On the Dimension of a Hyperbranched Polymer Synthesized from a Styrene Derivative

Branched polymers generally have smaller dimensions than those of corresponding linear polymers with the same degree of polymerization, which reduces the solution viscosity and makes the processing of production easier. Moreover, branched polymers possess a lot of chain ends where many functional groups can be introduced, and thus have potential in a variety of commercial applications. Dendrimers are typical examples possessing the abovementioned branched polymer characters, but they require so many steps of reactions for their preparation that they are unsuitable for industrial usage. Recently, Ishizu et al. have proposed a novel, one-pot reaction scheme to synthesize a hyperbranched polymer (HBP) by photopolymerization of N,Ndiethylamino dithiocarbamoylmethylstyrene (DCS), which can also initiate vinyl polymerization to afford branching points, so-called ‘‘inimer’’ 1 (Scheme 1). They estimated the degree of branching by a kinetic approach 2 and NMR 3 to be as high as ca. 0.3–0.4. The molecular characterization of such a HBP is an interesting subject not only industrially but also acedemically. Ishizu and Mori 1,4,5 measured the intrinsic viscosity [� ]o f their. HBP in toluene, and found that the [� ] value was smaller than that of the linear PS with the same molecular weight. However, this experimental result does not necessarily indicate that the HBP has a smaller size than that of the linear PS, because the hydrodynamic volume of the polymer chain is not proportional to [� ] itself but to [� ] multiplied by the molecular weight M, and the HBP and PS should be compared at the same degree of polymerization instead of the molecular weight. When the ½� � M value calculated from the results of Ishizu and Mori was compared with that for the linear PS with the same degree of polymerization, the former became larger than the latter. This indicates that their. HBP chain is larger than that of the linear PS in solution. We have recently carried out dynamic light scattering (DLS) measurements for the same HBP, and obtained the hydrodynamic radius being larger than that of the linear PS with the same degree of polymerization (see below). This result is consistent with ½� � M data of Ishizu and Mori, but seems to be inconsistent with the conventional character of branched polymers. In this communication, we report static and dynamic light scattering data for this. HBP in tetrahydrofuran (THF) and methyl ethyl ketone (MEK), and argue the chain dimension of the HBP in comparison with linear PS. In the argument, we have noticed that the repeating unit of this. HBP is not identical with that of PS. For PS, the phenyl ring attaches the polymer chain as the side group, but for the HBP the phenylene ring is included into the main chain (cf. Scheme 1).