Charge distribution and calcium affinity of sulfated alpha-L-galactans from ascidians. Comparison between linear and highly branched polymers

Calcium binding and charge distribution on highly branched and linear sulfated L-galactans from ascidians have been studied using a metallochromic indicator and conductimetric titrations. The distance between charged groups of the linear and highly branched galactans does not vary despite their marked differences in sulfate/total sugar molar ratios. These results indicate that the sulfated L-galactose units are concentrated in the central polysaccharide core and not intercalated among non-sulfated units. This inference is consistent with the chemical studies of these galactans. Surprisingly, calcium affinity increases with increasing amounts of non-sulfated sugar branches in the molecule. Thus, calcium binding in these polymers is not a simple function of availability of anion binding sites but a more complex calcium-polysaccharide interaction. (C) 1998 Elsevier B.V. Ltd. All rights reserved.

A strategy for synthesis of ion-bonded supramolecular star polymers by reversible addition-fragmentation chain transfer (RAFT) polymerization

We have developed a novel strategy for the preparation of ion-bonded supramolecular star polymers by RAFT polymerization. An ion-bonded star supramolecule with six functional groups was prepared from a triphenylene derivative containing tertiary amino groups and trithiocarbonate carboxylic acid, and used as the RAFT agent in polymerizations of tert-butyl acrylate (tBA) and styrene (St). Molecular weights and structures of the polymers were characterized by H-1 NMR and GPC. The results show that the polymerization possesses the character of living free-radical polymerization and the ion-bonded supramolecular star polymers PSt, PtBA, and PSt-b-PtBA, with six well-defined arms, were successfully synthesized.

Comparing tube models for predicting the linear rheology of branched polymer melts

The hierarchical and "bob" (or branch-on-branch) models are tube-based computational models recently developed for predicting the linear rheology of general mixtures of polydisperse branched polymers. These two models are based on a similar tube-theory framework but differ in their numerical implementation and details of relaxation mechanisms. We present a detailed overview of the similarities and differences of these models and examine the effects of these differences on the predictions of the linear viscoelastic properties of a set of representative branched polymer samples in order to give a general picture of the performance of these models. Our analysis confirms that the hierarchical and bob models quantitatively predict the linear rheology of a wide range of branched polymer melts but also indicate that there is still no unique solution to cover all types of branched polymers without case-by-case adjustment of parameters such as the dilution exponent alpha and the factor p(2) which defines the hopping distance of a branch point relative to the tube diameter. An updated version of the hierarchical model, which shows improved computational efficiency and refined relaxation mechanisms, is introduced and used in these analyses.

Hyperbranched polymers containing oxazoline monomers andsuccinic anhydride: applications in fast drying, low solvent coating formulations

tMelt-polycondensation of succinic acid anhydride with oxazoline-based diol monomers gave hyper-branched polymers with carboxylicacids terminal groups.1H NMR and quantitative13C NMRspectroscopy coupled with DEPT-13513C NMR experiment showed high degrees of branching (over 60%).Esterification of the acid end groups by addition of citronellol at 160◦C produced novel white spirit solubleresins which were characterized by Fourier transform-infrared (FTIR) spectroscopy, gel permeation chro-matography (GPC), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Blendsof the new hyperbranched materials with commercial alkyd resins resulted in a dramatic, concentrationdependent drop in viscosity. Solvent-borne coatings were formulated containing the hyperbranchedpolymers. Dynamic mechanical analysis studies revealed that the air drying rates of the new coatingsystems were enhanced compared with identical formulations containing only commercial alkyd resins.

Modelling polymers with side chains: MEH-PPV and P3HT

Modelling polymers with side chains is always a challenge once the degrees of freedom are very high. In this study, we present a successful methodology to model poly[2-methoxy-5-(2′-ethyl-hexyloxy)-p-phenylenevinylene] (MEH-PPV) and poly[3-hexylthiophene] (P3HT) in solutions, taking into account the influence of side chains on the polymer conformation. Molecular dynamics and semi-empirical quantum mechanical methods were used for structure optimisation and evaluation of optical properties. The methodology allows to describe structural and optical characteristics of the polymers in a satisfactory way, as well as to evaluate some usual simplifications adopted for modelling these systems. Effective conjugation lengths of 8-14.6 and 21 monomers were obtained for MEH-PPV and P3HT, respectively, in accordance with experimental findings. In addition, anti/syn conformations of these polymers could be predicted based on intrinsic interactions of the lateral branches. © 2013 Copyright Taylor and Francis Group, LLC.

