摘要:

The nature of the species that gives rise to living carbocationic polymerization (LP+Pzn) of isobutylene (IB) coinitiated by Friedel-Crafts acids (FCA) in the presence of electron pair donors (ED) has been investigated. It is proposed that the key species responsible for mediating LC+Pzn of IB are FCA·ED complexes, formed by Lewis acid-Lewis base interaction, where FCA = BCl3TiCl4, and ED = ethyl acetate, tetrahydrofuran, etc. Free EDs are inhibitors of IB polymerization. These findings are in sharp contrast to those of LC+Pzn of vinyl ethers coinitiated by EtAlCl2in which excess (i.e., free) EDs arerequiredfor the living polymerizations to occur. Comparison of IB polymerizations induced by the 2-chloro-2,4,4-trimethylpentane/BCl3and 2-acetyl-2,4,4-trimethylpentane/BCl3systems shows that these reactions do not proceed by the same intermediate (i.e., bytert-chlorides) and that the mechanisms of BC13- and TiC14-coinitiated living polymerizations are different. Experiments with the proton trap 2,6-di-tert-butylpyridine indicate that proton scavenging by FCA·ED complexes may be responsible for the narrow molecular weight distribution (MWD) products obtained in BC13-coinitiated LC+Pzn of isobutylene. These findings also prove thatRi(rate of initiation) > Rp(rate of propagation), the relation required for narrow MWD in living polymerizations.

ISSN:0022-233X    

DOI:10.1080/00222339108052082

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

The ring-opening polymerization of oxepan-2,7-dione was initiated with 1) cationic initiators such as AlCl3and BF3· (C2H5)2O, 2) anionic initiators such as CH3COO−K+and NaH, and 3) coordination-type initiators such as stannous 2-ethylhexanoate and dibutyltin oxide. The reactions were studied at 0, 20, and 40°C in methylene chloride. Oxepan-2,7-dione was also reacted with ϵ-caprolactone (2-oxepanone) in the presence of aluminum isopropox-ide as a catalyst to generate A-B block copolymers.

ISSN:0022-233X    

DOI:10.1080/00222339108052083

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

In an earlier paper, continuous thermodynamics was applied to calculate polymer fractionation procedures leading to lucid equations favorable for computer simulations. The present paper refines that treatment by applying more sophisticated Gibbs free energy relations. The simulation results agree closely with the experimental data, assuming the Flory-Huggins interaction parameter to be a function of the concentration.

ISSN:0022-233X    

DOI:10.1080/00222339108052084

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Spinoidal and critical points of the liquid-liquid equilibrium in random copolymer blends are calculated by application of continuous thermodynamics. Blends are composed of two copolymers, each consisting of two different monomer units. Both copolymers are characterized by divariate distribution functions with respect to molecular weight and to chemical composition. Based on a model for the excess Gibbs free energy of mixing, the necessary relations are derived for the calculation of spinoidal and critical points. The influences of the polydispersities of molecular weight and/or chemical composition on the instability limit are discussed. Miscibility maps are calculated on the basis of the critical point. Cloud-point curves are shown to be most sensitive to polydispersities if the excess Gibbs free energy of mixing exceeds only slightly the lowest value necessary for demixing.

ISSN:0022-233X    

DOI:10.1080/00222339108052085

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Novel polyisobutylene-polyisoprene (PIB-PIP) multiblock polymers have been synthesized and used for the preparation of UV-cured transparent flexible coatings. The block polymers were tailor-made by bidirectional living carbocationic polymerization of isobutylene (IB) followed by sequential isoprene (IP) addition. PIB-PIP multiblocks containing highly cyclizedtr-1,4-PIP sequences were mixed with a bisazide and photocrosslinked. Epoxidized PIB-PIP blocks were blended with a cationic photoinitiator and UV-cured. Blocks having 23 mol% total PIP content and PIB segments ofMn= 16,600 and 18,800, respectively, gave transparent flexible coatings with 45 kg/cm2tensile strength and 450% elongation. The coatings exhibited good adhesion to aluminum and are expected to have excellent barrier properties due to the presence of PIB sequences.

ISSN:0022-233X    

DOI:10.1080/00222339108052086

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

The kinetic study of the mechanism of photosensitized initiation of methyl methacrylate (MMA) polymerization by OS3(CO)12/CCI4at λ = 365 nm is presented. The monomer is found to participate in the initiation process. Observed initiation by Os3(CO)12/MMA is explained in the light of a hydrogen abstraction process and Os3(CO)12/CCI4/MMA as an electron transfer process. The ratio of the rate constants of the component reactions were evaluated. The observed values of the kinetic parameterkpk−1/2tdemonstrate that retardation does not occur in these reactions. The quantum yield of photoinitiation of Os3(CO)12/CCI4/MMA is significantly low, i.e., ∼00.013 as compared to that of other metal carbonyls such as Mn2(CO)10/CCI4/MMA and Re2(CO)10/CCI4/MMA, where the quantum yield of initiation is reported to be close to unity.

ISSN:0022-233X    

DOI:10.1080/00222339108052087

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

The behavior in the interfacial polycondensation of 4,4′-methylene dianiline (MDA) and ethylene diamine (EDA) in water with 1,2,4,5-benzenetetra acyl chloride (BTAC) in dichloromethane with tetrabutyl ammonium chloride (TBAC) as the catalyst was examined with ATR,1H NMR, a pH meter, and ESCA. As the BTAC is a tetrafunctional compound with high reactivity, the interfacial polycondensation reaction of BTAC and the diamine is a complicated reaction involving the competitive reaction of hydrolysis and amidation. ATR was employed for analyzing the change in the chemical structure on both sides of the interfacial layer during the reaction. A clear description of the reaction process was made. The interface reaction of this system takes place in the organic phase, and the reaction is diffusion-controlled. It is clear that the film grows toward the organic phase from the interface region until the reaction is over. When sodium carbonate or TBAC is added, the chemical structure of the top and bottom sides formed by interfacial polycondensation is quite different. TBAC assists the transfer of diamine from the water phase to the organic phase, and once TBAC links with diamine, the presence of hydrochloride will not damage their linkage.

ISSN:0022-233X    

DOI:10.1080/00222339108052088

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Block copolymers of styrene and methyl methacrylate were prepared by means of azo-benzoin initiators. In the first stage, prepolymers were synthesized by using these initiators. Photoactive prepolymers containing benzoin end groups were employed in the second stage for block copolymerization. The block copolymer structure was elucidated by means of extraction by appropriate solvents, GPC analysis, and IR and NMR spectral measurements. Mechanisms for initiation and possible termination for systems involving benzoin-type initiators are discussed in the light of results from studies of composition of the block copolymerization mixture. Structure and efficiency of the formation of the block copolymers depend greatly on both the relative reactivities of the photochemically derived radicals and the termination mode of polymerization.

ISSN:0022-233X    

DOI:10.1080/00222339108052089

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

ISSN:0022-233X    

DOI:10.1080/00222339108052090

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

This is a scanned image of the original Editorial Board page(s) for this issue.

ISSN:0022-233X    

DOI:10.1080/00222339108052081

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor