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The ternary neodymium versatate (NdV3)-based catalyst system, NdV3/SiCl4/Al(iso-Bu)2H, for the stereospecific polymerization of 1,3-butadiene (Bd) has been studied at a catalyst concentration of 0.11 mmol Nd per 100 g Bd. The effects of the concentration of SiCl4 following in situ activation, preformed at 20 °C in the presence and absence of isoprene and the substitution of Al(iso-Bu)2H with AlEt3 as alkylating agent, were established and compared to the performance of NdV3-based catalyst systems incorporating ethylaluminium sesquichloride (EASC), diethylaluminium chloride (DEAC) and t-butyl chloride (t-BuCl) as chloride sources. Comparable catalytic activity between the control catalysts based on EASC, DEAC and t-BuCl and the studied NdV3/SiCl4/Al(iso-Bu)2H system was achieved once the optimum concentration ratios of NdV3/SiCl4/Al(iso-Bu)2H = 1:1:25 were applied in conjunction with preforming the catalyst components in the presence of isoprene for 72 h at 20 °C. Polybutadiene cis-1,4 contents were consistently high (about 97 %) for all polymerizations. © 2000 Society of Chemical Industry

The functionalization reactions of polystyryllithium, polyisoprenyllithium and polybutadienyllithium in benzene with 3-dimethylaminopropyl chloride have been investigated in detail. The effects of addition mode (normal and inverse addition), added Lewis bases (THF and TMEDA), temperature and concentration have been investigated. The polymer products were analysed by SEC, 1 H and 13 C NMR spectroscopy and end-group titration. The pure ω-dimethylamino-functionalized polymers were quantitatively isolated by silica gel column chromatography. The functionalizations of polystyryllithium, polyisoprenyllithium and polybutadienyllithium by normal addition in benzene produce the corresponding w-dimethylamino-functionalized polymers in isolated yields of 67%, 85% and 90%, respectively. Functionalization efficiencies were improved by using the inverse addition procedure and by post-polymerization addition of Lewis bases before functionalization.

The novel syntheses of 4-(4,5-dihydro-4,4-dimethyl-2- oxazolyl)benzophenone, 1-[4-(4,5-dihydro-4,4-dimethyl-2-oxazolyl)phenyl]-1-phenylethanol and 4,5-dihydro-4,4-dimethyl-2-[4-(1-phenylethenyl)phenyl]oxazole (1) are described. ω-Oxazolyl polystyrene (2) was synthesized in quantitative yields by the reaction of poly(styryl)lithium with stoichiometric amounts of 4,5-dihydro-4,4-dimethyl-2-[4-(1-phenylethenyl)phenyl]oxazole (1) in toluene/tetrahydrofuran (4 :1 v/v) at -78°C. Deblocking of the oxazoline protecting group by acid hydrolysis followed by saponification quantitatively provides the corresponding aromatic carboxyl chain-end functionalized polystyrene (3). The functionalization agent and functionalized polymers were characterized by HPLC, thin layer chromatography, size exclusion chromatography, vapor phase osmometry, spectroscopy ( 1 H NMR, 13 C NMR and FTIR), potentiometry and elemental analysis.

Poly(styrene-block-ethylene oxide) (PS-PEO) diblock copolymers have been synthesized with predictable block molecular weights and narrow molecular weight distributions. sec-Butyllithium-initiated polymerization of styrene was effected in benzene solution followed by ω-end-group functionalization with ethylene oxide to form the corresponding polymeric lithium alkoxide (PSOLi). Block copolymerization of ethylene oxide initiated by the unreactive PSOLi was promoted by addition of dimethylsulfoxide and either potassium t-butoxide, potassium t-amyloxide or potassium 2,6-di-t-butylphenoxide. Although the PS-PEO block copolymer product contained some poly(ethylene oxide) homopolymer, the poly(ethylene oxide) block M n was in good agreement with the calculated value and the molecular weight distribution of the final block was generally narrow (M w /M n ≤ 1.1). The amount of PEO homopolymer was minimized using potassium 2,6-di-t-butylphenoxide rather than potassium t-alkoxides.

