Cationic polymerization of 3‐methylbutene‐1. I. Polymerizations at moderately low temperatures

Abstract

SynopsisThe cationic polymerization of 3-methylbutene-1 was investigated with the use of aluminum chloride and aluminum bromide initiators in the temperature range of -62 to -102°C. Polymerizations are homogeneous in the presence of pentane, and above -50°C. in methyl chloride. However, the polymer tends to precipitate below -5OOC. in methyl chloride. The molecular weight of poly-3-methylbutene-1 increases with decreasing temperatures a t the same conversion level. Significantly, the molecular weights increase with conversion and seem to reach their maximum a t high conversions. Higher molecular weights were obtained in n-pentane-alkyl chloride mixtures than in methyl chloride solution alone. The molecular weights are independent of catalyst concentrations in the range investigated (31.8-7.97 X loF4 mole/l. AlBr3 and 57.6-28.8 X mole/l. AlC13). The rate of homogeneous polymerization with aluminum bromide in propane solvent was studied. The rate is first order in monomer concentration and catalyst concentration and the rate constant is 0.610 l./mole sec. The apparent activation energy calculated from the Arrhenius plot is 6.57 kcal./mole. In methyl bromide the rate of polymerization increases significantly (effect of the dielectric constant). In toluene the molecular weight as well as the rate is strongly depressed indicating the preponderance of a chain breaking mechanism involving this solvent. 367

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.…”

“…polymerization was conducted above À120 8C, high conversions could be achieved, but the polymer formed was completely amorphous and rubbery. [27] This was most likely due to the presence of non-hydrogen-shifted repeat units in the polymer, although the NMR techniques of the day were not resolved enough to determine the specific content of the two repeat units in the polymer samples. [30] However, when the polymerization was conducted at À130 8C, the polymer was exclusively hydrogen shifted and consequently was 25-30% crystalline.…”

“…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 effect of temperature on the cationic isomerization polymerization of 3‐methyl‐1‐butene and 3‐chloro‐3‐methyl‐l‐butene

“…The activated complexes arc probably also involved in chain transfer [eqs. (7) and (9)] and termination [eqs. ( 8 ) arid (lo)] reactions which do not affect, polymer structure but do influence molecular weights and conversions.…”

“…Thus, a t steady state, the degree of polymerization should be unaffected by monomer concentration. Similarly, while diffusion should control the rates of reactions ( 2 ) and (3), the relative rates of reactions (5) and (6) to reactions (7), (S), (9), and (10) should be independent of diffusion.…”