Living cationic polymerization

The kinetics of the polymerization of styrene iniated by 1-chloro-1-phenyltehane/tin (IV) chloride in the presence of tetrabutylammonium chloride have been studied. Dilatometry studies at 25 °C were conducted and the orders of reaction were established. Molecular weight studies were conducted for these experiments using size exclusion chromatography. These studies indicated that transfer/termination reactions were present. The observed kinetics may be explained by a polymerization mechanism involving a single propagating species which is present in low concentrations. Reactions at 0 °C and -15 °C have shown that a "living" polymerization could be obtained at low temperatures. A method was derived to study the kinetics of a "living" polymerization by following the increase in degree of polymerization with time. Polymerizations of styrene were conducted using 1,4-bis(bromomethyl)benzene as a difunctional co-catalyst. These reactions produced polymers with broad or bimodal molecular weight distributions. These observations may be explained by the rate of initiation being slower than the rate of propagation or the presence of transfer/termination reactions. Reactions were conducted using a co-catalyst using a co-catalyst produced by the addition of 1,1-diphenylethane to 1,4-bis(bromomethyl)benzene. Size exclusion chromatography studies showed that the polymers produced had a narrower molecular weight distribution than those produced by polymerizations initiated by 1,4-bis(bromomethyl)benzene alone. However the polydispersity was still observed to increase with reaction time. This may also be explained by slow initiation compared to the rate of propagation. Polymerizations initiated by both bifunctional initiators were examined using the method of studying reaction kinetics by following the change in number average degree of polymerization. The results indicated that a straight line relationship could also be obtained with a non-living polymerization.

Living cationic polymerization of isobutene

The polymerization of isobutene initiated by 1-chloro-1-phenylethane has been investigated, and molecular weight studies conducted using size exclusion chromatography. Polymerizations carried out in a 40/60 (v/v) mixture of dichloromethaneIcyclohexane, using titanium (IV) chloride as a catalyst in the presence of pyridine at -30 °C were found to be controlled and living. The number average molecular weights of the polymers increased linearly with monomer conversion, and the molecular weight distributions were between 1.15 and 1.20. Efficiencies of initiation were between 80 and 100%, and evidence was found to suggest that backbiting to the initiator had occurred, resulting in the formation of cyclic oligomers during the early stages of polymerization. The kinetics of polymerization can be explained in terms of active species in. equilibrium with dormant species. The effects of temperature. and dielectric constant on this equilibrium were studied and a model based upon the Fuoss equation was developed. Pyridine was found to behave as proton trap in the system, and when it was used in excess the rate of polymerization was retarded. By assuming that the catalyst and pyridine formed a one to one complex, it was possible to show that the reaction was second order with respect to the catalyst. The synthesis of low molecular weight polyisobutenes was studied. When the concentration of initiator was increased relative to that of the isobutene, such that the theoretical degree of polymerization was 20 or less, the rate of initiation was slow compared to propagation. The efficiency of initiation in these polymerizations was typically between 30 and 40 %. Optimal conditions of temperature. and.catalyst concentration were established, leading to a 60 % efficiency of initiation. A one-pot synthesis of phenol end-capped polyisobutene was attempted by adding phenol at the end of a living polymerization. Evidence to substantiate the existence of capped polymer chains in the resultant product was inconclusive. Block copolymerizations of oxetane and isobutene were conducted using 1-chloro-1phenylethane/TiCl4, but no copolymer or oxetane homopolymer could be isolated.

