Intramolecular hydride shift polymerization by cationic mechanism. I. Introduction and structure analysis of poly‐3‐methylbutene‐1

Abstract

The low temperature cationic polymerization of 3‐methylbutene‐1 proceeds by intramolecular hydride shift mechanism. The secondary carbonium ion rearranges to a tertiary one prior to propagation. Thus the repeat unit of cationically obtained poly‐3‐methylbutene‐1 is not the expected or 1,2 structure but an α,α′‐dimethylpropane‐type 1,3 unit, e.g.,

gem‐Dimethyl Effects in the Thermal Behavior of Polyethylene

“…[24][25][26][27][28][29][30] Instead of yielding the expected product of olefin polymerization (polyethylene with an isopropyl group on every other carbon), the polymerization proceeded via a 2,3-type hydride shift to form a tertiary carbocation during each propagation step, yielding a gemdimethyl on every third carbon. They reported that if the Scheme 1.…”

“…In related work conducted in the early 1960's, Kennedy and coworkers synthesized polyethlene with gem ‐dimethyl groups on every third carbon via a cationic polymerization of 3‐methyl‐1‐butene in the presence of aluminum chloride 24–30. Instead of yielding the expected product of olefin polymerization (polyethylene with an isopropyl group on every other carbon), the polymerization proceeded via a 2,3‐type hydride shift to form a tertiary carbocation during each propagation step, yielding a gem ‐dimethyl on every third carbon.…”

The NMR of Polymers

“…we obtain (II- 59) With these conditions the constant components of the envelopes B(t) and A(t) are, respectively, the absorption and dispersion signals, corresponding to the effective exciting field wlJo(f3) with amplitudes increased by a factor J o (f3). When {:J = 0, these expressions revert to the normal functions of v and u [see expression (I- 88)].…”

“…From the relative intensity of the peaks of methyl and methylene protons of a polymer of 3-methylbutene-1 it was established [59] that the chain of the polymer consists of a-dimethylpropane units By treating germanium diiodide with acetylene and methylating the product with methylmagnesium iodide, Vol'pin and his coworkers [37] synthesized a polymer with alternating double bonds and germanium atoms in the chain. 'rhe NMR spectrum of a solution of the polymer contained only two peaks with a ratio of intensities of 1: 3 and chemical shifts reliitive to benzene of 0.3 • 10-6 and 7.0 • 10-6 • These peaks correspond to methyne and methyl protons, proving the structure of the polymer…”