Monomer Mechanism (monomer + mechanism)

Distribution by Scientific Domains

Kinds of Monomer Mechanism

  • activated monomer mechanism

  • Selected Abstracts

    Cationic copolymerization of ,-caprolactone and L,L -lactide by an activated monomer mechanism

    gorzata Ba
    Abstract The cationic homopolymerization and copolymerization of L,L -lactide and ,-caprolactone in the presence of alcohol have been studied. The rate of homopolymerization of ,-caprolactone is slightly higher than that of L,L -lactide. In the copolymerization, the reverse order of reactivities has been observed, and L,L -lactide is preferentially incorporated into the copolymer. Both the homopolymerization and copolymerization proceed by an activated monomer mechanism, and the molecular weights and dispersities are controlled {number-average degree of polymerization,=,([M]0 , [M]t)/[I]0, where [M]0 is the initial monomer concentration, [M]t is the monomer concentration at time t, and [I]0 is the initial initiator concentration; weight-average molecular weight/number-average molecular weight ,1.1,1.3}. An analysis of 13C NMR spectra of the copolymers indicates that transesterification is slow in comparison with propagation, and the microstructure of the copolymers is governed by the relative reactivity of the comonomers. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 7071,7081, 2006 [source]

    Hyperbranched polyethers by ring-opening polymerization: Contribution of activated monomer mechanism

    Przemys, aw Kubisa
    Abstract Propagation in the cationic ring-opening polymerization of cyclic ethers involves nucleophilic attack of oxygen atoms from the monomer molecules on the cationic growing species (oxonium ions). Such a mechanism is known as the active chain-end mechanism. If hydroxyl groups containing compounds are present in the system, oxygen atoms of HO groups may compete with cyclic ether oxygen atoms of monomer molecules in reaction with oxonium ions. At the proper conditions, this reaction may dominate, and propagation may proceed by the activated monomer mechanism, that is, by subsequent addition of protonated monomer molecules to HO terminated macromolecules. Both mechanisms may contribute to the propagation in the cationic polymerization of monomers containing both functions (i.e., cyclic ether group and hydroxyl groups) within the same molecule. In this article, the mechanism of polymerization of three- and four-membered cyclic ethers containing hydroxymethyl substituents is discussed in terms of competition between two possible mechanisms of propagation that governs the structure of the products,branched polyethers containing multiple terminal hydroxymethyl groups. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 457,468, 2003 [source]

    Synthesis of Organosilica Films Through Consecutive Sol/Gel Process and Cationic Photopolymerization

    Davy-Louis Versace
    Abstract The cationic photopolymerization of epoxy polysilsesquioxane resins synthesized through a acid-catalyzed sol/gel process is studied. To elucidate the effect of the organic substituent on sol/gel reaction kinetics, two organotrimethoxysilanes with different organic groups were employed. Effects of UV irradiation on the microstructure of the epoxy-functional polysilsesquioxanes were also studied. 29Si solid-state MAS NMR proved that UV-generated Brönsted acids favored a work-up of the silicate network by promoting new sol/gel condensation reactions. There was a significant slowdown of epoxy conversion rates with increasing sol aging, which may be due to a competition between an active chain end and an activated monomer mechanism for the epoxy cationic polymerization. [source]

    Photoinitiated curing of mono- and bifunctional epoxides by combination of active chain end and activated monomer cationic polymerization methods

    Marco Sangermano
    Abstract Photoinitiated cationic polymerization of mono- and bifunctional epoxy monomers, namely cyclohexeneoxide (CHO), 4-epoxycyclohexylmethyl-3,,4,-epoxycyclohexanecarboxylate (EEC), respectively by using sulphonium salts in the presence of hydroxylbutyl vinyl ether (HBVE) was studied. The real-time FTIR spectroscopic, gel content determination, and thermal characterization studies revealed that both hydroxyl and vinyl ether functionalities of HBVE take part in the polymerization. During the polymerization, HBVE has the ability to react via both active chain end (ACE) and activated monomer mechanisms through its hydroxyl and vinyl ether functionalities, respectively. Thus, more efficient curing was observed with the addition of HBVE into EEC-containing formulations. It was also demonstrated that HBVE is effective in facilitating the photoinduced crosslinking of monofunctional epoxy monomer, CHO in the absence of a conventional crosslinker. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4914,4920, 2007 [source]