From amphiphilic block copolymers to ferrocenyl-functionalized polymers for biosensoric applications

The present thesis can be divided in three main parts. In all parts new polymer architecturesrnwere synthesized and characterized concerning their special features.rnThe first part will emphasize the advantage of a polystyrene-block-(hyperbranchedrnpolyglycerol) copolymer in comparison to an analogue polystyrene-block-(linear polyglycerol)rncopolymer. Therefore a synthethic route to prepare linear block copolymersrnhas been developed. Two strategies were examined. One strategy was based on thernclassic, sequential anionic polymerization; the second strategy was based on arn“Click-Chemistry” coupling reaction. In a following step glycidol was hypergraftedrnfrom these block copolymers by applying a hypergrafting reaction with glycidol. Thernbehavior of the amphiphilic block copolymers synthesized was studied in differentrnsolvents. Furthermore the polarity of the solvent was changed to form the correspondingrninverse micelles. DLS, SLS, SEC-MALLS-VISCO, AFM and Cyro TEMrnmeasurements were performed to obtain a visual image from the appearance of thernaggregates. It was found that a linear-hyperbranched architecture is necessary, ifrnwell defined, monodisperse aggregates are required, e.g. for the preparation of orderedrnnanoarrays. Linear-linear block copolymers formed only polydisperse aggregates.rnAdditionally it was found that size distribution could be improved dramaticallyrnby passing the aggregates through a SEC column with large pores. The SEC columnsrnacted like a template in which the aggregates adopt a more stable conformation.rnIn the second part anionic polymerization was employed to synthesize silaneendfunctionalizedrnmacromonomers with different molecular weights based on polybutadienernand polyisoprene. These were polymerized by a hydrosilylation reaction inrnbulk to obtain branched polymers, using Karstedt’s catalyst. Surprisingly the additionrnof monofunctional silanes during the polymerization had only a minimal effect concerningrnthe degree of polymerization. It was possible to introduce silanes without increasingrnthe overall number of reaction steps by a very convenient “pseudo-copolymerization”rnmethod. All branched polymers were analyzed by SEC, SEC-MALLS,rnSEC-viscometry, 1H-NMR-spectroscopy and DSC concerning their branching ratio.rnThe branching parameters for the branched polymers exhibited similar characteristicsrnas hyperbranched polymers based on AB2 monomers. Detailed kinetic study showedrnthat the polymerization occurred very rapidly in comparison to the hydrosilylation polymerizationrnof classical AB2 type carbosilanes monomers.rnThe last part will deal with ferrocenyl-functionalized polymers. On the one hand,rnferrocenyl-functionalized polyglycerols (PG) were studied. Esterification of PGs withrndifferent molecular weight using ferrocenemonocarboxylic acid gave the ferrocenylrnfuntionalized polymers in high yields. On the other hand three different block copolymersrnwere prepared with different ratios of styrene to butadiene units (10:1, 4:1, 2:1).rnThe double bonds of the 1,2-PB block were hydrosilylated using silanes bearing onern(HSiMe2Fc) or two (HSiMeFc2) ferrocene units. High degrees of functionalizationrnwere obtained (up to 83 %). In this manner, six different ferrocenyl-rich block copolymersrnwith different fractions of ferrocene were prepared and analyzed, employingrnNMR-spectroscopy, SEC, SEC/MALLS/viscometry, DLS and cyclic voltammetry. Thernredox properties of the studied polymers varied primarily with the nature of the silanernunit attached. Additionally, the redox properties in solution of the studied polymersrnwere influenced by the block length ratio of the block copolymers. Unexpectedly, withrnincreasing block length of the ferrocenyl block the fraction of active ferrocenes decreased.rnNevertheless, in case of thin monolayer films this behaviour was not observed.rnAll polymers (PG and PS-b-PB based) exhibited good electrochemical propertiesrnin a wide range of solvents, which rendered them very interesting for biosensoricrnapplications.

