ISSN:0022-233X    

DOI:10.1080/00222338208077217

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

It has been shown that in addition to classical living polymerizations, several other polymerization systems exist that may exhibit partially living so-called quasiliving character. The single requirement for quasiliving polymerization is the absence of irreversible termination. The various possible living systems have been classified by taking into consideration the absence or reversibility of termination and the absence, reversibility, or irreversibility of chain transfer. In regard to chain transfer, both unimolecular and/or bimolecular processes have been considered. A comprehensive examination of all possibilities yielded, in addition to the classical terminationless-transferless living system, five quasiliving systems. Kinetic analysis led to equations defining these systems and to diagnostic techniques useful for the classification and characterization of the mechanism of living carbocationic polymerizations.

ISSN:0022-233X    

DOI:10.1080/00222338208077218

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

A detailed analysis of elementary reactions of carbocationic polymerization culminated in the prediction and subsequent experimental demonstration of quasiliving polymerization. Quasiliving polymers are formed in a system provided that the process of chain termination and chain transfer to monomer are absent or reversible, i.e., the propagating ability of the chain end is maintained throughout the experiment, and the molecular weight increases in proportion to the cumulative amount of monomer added. The chain end can be active (carbocation) or dormant (reactivable polymeric olefin or cation source). Chain transfer is suppressed by keeping the monomer concentration low. Quasiliving polymerizations are maintained by continuous slow feeding of dilute monomer to a charge containing the initiating or propagating species (quasiliving polymerization technique). A comprehensive kinetic scheme has been developed that describes quasiliving polymerization in quantitative terms. Quasiliving polymerization was demonstrated experimentally in the “H2O”/BCl3/α-methylstyrene and cumyl chloride/BCl3/α-methylstyrene systems.Mnversus monomer input plots are linear over wide ranges, indicating quasiliving conditions, and poly(α-methylstyrenes) withMn> 2 × 105have been obtained, Molecular weight distributions were found progressively to narrow and dispersion ratiosMw/Mnto decrease.

ISSN:0022-233X    

DOI:10.1080/00222338208077219

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

The polymerization of isobutylene has been investigated by the use of the steady, slow, continuous monomer addition technique in the presence of a variety of initiating systems, i.e., “H2O”/TiCl4, “H2O”/AlCl3, C6H5C(CH3)2Cl/TiCl4, p-ClCH2C6(CH3)4* CH2Cl/AlCl3at -50°C. Quasiliving polymerizations have been obtained with the “H2O” and C6H5(CH3)2Cl/TiC14systems in 60/40 v/v n-hexane/methylene chloride solvent mixtures with very slow monomer input. After a brief “flash” polymerization, theMnof PIB increased linearly with the cumulative amount of monomer added (consumed); however, the number of polymer molecules formed also increased, indicating the presence of chain transfer to monomer. With the “H2O”/TiCl4initiating system,Mn,maxwas 56,000 andMw/Mn< 2.0. By the use of the C6H5C(CH3)2CL/TiCl4initiating system, quasiliving polymerization has been achieved and chain transfer could virtually be eliminated.

ISSN:0022-233X    

DOI:10.1080/00222338208077220

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

The mechanism of polymerization of p-tert-butylstyrene (ptBuSt) initiated by the cumyl chloride/BCl3initiating system in CH2Cl2at -50°C has been investigated. At and below ∼0.4 M ptBuSt, quasiliving polymerizations proceed, i.e., initiation is instantaneous, termination is absent or reversible, and chain transfer to monomer can be suppressed or eliminated. In the quasiliving range theMnversus [ptBuSt]0plot is linear and passes through the origin, and aMw/Mndecreases much below 2.0 with decreasing [ptBuSt]. GPC traces change from broad multimodal to narrow monomodal and the color of polymerization charges change from colorless to golden-yellow with decreasing [ptBuSt]. The effect of temperature jump subsequent to monomer addition has been examined; however, it does not explain the peculiar monomer concentration effect on the mechanism. Changes in the ionicity may be responsible for this phenomenon.

ISSN:0022-233X    

DOI:10.1080/00222338208077221

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

Quasiliving polymerization of indene, i.e., an increase of the molecular weight of polyindenes with the cumulative amount of consumed monomer, has been demonstrated using the “H2O”/ BCl3, 2-chloroindene/BCl, “H2O”/TiCl4, 2-chloroindene/TiCl4, and cumyl chloride/TiCl4initiating systems in CH2Cl2solvent at -50°C. However, chain transfer operates in every system investigated, and sets a limit toDPn,max. The efficiency of the 2-chloroindene and cumyl chloride initiators is very low. The behavior of BCl3and TiCl4coinitiators on the polymerization has also been investigated.