Living cationic polymerization of styrene monomers

This thesis describes an experimental investigation of synthesis of polystyrene under various polymerization conditions such as solvent polarity, temperature, initial concentrations of initiator, catalyst, monomer and added salts or co-catalyst, which was achieved using the living cationic polymerization technology in conjunction with gel permeation chromatography (GPC) and NMR spectroscopy. Polymerizations of styrene were conducted using 1-phenyl ethylchloride (1-PEC) as an initiator and tin tetrachloride (SnCI4) as a catalyst in the presence of tetra-n-Butylammonium chloride (nBu4NCI). Effects of solvent polarity varied by mixing dichloromethane (DCM) and less polar cyclohexane (C.hex), temperature, initial concentrations of SnC14, 1-PEC and nBu4NCI on the polymerizations were examined, and the conditions under which a living polymerization can be obtained were optimised as: [styrene]o ~ 0.75 - 2 M; [1-PEC]o ~ 0.005 - 0.05 M; [SnCI4Jo ~ 0.05 - 0.4 M; [nBu4NCIJo ~ 0.001 - 0.1 M; DCM/C.hex ~ 50/0 - 20/30 v/v; T ~ 0 to -45°C. Kinetic studies of styrene polymerization using the Omnifit sampling method showed that the number average molecular weight (Mn) of the polymers obtained increased in direct proportion to monomer conversion and agreed well with the theoretical Mn expected from the concentration ratios of monomer to initiator. The linearities of both the 1n([MJoI[M]) vs. time plot and the Mn vs. monomer conversion plot, and the narrow molecular weight distribution (MWD) measured using GPC demonstrated the livingness of the polymerizations, indicating the absence of irreversible termination and transfer within the lifetimes of the polymerizations. The proposed 'two species' propagation mechanism was found to apply for the styrene polymerization with 1-PEC/SnCI4 in the presence of nBu4NCl. The further kinetic experiments showed that living styrene polymerizations were achieved using the 1-PEC/SnCI4 initiating system in mixtures of DCM/C.hex 30/20 v/v at -15°C in the presence of various bromide salts, tetra-n-butylammonium bromide, tetra-n-pentylammonium bromide, tetra-n-heptylammonium bromide, and tetra-n-octylammonium bromide, respectively. The types of the bromide salts were found to have no significant effect on monomer conversion, Mn, polydispersity and initiation efficiency. Living polymerizations of styrene were also achieved using titanium tetrachloride (TiCI4) as a catalyst and 1-PEC as an initiator in the presence of a small amount of 2,6-di-tert-butylpyridine or pyridine instead of nBu4NCl. GPC analysis showed that the polymers obtained had narrow polydispersities (P.D. < 1.3), and the linearities of both the In([MJo/[MJ) vs. time plot and the Mn vs. monomer conversion plot demonstrated that the polymerizations are living, when the ratio of DCM and C.hex was less than 40 : 10 and the reaction temperature was not lower than -15°C. The reaction orders relative to TiCl4 and 1-PEC were estimated from the investigations into the rate of polymerization to be 2.56 and 1.0 respectively. lH and 13C NMR analysis of the resultant polystyrene would suggest the end-functionality of the product polymers is chlorine for all living polymerizations.

The cationic ring-opening polymerization of cyclic ethers

The kinetics and mechanisms of ring opening polymerization and copolymerizntion of different cyclic ethers were studied using mainly a cationic system of iinitiation. BF30Et2/ethanediol. The cyclic ethers reacted differently showing that ring strain and basicity are the main driving forces in cationic ring opening polymerizaion. In most cases it was found that the degree of polymerization is controlled kinetically via terminations with the counterion and the monomers, and that the contribution of each type of reaction to the overall termination differs markedly. The Gel permeation chromatography studies showed that the molecular weight distribution of the samples of polyoxetanes were bimodal. This was in accordance with previous work establishing that the cyclic tetramer is found in much higher proportions than any of the other cyclic oligomers. However the molecular weight distribution of the copolymers made from oxetane and THF or from oxetane and oxepane were shown to be unimodal. These observations could be explained by a change in the structure of the growing end involved in the cationic polymerization. In addition crown ethers like dibenzo-crown-6 and compounds such as veratrole are believed to stabilise the propagating end and promote the formation of living polymers from oxetane.

Synthesis of a (sic)-shaped amphiphilic block copolymer by the combination of atom transfer radical polymerization and living anionic polymerization

The functionalization of monomer units in the form of macroinitiators in an orthogonal fashion yields more predictable macromolecular architectures and complex polymers. Therefore, a new there exists E-shaped amphiphilic block copolymer, (PMMA)(2)-PEO-(PS)(2)-PEO-(PMMA)(2) [where PMMA is poly(methyl methacrylate), PEO is poly (ethylene oxide), and PS is polystyrene], has been designed and successfully synthesized by the combination of atom transfer radical polymerization (ATRP) and living anionic polymerization. The synthesis of meso-2,3-dibromosuccinic acid acetate/diethylene glycol was used to initiate the polymerization of styrene via ATRP to yield linear (HO)(2)-PS2 with two active hydroxyl groups by living anionic polymerization via diphenylmethylpotassium to initiate the polymerization of ethylene oxide. Afterwards, the synthesized miktoarm-4 amphiphilic block copolymer, (HO-PEO)(2)-PS2, was esterified with 2,2-dichloroacetyl chloride to form a macroinitiator that initiated the polymerization of methyl methacrylate via ATRP to prepare the there exists E-shaped amphiphilic block copolymer.

