased up to 0.3 mole per mole of catalyst, the yield of crystalline polymer increased remarkably, whereas that of amorphous one remained nearly constant, and the isotactic dyad content (I) increased remarkably while syndiotactic one (S) remained almost constant. Thus, the striking parallel was observed between the yield of crystalline polymer and the isotactic dyad content, and between the yield of amorphous polymer and the syndiotactic dyad content. It is therefore concluded that water contributes more remarkably to the formation... 

The high-molecular-weight poly (propylene oxide) produced with hexacyanometalate salt complexes shows no crystallinity. Moreover, it was shown by Price et al. (18) and confirmed in our laboratory that these polymers have more than 953 head-to-tail enchainment. The amorphous fractions of partially crystalline polymers made with metal-alkyl and ferrio-chloride-based catalysts were shown by those authors to have considerable head-to-head enchainment. They postulated that this was the cause of the amorphous nature of these fractions. It seems clear, however, that the amorphous nature of the polymers prepared with hexacyanometalate salt complexes must be the result of their low degrees of tacticity. 

The polymerisation of racemic propylene oxide with coordination catalysts leads to a polymer that can be fractionated into crystalline and amorphous polypropylene oxide)s ... 

Characterizing the Stereosequence Length of Propylene Oxide Polymers. The samples used in this study were the crystalline fractions of propylene oxide polymers made with various catalysts. Two methods were used to separate the fraction showing crystalline order (as judged from x-ray diffraction patterns) from the amorphous fraction ... 

Figure 1. Specific volume change vs. temperature for crystalline fractions of propylene oxide polymers from different catalysts...

Table I. Temperature of Melting and Percent Crystallinity of Crystalline Fractions of Propylene Oxide Polymers from Different Catalysts...

When the polymerizations was carried out with a separately prepared ferric chloride-propylene oxide catalyst, the 1-monomer formed a high molecular weight polymer which could be separated into an amorphous fraction with low optical rotation and a crystalline form with the same optical rotation as had been obtained with potassium hydroxide initiation. 

The above conclusions were based on the following observations. Both L and dl-propylene oxide gave mixtures of amorphous and crystalline polymer, practically identical except for optical activity. Only the crystalline fraction from the (-propylene oxide... 

Near the time of Natta s discovery of stereoselective alkene polymerization, Baggett and Pruitt reported that iron (III) chloride was capable of forming poly(propylene oxide) that could be divided into amorphous as well as crystalline materials using solvent fractionation." Soon thereafter, Natta et al. and Price et al. provided evidence that the crystalline material was isotactic poly(propylene... 

For example, propylene oxide of different optical purities, was polymerized using ZnEt2-HoO (1 0.7) system prepared in situ (13). As shown in table I tne % of crystalline fraction as well as the tacticity are increased with an increase of the optical purity. 

On the other hand, with the same initiator, the stereoselectivity is very different depending on the nature of the monomer. Almost purely isotactic products are obtained with t-butyl-thiirane while less than 30 % of crystalline fraction is isolated in the case of propylene oxide (table I). 

The rate at which these spherulites grow is also affected by tacticity. Measurements were made of the Isothermal rate of spherulitic growth on a hot stage of a microscope. For this purpose, a sequence camera was used to photograph automatically the growing spherulites during crystallization. Dilatometric measurements were also made on these polymers in order to determine the rate of isothermal crystallization from the melt. The fraction of the polymer which had crystallized at any time was calculated from the measured density and the known values of the density of crystalline and amorphous poly(propylene oxide) (8,2,... 

Dr. Price also showed that ferric chloride-catalyzed polymerization of either i.- or dJl-propylene oxide gave polymeric material which could be separated into amorphous, intermediate molecular weight and crystalline, high molecular weight fractions [eqs. (4) and (5)]. 

Few results have been reported on the effect of temperature on stereoelection. Propylene oxide was polymerized at various temperatures. It was found that the overall stereoelectivi-ty is not modified when the temperature is changed from +80 to -8° [13]. However the rate of polymerization is decreased (by a factor of 10 ) and the distribution of different fractions in the polymer modified. With a lowering of the temperature the proportion of crystalline fraction is increased up to 70% (Figure 11). The behaviour of propylene sulfide is similar to that of propylene oxide, r being not modified between +30° and -30°, while the crystallinity was increased in the latter case [24]. 

Furukawa and coworkers demonstrated that the effectiveness of diethylzinc increased with controlled addition of water, methanol, or oxygen (81, 82) (Tables 6 and 7). These polymerization systems with propylene oxide produced a substantial fraction of crystalline polymer (16 percent in the case of water/diethylzinc). In some cases, poly(propylene oxide) was prepared with molecular weights estimated to be tens of millions (84). Efforts to understand these polymerization systems centered on identifying the coordination sites available as initiation sites on different metal alkoxides and on differentiating cationic initiation systems from coordinate initiation systems. In some cases, very similar systems led to quite different polymerization reactions and sometimes very different polymer products. 

It is possible, then, to produce crystalline, stereospecific poly(propylene oxide) from optically pure isomer and racemic monomer with a variety of initiators (77) and to determine the product distribution of crystalline and amorphous fractions as well as the optical activity of the products. Further, in a penetrating series of experiments, Furukawa, Tsuruta, and co-workers used optically active coinitiators, including menthol and borneol, and optically active alkylzinc, di-2-methylbutylzinc/H20, to prepare crystalline polymer with optical activity from d,l-monomer, observing enrichment of unreacted monomer with the unreacted enantiomer monomeric species (79, 89-92). 

Allen, Booth, and Jones (96) investigated the intrinsic viscosity-molecular weight behavior of amorphous and crystalline fractions, as well as whole polymers of poly(propylene oxide), and found that their combined behavior could be described by the following Mark-Houwink equations. 

---