The synthesis of block copolymers in an environmentally friendly medium was carried out in emulsion polymerizations through the reversible addition‐fragmentation chain transfer process, using a transfer active xanthate (MADIX) agent, under batch and starved‐feed conditions. First, ab initio experiments were carried out to prepare a seed of PBA dormant chains (i.e., poly(butyl acrylate) (PBA) polymer attached with a transfer active xanthate). The M̄n and polydispersity were predicted accurately with numerical simulations and equations derived by Müller from the method of moments. Those seeds were then used in a second‐stage polymerization under starved‐feed and batch conditions to prepare composite polymer colloids of block PBA‐co‐poly(styrene). Under starved feed conditions, approximately 90% of total polymer consisted of blocks, whereas under batch conditions only 70% consisted of blocks, which is proposed to be due a higher entry efficiency and thus greater termination rate. The films of these latexes were examined by atomic force microscopy. Surfactant migration to the surface increased with an increase in the amount of MADIX, resulting from a combination of a smaller particle size and a lower average molecular weight. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4206–4217, 2000

An enzymatic tandem reaction is described in which the enzymes phosphorylase and Deinococcus geothermalis glycogen branching enzyme (Dg GBE) catalyze the synthesis of branched polyglucans from glucose‐1‐phosphate (G‐1‐P). Phosphorylase consumes G‐1‐P and polymerizes linear amylose while Dg GBE introduces branching points on the α‐(1 → 6) positions by reshuffling short oligosaccharides. The resulting branched polyglucans have an unusually high degree of branching of 11%.

Branching enzyme (EC 2.4.1.18; glycogen branching enzyme; GBE) catalyzes the formation of ␣1,6-branching points in glycogen. Until recently it was believed that all GBEs belong to glycoside hydrolase family 13 (GH13). Here we describe the cloning and expression of the Thermus thermophilus family GH57-type GBE and report its biochemical properties and crystal structure at 1.35-Å resolution. The enzyme has a central (␤/␣) 7 -fold catalytic domain A with an inserted domain B between ␤2 and ␣5 and an ␣-helix-rich C-terminal domain, which is shown to be essential for substrate binding and catalysis. A maltotriose was modeled in the active site of the enzyme which suggests that there is insufficient space for simultaneously binding of donor and acceptor substrates, and that the donor substrate must be cleaved before acceptor substrate can bind. The biochemical assessment showed that the GH57 GBE possesses about 4% hydrolytic activity with amylose and in vitro forms a glucan product with a novel fine structure, demonstrating that the GH57 GBE is clearly different from the GH13 GBEs characterized to date.

Densely packed polysaccharide brushes consisting of α-d-glucose residues were grafted from modified silicon substrates. Potato phosphorylase was herein used to grow linear polysaccharide chains from silicon tethered maltoheptaose oligosaccharides using glucose-1-phosphate as donor substrate. The combined use of potato phosphorylase and Deinococcus geothermalis branching enzyme resulted in a hyperbranched brush coating as the latter one redistributes short oligosaccharides from the α(1–4)-linked position to the α (1–6)-linked position in the polysaccharide brush. The obtained grafting density of the brushes was estimated on 1.89 nm–2 while the thickness was measured with ellipsometric techniques and determined to be between 12.2 and 20.2 nm.

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