Page 203 - Carrahers_Polymer_Chemistry,_Eighth_Edition

166 Carraher’s Polymer Chemistry

Cl CH 3 H 2 C CH 2
MAO Zr +
Zr Zr CH 3
Cl CH 3

H 2 C
CH 2
CH 3 H 2 C CH 2
+ Zr +
Zr
CH 2
CH 3
H 2 C

CH 2

R
Zr + H
Zr + R
H
H

FIGURE 5.1 Proposed mechanism for soluble stereoregulating catalyst polymerizations.

Use of materials produced from single-site catalysts in areas employing thin films is increasing.
For instance, bananas are generally produced at one location and shipped and stored to other loca-
tions for sale. Even when picked green, they ripen rapidly when exposed to oxygen. Regular LLDPE
is generally employed as a thin fi lm to protect bananas for shipment and storage. Regular LLDPE
permits some transfer of oxygen, and because of the somewhat pointed nature of bananas the fi lm
may be punctured. Single-site metallocene-based LLDPE is less permeable and less apt to tear and
is now replacing regular LLDPE in this use. Its use is also increasing in the containment of heavier

materials such as topsoil and water-purification salt utilizing thicker films. In both cases, thinner
films, and consequently less film material, is necessary to give an equal or better job performance.

Single-site produced materials also offer better clarity, toughness, and easy sealability.
5.7 POLYETHYLENES
Tupperware was the idea of Earl Silas Tupper, a New Hampshire tree surgeon and plastics innova-
tor. He began experimenting with PE during the early part of World War II. In 1947, he designed
and patented the famous “Tupper seal” that “sealed in” freshness. To close the container it had to
be “burped” to remove air. Tupperware was also bug proof, spill proof, did not rot or rust, and did
not break when dropped. Even with all of these advantages, few were sold. Enter Brownie Wise, a
divorced single mother from Detroit who desperately needed to supplement her income as a sec-
retary. Her idea—“Tupperware Parties.” By 1951, Tupper had withdrawn all of the Tupperware
from the stores and turned over their sales to Brownie Wise with the only source of the ware being
through the Tupperware Parties.
The initial synthesis of PE is attributed to many. In 1898, Han von Pechmann prepared it by
accident while heating diazomethane. His colleagues Eugen Bamberger and Friedrich Tschirner
characterized the white solid as containing methylene units and called it polymethylene. PE, from
the ethylene monomer, was probably initially synthesized by M. E. P. Friedrich while a graduate

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