Trapping of branched DNA in microfabricated structures.

We have observed electrostatic trapping of tribranched DNA molecules undergoing electrophoresis in a microfabricated pseudo-two-dimensional array of posts. Trapping occurs in a unique transport regimen in which the electrophoretic mobility is extremely sensitive to polymer topology. The arrest of branched polymers is explained by considering their center-of-mass motion; in certain conformations, owing to the constraints imposed by the obstacles a molecule cannot advance without the center of mass first moving a short distance backwards. The depth of the resulting local potential well can be much greater than the thermal energy so that escape of an immobilized molecule can be extremely slow. We summarize the expected behavior of the mobility as a function of field strength and topology and point out that the microfabricated arrays are highly suitable for detecting an extremely small number of branched molecules in a very large population of linear molecules.

Thiol-ene Clickable Hyperscaffolds Bearing Peripheral Allyl Groups

Radical catalyzed thiol-ene reaction has become a useful alternative to the Huisgen-type click reaction as it helps to expand the variability in reaction conditions as well as the range of clickable entities. Thus, direct generation of hyper-branched polymers bearing peripheral allyl groups that could be clicked using a variety of functional thiols would be of immense value. A specifically designed AB(2) type monomer, that carries two allyl benzyl ethers groups and one alcohol functionality, was shown to undergo self-condensation under acid-catalyzed melt-transetherification to yield a hyperbranched polyether that carries numerous allyl end-groups. Importantly, it was shown that the kinetics of polymerization is not dramatically affected by the change of the ether unit from previously studied methyl benzyl ether to an allyl benzyl ether. The peripheral allyl groups were readily clicked quantitatively, using a variety of thiols, to generate an hydrocarbon-soluble octadecyl-derivative, amphiphilic systems using 2-mercaptoethanol and chiral amino acid (N-benzoyl cystine) derivatized hyperbranched structures; thus demonstrating the versatility of this novel class of clickable hyperscaffolds. (C) 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 49:1735-1744, 2011

Synthesis of symmetric H-shaped block copolymer by the combination of ATRP and living anionic polymerization

A novel fluorescent dye labeled H-shaped block copolymer, (PMMA-Fluor-PS)(2)-PEO-(PS-Fluor-PMMA)(2), is synthesized by the combination of atom transfer radical polymerization (ATRP) and anionic polymerization (AP). To obtain the designated structure of the copolymer, a macroinitiator, 2,2-dichloro acetyl-PEO-2,2-dichloro acetyl (DCA-PEO-DCA), was prepared from DCAC and poly(ethylene oxide). The copolymer was characterized by H-1 NMR, GPC and fluorescence spectroscopy.

Syntheses and ethylene polymerization behavior of supported salicylaldimine-based neutral nickel(II) catalysts

Two novel salicylaldimine-based neutral nickel(II) complexes, [(2,6-iPr(2)C(6)H(3))NCH(2-ArC6H3O)]Ni(PPh3)Ph (6, Ar = 2-(OH)C6H4; 8, Ar = 2-OH-3-(2,6-iPr(2)C(6)H(3)NCH)C6H3), have been synthesized, and their structures have also been confirmed by X-ray crystallography, elemental analysis, and H-1 and C-13 NMR spectra. An important structural feature of the two complexes is the free hydroxyl group, which allows them to react with silica pretreated with trimethylaluminum under immobilization by the formation of a covalent bond between the neutral nickel(II) complex and the pretreated silica. As active single-component catalysts, the two complexes exhibited high catalytic activities up to 1.14 and 1.47 x 10(6) g PE/mol(Ni)center dot h for ethylene polymerization, respectively, and yielded branched polymers. Requiring no cocatalyst, the two supported catalysts also showed relatively high activities up to 4.0 x 10(5) g PE/mol(Ni)center dot h and produced polyethylenes with high weight-average molecular weights of up to 120 kg/mol and a moderate degree of branching (ca. 13-26 branches per 1000 carbon atoms).

