Well-defined higher-molecular-weight polyacrylonitrile via RAFT technique in the presence of disulfide compounds as a source of chain transfer agent
ABSTRACT Well-defined polyacrylonitrile with a higher number-average molecular weight () up to 200,000 and a lower polydispersity index (PDI, 1.7–2.0) was firstly obtained via reversible addition–fragmentation chain transfer (RAFT) process. This was achieved by selecting a stable, easy way to prepare disulfide compound intermediates including bis(thiobenzoyl) disulfide (BTBDS) and bis(thiophenylacetoyl) disulfide (BTPADS) to react with azobis(isobutyronitrile) to directly synthesize RAFT agents in situ. The polymerization of acrylonitrile (AN) displays the characteristics of controlled/living radical polymerization as evidenced by pseudo first-order kinetics of polymerization, linear evolution of molecular weight with increasing monomer conversion, and narrow PDIs. The polymerization rate and the efficiency for producing RAFT agent of BTPADS system are obviously higher than those of BTBDS system, whereas the control of the latter over the polymerization is superior to that of the former. 1H NMR analysis has confirmed the dithioester chain-end functionality of the resultant polymer. The RAFT copolymerizations of AN and the comonomers including methyl acrylate, itaconic acid, methyl methacrylate, n-butyl acrylate, 2-hydroxyethyl acrylate, and acrylamide were also successfully carried out using the same polymerization system.
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Conference Paper: Reducing the data size of spatial databases using sign vectors[Show abstract] [Hide abstract]
ABSTRACT: In this paper, we describe a method for effectively expressing spatial geometric data in spatial database systems. The hyperplane is used to split a space into convex polytopes, each having a position vector. These position vectors are used to evaluate the spatial operations: the intersection, the union and the difference between two complexes of convex polytopes in any dimension. First, we explain the idea to represent a spatial object as a set of polytopes induced by hyperplanes, which must be stored in databases. We then present the conversion algorithms between position vectors and sign vectors of the complex model in any dimension. Next, we propose algorithms for compressing and uncompressing the sign vector to be stored in the database data. These algorithms are invoked when evaluating spatial operations. The above algorithms are implemented on an object database system. We also present the results of experimental tests to evaluate the data size of the spatial database.TENCON 2004. 2004 IEEE Region 10 Conference; 12/2004
- Australian Journal of Chemistry - AUST J CHEM. 01/2009; 62(11).