Stereochemistry of Polymers

Average Number of Carbon Atoms Boiling Range (°C) Name Physical State at Room Temperature Typical Uses 

50-1000 Decomposes Tough waxy to solid Wax coatings of food containers 

1000-5000 Decomposes Polyethylene Solid Bottles, containers, films 

The distance between the carbon atoms is 1.54 A or 0.154 nm. The apparent zigzag distance between carbon atoms in a chain of many carbon atoms is 0.126 nm. Thus, the length 

FIGURE 2.1 Simulated structure of linear high-density polyethylene (HDPE) contrasted with the structural formula of linear or normal decane. 

In 1953, Karl Ziegler (1898-1973), at the Max Planck Institute for Coal Research, discovered that a mixture of catalysts, triethylaluminum [(C2H5)3A1] and titanium tetrachloride (TiCl4), drastically lowers the pressure and temperature required to polymerize ethylene (CH2=CH2). 

The white, powdery polyethylene formed was easily isolated from the reaction vessel for further processing. This low-pressure (high-density) polyethylene was a tougher polymer and its molded products held up better to force. Ziegler also discovered that polymers, like polypropylene or polystyrene, in which the head and tail of the monomer are different (e.g., propylene [CH2=CHCH3]), are specifically head-to-tail (H-T) in structure and not a mixture of H-H, T-T, and H-T. 

Stereoregular polymers synthesized with (A and B) and without (C) the Ziegler-Natta catalyst A) isotactic polypropylene B) syndiotactic polypropylene C) atactic polypropylene 

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Throughout the years, it has been customary that Professors at the Institute pursue their own research projects with the assistance of the younger members and in close coordination with Mark. Among the projects conducted by these Professors under Mark s influence between 1940 and 1960 are T. Alfrey s study of mechanical properties, R. B. Mesrobian on graft copolymerization, M. Goodman on the stereochemistry of polymers, F. R. Eirich on... 

For each initiator, indicate the (1) type of symmetry, (2) symmetry elements, and (3) stereochemistry of polymer produced. 

There are four types of possible stereoregular structures for each frans-1,4 polymer of 1,4-disubstituted butadiene (Fig. 13). The stereochemistry of polymers is represented by two kinds of relationship as follows, one of which is the relative configuration between the two repeating monomer units. When all the... 

Discuss the structure and stereochemistry of polymers in terms of both regular and irregular features. (Problems 24.24 and 24.35)... 

Because the stereochemistry of polymers is independent of the initiator used, the stereoregulating effect of the counterions was excluded. 

Stereochemistry of polymers plays an important role in determining their properties. Different isomers of a polymer can be obtained starting with the same monomer but having the monomer molecules connected in different ways. For example, a monosubstituted vinyl monomer, in theory, can polymerize head-to-tail (H-T), head-to-head (H-H), or irregularly, as shown below ... 

The stereochemistry of products derived from reactions of coordinated olefins and the stereochemistry of polymers formed in reactions catalyzed by transition metals are ultimately determined by the conformational stability of 7r-complexed intermediates. For example, the cisitrans ratios and the relative amounts of 1,2- versus 1,4-polymer units obtained in diene polymerization are determined by stabilities of syn and anti isomers of vr-allyls and the relative stabilities of various orientations of substituted olefins bound to metals (105). The interconversion rates of these isomers and the thermodynamic preferences of olefin-metal conformations should explain observed product distributions and provide a rational basis for catalyst design. 

Coordination effect on stereochemistry of polymers inspired scientists to look for various catalysts that would result in a selected type of polymer. In the following section, the application of transition metal-based catalysts in polymerization of olefins will be demonstrated. 

The stereochemistry of polymer chains often significantly controlled polymerization methods and molecular designs. 

Figure 1.8 Stereochemistry of polymers from a-olefins and vinyl monomers (a) isotactic and (b) syndiotactic polymers. Atactic polymers show no preference for either isotactic or syndiotactic...

Stereochemistry of Polymers Formed by Metathesis Polymerization of Bicyclic and Polycyclic Olefins... 

Stereochemistry of Polymers Prepared from Bicyclic Olefin Monomers Employing... 

STEREOCHEMISTRY OF POLYMERS PREPARED FROM BICYCLIC OLEFIN MONOMERS EMPLOYING CONVENTIONAL METATHESIS CATALYSTS... 

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