Novel furan polymer materials based on the reversible Diels-Alder reaction

A futura e inevitável escassez dos recursos fósseis, juntamente com o aumento imprevisível dos seus preços, levou, nas últimas décadas, a um aumento impressionante de iniciativas dedicadas não só à procura de fontes alternativas de fornecedores de energia, mas também de produtos químicos e polímeros a partir de fontes renováveis, em particular da biomassa vegetal. Entre estes, os polímeros derivados de monómeros furânicos constituem uma classe única de materiais cujas estruturas podem, em princípio, simular virtualmente os seus homólogos actualmente derivados de recursos fósseis. O anel furânico é uma estrutura heterocíclica com um carácter diénico pronunciado, o que torna-o um dieno particularmente apropriado para a reacção de Diels-Alder (DA) com dienófilos como a maleimida. Um dos aspectos mais relevantes da reacção de DA é a sua reversibilidade em função da temperatura, a qual permite que os aductos sejam facilmente revertidos nos seus precursores por aumento da temperatura (reacção de retro-DA). No caso específico da combinação furano-maleimida, a formação do aducto predomina até cerca de 60ºC, enquanto a reacção inversa é dominante acima de 100ºC. A combinação desta característica da reacção de DA com a química de compostos furânicos pode abrir um novo caminho para a preparação de materiais macromoleculares funcionais com base em fontes renováveis e com aplicações promissoras como auto-reparação e reciclabilidade. O principal objectivo desta Tese, é a síntese e caracterização de novos materiais poliméricos termo-reversíveis, aplicando a reacção de DA a monómeros complementares com estruturas dos tipos furânico (o dieno, designado por A) e de maleimida (o dienófilo, designado por B). A primeira etapa neste trabalho envolveu a síntese, purificação e caracterização de novos monómeros furânicos e de maleimida do tipo AA, A3, BB, B3, AB, AB2, cada um com diferentes grupos separadores das funções reactivas. Posteriormente, estes monómeros foram polimerizados e despolimerizados por ciclos de DA/retro-DA utilizando diferentes combinações. A formação e dissociação de todos os aductos de DA foram seguidas por ambas espectroscopias de UV e RMN de 1H. O primeiro sistema de DA estudado foi uma combinação modelo entre reagentes mono-funcionais (-A+-B), nomeadamente o acetato furfurílico (FA) e a N-metilmaleimida (MM), ambos comercialmente disponíveis. O objectivo desta abordagem foi estudar a cinética e o equilíbrio da formação/dissociação dos aductos de DA e obter indicações sobre as condições mais adequadas a serem usadas na preparação dos correspondentes novos materiais macromoleculares. Além disso, pretendia-se verificar a presença ou ausência de reacções secundárias que poderiam intervir em ambas as vias directa e inversa das reacções, mesmo após vários ciclos. A espectroscopia de UV forneceu informação quantitativa sobre a cinética de formação do aducto através da diminuição progressiva da absorvência máxima a 293 nm correspondente ao grupo maleimida, a diferentes temperaturas (35, 50, 65 ºC) Reciprocamente, a correspondente reacção de retro-DA foi seguida a 90 ºC através do aumento do mesmo pico. A reversibilidade destes sistemas foi verificada com sucesso após uma sequência de ciclos de DA/retro-DA. Adicionalmente, verificou-se que os espectros originaram um ponto isosbéstico, provando que estes sistemas não envolvem quaisquer reacções secundárias. Uma vez que foi usado um excesso de FA, as reacções de DA modelo apresentaram um comportamento cinético de pseudo-primeira ordem, com a constante de velocidade k mais alta (2.1x10-5 dm3mol-1s-1) para T=65 ºC. A correspondente energia de activação foi de 39.0 kJ.mol-1. A reacção de retro-DA seguiu um comportamento de primeira ordem, com constante de velocidade de 1.6x10-6 s-1. A evolução deste sistema por RMN de 1H a 65ºC deu-nos informações mais detalhadas sobre a sua evolução estrutural, ou seja, à medida que a intensidade dos picos atribuídos à formação do aducto aumentaram progressivamente ao longo do tempo, os pertencentes aos reagentes iniciais diminuiram proporcionalmente. O “rendimento final”, calculado após 20 dias à temperatura ambiente, foi de aproximadamente 70%. A reacção de retro-DA foi depois seguida a 90ºC, observando-se tal como na espectroscopia de UV, o deslocamento da reacção no sentido da regeneração dos reagentes de partida. A viabilidade de múltiplos ciclos de DA/retro-DA estabelecidos pela espectroscopia de UV foi igualmente confirmada por RMN de 1H. O passo seguinte envolveu o estudo de um sistema de policondensação linear baseado no crescimento gradual por reacção de DA entre um monómero bisfurânico A-A