Abstract
Summary: Ethylene glycol dimethacrylate (1) was polymerized at 70 and 80 °C in benzene using high concentrations of the initiator, dimethyl 2,2′‐azobisisobutyrate (2). When the concentrations of 1 and 2 were 0.10 and 0.50 mol · L^−1^, respectively, the polymerization proceeded homogeneously without any gelation to yield a soluble polymer. The polymerization system involved ESR‐detectable polymer radicals in high concentration (3.1 × 10^−6^–7.5 × 10^−6^ mol · L^−1^ at 70 °C). The polymer formed at 80 °C after 4 h consisted of units of 1 with (4 mol‐%) and without (38 mol‐%) a double bond and a methoxycarbonylpropyl group (58 mol‐%) as the fragment of 2. Thus, the initiator‐fragment incorporation radical polymerization proceeds in the present polymerization to yield a hyperbranched polymer. The polymer showed an upper critical solution temperature (31 °C on cooling and 32 °C on heating) in an acetone/water mixture (4:1 v/v). The intrinsic viscosity of the polymer was very low (0.047 dL · g^−1^) at 30 °C in benzene despite its considerably high molecular weight ($\overline M _{\rm w}$ = 5.7 × l0^5^ by MALLS). TEM confirmed that the individual polymer molecules were nanoparticles with diameters of 5–15 nm. The polymer was able to solubilize for the dye probe, Rhodamine 6G, by encapsulation in its hyperbranched structure.
Hyperbranched structure of the resulting polymer.
magnified imageHyperbranched structure of the resulting polymer.