A living functionalization method for group transfer polymerization (GTP) has been developed for poly(alkyl methacrylates) using the sterically hindered monomer, methyl-2-phenylpropenoate (MPHA). The end-capping reactions of MPHA with living trimethylsilyl ketene acetal-ended poly(methyl methacrylate) (PMMA) chain ends have been systematically studied and characterized by size exclusion chromatography, vapor pressure osmometry, ultraviolet-visible, 1H and 13C nuclear magnetic resonance spectroscopy. Although oligomerization of MPHA is observed at - 78° C, this is reversible and only monoaddition is observed at room temperature. In principle, various functional groups can be introduced into poly(alkyl methacrylates) via substituents on the aromatic ring of MPHA and related monomers. Amino-functionalized PMMA was prepared by end-capping reactions of living trimethylsilyl ketene acetal-ended PMMA with methyl E-3-(2-dimethylaminophenyl)-2-phenylacrylate.

ω,ω-Diphenolpolystyrenes (6) can be synthesized in quantitative yields by reacting poly(styryl)lithium with 1,1-bis(4-t-butyldimethylsiloxyphenyl)ethylene (1), followed by methanol termination and hydrolysis with dilute acid. The initially formed 1,1-bis(4-t-butyldimethylsiloxyphenyl)alkyllithium can be reacted with additional styrene monomer to form a polystyrene internally substituted with two in-chain phenol groups after methanol termination and acid hydrolysis. The diphenol-substituted polystyrene condensation macromonomers have been characterized by end-group titration, size exclusion chromatography, thin-layer chromatography, and ultraviolet-visible, 1H and 13C NMR spectroscopy. Chain-extension reactions of 6 (Mn = 2.6 × 103g mol−1) with bis(trichloromethyl)carbonate produced the corresponding comb-type, branched polymer with estimated Mn(SEC, polystyrene standards) = 1.2 × 104g mol−1 and no detectable residual condensation macromonomer. The second order rate constants for the addition reaction of excess poly(styryl)lithium with 1 and with 1-(4-t-butyldimethylsiloxy-phenyl)-1-phenylethylene (3) have been estimated to be 1.7 × 10−3M−1/2S−1 and 3.2 × 10−3M−1/2S−1 respectively. A sigma value (σ) of −0.46 has been estimated for the t-butyldimethylsiloxy substituent.

Anionic copolymerizations of styrene (M1) with excess 1-(4-dimethyl-aminophenyl)-1-phenylethylene (M2) were conducted in benzene at 25°C for 24h, using sec-butyllithium as initiator. Narrow molecular weight distribution copolymers with M;n = 16.1 × 103 g/mol (Mw/Mn = 1.04) and 38.2 × 103g/mol (Mw/Mn = 1.05), and 24 and 38 moles of M2 per macromolecule, respectively, were characterized by size exclusion chromatography, 1H NMR spectroscopy and DSC. The monomer reactivity ratio, r1 = 5.6, was obtained from the copolymer composition at complete consumption of M1, assuming that the rate constant k22 =0,i.e. r2 =0. The polymers exhibited Tg values of 128 and 119°C, respectively, which correspond to an estimated Tg = 217°C for the hypothetical homopolymer of M2.

Seven experimental criteria for living polymerizations are critically reviewed. The limitations of the use of linear plots of Mn (or X;n) versus conversion and linear plots of the number of polymer chains versus conversion are illustrated by an example of alkyllithium-initiated polymerization of styrene by incremental additions of styrene with deliberate termination (5% per incremental monomer addition). The experimental criteria of using narrow molecular weight distribution and the formation of block copolymers are illustrated with practical examples and size exclusion chromatography data. The use of the terms ‘living polymerization with reversible termination’ and ‘living polymerization with reversible chain transfer’ are proposed.

The adduct (3) from 2 moles of sec-butyllithium with 1,3-bis(1-phenyl-ethenyl)benzene has been prepared and evaluated as a hydrocarbon-soluble, dilithium initiator for butadiene and styrene polymerization in cyclohexane or benzene solution. Under high vacuum conditions with purified reagents, bimodal molecular weight distributions are observed for polybutadienes with Mn < 150 × 103 g/mol and for polystyrenes with Mn < 50 × 103 g/mol; monomodal distributions are observed only for higher molecular weights. Addition of tetrahydrofuran ([THF]/[Li] = 14 to 32) or preformed lithium sec-butoxide ([LiOBu]/[3] = 1·1) produces narrow, monomodal molecular weight distributions even at Mn = 26·2 × 103 g/mol polybutadiene and at Mn = 10 × 103 g/mol for polystyrene. Added lithium sec-butoxide is the preferred additive since high 1,4-polybutadienes are obtained. These results provide an explanation for the contradictory results reported previously; under less rigorous experimental conditions, oxygen and hydroxylic impurities can form lithium alkoxides in situ.