ISSN:0022-233X    

DOI:10.1080/00222338208077222

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

Quasiliving carbocationic polymerization of isobutyl vinyl ether (IBVE) was achieved with the p-dicumyl chloride (p-DCC)/AgSbF6initiating system in methylene chloride solvent at -70 and -90°C. The monomer was introduced as a steady, continuous stream to a premixed, well-stirred initiator solution (quasiliving technique). The number-average molecular weights (Mn) of poly(IBVE) increased linearly with thecumulative weight of added monomer (WIBVE), and linearMnversus WIBVEplots passing through the origin were obtained.Mn's were inversely proportional to the initial initiator concentration ([p-DCC]0) and were in agreement with theoretical values (WIBVE/[p-DCC]0) expected for quasiliving systems, The number of polymer chains produced per unit initiator (p-DCC) was close to unity and remainec unchanged during the early stages of the reactions. The poly-(IBVE) exhibited narrow molecular weight distributions withMw/Mnranging from 1.4 to 1.7. Polymerizations using methylene chloride solvent at highertemperatures (-30 and -50°C) also yielded linear ascendingMnversus WIBVEplots; however, they showed intercepts. Using a nonpolar solvent (n-heptane),Mndid not increase with WIBVE(-50°C) orMnversus WIBVEplots were strongly curved (-70°C), indicating slow initiation and the absence of quasiliving conditions. Evidently optimum conditions for quasiliving IBVE polymerization prevail only in polar media at lower temperatures.

ISSN:0022-233X    

DOI:10.1080/00222338208077223

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

Poly(α-methylstyrene-b-isobutyl vinyl ether-b-α-methylstyrene) triblock polymers have been prepared by blocking α-methyl-styrene (αMeSt) from biheaded quasiliving poly(isobuty1 vinyl ether) (PIBVE) cations generated with the bifunctional p-dicumyl chloride/AgSbF6initiating system in methylene chloride solvent at -90°C. The products were fractionated with 2-propanol, a good solvent for PIBVE and a nonsolvent for PaMeSt. The 2-propanol-insoluble fractions had much higher molecular weights (Mn= 30,500–69,100) than the starting PIBVE (Mn=6,600–10,600) and contained 13–29 wt% IBVE together with 87–71 wt% αMeSt units. The 2-propanol-soluble fractions (Mn= 7,300–11,600) contained ∼90 wt% IBVE and ∼10 wt% αMeSt units.

ISSN:0022-233X    

DOI:10.1080/00222338208077224

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

Quasiliving carbocationic polymerization of methyl vinyl ether (MVE) was achieved with the p-dicumyl chloride (p-DCC)/AgSbF6initiator system by the slow and continuous monomer-addition (quasiliving) technique. A polar solvent (CH2Cl2) and a low reaction temperature (-70°C) were optimum for the quasiliving MVE polymerization. Under these conditions, the number-average molecular weight (Mn) of poly(MVE) increased linearly with the cumulative weight of added monomer (WMVE), and linearMnversus WMVEplots passed through the origin.Mn's were inversely proportional to the initial initiator (p-DCC) concentration. Reactions in a nonpolar solvent (toluene) at -70°C or in a polar solvent (CH2Cl2) at −30°C resulted in deviations from these quasiliving characteristics. Block polymerization of MVE from quasiliving poly(isobutyl vinyl ether) dications by the quasiliving technique (p-DCC/AgSbF6initiator, CH2Cl2solvent,(-70°C) led to novel isobutyl vinyl ether (IBVE)-MVE block polymers in high yield (>93 wt%) and at high blocking efficiency. The block polymers, most likely poly(MVE-b-IBVE-b-MVE), havingMn= 10,900–14,000 [Mn(center block) = 6,200–9,0001, were soluble in n-heptane and insoluble in water, and gave hazy homogeneous solutions when dissolved in methanol at room temperature.

ISSN:0022-233X    

DOI:10.1080/00222338208077225

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

Forced ideal carbocationic copolymerization of α-methylstyrene (αMeSt) with p-tert-butylstyrene (ptBuSt) and (αMeSt) with styrene (St) has been achieved by continuous monomer feed addition to a cumyl chloride/BCl3charge at -50°C by keeping the feeding rate of the monomer mixtures equal to the overall rate of copolymerization, The composition of the copolymers was identical to the composition of the monomer feeds over the entire concentration range. A quantitative expression has been derived to show that under forced ideal copolymerization conditions the composition of the copolymer can be controlled by the composition of the feed. Further, conditions have been found for forced ideal quasiliving copolymerizations, i.e., the number-average molecular weight of the copolymers increased almost linearly with the cumulative weight of consumed monomers by the use of suitably slow, continuous feed addition in the presence of relatively nonpolar solvent mixtures (60/40 v/v n-hexane + methylene chloride). In polar solvent (methylene chloride) the molecular weight increase was less pronounced due to chain transfer to monomer involving indane-skeleton formation; however, with charges containing large amounts of ptBuSt the molecular weight increase was surprisingly strong. Interestingly, ptBuSt does not homopolymerize in 60/40 v/v n-hexane/methylene chloride but it readily copolymerizes with αMeSt. This observation was explained by examining the relative rates of terminations of the cationic species involved. Conditions have been found for the pronounced quasiliving polymerization of St. In forced ideal quasiliving copolymerizations neither the molecular weights of αMeSt/ptBuSt or αMeSt/St copolymers nor the initiating efficiencies of the initiating systems used show a depression. The microstructure of representative αMeSt/ptBuSt copolymers obtained under forced ideal quasiliving conditions has been analyzed by13C-NMR spectroscopy. According to these studies, true copolymers have formed and resonance peaks for various triads have been deduced.

ISSN:0022-233X    

DOI:10.1080/00222338208077226

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor