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1 H-NMR spectrum of n -hexane soluble portion of poly(cyclohexene oxide) obtained by using polysilane and ETM.
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Poly(methyl phenyl silane) (PhMeSi)n was used in combination with the addition–fragmentation agents (AFA), namely 2-ethoxycarbonyl-2-propenylpyridinium hexafluoroantimonate (EPP+), ethyl-α-tetrahydrothiophenium methyl acrylate hexafluoroantimonate (ETM+) and 2-ethoxycarbonyl-propenyl triphenyl phosphonium hexafluroantimonate (ethoxy carbonly allyl...
Context in source publication
Context 1
... the polymer was reprecipitated into methanol. This procedure was employed to separate unreacted poly(methyl phenyl silane) which does not dis- solve in n-hexane, from poly(cyclohexene oxide) (PCHO). As can be seen from the 1 H-NMR spectrum of the extracted poly(cyclohexene oxide) the polymers obtained in this way do not contain polysilane chains (Fig. 3). Since polysilanes are not incorporated into poly(cyclohexene oxide), the oc- currence of the electron transfer mechanism according to reactions seems to be unlikely, and the polymerization is initiated via addition-fragmentation ...
Citations
This perspective article is prepared to the memory of Anthony Ledwith who discovered Free Radical Promoted Cationic Polymerization (FRPCP) as a versatile photoinitiating system for cationic polymerization about four decades ago. Mechanistically, distinct modes for the photochemical formation of electron donor radicals at UV, Vis and NIR range that can be oxidized to reactive cations to initiate cationic polymerization of oxiranes and vinyl monomers are discussed. The dual polymerization strategies that have been applied to combine FRPCP with the other modes of polymerization processes are presented.
The photochemistry of the heteroarene N-oxides and their derivatives is complex and multifaceted. This review discusses the photochemistry of heteroarene N-oxides in light of new studies of these species, as well as recent studies of nitrene intermediates that have been proposed as potential photochemical intermediates. Recent developments in the photochemistry of N-alkoxyheteroarenium salts are also discussed, as well as the photochemistry of the N-hydroxypyridone and N-hydroxypyrithione systems, which may be thought of as tautomeric forms of the N-oxides.
Polysilanes upon UV irradiation give rise to silyl macroradicals which are capable to initiate radical polymerization. Hence, chiral block functional polysilanes were synthesized by UV irradiation of poly(methylphenylsilane) (PMPS) with a vinyl chiral monomer, (R)-N-(1-phenylethyl)methacrylamide (R-NPEMAM). The synthesized copolymer samples were characterized by FTIR, NMR, and UV–vis spectroscopy. The number and weight average molecular weights of PMPS and synthesized chiral-block-PMPS were measured by GPC analysis. Two glass transition temperatures (Tg) of the synthesized materials clearly indicate the formation of chiral-block-PMPS copolymers. SEM analysis also indicated the synthesized organic–inorganic block copolymers. The optical and chiroptical properties of the synthesized materials were studied. The cotton effect is observed not only at 276 nm due to aromatic ring of the chiral monomer units but also at 325 nm which is associated with the Si–Si conjugation of PMPS block of synthesized functional polysilanes. Such tunable chirality may find potential application in optoelectronics. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016
The branched polysilane [(PhMeSi)0.8-co-(Et3Si(CH2)2Si)0.2]n (PS-1) as well as the network polysilane [Et3Si(CH2)3Si]n (PS-2) have been investigated as new polymerization photoinitiating structures. The behavior of PS-1 was compared with that of [(PhMeSi)]n to demonstrate the enhancement of the photoinitiation for the branched system. As a result of the Si–Si bond cleavage under light and the formation of reactive silyl radicals or silyl cations, these compounds act as efficient photoinitiators (PIs) for free radical photopolymerization (FRP) and free radical promoted cationic polymerization (FRPCP). The polymerization initiating ability of PS-1 is higher than that of PS-2 under air. The initiating ability for the ring-opening polymerization of epoxides is excellent for PS-1. These polymeric PIs overcome the classical oxygen inhibition in FRP or FRPCP.
New co-initiators based on group 14 elements (disilanes, polysilanes, digermanes, distannanes) are proposed. Under their photosensitized excitation, in the presence of benzophenone BP or a thiopyrylium salt TP, a metal−metal bond cleavage is observed. The generated radicals are excellent initiating species for free radical photopolymerization, FRP, and free radical promoted cationic photopolymerization, FRPCP. In FRP, when working both in laminate and under air, the new combinations are found highly reactive and, in most cases, better than the BP/ethyl dimethylaminobenzoate or Eosin/methyldiethanolamine reference systems. Their ability in FRPCP under air is also found excellent. The associated mechanisms are questioned on the basis of laser flash photolysis and ESR experiments.
Poly(hydrosilane)s, [R(H)Si](n) [R = Ph, Si(CH(2))(3)SiMe(2)Th, cy-Hex], are investigated as sources of silyl radicals. The Si-H bonds in these oligomers exhibit good to excellent hydrogen donating properties which ensure the formation of reactive silyl radicals. For free radical photopolymerization, the polymerization initiating properties of these structures are checked. These polymers are found to be advantageous to overcome the classical oxygen inhibition of the FRP process. Their ability in FRPCP is also evaluated for an epoxy monomer. The mechanisms are investigated through ESR and laser flash photolysis experiments.
