Zsolt Fodor

Living carbocationic polymerization of styrene in the presence of proton trap

Abstract The living polymerization of styrene was achieved with the 2,4,4-trimethyl-2-pentyl chloride/TiCl4/MeCl:methylcyclohexane 40:60 v:v/−80°C polymerization system in the presence of di-tert-butylpyridine in concentrations comparable to the concentration of protic impurities. It was determined that the living nature of the polymerization is not due to carbocation stabilization. The polymerization is second order in TiCl4. Side reactions, namely polymerization by direct initiation and intermolecular alkylation, are operational, and a careful selection of experimental conditions is necessary to minimize their effect and obtain apparently living behavior. Polymerization by direct initiation can be minimized by increasing the initiator concentration, and intermolecular alkylation can be reduced by quenching the polymerization system when the conversion reaches close to 100%.

Polyisobutylene-Based Thermoplastic Elastomers. I. Synthesis and Characterization of Polystyrene-Polyisobutylene-Polystyrene Triblock Copolymers

Abstract Polystyrene-polyisobutylene-polystyrene triblock copolymer thermoplastic elastomers have been synthesized by living carbocationic sequential copolymerization using the tert-butyl dicumyl chloride/TiCl4/methylcyclohexane:methyl chloride (60:40 v:v)/ −80°C system in the presence of the proton trap 2,6-di-tert-butylpyridine. Structure-property relationships have been examined by varying the Mn of the PIB middle block (39,000 to 156,000) and that of the PSt end-segment (1,000 to 19,000). The tensile strength is controlled by the molecular weight of the PSt segment and independent of the PIB middle block length in the studied range. Phase separation starts when the Mn of the PSt segment reaches ∼ 5,000, and it is complete when the Mn reaches ∼ 15,000. These triblocks exhibited 23-25 MPa tensile strength, similar to that of styrenic thermoplastic elastomers obtained by anionic polymerization.

Synthetic applications of nonpolymerizable monomers in living cationic polymerization : functional polyisobutylenes by end-quenching

Abstract The chemistry and kinetics of 1,1-diphenylethylene (DPE) addition to living polyisobutylene was studied at -80°C in methyl chloride/n-hexanes or methylcyclohexane 40/60 v/v. Only monoaddition occurred even when large (9-fold) excess of 1,1-diphenylethylene was used. The kinetics of addition was established by 1H-NMR spectroscopy and by conductivity measurements. The methanol-quenched polymer of the DPE-capped PIB carried exclusively –OCH3 functionality, suggesting that all diphenyl alkyl chain-ends are ionized, which was confirmed by conductivity studies. It was determined that the diphenyl alkyl chain-ends are completely ionized when [TiCl4]/[chain end] ≥ 2 for chain-end concentrations ≥ 10−3 M. Close to quantitative end-quenching was achieved with 1-methoxy-1-(trimethylsiloxy)-2-methyl-1-propene and 1-cyclohexenyloxy-trimethylsilane.

Polyisobutylene-Based Thermoplastic Elastomers. IV. Synthesis of Poly (Styrene-block-Isobutylene-block-Styrene) Triblock Copolymers Using n-Butyl Chloride as Solvent

Abstract The polymerization of isobutylene and styrene was studied using the 2-chloro-2,4,4-trimethylpentane/TiCl4 initiating system in the presence of a proton trap in halogenated hydrocarbons as solvents at −80°C. The polymerization of isobutylene was found to be living, and both homopolymers were soluble in n-butyl chloride. However, side reactions, namely polymerization by direct initiation and intra- and inter-molecular alkylation, are operational in the polymerization of St in n-butyl chloride. Polymerization by direct initiation can be minimized by increasing the initiator concentration, and intermolecular alkylation can be reduced by quenching the polymerization system when conversion reaches ∽ 100%. A careful selection of the experimental conditions was necessary to minimize intramolecular alkylation and obtain complete styrene conversion. Polystyrene-polyisobutylene-polystyrene triblock copolymers prepared under these conditions by sequential monomer addition in n-butyl chloride exhibited ∽ 24 M...

Polyisobutylene-Based Thermoplastic Elastomers. II. Synthesis and Characterization of Poly(p-Methylstyrene-block-isobutylene-block-p-Methylstyrene) Triblock Copolymers

Abstract The synthesis of poly(p-methylstyrene)–polyisobutylene–poly(p-methylstyrene) triblock copolymer was accomplished by sequential monomer addition. The synthesis involves the living polymerization of isobutylene by the TiCl4/methylchloride:hexanes, 40:60 v:v/ −80°C system in the presence of di-tert-butylpyridine using di- or trifunctional initiator. When the polymerization of isobutylene is complete, the living polyisobutylene chain end is converted to the corresponding diphenyl alkyl end by capping with 1,1-diphenyl ethylene. Subsequently, titanium(IV)-isopropoxide is added to decrease the Lewis acidity and p-methylstyrene is introduced. The best triblocks exhibited ∼22 MPa tensile strength.

Living Carbocationic Polymerization of p-Methylstyrene and Sequential Block Copolymerization of Isobutylene with p-Methylstyrene

Abstract A novel scheme was developed for the synthesis of pure polyisobutylene-poly(p-methylstyrene) block copolymers by sequential monomer addition. The synthesis involves the living polymerization of isobutylene by the TiCl4/methyl chloride:methylcyclohexane or hexanes 40:60 v:v/ -80°C system in the presence of di-tert-butylpyridine. When the polymerization of isobutylene is complete, the living polyisobutylene chain end is transformed to the corresponding diphenyl alkyl end by capping with 1,1-diphenylethylene. Subsequently, titanium(IV) isopropoxide or titanium(IV) butoxide is added to decrease the Lewis acidity followed by the addition of p-methylstyrene. The success of the method was demonstrated by p-methylstyrene homopolymerization experiments initiated by 2-chloro-2,4,4-trimethylpentane that resulted in ∼ 100% initiator efficiencies when the TiCl4/titanium(IV) isopropoxide or -butoxide ratio was less than 25/7, as well as by the clean synthesis of polyisobutylenepoly(p-methylstyrene) diblock cop...

The Living Cationic Polymerization of α-Methylstyrene with BCI3 as Coinitiator

ABSTRACT The cationic polymerization of α-methylstyrene (αMeSt) was studied using the cumyl chloride (CumCl), (CH3)3C-CH2- C(CH3)2-CH2-C(Ph)2-OCH3 (TMPDPEOMe) or (CH3)2C(Ph) CH2C(CH3)(Ph)Cl (the HCl adduct of αMeSt dimer, DiαMeStHCl)/BCl3 initiator/coinitiator systems in the presence of proton trap in methyl chloriderhexanes (MeCl:Hex) or MeCl: methylcyclohexane (MeChx) mixtures at −80 and −60°C. While CumCl is not an efficient initiator in conjunction with BCl3, TMPDPEOMe and Di αMeStHCl were found to be very efficient initiators. The polymerization was much faster in the MeCl:Hex mixture than in MeCl:MeChx. The polymerization rate was also higher at −80°C than at −60°C in the same solvent. The polymerization was found to be living at −80°C, as well as at −60°C, giving rise to poly(α-methylstyrene) (PαMeSt) with controlled molecular weight and narrow molecular weight distribution (Mw/Mn ∼ 1.1-1.2). The chain ends remained living for up to 40 minutes under monomer starved conditions at −80°C, but they rap...