We describe the synthesis of ultrahigh molecular weight water-soluble polymers via photoiniferter polymerization under inverse miniemulsion conditions. The catalyst-free heterogeneous process is mediated using low-intensity UV irradiation and offers rapid polymerization rates, excellent molecular weight control, polymer end-group fidelity, temporal control, advanced architectures, and most notably, viscosity control. We refined the polymerization conditions by considering the nature of the surfactant, costabilizer, and iniferter agent to achieve acrylamido homopolymers and block copolymers of molecular weights exceeding 1,000,000 Da at ambient temperature. This approach to well-defined ultrahigh molecular weight polymers overcomes the complications of high viscosity to facilitate eventual scale-up.

We report on a fundamental feature of photoiniferter polymerizations mediated with trithiocarbonates and xanthates. The polymerizations were found to be highly dependent on the activated electronic excitation of the iniferter. Enhanced rates of polymerization and greater control over molecular weights were observed for trithiocarbonate-and xanthate-mediated photoiniferter polymerizations when the n → π* transition of the iniferter was targeted compared to the polymerizations activating the π → π* transition. The disparities in rates of polymerization were attributed to the increased rate of C−S photolysis which was confirmed using model trapping studies. This study provides valuable insight into the role of electronic excitations in photoiniferter polymerization and provides guidance when selecting irradiation conditions for applications where light sensitivity is important.

The synthesis, structure, and magnetic properties of three related iron(III)-oxo clusters are reported, [ F e 7 O 3 ( O 2 C P h ) 9 ( m d a ) 3 ( H 2 O ) ]( 1 ) , [Fe 2 2 O 1 4 (OH) 3 (O 2 CMe) 2 1 (mda) 6 ](ClO 4 ) 2 (2), and [Fe 24 O 15 (OH) 4 (OEt)(O 2 CMe) 21 (mda) 7 ](ClO 4 ) 2 (3), where mdaH 2 is N-methyldiethanolamine. 1 was prepared from the reaction of [Fe 3 O(O 2 CPh) 6 (H 2 O) 3 ](NO 3 ) with mdaH 2 in a 1:2 ratio in MeCN, whereas 2 and 3 were prepared from the reaction of FeCl 3 /NaO 2 CMe/mdaH 2 in a 2:∼13:2 ratio and FeCl 3 / NaO 2 CMe/mdaH 2 /pyridine in a 2:∼13:2:25 ratio, respectively, both in EtOH. The core of 1 consists of a central octahedral Fe III ion held within a nonplanar Fe 6 loop by three μ 3 -O 2− and three μ 2 -RO − arms from the three mda 2− chelates. The cores of the cations of 2 and 3 consist of an A:B:A three-layer topology, in which a central Fe 6 (2) or Fe 8 (3) layer B is sandwiched between two Fe 8 layers A. The A layers structurally resemble 1 with the additional Fe added at the center to retain virtual C 3 symmetry. The central Fe 6 layer B of 2 consists of a {Fe 4 (μ 4 -O) 2 (μ 3 -OH) 2 } 6+ cubane with an Fe on either side attached to cubane O 2− ions, whereas that of 3 has the same cubane but with an {Fe 3 (μ 3 -O)(μ-OH)} unit attached on one side and a single Fe on the other. Variable-temperature dc and ac magnetic susceptibility studies revealed dominant antiferromagnetic coupling in all complexes leading to ground-state spins of S = 5 / 2 for 1 and S = 0 for 2 and 3. All Fe 2 pairwise exchange parameters (J ij ) for 1−3 were estimated by two independent methods: density functional theory (DFT) calculations using broken symmetry methods and a magnetostructural correlation previously developed for high-nuclearity Fe III /O complexes. The two approaches gave satisfyingly similar J ij values, and the latter allowed rationalization of the experimental ground states by identification of the spin frustration effects operative and the resultant relative spin vector alignments at each Fe III ion.