Conversion of alpha-methylstyrene-type monomers in the formation of copolymers with conjugated diene monomers

A copolymer of at least one alpha-methylstyrene-type monomer and at least one conjugated diene monomer characterized by a structure comprising a block of homopolymeric alpha-methylstyrene-type monomer and a block of random poly(conjugated diene/alpha-methylstyrene-type monomer) prepared by the process which comprises

• (a) polymerizing under solution polymerization conditions at a first relatively low polymerization temperature in the range of about 0.degree. C. to 40.degree. C. employing a hydrocarbylmonolithium initiator and a first ratio of monomer:polymerization diluent at least one alpha-methylstyrene-type monomer in the further presence of an effective amount of a first polar activator selected from organic polar compounds which have a dielectric constant of between 2 and 9, do not contain an active hydrogen atom, and do contain oxygen, sulphur, or nitrogen, thereby producing a polymerization admixture comprising living poly(alpha-methylstyrene-type monomer) and residual alpha-methylstyrene-type monomer,
• (b) adding to the resulting polymerization admixture a small capping amount of a conjugated diene monomer of at least about one mole per mole of living poly(alpha-methylstyrene-type monomer) optionally with a second amount of diluent, while maintaining solution polymerization conditions within said relatively low first polymerization temperature, and polymerizing said small capping amount of conjugated diene monomer,
• (c) adding a further amount of conjugated diene monomer and a further amount of polymerization diluent, and increasing the polymerization temperature to a second polymerization temperature substantially higher than said first polymerization temperature and in the range of about 50.degree. C. to 140.degree. C., an polymerizing said further amount of conjugated diene monomer in the presence of a second organic polar activator selected from alkali metal alkoxides other than of lithium in an amount sufficient to provide 10:1 to 1:10 molar ratio of alkali metal relative to lithium, thereby substantially random copolymerizing said conjugated diene monomer and at least a portion of said residual alpha-methylstyrene-type monomer, and
• thereafter terminating the resulting polymerization reaction mixture, thereby preparing said copolymer.

A process to increase the conversion of an alpha-methylstyrene-type monomer in a process to prepare a copolymer of an alpha-methylstyrene-type hydrocarbon monomer and a conjugated diene hydrocarbon monomer containing a block of poly(alpha-methylstyrene-type monomer) homopolymer and a block of random copolymer of (conjugated diene/alpha-methylstyrene-type monomer), which comprises:

• polymerizing, under solution polymerization conditions employing a hydrocarbon diluent and a hydrocarbonmonolithium initiator at a first lower polymerization temperature in the range of about 0.degree. C. to 40.degree. C., said alpha-methylstyrene-type monomer in the presence of about 0.1 to 10 parts by weight of a first polar activator per 100 parts total monomers charged, and a ratio of alpha-methylstyrene-type monomer:diluent of about 9:1 to 1:5, thereby forming a polymerization admixture containing a living poly(alpha-methylstyrene-type monomer) and residual alpha-methylstyrene-type monomer,
• adding thereto a small capping amount of conjugated diene monomer in the ratio of about 1 to 100 moles conjugated diene per mole of living poly(alpha-methylstyrene-type monomer), and added diluent to the extent of about 10:1 to 1000:1 weight ratio of added diluent to conjugated diene added for capping, and polymerizing said capping conjugated diene at said lower polymerization temperature and without further initiator addition, thereby forming a poly(conjugated diene) cap effective to substantially prevent depolymerization of said poly(alpha-methylstyrene-type monomer), and
• thereafter adding a substantial further amount of conjugated diene monomer, such that the total monomer charge is in the weight ratio of 5:95 to 95:5 conjugated diene:alpha-methylstyrene-type monomer, and further diluent wherein said further diluent is sufficient to provide about 3:1 to 25:1 weight ratio of total diluent:total monomers added in all steps, and polymerizing said further amount of conjugated diene monomer at a second higher polymerization temperature in the range of about 50.degree. C. to 120.degree. C. without further initiator addition in the presence of about 10:1 to 1:10 molar ratio relative to lithium of a second polar activator effective to substantially increase conversion of said residual alpha-methylstyrene-type monomer during polymerization of said further conjugated diene monomer at said higher polymerization temperature, such that total conversion of said alpha-methylstyrene-type monomer is a least about 80 weight percent,
• wherein said first polar activator is selected from the group consisting of dimethyl ether, diethyl ether, diamyl ether, dimethoxyethane, bis(2-ethoxyethyl) ether, tetrahydrofuran, hexamethylphosphoramide, tributylamine, hexamethylenetetramine, and mixtures, and
• wherein said second polar activator is an alkoxide of an alkali metal other than lithium.