Irregular cationic lipotetrapeptides for pharmaceutical multifunctional transport systems

New cationic branched lipotetrapeptides based on l-amino acids and higher alkanols were prepared. Study of their physicochemical and membrane-forming properties revealed that phase transition temperature of these amphiphiles locates in the range of physiological norm. The particle sizes of liposomal dispersions with high aggregation stability are in dimension applicable to penetrate into small blood vessels.     

Photoinitiated cationic polymerization of monofunctional benzoxazine

The photoinitiated ring‐opening cationic polymerization of a monofunctional benzoxazine, 3‐phenyl‐3,4‐dihydro‐2H‐1,3‐benzoxazine, with onium salts such as diphenyliodonium hexafluorophosphate and triphenylsulfonium hexafluorophosphate as initiators was examined. The structures of the polymers thus formed were complex and related to the ring‐opening process of the protonated monomer either at the oxygen or nitrogen atoms. The phenolic mechanism also contributed, but its influence decreased with decreasing monomer concentration. Thermal properties of the polymers were also investigated by differential scanning calorimetry and thermogravimetric analysis. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3320–3328, 2003     

Photoinitiated cationic polymerization by dialkylphenacylsulfonium salts

Dialkylphenacylsulfonium salts in which the anions are of the general type BF, AsF, PF, and SbF are a new class of useful photoinitiators for cationic polymerization. On irradiation these salts underwent reversible ylid formation with the simultaneous generation of strong Br?nsted acids. The photoinitiated cationic polymerization of a number of monomers with dialkylphenacylsulfonium salts demonstrated the utility of these new photoinitiators.     

Photoinitiated cationic polymerization with triarylsulfonium salts

Triarylsulfonium salts Ar₃S⁺MX with complex metal halide anions such as BF, AsF, PF, and SbF are a new class of highly efficient photoinitiators for cationic polymerization. In this article we describe several synthetic routes to the preparation of these compounds along with their physical and spectroscopic properties. Mechanistic studies have shown that when these compounds are irradiated at wavelengths of 190–365 nm carbon–sulfur bond cleavage occurs to form radical fragments. At the same time the strong Br??nsted acid HMX_n, which is the active initiator of cationic polymerization that takes place in subsequent “dark” steps, is also produced. A study of the parameters that affect the photolysis of triarylsulfonium salts is reported with a measurement of the absolute quantum yields. The cationic polymerizations of four typical monomers—styrene oxide, cyclohexene oxide, tetrahydrofuran, and 2-chloroethyl vinyl ether—with triarylsulfonium salt photoinitiators are described.     

Photoinitiated cationic polymerization with triarylsulfonium salts

Triarylsulfonium salts Ar₃S⁺MX_n⁻ with complex metal halide anions such as BF₄⁻, AsF₆⁻, PF₆⁻, and SbF₆⁻ are a new class of highly efficient photoinitiators for cationic polymerization. In this article we describe several synthetic routes to the preparation of these compounds along with their physical and spectroscopic properties. Mechanistic studies have shown that when these compounds are irradiated at wavelengths of 190–365 nm carbon-sulfur bond cleavage occurs to form radical fragments. At the same time the strong Brϕnsted acid HMX_n, which is the active initiator of cationic polymerization that takes place in subsequent “dark” steps, is also produced. A study of the parameters that affect the photolysis of triarylsulfonium salts is reported with a measurement of the absolute quantum yields. The cationic polymerizations of four typical monomers—styrene oxide, cyclohexene oxide, tetrahydrofuran, and 2-chloroethyl vinyl ether—with triarylsulfonium salt photoinitiators are described.     

Photoinitiated cationic polymerization by triarylselenonium salts

Triarylselenonium salts with complex metal halide anions such as BF, AsF, and SbF have been prepared and have been shown to be efficient photoinitiators of cationic polymerization. The photolysis rates of these compounds were studied and their quantum yields of photolysis were reported. Use of specific triarylselenonium salts in the polymerizations of cyclohexene oxide, epichlorohydrin, and 2-chloroethyl vinyl ether are described.     

Photoinitiated cationic polymerization of epoxy alcohol monomers

A series of epoxy alcohols were prepared by simple, straightforward methods. These compounds were very reactive monomers that polymerized rapidly on UV irradiation in the presence of cationic photoinitiators. The kinetics of the cationic photopolymerization of these monomers were studied with diaryliodonium salt photoinitiators and real‐time IR spectroscopy. The rate of epoxide ring‐opening polymerization was enhanced markedly by the presence of the hydroxy group. Using model compounds, the monomers were shown to polymerize via an activated monomer mechanism. Simple epoxy alcohols polymerized to give polymers with a hyperbranched structure. The novel monomers also were observed to accelerate the rate of the photopolymerization of mono‐ and multifunctional epoxides. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 389–401, 2000     

Photoinitiated cationic polymerization of oxetane formulated with oxirane

Photoinitiated cationic polymerization of oxetane, oxirane (epoxide), and a formulation of both was carried out and their reactivity compared. To investigate a formulated system of oxetane and oxirane in photoinitiated cationic polymerization, computational and experimental methods were used. In the computational study, we employed a semiempirical molecular orbital method (AM1). On the other hand, the reactivities of each system were evaluated and compared experimentally by a real-time FT-IR method. The computational study reveals that oxetane seems to polymerize in S_N2 mechanism, but two possibilities, of S_N1 mechanism through the α-cleavage and of S_N2 mechanism through β-cleavage, are implied for oxirane. Using the real-time FT-IR method, the formulation of oxetane and oxirane was proved to possess rather high reactivities of oxetane toward photoinitiated cationic polymerization. The formulated system exhibited slightly lower number-average molecular weight than oxetane but higher than oxirane. These experimental observations are well explained in terms of the calculated reaction paths. © 1995 John Wiley & Sons, Inc.     

