Search

Cationic ring-opening polymerization of 3-ethyl-3-hydroxylmethyl oxetane was carried out using BF3·O(C2H5)2 as initiator, and a branched polyether was formed. Typical SEC curves show that the polymer consists of two fractions: one has higher molecular weight (11.7×104∼ 9.2×104) and the other has lower molecular weight (3.8×103∼4.0×103). This probably resulted from the chain-tran sfer reaction of two propagating polymer chains. The structure of the polyEHMO formed was characterized by 1H and 13C NMR spectra. The degree of branching is mainly affected by the propagation mechanism. As the molar ratio of [I]0/[EHMO]0 in feed increased, the degree of branching also increased.

Liang Qiu, Chun-Yan Hong, Cai-Yuan Pan Chinese Academy of Sciences Key Laboratory of Soft Matter Chemistry, Department of Polymer Science and Engineering, University of Science and Technology of China, Hefei, Anhui, People’s Republic of China Abstract: Redox- and pH-sensitive branched star polymers (BSPs), BP(DMAEMA-co-MAEBA-co-DTDMA)(PMAIGP)ns, have been successively prepared by two steps of reversible addition–fragmentation chain transfer (RAFT) polymerization. The first step is RAFT polymerization of 2-(N,N-dimethylaminoethyl)methacrylate (DMAEMA) and p-(methacryloxyethoxy)benzaldehyde (MAEBA) in the presence of divinyl monomer, 2,2'-dithiodiethoxyl dimethacrylate (DTDMA). The resultant branched polymers were used as a macro-RAFT agent in the subsequent RAFT polymerization. After hydrolysis of the BSPs to form BP(DMAEMA-co-MAEBA-co-DTDMA)(PMAGP)ns (BSP-H), the anticancer drug doxorubicin (DOX) was covalently linked to branched polymer chains by reaction of primary amine of DOX and aldehyde groups in the polymer chains. Their compositions, structures, molecular weights, and molecular weight distributions were respectively characterized by nuclear magnetic resonance spectra and gel permeation chromatography measurements. The DOX-loaded micelles were fabricated by self-assembly of DOX-containing BSPs in water, which were characterized by transmission electron microscopy and dynamic light scattering. Aromatic imine linkage is stable in neutral water, but is acid-labile; controlled release of DOX from the BSP-H-DOX micelles was realized at pH values of 5 and 6, and at higher acidic solution, fast release of DOX was observed. In vitro cytotoxicity experiment results revealed low cytotoxicity of the BSPs and release of DOX from micelles in HepG2 and HeLa cells. Confocal laser fluorescence microscopy observations showed that DOX-loaded micelles have specific interaction with HepG2 cells. Thus, this type of BSP micelle is an efficient drug delivery system. Keywords: RAFT polymerization, controlled release, doxorubicin, branched star polymer, pH-sensitive

The copolymerization of 2-phenyl-4-methylene-1,3-dioxolane (PMDO) with acrylonitrile (AN) or with methyl methacrylate (MMA) gives rise to a copolymer spontaneously or in the presence of radical initiator. Higher yield of copolymers can be got in the presence of radical initiator. The structures of the obtained copolymers, confirmed by IR, 1H-, and 13C-NMR spectra, indicate that no ring-opening polymerization of PMDO takes place during copolymerization with AN or MMA. PMDO would not copolymerize with styrene (ST). During copolymerization, the formation of weak charge-transfer (CT) complexes with a mole ratio of unity for PMDO-AN and with more than unity for PMDO-MMA was demonstrated by NMR. The determination of their equilibrium constants (K) and ΔA comp was attempted by using the Hanna-Ashbough equation with NMR spectroscopy. Based on the different ΔA comp values and chemical shifts of the accepter protons in the complex, the structural peculiarities of complexes are discussed. The contribution o...

Since free radical ring-opening polymerization made it possible to introduce functional groups, such as esters, carbonates, thioesters, and amides, into the backbone of an addition polymer, it was reasoned that simple hydrolysis of these copolymers would produce the desired oligomers that could be terminated with various combinations of hydroxyl, amino, thiol, and carboxy1 groups. Thus the copolymerization of 2-methylene-1,3-dioxepane and styrene (r1=0.021 and r2=22.6) gave a copolymer containing 10 mole-percent of an ester-containing unit with 100% ring opening at 120°C. Hydrolysis of this copolymer gave an oligomer terminated with a hydroxyl group and a carboxylie acid group. Similarly the copolymerization of 2-methylene-1,3-dioxepane and ethylene gave a series of biodegradable polyethylene copolymers containing 2.1 to 10.4% ester-containing units. Hydrolysis of these copolymers gave a series of ethylene oligomers with nine to forty-seven ethylene units and terminated with a hydroxyl group and ...