Intramolecular chloride shift polymerization by cationic mechanism. Polymerization of 3-chloro-3-methyl-1-butene and the effect of temperature on polymer structure

The cationic polymerization of 3-chloro-3-methyl-1-butene was investigated in the temperature range from ?30° to ?130°C. The structure of the polymer was characterized by NMR spectroscopy and was found to be a mixture of about equal portions of repeating units. Changing the temperature from ?30° to ?130°C. affects only slightly the respective amounts of these structures. No evidence for methide shift polymerization was found. These results are discussed in terms of an earlier proposed mechanism.     

The electro-initiated cationic polymerization of indene, 1

The electro-initiated anodic polymerization of indene in ethylene dichloride solutions of tetraethylammonium hexachloroantimonate and tetrabutylammonium perchlorate as background electrolytes was studied. The polymerization was conducted either under continuous electrolysis or by addition of the monomer to the pre-electrolysed solution of the salt. The polymer formation was affected by the amount of electricity, the monomer concentration, and the nature of the electrolytes. The rate and degree of polymerization with the hexachloroantimonate salt are relatively high in comparison with the perchlorate salt. The characteristically colored species, formed during polymerization, were investigated spectrophotometrically. Mechanisms for the initiation processes of both procedures were elucidated.     

Cationic polymerization of 3-methylenecyclohexene and 2-methyl-1,3-pentadiene

To investigate the effect of a cyclic structure on the reactivity of conjugated dienes in cationic polymerization, a cyclic diene 3-methylenecyclohexene ( 1 ) and the corresponding linear diene 2-methyl-1,3-pentadiene ( 2 ) were synthesized and polymerized. Cationic polymerizations and copolymerizations showed that 1 was more reactive than 2 . The conjugated double bonds in 1 were proved to be less resonance-stabilized than that in 2 . However, the conjugate cation 1 was found to be more stable than that of 2 . The combination of these two factors made the cyclic diene more reactive than the linear d+. Cationic polymerizations of 2 were fast and non-stationary, giving low molecular weight polymers. The polymerizations proceeded mainly by the 1,4 route and to a smaller extent by the 1,2 route. A brief discussion on the stereochemistry in some electrophilic addition reactions of methyl-substituted butadienes is also given.     

The electro-initiated cationic polymerization of indene, 2. Kinetics of polymerization

The electrolytically initiated anodic polymerization of indene in the solutions of tetraethylammonium hexachloroantimonate and tetrabutylammonium perchlorate in nitrobenzene under constant electric current and constant potential electrolysis conditions was studied. The polymerization was followed either under continuous electrolysis or by addition of the monomer to the pre-electrolysed solution of the salt. The monomer consumption follows the first-order rate-law, log[M]₀/[M]_t=kt, and the rate constant of the polymerization increases with increasing current level. The polymer formation was greatly affected by the change of the dielectric constant of the medium, the anode material, and the nature of the supporting electrolyte. The mode of initiation process depends upon the type of the salt. Mechanisms for the initiation reaction were elucidated.     

Anionic polymerization of 4-methyl-2-oxetanone

Potassium solutions, obtained by contacting the metal mirror with a THF solution of a crown ether were found to initiate the anionic polymerization of 4-methyl-2-oxetanone ( 1 ) (β-butyrolactone). The tacticity of the resulting polymer 2 was established by means of ¹³C NMR spectroscopy. The results indicate that living polymers of 1 were formed, and the polymerization proceeds without abstraction of hydrogen from the monomer and no termination and transfer reactions take place.     

Oxidative polymerization of 2,6-bis(3-methyl-2-butenyl)phenol

Oxidative polymerization of 2,6-bis(3-methyl-2-butenyl)phenol ( 1 ) was carried out by copperpyridine catalyst. 1 was oxidatively polymerized to yield poly[oxy-2,6-bis(3-methyl-2-butenyl)-1,4-phenylene] ( 2 ) in a similar manner as it has been observed for 2,6-dimethylphenol ( 3a ). 2 is an oily material with a degree of polymerization of 6,2. 1 and 3a copolymerized with similar reactivity to form the copolymer 4 (degree of polymerization 16 to 29). The 3-methyl-2-butenyl groups in the polymer show enough chemical reactivity for an addition of bromine or graft-polymerization.     

Cationic polymerization of 2-methyl-1.3-dioxepane

2-Methyl-1.3-dioxepane was polymerized in 1.2-dichloroethane with triethyl oxonium tetrafluoroborate and boron trifluoride as initiators. This polymerization involves a monomer-polymer equilibrium and the polymer consists of regularly alternating tetrahydrofuran and acetaldehyde units. The thermodynamic parameters for the polymerization were determined from the temperature dependence of the equilibrium monomer concentration as follows: ΔH_SS = ?2.1 ± 0.3 kcal/mole and ΔS⁰_SS = ?8.9 ± 1.3 cal/mole deg. The ceiling temperature for the 1 mole/1. solution is ?37°C. The attempted polymerization of 2.2-dimethyl-1.3-dioxepane gave only a crystalline cyclic dimer.     

