Polymerization of ethyl and benzyl diazoacetates (EDA and BDA) initiated with π-allylPdCl-based systems [π-allylPdCl/NaBPh4, π-allylPdCl/NaBArF 4 (ArF = 3,5-{CF3}2C6H3), and π-allylPdCl] is described. Initiation efficiencies of the π-allylPdCl-based systems are much higher than those of the previously reported (NHC)­Pd/borate (NHC = N-heterocyclic carbene) systems, and the new systems are capable of polymerizing the alkyl diazoacetates at low temperatures (0 ∼ −20 °C), where the (NHC)­Pd/borate systems cannot initiate the polymerization. MALDI–TOF–MS analyses of the polymers obtained from EDA provide information for the chain-end structures of the polymers, based on which initiation and termination mechanisms are proposed. Interestingly, EDA polymerization by the π-allylPdCl-based systems in the presence of alcohols (EtOH, nPrOH, and nBuOH) or water was found to afford RO- or HO-initiated polymers as major products, as confirmed by MALDI–TOF–MS analyses.

Toward development of tumor-specific chemotherapy, we designed a new type of liposomes with temperature-triggered drug release and magnetic resonance imaging (MRI) functions.We prepared the multi-functional liposomes by incorporation of thermosensitive poly (2-ethoxy(ethoxyethyl)

Two types of polymerization of hydroxy-containing diazoacetates are described. The polymerization of hydroxycontaining diazoacetates using palladium complexes proceeded successfully under chain-growth mechanism even without a protecting group to give C−C main chain polymers bearing a hydroxy-containing ester substituent on each carbon of the backbone. The resulting polymers had a slightly branched structure due to chain transfer reaction with the hydroxy groups, while the polymers obtained by polymerization of silyl-protected diazoacetates and subsequent deprotection had a completely linear structure. The hydroxy-containing polymers with an appropriate hydrophilic/hydrophobic balance showed a lower critical solution temperature-type phase separation in an aqueous medium. On the other hand, the polymerization of hydroxy-containing diazoacetates using InCl 3 as a catalyst proceeded under step-growth mechanism to give oligomers having a distinct repeating unit (ester−ether), where a new ether bond was generated through O−H insertion reaction of diazocarbonyl groups into hydroxy groups. ■ INTRODUCTIONRecently, polymerization of alkyl diazoacetates has received attention as a useful method for preparing C−C main chain polymers bearing an ester substituent on each carbon of the backbone. 1,2 The resulting polymers, "poly(substituted methylene)s", are expected to have unique properties due to the structural characteristics of dense packing of the substituents around the polymer chain compared to vinyl polymer analogues, i.e., poly(acrylate)s and poly(methacrylate)-s. For example, we have recently reported palladium-mediated polymerization of pyrenylmethyl diazoacetate and demonstrated that the efficiency of intrachain eximer formation of the resulting pyrene-containing poly(substituted methylene)s is much higher than that of the corresponding pyrene-containing poly(methacrylate)s. 3 The palladium-based initiating systems are effective for polymerization of alkyl diazoacetates bearing various ester groups, affording poly(alkoxycarbonylmethylene)s with a variety of side chain ester groups. 4 However, the substituents were limited to hydrophobic groups for the polymerization of diazocarbonyl compounds so far. The availability of hydrophilic groups including hydroxy group would allow us to prepare a new type of hydrophilic polymeric material.Polymers based on 2-hydroxyethyl methacrylate (HEMA) or related hydroxy-containing monomers have been widely used in the biomedical field such as contact lenses, owing to their biocompatibility and lack of toxicity. 5 Most of the polymers of HEMA reported before the late 1990s were synthesized via free

Pd-initiated polymerization of cyclophosphazene-containing diazoacetates proceeded in a controlled manner.