e um do tipo bismaleimida B-B, seguindo a mesma abordagem que no sistema modelo. O poliaducto linear foi obtido a partir de soluções equimolares dos monómeros, por reacção de DA a 65ºC. O progresso desta polimerização foi seguido por espectroscopia de UV e RMN de 1H e, mais qualitativamente, pelo aumento da viscosidade do meio. A reacção seguiu um comportamento de segunda ordem, com uma constante de velocidade de 9.4x10-6 dm3mol-1s-1, e observou-se novamente um ponto isosbéstico nos dados de UV. Os espectros de RMN apresentaram o padrão esperado, nomeadamente o aumento progressivo dos sinais associados ao aducto e a correspondente diminuição dos grupos furano e maleimida livres. A despolimerização do poliaducto através da reacção de retro-DA foi seguida a 110ºC usando as mesmas técnicas. Os dados de UV mostraram o retorno progressivo da absorção dos grupos de maleimida, seguindo um comportamento cinético de primeira ordem, com constante de velocidade de 2.5x10-6 s-1, até à completa regeneração de ambos os monómeros. Os espectros de RMN providenciaram mais uma vez informação estrutural sobre o progresso da despolimerização, a qual foi acompanhada por uma diminuição progressiva da viscosidade. Adicionalmente, para seguir a retro- DA, adicionou-se um excesso de composto furânico monofuncional, nomeadamente o 2,5-dimetilfurano (DMFu), ao sistema de modo a bloquear as funções maleimida complementares, evitando assim a repolimerização após arrefecimento. Os productos isolados foram então o monómero bisfurânico AA, DMFu que não reagiu e o bisaducto não-polimerizável de BB com DMFu. Este resultado indicou claramente que o polímero foi de facto revertido nos seus monómeros durante a reacção de retro-DA. O terceiro sistema estudado foi outra polimerização linear, seguindo as mesmas condições experimentais que os anteriores, mas com uma estratégia diferente de modo a contornar o problema clássico de assegurar a estequiometria exacta dos monómeros. As estruturas dos monómeros utilizados incorporam ambos os grupos reactivos, i.e, moléculas do tipo A-B. A polimerização prematura destes monómeros intrinsecamente reactivos foi evitada com a protecção do grupo maleimida na forma de um aducto de DA com furano, até a incorporação do substituinte furânico na outra extremidade. Portanto, a policondensação destes monómeros foi iniciada após a desprotecção in situ deste composto mediante aquecimento, seguido de arrefecimento até à temperatura adequada para polimerizar. Os resultados obtidos por UV e RMN sugerem que de facto o uso de monómeros do tipo A-B oferece um melhor sistema linear. Em seguida, foram estudados sistemas de policondensação não-linear por reacção de DA, entre monómeros (um ou ambos) com funcionalidade superior a dois, nomeadamente sistemas do tipo A3+B-B ou A-A+B3, seguindo mais uma vez as mesmas condições experimentais. Uma vez que utilizam monómeros complementares contendo, em média, mais de duas funcionalidades, estes sistemas conduzem a materiais reticulados. Nestes estudos, foram usadas três razões molares de [maleimida]/[furano], nomeadamente 1.0, 0.75 e 0.5, de modo a estudar ambas as situações de não-gelificação e reticulação. Ambos sistemas apresentaram um comportamento regular e boa reciclabilidade quer para gerar situações que possam conduzir à formação de redes a diferentes graus de conversão, ou que possam parar antes da sua obtenção, conforme previsto pela equação de Flory-Stockmayer. Como esperado, a utilização de grupos complementares em quantidades estequiométricas produziu o espessamento mais rápido e a reticulação quase completa; à medida que a quantidade relativa de monómero trifuncional decresceu, as reacções pararam antes da reticulação, ou seja, originaram meios altamente viscosos contendo polímeros solúveis altamente ramificados. As reacções de retro-DA a 110 ºC conduziram à gradual dissolução das partículas de gel (quando presentes), tendo sido comprovado pelos espectros de UV e de RMN de 1H, evidenciado a regeneração dos monómeros. Tal como no sistema do tipo A-A+B-B, a reacção de retro-DA foi seguida adicionando um excesso de DMFu ao sistema reaccional. Como esperado, os produtos finais foram os monómeros furânicos, o DMFu em excesso e o trisaducto ou o bisaducto maleimida-DMFu, o que confirma a eficiência da despolimerização com regeneração dos monómeros iniciais. O último sistema de policondensação por reacção de DA envolveu um monómero assimetricamente substituído do tipo AB2, capaz de originar estruturas macromoleculares hiper-ramificadas que não reticulam. Este estudo preliminar deste sistema foi seguido nas mesmas condições experimentais que os anteriores, apresentando um comportamento com as características esperadas.

