RESEARCH tent lex-els, got t h e m by varying time a n d t e m p e r a t u r e in the process* Among t h e properties Cotnpton a n d Etchells tested and found improved a r e resin retention, tensile strength, chlorine retention, a n d iaundcrability. Some of their results: • Resin retained in fabric containing urea formaldehyde is Sl*?e after 1 5 laiinderings, c o m p a r e d to 5 4 9r for t h e lîoncyanoetbyîated fabric. • Resin retained in fabrics t r e a t e d with melamine formaldehyde and m o d i fied urea formaldehyde ranges from 9 0 to 9 5 c * , c o m p a r e with 77 t o 8 7 % for t h e noncyanoethylated fabrics. Property behavior of the eyanoethylated resin-treated fabrics varies w i t h t h e resin and nitrogen content. But, says Compton, m a n y improvements c a n b e m a d e simultaneously b y properly selecting t h e aminoplast resin and varying t h e extent of cyanoethylation.
How cis-1 s op re ne Polymerizes M o n o m e r a n d lithium c a t a lyst f o r m coordination c o m p l e x which produces stereoregular polymer
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Isoprene can b e polymerized u s -
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NATIONAL ing any of t h e MEETING alkali metals as Rubber catalyst. But Chemistry when the reaction is catalyzed b y lithium or organolithium comp o u n d s in the absence of solvents containing oxygen, a stereoregular polymer results—more t h a n 9 3 % cis-1,4-polyisop r e n e . T h e ability of the lithium atom to b e h a v e as if it were divalent causes this stereospecific effect, R. S. Stearns and L. E . F o r m a n of Firestone T i r e and R u b b e r told the Division of R u b ber Chemistry. Stearns concludes that the stereospecific polymerization mechanism d e pends on two things: t h e electronic structure of t h e lithium atom a n d t h e molecular structure of isoprene. E x perimental data that support this conclusion: Inherent viscosity of the polymer increases linearly as the catalyst concentration decreases and is indep e n d e n t of temperature; the micro52
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as Isoprene Adds Kead-to-Tail This W a y
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s t r u c t u r e of t h e polymer improves as t h e a m o u n t of catalyst decreases. One property that sets lithium a p a r t from other alkali metals is the t e n d ency of t h e s a n d ρ orbitals t o hybridize L i t h i u m ' s tendency to hybridize is twice a s great as t h a t of t h e other alkali rneiais. ne^t-tit: l i i u u u m twtia^va «S a polyvalent atom in m a n y reactions. Complexes h a v e b e e n p r e p a r e d that s h o w lithium can have a valence of t w o o r even three. Another factor: O r ganolithium c o m p o u n d s show great stability in retaining the stereo con figuration. Monomeric isoprene contains a b o u t 85*/r cts-isoprene. As Stearns sees it, t h e first step in p r o d u c i n g cw-polyisop r e n e is forming a complex b e t w e e n a carbon-bound lithium a t o m a n d cis~ isoprene. This coordination complex results from orbital o v e r l a p . A c c o r d ing to Stearns, olefinic h y d r o c a r b o n s w i t h cis configuration coordinate m o r e strongly than those w i t h trans con figuration. And lithium h a s a t e n d e n c y t o select resonating ci-s-isoprene mole cules a n d reject the trans. In t h e next step, t h e cis coordination complex rearranges t o form a n acti vated complex. This c a n be repre sented by a six-membered ring ( s e e diagram). As carbon atom C 2 a p p r o a c h e s C 2 , the Cj-to-lithium b o n d is stretched. As carbon atom C 5 a p p r o a c h e s the lithium atom the orbital
overlap becomes g r e a t e r than that for t h e stretched C*— Li b o n d . The strained Cj—Li b o n d breaks and the covalent carbon-carbon b o n d C%~—C2 forms. Result; head-to-tail addition of cis-isoprene units. This reaction appears t o be analogous to t h e Oielsζ^ΛΟΓ
Th i*=* p r o
posed mechanism can b e considered as the addition of a diradical t o a polar ized but covalent carbon-lithium b o n d . About 5 to 7f/r of t h e p o l y m e r in cis-isoprene is formed b y 3,4 addition. This can b e accounted for by the other resonance structures of isoprene.
Painless Hypos Through EPC Electrophoretic chromatog r a p h y promises to t a k e the "hot" out o f shots, g i v e uni versal vaccine Vaccinations ACS frequently proreac> NATIONAL d u c e s i d e MEETING tions like fever o r muscular sore Analytical ness. A novel Chemistry m e t h o d for puri fying biological substances may get rid o f the u s u a l 'Tdck" in v a c c i n e in jections b y separating culpable compo-
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