Self-condensing vinyl polymerization was used to produce dendritic polymers with both highly branched structures and numerous reactive groups. A vinyl monomer will undergo self-polymerization if it contains a pendant group that can be transformed into an initiating moiety by the action of an external stimulus. The self-polymerization combines features of a classical vinyl polymerization process with those of a polycondensation because growth is accomplished by the coupling of reactive oligomers. Highly branched, irregular dendritic structures with a multiplicity of reactive functionalities are obtained by polymerization of 3-(1-chloroethyl)-ethenylbenzene.

Significant progress was reported recently with living cationic polymerization in the presence of an added base.

An aqueous solution and cross-linked gel of poly-(N-isopropylacrylamide) (PNIPAM) undergo phase separation upon heating around 32 C. 1 Heskins and Guillet 2 studied the phase separation behavior of one unfractionated PNIPAM sample using a visible observation method. Later Fujishige et al.3 studied the phase transition temperature of an aqueous solution of fractionated PNIPAM samples using 500 nm wavelength light transmission and concluded that the phase separation temperature was independent of either the molecular weight (within the range of 50,000-8,400,000) or its concentration (within the range of 0.01-1%). However, Schild and Tirrell 4 observed the effect of the molecular weight and the concentration on the phase separation temperature of aqueous PNIPAM samples. Recently, using two well characterized samples (M w ¼ 49;400 with M w =M n ¼ 1:21 and M w ¼ 101;000 with M w =M n ¼ 1:23) studied over the wide concentration range of 0.58-70 wt %, Tong et al.5 reported that the phase separation temperature inversely depends on the molecular weight and concentration of PNIPAM. Thus, there have been relatively large numbers of papers dealing with the effects of molecular weights on the phase separation of PNIPAM. It has been reported earlier that the phase separation is due to the formation of hydrophobic bonding among the side chains of a polymer in an aqueous solution.6-9 However, there is no report about the effect of tacticity on the phase separation temperature of aqueous PNIPAM solutions. One of our groups recently reported the effect of tacticity on the phase transition temperature of PNIPAM. 10Very recently, one of our groups has also reported the synthesis of stereo and molecular weight controlled PNIPAM using the RAFT polymerization in the presence and absence of Lewis acids.11 Using the same technique, we prepared a series of PNIPAM samples with different meso diad (m) values in the range of 45-72% having the molecular weight (M n ) of 37;000 AE 3000 and polydispersity (M w =M n ) in the range of 1.2-1.3. These polymers were used for the determination of the phase separation temperature of aqueous PNIPAM solutions and the novel inverse dependency of the tacticity on the phase separation temperature was observed. EXPERIMENTAL N-Isopropylacrylamide (NIPAM) (Wako, > 98%) was recrystallized twice from hexane. AIBN (Kishida, 99%) was recrystallized from methanol. Y(OTf) 3 (Aldrich, 98%) and Sc(OTf) 3 (Aldrich, 98%) were dried under vacuum before use. Dehydrated methanol (Kanto, > 99:8%) and dehydrated toluene (Kanto, > 99:5%) were used as received. 1-Phenylethyl phenyldithioacetate (PEPD) 12 was synthesized according to the literature. The polymerizations were performed in a methanol-toluene mixture at 60 C using 2.23 M NIPAM monomer, 0.80 mM AIBN as the initiator and 8.94 mM PEPD as the RAFT agent in the absence y

We examined the antibacterial and hemolytic activities in a series of amphiphilic block and random copolymers of poly(vinyl ether) derivatives prepared by base-assisting living cationic polymerization. Block and random amphiphilic copolymers with similar monomer compositions showed the same level of activity against Escherichia coli . However, the block copolymers are much less hemolytic compared to the highly hemolytic random copolymers. These results indicate that the amphiphilic copolymer structure is a key determinant of activity. Furthermore, the block copolymers induced dye leakage from lipid vesicles consisting of E. coli -type lipids, but not mammalian lipids, while the random copolymers disrupted both types of vesicles. In addition, both copolymers displayed bactericidal and hemolytic activities at concentrations 1 or 2 orders of magnitude lower than their critical (intermolecular) aggregation concentrations (CACs), as determined by light scattering measurements. This suggests that polymer aggregation or macromolecular assembly is not a requisite for the antibacterial activity and selectivity against bacteria over human red blood cells (RBCs). We speculate that different single-chain conformations between the block and random copolymers play an important role in the antibacterial action and underlying antibacterial mechanisms.

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