alpha-Methylstyrene

Abstract: We describe the use of poly(alpha-methylstyrene peroxide) (P alpha MSP), an alternating copolymer of alpha-methylstyrene and oxygen, as initiator for the radical polymerization of vinyl monomers. Thermal decomposition of P alpha MSP in 1,4-dioxane follows first-order kinetics with an activation energy (E(a)) of 34.6 kcal/mol. Polymerization of methyl methacrylate (MMA) and styrene using P alpha MSP as an initiator was carried out in the temperature range 60-90 degrees C. The kinetic order with respect to the initiator and the monomer was close to 0.5 and 1.0, respectively, for both monomers. The E(a) for the polymerization was 20.6 and 22.9 kcal/mol for MMA and styrene, respectively. The efficiency of P alpha MSP was found to be in the range 0.02-0.04. The low efficiency of P alpha MSP was explained in terms of the unimolecular decomposition of the alkoxy radicals which competes with primary radical initiation. The presence of peroxy segments in the main chain of PMMA and polystyrene was confirmed from spectroscopic and DSC studies. R(i)'/2I values for P alpha MSP compared to that of BPO at 80 degrees C indicate that P alpha MSP can be used as an effective high-temperature initiator.

Abstract: The first efficient synthesis of poly(α-methylstyrene-b-isobutylene-b-α-methylstyrene) (PαMeSt-PIB-PαMeSt) triblock copolymer thermoplastic elastomers (TPEs) has been accomplished by living cationic polymerization using sequential monomer additions. Living PIB was prepared by the 5-tert-butyl-1,3-bis(1-chloro-1-methylethyl)benzene (tBuDicumcl)/TiclJHex :Mecl 60 :40 v :v/-80°C polymerization system. The living ends were capped by 1,1-diphenylethylene (DPE). TiCl 4 was replaced by SnBr 4 , followed by the addition of αMeSt. Triblock copolymers with close to theoretical molecular weights and narrow molecular weight distributions (M w /M n ∼1.1) were obtained. Homopolymer and diblock contamination have been found to be negligible. The thermal stability of the triblock copolymer was characterized by thermogravimetric analysis. Microphase separation was evidenced by the two glass transitions (at -65 and +180°C) observed by differential scanning calorimetry and in dynamic mechanical analysis. Triblock morphology was examined by transmission electron microscopy. Compression-molded samples with 16-45 wt % PαMeSt exhibited 12-24.5 MPa tensile strength, apparently directly related to the PαMeSt content and independent of the PIB molecular weight.

Abstract: A new hydrocarbon-soluble (additive-free) dicarbanionic organolithium initiator, obtained by a simple halogen−lithium exchange reaction (Gilman's reaction) from a diarylhalide containing a side C15 alkyl chain, has been designed and used to initiate the anionic polymerization of butadiene and styrene. The dilithiated species formed afford well-defined poly(styrene-b-butadiene-b-styrene) (SBS) triblock copolymers with a high percentage of 1,4-microstructure polybutadiene (91%) and excellent mechanical properties, such as ultimate tensile strength higher than 30 MPa and elongation at a break of 1000%. This represents a breakthrough in the synthesis of SBS polymers, one of the most used thermoplastic elastomers.

Abstract: Fast copolymerizations of styrene and alpha-methylstyrene can be achieved in emulsion systems where free-radical reactions in the bulk or solution are inefficient. The Smith–Ewart–Gardon theory of emulsion polymerization was developed for homopolymerizations but should extend to this copolymerization since the particular comonomers meet the basic assumptions of this model. Sodium lauryl sulfate surfactant provided faster initial polymerization rates, but steady-state conversions were faster with potassium laurate, especially at higher alpha-methylstyrene contents. This is ascribed to acceleration of potassium persulfate decomposition by the former soap. Monomer concentration in the polymerizing particles was constant during steady reaction rates. The rate of volume growth of particles during this interval was generally as predicted by theory. The number of particles and particle sizes could be predicted well if allowance was made for initiator wastage reactions. The observed average number of radicals per particle appeared to be 0.5. Analysis of the composition of monomer droplets and proton NMR analyses of copolymer compositions provided independent confirmations that the present emulsion copolymerization was consistent with the terminal copolymerization model.