摘要:

AbstractOur objective is to prepare polymeric rotaxanes, materials in which many macrocycles are threaded by a linear macromolecule, in quantities sufficient to investigate the unique properties that we expect this unusual supramolecular architecture to confer. The design and synthesis of the macrocyclic components, “blocking groups” to constrain the macrocycles, and the polyrotaxanes are described. Model monomeric system has been synthesized and studied to ascertain their conformation. Step growth and chain growth approaches are descri

ISSN:0258-0322    

DOI:10.1002/masy.19910420133

出版商:Hüthig&Wepf Verlag    

年代:1991

数据来源: WILEY

摘要:

AbstractAn advanced process for manufacturing trioxane ethylene oxide copolymer has been developed.First, a new technology for production of highly concentrated aqueous formaldehyde was developed by oxidizing methylal. Whereas oxidation of methanol yields 1 mol of water per mole of formaldehyde, methylal oxidation produces only 1 mol of water for every 3 mol of formaldehyde.Thus the output from methylal oxidation is more than 70% formaldehyde, compared with 55% from methanol.The relatively high formaldehyde concentration enhances formation of trioxane.Purified trioxane is copolymerized with ethylene oxide in the presence of an end‐capping agent such as methylal producing an end‐capped polymer with high thermal stability.Two new intermediates in the initiation reaction of the copolymerization, 1,3,5,7‐tetraoxacyclononane (TOCN) and 1,3,5,7,10‐ pentaoxacyclododecane(POCD) were isolated and a new initiation mechanism was proposed.A commercial plant employing this process with a capacity of 15 000 tons/year is operati

ISSN:0258-0322    

DOI:10.1002/masy.19910420134

出版商:Hüthig&Wepf Verlag    

年代:1991

数据来源: WILEY

摘要:

Abstract1H NMRin situstudies of the initial processes involved in the cationic bulk homo‐ and copolymerization of trioxane indicate that the historically termed “induction period” has a kinetic rather than thermodynamic origin. The generation of cyclic acetals takes place through a process kinetically equivalent to insertion rather than back‐biting. The roles played by H2O, formaldehyde, tetraoxane and trioxepane have been further cl

ISSN:0258-0322    

DOI:10.1002/masy.19910420135

出版商:Hüthig&Wepf Verlag    

年代:1991

数据来源: WILEY

摘要:

AbstractCationic copolymerization of trioxane with 5‐ethyl‐5‐hydroxymethyl‐1,3‐dioxane gives low‐molecular‐weight copolymer (m̌n: 2∼6×103) with methylol pendent as well as end groups. Detailed1H NMR assignment for the copolymer has been completed. The polymer is thermally stable up to 220°C and shows a high apparent crystallinity of 69%. The methylol group of the acetal copolymer has been demonstrated to react with acyl chloride and isocyanate groups of a second compound to form graft or crosslink. The copolymerization is characterized by high level

ISSN:0258-0322    

DOI:10.1002/masy.19910420136

出版商:Hüthig&Wepf Verlag    

年代:1991

数据来源: WILEY

摘要:

AbstractCationic copolymerization of trioxane with 2,3‐epoxypropyl acrylate gives thermally stable crosslinked copolymer in high yield. The structure of the crosslinked copolymer has been characterized by solid state13C NMR spectroscopy. The comonomer acrylate group functions as a crosslinking agent in the polymerization process as well as a bound stabilizer in the resulting network. The crystallinity of the copolymer is unusually low compared to copolymers with comparable incorporation levels of the comonomers. The crosslinked acetal copolymer has the potential for further modification through its pendant acrylate grou

ISSN:0258-0322    

DOI:10.1002/masy.19910420137

出版商:Hüthig&Wepf Verlag    

年代:1991

数据来源: WILEY

摘要:

AbstractFluorescent‐labeling reactions of poly(styryl)lithium were effected with either 2‐(1‐phenylethenyl)naphthalene or 1‐phenyl‐1‐(1‐pyrenyl)ethylene followed by functionalization of the resulting 1‐phenyl‐1‐arylalkyllithium species with ethylene oxide. The resulting polymeric alkoxylithiums were used to initiate the anionic polymerization of ethylene oxide in a mixture of benzene and dimethyl sulfoxide. A series of block copolymers [Mn(PS)=5.1 × 103g/mol); Mw/Mn=1.02] with 20–40wt% ethylene oxide were characterized by thin‐layer chromatography, size exclusion chromatography,1H NMR and quantitative UV‐visible spectroscopy. Fluorescence measurements on the block copolymers were carried out in 1,2‐dichloroethane with varying amounts of methanol. No excimer formation was detected for either naphthalene‐ or pyrene‐labeled block copolymers. Energy transfer from the naphthalene‐ to the pyrene‐labeled polymers was observed at about 80 vol.% methanol. These results are discussed in relationship to the interfacial boundary distances in the block copolymer micelles as deduced by appl

ISSN:0258-0322    

DOI:10.1002/masy.19910420138

出版商:Hüthig&Wepf Verlag    

年代:1991

数据来源: WILEY

摘要:

AbstractIn the Activated Monomer (AM) polymerization of substituted oxiranes (propylene oxide ‐ PO, epichlorohydrin ‐ ECH), the microstructure of the chain is governed exclusively by the kinetics of the propagation step. In the copolymerization of ECH with 5‐membered (tetrahydrofuran ‐ THF) or 6‐membered (1,4‐dioxane ‐ Diox) cyclic ethers, the distribution of comonomer units depends on both kinetic and thermodynamic factor, which allows preparation of oligodiols having regular (i.e. alternating) distribution of comonomer units

ISSN:0258-0322    

DOI:10.1002/masy.19910420139

出版商:Hüthig&Wepf Verlag    

年代:1991

数据来源: WILEY

摘要:

AbstractThe polymerization of cyclohexene oxide with several ZnEt2‐modified initiator systems known to be stereospecific for the polymerization of chiral monosubstituted oxiranes was studied. Among chiral initiator systems only ZnEt2/(1S,2R) ephedrine system allowed us to prepare polymers with high optical activities. The sign of the latter changes with polymer conversion. Fractionation experiments and1H and13C NMR studies have shown that the polymers obtained with ZnEt2/(1S,2R)‐ephedrine and ZnEt2/ 1‐methoxy‐2‐propanol systems were a mixture of isotatic as well as syndiotactic polymers. A mechanism of polymerization is proposed to explain this unusu

ISSN:0258-0322    

DOI:10.1002/masy.19910420140

出版商:Hüthig&Wepf Verlag    

年代:1991

数据来源: WILEY

摘要:

AbstractQuasi‐living cationic polymerization of 3‐azidomethyl‐3‐methyloxetane (AMMO) was achieved with a bis(chlorodimethylsilyl)benzene/silver hexafluoroantimonate (BSB/AgSbF6) initiating system in methylene chloride at −78°C. The average molecular weight (Mn) increased linearly with an increasing monomer/ initiator ([M]/[I]) ratio and a linear Mnvs. [M]/[I]ratio plot passes through the origin. Mn's observed were higher than the calculated value. This indicates the initial loss of initiator or slow initiation during the polymerization of AMMO with BSB/AgSbF6initiating system, or the combination of both. Theoretically, in a system where the initiation is slower than the propagation, a diblock copolymer will be formed. Similarly, impurities, such as water, will cause chain transfer to the propagating chains during polymerization and form a homopolymer and a diblock copolymer in addition to the desired triblock copolymer. In short, a perfect triblock copolymer will be formed for a difunctional cationic initiator when the system is pure and dry and the initiation of polymerization is faster than the p

ISSN:0258-0322    

DOI:10.1002/masy.19910420141

出版商:Hüthig&Wepf Verlag    

年代:1991

数据来源: WILEY

ISSN:0258-0322    

DOI:10.1002/masy.19910420102

出版商:Hüthig&Wepf Verlag    

年代:1991

数据来源: WILEY