Lignin is evaluated as a nature-inspired broad-spectrum sun blocker in sunscreen lotions.

Surfaces based on grafted poly(2-methacryloyloxyethyl phosphorylcholine) (poly(MPC)) "brushes" with a constant graft density of 0.39 chain/nm2 and chain length from 5 to 200 monomer units were prepared by surface-initiated atom transfer radical polymerization (ATRP) on silicon wafers. The chain length and layer thickness of the poly(MPC) grafts were varied via the ratio of MPC to sacrificial initiator. The surfaces were characterized by water contact angle, XPS, and AFM. The effect of poly(MPC) chain length on fibrinogen and lysozyme adsorption was studied in TBS buffer at pH 7.4. The adsorption of both proteins on the poly(MPC)-grafted surfaces was greatly reduced compared to the unmodified silicon. Adsorption decreased with increasing chain length of the poly(MPC) grafts. Grafts of chain length 200 (MW 59 000) gave adsorption levels of 7 and 2 ng/cm2, respectively, for fibrinogen and lysozyme at 1 mg/mL protein concentration, corresponding to reductions of greater than 98% compared to the unmodified silicon. Adsorption experiments using mixtures of the two proteins showed that the suppression of protein adsorption on the poly(MPC)-grafted surfaces was not strongly dependent on protein size or charge.

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Poly(4,8-dialkyl-2,6-bis(3-alkylthiophen-2-yl)benzo[1,2-b:4,5-b‘]dithiophene) 1 represents a new class of polymer semiconductors which self-assemble into higher structural orders without thermal annealing and provide excellent field-effect transistor performance with mobility up to 0.25 cm2 V-1 s-1 when used as a solution-processed thin-film semiconductor in thin-film transistors.

We report an ab initio emulsion reversible addition−fragmentation chain transfer (RAFT) polymerization of styrene using poly(acrylic acid-b-styrene) trithiocarbonate as surfactant and RAFT agent. The system is characteristic of high polymerization rate, controlled polymer molecular weight, and free of coagulum. Design of the amphiphilic RAFT agent is found to be critical for the success. Poly(acrylic acid) neutralization increased the colloidal stability but led to uncontrolled molecular weight development and broad molecular weight distribution, attributed to small size and thus large number of micelles resulting in continuous particle nucleation. Polystyrene with molecular weight up to 120 kg/mol and block styrene−butylacrylate copolymer with well-controlled molecular weight were readily synthesized with this method.

A kinetic model has been developed for reversible addition-fragmentation transfer (RAFT) polymerization with the method of moments. The model predicts the monomer conversion, number-average molecular weight, and polydispersity of the molecular weight distribution. It also provides detailed information about the development of various types of chain species during polymerization, including propagating radical chains, adduct radical chains, dormant chains, and three types of dead chains. The effects of the RAFT agent concentration and the rate constants of the initiator decomposition, radical addition, fragmentation, disproportionation, and recombination termination of propagating radicals and cross-termination between propagating and adduct radicals on the kinetics and polymer chain properties are examined with the model.

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Our high-temperature and high-pressure continuous stirred-tank reactor (CSTR) has been used for the polymerization of ethylene with the constrained geometry metallocene system, [C5-Me4(SiMe2N t Bu)]TiMe2 (CGC-Ti)/ tris(pentafluorophenyl)boron (TPFPB)/ modified methylaluminoxane (MMAO), in Isopar E solution at 500 psig. Polyethylenes (PE) with long chain branching (LCB) densities up to 0.44 carbons/10 000 carbons, melt flow index ratios of 7.4-25.7, and narrow polydispersity indexes about 2 were synthesized. The polymerization variables included temperature, mean residence time, and ethylene feed concentration. Polyethylene chains terminated mainly by transfer to monomer yielded macromonomers for the LCB formation. The CGC-Ti catalyst appeared to be single site type, and active centers showed an exponential decay with mean residence time. The rate constants and their activation energies of the ethylene propagation, LCB, chain transfer to monomer, and chain transfer to hydrogen were estimated. The presence of methyl side chains in PEs produced at elevated temperatures indicated that the open structure of CGC-Ti catalyst allowed macromonomers to have 2,1-insertion.