Photoinitiated cationic oligomerization of aryl 1-propenyl ethers

A series of aryl 1-propenyl ethers (ArPE) were prepared by the isomerization of the corresponding allyl aryl ethers (AArE) and used for photoinduced cationic polymerization studies. Attempted polymerization reactions using diaryliodonium salts as photoinitiators generally resulted in low yields of oligomers. Further studies revealed that these compounds have much lower reactivity in cationic vinyl polymerization as compared to their alkyl analogues. Moreover, side reactions resulting from chain transfer due to Friedel–Crafts alkylations take place and compete with vinyl polymerization. These side reactions are responsible for the low molecular weights observed in the cationic photopolymerization of aryl 1-propenyl ether monomers. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3017–3025, 1999     

Photoinitiated cationic polymerization by dialkyl-4-hydroxyphenylsulfonium salts

On irradiation with ultraviolet light, dialkyl-4-hydroxyphenylsulfonium salts undergo reversible photodissociation and in the process generate ylids and Brønsted acids. When the anions are nonnucleophilic in character, as, for example, BF₄^?, AsF₆^?, PF₆^?, and SbF₆^?, the strong acid which is produced is capable of initiating cationic polymerization. The polymerization of several monomers was carried out to demonstrate the general applicability of these new photoinitiators.     

Photoinitiated cationic polymerization using o-phthaldehyde and pyridinium salt

The cationic polymerization of cyclohexene oxide (CHO), n-butyl vinylether (BVE), N-vinylcarbazole (NVC), and 4-vinyl cyclohexenedioxide (4-VCHD) is initiated upon UV irradiation (Λ_inc. = 350 nm) of dichloromethane solution containing N-ethoxy-2-methyl-pyridinium hexafluorophosphate (EMP⁺PF₆) and o-phthaldehyde. A feasible initiation mechanism involves formation of biradical by intramolecular hydrogen abstraction of triplet o-phthaldehyde. Oxidation of these radicals by EMP⁺ ions yields protons capable of initiating the cationic polymerization. © 1995 John Wiley & Sons, Inc.     

Living cationic polymerisation of styrene in an ionic liquid

For the first time, living cationic polymerisation of styrene has been carried out in room temperature ionic liquids under mild reaction conditions and using mild acid catalysts (e.g. organoborate acids) to obtain polymers of narrow polydispersity.     

Some studies on the photo-initiated cationic polymerisation of epoxides

Several triarylsulphonium and diaryliodonium compounds have been synthesised. Alkylarylsulphonium compounds were obtained by alkylating diaryl sulphides with trialkyloxonium salts and by reaction of diaryl sulphides with alkyl halides in the presence of silver tetrafluoroborate. Photolysis of the sulphonium salts in methanol gave diaryl sulphides and, in the case of triarylsulphonium compounds, the appropriate aromatic hydrocarbon and its methyl ether. Diaryliodonium tetrafluoroborates and pentafluorophosphates gave aryl fluorides, biaryls and aromatic hydrocarbons. The decomposition of the salts is suggested as occurring via both free radical and ionic pathways. The ability of the compounds to sensitise the polymerisation of epoxy resins was found to be dependent upon the counterion (hexafluorophosphates being more efficient than tetrafluoroborates) and upon the structure of the cation. Sensitised cationic initiated polymerisation was also investigated and it was found that both excited singlet state and triplet state sensitisers were effective.     

Synthesis of branched polystyrenes via cationic polymerisation

Branched polystyrenes have been prepared rapidly (within 15 min) and in good yields (40-99%) in dichloromethane solution at 0 °C via cationic copolymerisation of styrene (St) with divinylbenzene (DVB) using SnCl₄ as the initiator. All reaction components were deliberately used as supplied to evaluate whether such a simple approach could provide a facile synthesis of branched polymers and this has proved to be the case. The only additional experimental precaution was to avoid condensation of atmospheric moisture during the reactions. No additional chain regulating species was required to avoid crosslinking providing the St/DVB mole feed ratio was ?100/5. The intrinsic chain transfer to monomer reaction seems to be sufficient to reduce the length of the primary polymer chains and hence inhibit crosslinking and gelation in the case of the above mole feed ratios. The branching architecture of the products has been evaluated by ¹H NMR and MALS-SEC analyses.     

Photoinitiated cationic polymerization of cycloaliphatic epoxide with siloxane or alkoxysilane functionalized polyol coatings

Polyols were reacted with tetraethyl orthosilicate (TEOS) or 3-isocyanatopropyltriethoxysilane (IPTES) to form siloxane functionalized polyols. The UV-reactivity of these siloxane functionalized polyols were investigated using real-time FT-IR spectroscopy. The reactivity of TEOS modified polyols was dependent on the relative humidity. However, for the IPTES functionalized polyols the effect of relative humidity was dependent on the degree of IPTES functionalization. When the polyols were only partially functionalized with IPTES, the effect of relative humidity was minimal. However, when polyols were fully functionalized with IPTES, the curing was dependent on relative humidity. The siloxane functionalized polyols were formulated with a cycloaliphatic epoxide and cationic photoinitiator. The photo-induced curing kinetics of these cycloaliphatic epoxide/siloxane functionalized polyol coatings were also investigated. Unlike the TEOS functionalized polyols, the addition of IPTES functionalized polyols into the formulation inhibited the curing speed. This inhibition was attributed to the basicity nitrogen of the urethane linkage. The effect of relative humidity on the UV-curing reaction of cycloaliphatic epoxide coatings was lowered by the incorporation of the TEOS functionalized polyols.