Cyclotetrasiloxane Frameworks for the Chemoenzymatic Synthesis of Oligoesters

Immobilized lipase B from Candida antarctica (Novozym® 435, N435) was utilized as part of a chemoenzymatic strategy for the synthesis of branched polyesters based on a cyclotetrasiloxane core in the absence of solvent. Nuclear magnetic resonance spectroscopy and matrix-assisted laser desorption ionization time-of-flight mass spectrometry were utilized to monitor the reactions between tetraester cyclotetrasiloxanes and aliphatic diols. The enzyme-mediated esterification reactions can achieve 65– 80% consumption of starting materials in 24–48 h. Longer reaction times, 72–96 h, resulted in the formation of cross-linked gel-like networks. Gel permeation chromatography of the polymers indicated that the masses were Mw ¼ 11 400, 13 100, and 19 400 g mol 1 for the substrate pairs of C7D4 ester/ octane-1,8-diol, C10D4 ester/pentane-1,5-diol and C10D4 ester/octane-1,8-diol respectively, after 48 h. Extending the polymerization for an additional 24 h with the C10D4 ester/octane-1,8-diol pair gave Mw ¼ 86 800 g mol 1. To the best of our knowledge this represents the first report using lipase catalysis to produce branched polymers that are built from a cyclotetrasiloxane core.

Scaling and branching in wet sonogels as a function of the volume fraction of the liquid phase

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Thermostimulated sol-gel transition in suspensions of sulfate zirconium oxychloride

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Tetraurea derivatives of calix[4]arenes and oligocalix[4]arenes, synthesis and self-assembly = Tetraharnstoff-Derivate von Calix[4 ]arenen und Oligocalix[4]arenen, Synthese und Selbstorganisierung

Wide rim tetraurea calix[4]arenes form hydrogen bonded dimeric capsules in apolar solvents in the presence of a suitable guest, which must be included in the cavity. The monomeric and dimeric form are never observed simultaneously under usual conditions. In general the combination of two different alkyl or aryl tetraurea derivatives results in the mixture of two homodimers and a heterodimer, however, only the heterodimeric species is observed in the 1:1 mixture of aryl and tosyl ureas. The (hetero)dimerization of oligourea calix[4]arenes (units) was used to construct larger structures via self-assembly of multiple calixarenes (building blocks) containing two (or more) covalently connected units. Among these self-assembled structures linear or branched polymers, cyclic oligomers and well-organized dendrimers were envisaged. The synthesis of the building blocks requires the preparation of calix[4]arene units possessing one (or more) functional group at the narrow or wide rim. Finally the oligourea units were covalently connected either directly or via suitable spacers within appropriate building blocks using amide bonds. Self-assembly properties of such building blocks were investigated.