The cationic polymerization of 2-alkenylfurans, 2. A side reaction leading to polyunsaturated products

A spectroscopic and conductimetric study of the cationic polymerization of 2-vinylfuran (1) and 2-methyl-5-venylfuran (2) showed the existence of an important side reaction originating from a hydride-ion shift from an unsaturated polymer molecule to an active species. The resulting allylic carbocation, in equilibrium with a doubly unsaturated polymer molecule, can react further and the repetition of the mechanism on progressively more conjugated species leads to the formation of a series of highly charge-delocalized carbenium ions absorbing throughout the visible region of the spectrum (and giving high electrical conductivity) and of neutral polyconjugated polymer molecules. Since the hydride-ion abstraction occurs from the tertiary carbon atom of the vinylic chain, vinylidene polymers of monomers such as 2-isopropenylfuran (3) and 2-isopropenyl-5-methylfuran (4) are not susceptible to it. Indeed, their cationic polymerization proceeds without colour formation and conductivity increase.     

Polylactones, 7. The mechanism of cationic polymerization of β-propiolactone and ϵ-caprolactone

Homopolymerisations of β-propiolactone and ?-caprolactone, initiated by means of methyl trifluorosulfonate, triethyloxonium tetrafluoroborate or acetylium perchlorate, were investigated. Both ¹H and ¹³C NMR spectra proved that the alkylating initiators yield polyesters with alkyl ester end groups, indicating a chain growth via alkyl-oxygen cleavage of the lactone. At temperatures below 100°C cationic polymerizations initiated by alkylating reagents were found to proceed via end groups which may cause degradation due to back-biting. When ?-caprolactone was reacted with excess methyl triflate, high concentration of triflate ester end groups were formed, whereas in the case of β-propiolactone active end groups were not detectable by ¹H NMR spectroscopy. Initiation with acetylium perchlorate yielded a polyester with acetate end groups. Acetate end groups were also obtained, when “living” polymers, initiated with methyl triflate, were reacted with acetic anhydride. It could be shown that the formation of acetate end groups does not indicate an electrophilic attack at the endocyclic oxygen. Furthermore, it is discussed that any experimental evidence for a cationic chain growth via acyloxygen bond cleavage is lacking.     

Electroinitiated cationic polymerization of propylene sulfide

The electroinitiated cationic polymerization of propylene sulfide in 1,2-dichloroethane solvent has been investigated between 30 and 60°C. The polymerization once initiated by a fast pulse of high intensity current goes to high conversion. The kinetics of monomer consumption linearly depends on both supplied charge and monomer concentration thus allowing an easy determination of the specific propagation rates. The molecular weights of the obtained poly(propylene sulfide) are relatively high and depend on the conversion, on the charge amount initially furnished to the system, and on the reaction temperature.     

Oxidative polymerization of 2-(2-butenyl)- and 2-(3-methyl-2-butenyl)-6-methylphenol

2-(2-Butenyl)-6-methylphenol ( 1a ) and 2-(3-methyl-2-butenyl)-6-methylphenol ( 1b ) were oxidatively polymerized in the presence of a copper-pyridine catalyst to yield poly[oxy-2-(2-butenyl)-6-methyl-1, 4-phenylene] ( 2a ) and poly[oxy-2-(3-methyl-2-butenyl)-6-methyl-1,4-phenylene] ( 2b ) with molecular weights >10⁴. The polymerization rates were in the order 1b > 1a > 1a > 2,6-dimethylphenol ( 3 ), and this order agreed with those of the rate constant of the electron-transfer step and of the redox potential. The 2-butenyl and 3-methyl-2-butenyl group in 2 showed enough chemical reactivity for addition of bromine and epoxidation.     

Anionic block polymerization of β-lactones initiated by potassium solutions, 1. Synthesis of poly(4-methyl-2-oxetanone-block-2-oxetanone)

The block polymerization of 4-methyl-2-oxetanone (β-butyrolactone) with 2-oxetanone (β-propiolactone) proceeds fast with a yield of more than 90%, in the presence of potassium solutions in THF containing 18-crown-6. Poly(4-methyl-2-oxetanone-block-2-oxetanone) polymers having the expected molecular weight and composition are formed by this way. Their glass transition and melting temperatures as well as their melting enthalpies, determined by DSC, show a strict correlation with block polymer composition.     

The mechanism of the initiation reaction of the cationic polymerization of tetrahydrofuran by stable cationic salts

The mechanism of the initiation reaction for the polymerization of cyclic ethers and lactones by triethyloxonium-, acetyl- and dioxolenium-salts was studied. Triethyloxonium salts initiate the polymerization of cyclic ethers simply by the alkyl exchange reaction. Cyclic esters react with triethyloxonium salts at both ether and carbonyl oxygens but the polymerization proceeds by the acyl-oxygen fission. The k_p value of the polymerization of THF by triethyloxonium salts is almost constant independent of gegenanion. Acetyl cation initiates the polymerization of THF partly by bonding mechanism, but dioxolenium salt initiates completely by bonding.