Estudo do efeito da adição de poli(glicol etilênico-b-glicol propilênico) na formação de dispersões aquosas poliuretânicas à base de poli(glicol propilênico)

Foram produzidas dispersões aquosas não-poluentes e inovadoras de poli(uretano-uréia) à base de poli(glicol propilênico) (PPG) e de copolímeros em bloco, poli(glicol etilênicob-glicol propilênico), (EG-b-PG) com teor de 7% de unidades de glicol etilênico. Os poli(uretano-uréia)s foram preparados, em duas etapas, pelo método do prepolímero. Na primeira etapa, foram obtidos anionômeros, sintetizados em massa, à base do copolímero EG-bPG, PPG, ácido dimetilol propiônico (DMPA) (gerador dos sítios aniônicos) e diisocianato de isoforona (IPDI). Ainda na primeira etapa, os grupos carboxílicos do DMPA foram submetidos à neutralização com trietilamina (TEA). Na segunda etapa, foi realizada a dispersão do prepolímero anionômero e, em seguida, foi conduzida a reação de extensão de cadeia com a hidrazina (HYD). Nas diferentes formulações, foram variadas a razão NCO/OH e as proporções de PPG e do copolímero em bloco EG-b-PG. Além disso, foram obtidas dispersões aquosas programadas para teores de sólidos de 40 e 50%. As dispersões foram avaliadas quanto ao teor de sólidos totais, tamanho médio de partícula e viscosidade. Os filmes, obtidos por vazamento das dispersões, foram avaliados quanto à absorção de água, termogravimetria (TG) e propriedades mecânicas (ensaio de tração). Os filmes vazados e os monômeros foram caracterizados por espectrometria na região de infravermelho (FTIR) As dispersões obtidas se mostraram adequadas para serem aplicadas como revestimento para madeira, metais e vidro

Efficient Synthesis of Single-Chain Polymer Nanoparticles via Amide Formation

Single-chain technology (SCT) allows the transformation of individual polymer chains to folded/collapsed unimolecular soft nanoparticles. In this work we contribute to the enlargement of the SCT toolbox by demonstrating the efficient synthesis of single-chain polymer nanoparticles (SCNPs) via intrachain amide formation. In particular, we exploit cross-linking between active methylene groups and isocyanate moieties as powerful "click" chemistry driving force for SCNP construction. By employing poly(methyl methacrylate)- (PMMA-) based copolymers bearing beta-ketoester units distributed randomly along the copolymer chains and bifunctional isocyanate cross-linkers, SCNPs were successfully synthesized at r.t. under appropriate reaction conditions. Characterization of the resulting SCNPs was carried out by means of a combination of techniques including size exclusion chromatography (SEC), infrared (IR) spectroscopy, proton nuclear magnetic resonance (H-1 NMR) spectroscopy, dynamic light scattering (DLS), and elemental analysis (EA).

Year-class formation in Pacific herring (Clupea pallasi) estimated from spawning-date distributions of juveniles in San Francisco Bay, California

Inter and intra-annual variation in year-class strength was analyzed for San Francisco Bay Pacific herring (Clupea pallasi) by using otoliths of juveniles. Juvenile herring were collected from March through June in 1999 and 2000 and otoliths from subsamples of these collections were aged by daily otolith increment analysis. The composition of the year classes in 1999 and 2000 were determined by back-calculating the birth date distribution for surviving juvenile herring. In 2000, 729% more juveniles were captured than in 1999, even though an estimated 12% fewer eggs were spawned in 2000. Spawning-date distributions show that survival for the 2000 year class was exceptionally good for a short (approximately 1 month) period of spawning, resulting in a large abundance of juvenile recruits. Analysis of age at size shows that growth rate increased significantly as the spawning season progressed both in 1999 and 2000. However, only in 2000 were the bulk of surviving juveniles a product of the fast growth period. In the two years examined, year-class strength was not predicted by the estimated number of eggs spawned, but rather appeared to depend on survival of eggs or larvae (or both) through the juvenile stage. Fast growth through the larval stage may have little effect on year-class strength if mortality during the egg stage is high and few larvae are available.