ABSTRACT

Acknowledgment................................................................................................................ 254

References .......................................................................................................................... 254

When propylene was first polymerized in the mid-1930s, the product was a low-melting

solid of no possible value as a resin from which synthetic fibers could be prepared. By the

mid-1950s, research had led to the preparation of a new kind of polypropylene that had all

or most of the pendant methyl groups in a regular position with respect to the polymer

backbone. Commercial production of these stereospecific polymers utilized catalysts that

were generally based on a combination of TiCl3 and an aluminum alkyl. The stereospecific

resin with all the methyl groups in the same position, rather than regular alternating

positions, was called isotactic polypropylene. This resin was crystallizable with melt

temperatures in the range of 160-1748C, and fibers capable of retaining molecular orientation at normal-use temperatures could be prepared. Since then, catalyst and process

improvements have resulted in approximately a tenfold increase in polymer yield per

simplified purification The percent

noncrystalline resin has been reduced, and clean, gel-free resin required for modern fiber

processes is now readily available. Isotactic polypropylene, as originally produced, had a

very broad molecular weight distribution compared to most synthetic fiber resins. Poly-

propylene resin with a narrower molecular weight distribution, which is beneficial to the

same fiber processes, is now manufactured.