SUMMARY Propene polymerizations were performed using the two ansa-zirconocene catalyst systems dimethylsilylbis( 1 -indenyl)zirconium dichloride/methylaluminoxane and dimethylsilylbis(2-methyl-1 -indeny1)zirconium dichloride/methylaluminoxane. The polymerization rate was observed by continuously monitoring the monomer consumption. Reaction rate profiles were obtained in the temperature range from 40 "C to 130°C at pressures between 1 and 2.5 bar and catalyst concentrations from 4.6-10" M to 4.2. lCr5 M. Isotacticity, as measured by NMR, melting point and molecular weight decreases markedly at higher temperatures. Small amounts of 1,3-inserted monomer (el mol-%) was observed at polymerization temperatures above 80 "C. No 2,1-inserted monomer was detected. A kinetic model was developed that describes the polymerization rate for Me2Si(Ind)2ZrC12 as the catalyst over the entire observed temperature range, and the polymerization rate for Me&Si(2-Me-Ind)&C12 in a limited temperature range. The model includes an activation reaction, latent sites that may revert to active sites and a permanent deactivation that is second order with respect to the active sites. The activation energy for the propagation reaction was found to be 37 kT/mol for Me2Si(Ind)2ZrC12 and 32 kJ/mol for Me2Si(2-Me-Ind)2ZrClJMAO. Several kinetic models are compared and discussed.
Microbubbles (MBs) are routinely used as contrast agents for ultrasound imaging. The use of ultrasound in combination with MBs has also attracted attention as a method to enhance drug delivery.We have developed a technology platform incorporating multiple functionalities, including imaging and therapy in a single system consisting of MBs stabilized by polyethylene glycol (PEG) coated polymeric nanoparticles (NPs). The NPs, containing lipophilic drugs and/or contrast agents, are composed of the widely used poly(butyl cyanoacrylate) (PBCA) polymer and prepared in a single step. MBs stabilized by these NPs are subsequently prepared by self-assembly of NPs at the MB air/liquid interface. Here we show that these MBs can act as contrast agents for conventional ultrasound imaging. Successful encapsulation of iron oxide NPs inside the PBCA NPs is demonstrated, potentially enabling the NPs/MBs to be used as magnetic resonance imaging (MRI) and/or molecular ultrasound imaging contrast agents. By precise tuning of the applied ultrasound pulse, the MBs burst and the NPs constituting the shell are released. This could result in increased local deposit of NPs into target tissue providing improved therapy and imaging contrast compared to freely distributed NPs.
Abstract:The uptake and toxicity of two poly(methylmethacrylate)-based plastic nanoparticles 21 (PNPs) with different surface chemistries (medium and hydrophobic) was assessed using aquatic 22 organisms selected for their relevance based on the environmental behaviour of the PNPs. Pure 23 poly(methylmethacrylate) (medium; PMMA PNPs) and poly(methylmethacrylate-co-24 stearylmethacrylate) copolymer (hydrophobic; PMMA-PSMA PNPs) of 86-125 nm were synthesised 25 using a mini emulsion polymerisation method. Fluorescent analogues of each PNP (FPNPs) were 26 also synthesised using monomer 7-[4-(trifluoromethyl)coumarin]acrylamide and studied. Daphnia 27 magna, Corophium volutator and Vibrio fischeri were employed in a series of standard acute 28 ecotoxicity tests, being exposed to the PNPs at three different environmentally realistic 29 concentrations (0.01, 0.1, and 1.0 mg L -1 ) and a high concentration 500-1000 mg L -1 . In addition, 30 sublethal effects of PNPs in C. volutator were determined using a sediment reburial test whilst the 31 uptake and depuration of FPNPs was studied in D. magna. The PNPs and FPNPs did not exhibit any 32
The encapsulation of organic liquids in polyurethane nanocapsules by interfacial miniemulsion polycondensation of isophorone diisocyanate and propanetriol has been performed. The influence of type and amount of encapsulated organic liquid has been studied and it was found that the encapsulation efficiency is dependent on the water solubility of the organic liquids, their interfacial tension against water and their compatibility with polyurethane. It was also shown how different types of surfactants and variations in pH and ionic strength of the continuous phase affected the stability during polymerization and the diameter of the miniemulsion droplets and the resulting nanocapsules. The long-chained anionic surfactant Disponil FES77 can be utilized over a larger pH range than SDS due to the contribution of steric stabilization. Relatively narrow size distributions were obtained.
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