Synthesis of asymmetric H-shaped block copolymer by the combination of atom transfer radical polymerization and living anionic polymerization

A new asymmetric H-shaped block copolymer (PS)(2)-PEO-(PMMA)(2) has been designed and successfully synthesized by the combination of atom transfer radical polymerization and living anionic polymerization. The synthesized 2,2-dichloro acetate-ethylene glycol (DCAG) was used to initiate the polymerization of styrene by ATRP to yield a symmetric homopolymer (Cl-PS)(2)-CHCCCCH2CH2OH with an active hydroxyl group. The chlorine was removed to yield the (PS)(2)-CHCOOCH2CH2OH ((PS)(2)-OH). The hydroxyl group of the (PS)(2)-OH, which is an active species of the living anionic polymerization, was used to initiate ethylene oxide by living anionic polymerization via DPMK to yield (PS)(2)-PEO-OH. The (PS)(2)-PEO-OH was reacted with the 2,2-dichloro acetyl chloride to yield (PS)(2)-PEO-OCCHCl2 ((PS)(2)-PEO-DCA). The asymmetric H-shaped block polymer (PS)(2)-PEO-(PMMA)(2) was prepared via ATRP of MMA at 130 degrees C using (PS)(2)-PEO-DCA as initiator and CuCl/bPy as the catalyst system. The architectures of the asymmetric H-shaped block copolymers, (PS)(2)-PEO-(PMMA)(2), were confirmed by H-1 NMR, GPC and Fr-IR.

Strontium-based initiator system for ring-opening polymerization of cyclic esters

An amino isopropoxyl strontium (Sr-PO) initiator, which was prepared by the reaction of propylene oxide with liquid strontium ammoniate solution, was used to carry out the ring-opening polymerization (ROP) of cyclic esters to obtain aliphatic polyesters, such as poly(epsilon-caprolactone) (PCL) and poly(L-lactide) (PLLA). The Sr-PO initiator demonstrated an effective initiating activity for the ROP of epsilon-caprolactone (epsilon-CL) and L-lactide (LLA) under mild conditions and adjusted the molecular weight by the ratio of monomer to Sr-PO initiator. Block copolymer PCL-b-PLLA was prepared by sequential polymerization of epsilon-CL and LLA, which was demonstrated by H-1 NMR, C-13 NMR, and gel permeation chromatography. The chemical structure of Sr-PO initiator was confirmed by elemental analysis of Sr and N, H-1 NMR analysis of the end groups in epsilon-CL oligomer, and Fourier transform infrared (FTIR) spectroscopy. The end groups of PCL were hydroxyl and isopropoxycarbonyl, and FTIR spectroscopy showed the coordination between Sr-PO initiator and model monomer gamma-butyrolactone. These experimental facts indicated that the ROP of cyclic esters followed a coordination-insertion mechanism, and cyclic esters exclusively inserted into the Sr-O bond.

The ring opening polymerization of ring strained cyclic ethers

The kinetics and mechanisms of the ring-opening polymerization of oxetane were studied using cationic and coordinated anionic catalysts. The cationic initiators used were BF30Et2!/ethanol, BF30Et2!/ethanediol and BF30Et2/propantriol. Kinetic determinations with the BF30Et2/diol system indicated that a 1: 1 BF3:0H ratio gave the maximum rate of polymerization and this ratio was employed to detenmne the overall rates of polymerization. An overall second-order dependence was obtained when the system involved ethanediol or propantriol as co-catalyst and a 3/2-order dependence with ethanol, in each case the monomer gave a first-order relationship. This suggested that two mechanisms accounted for the cationic polymerization. These mechanisms were investigated and further evidence for these was obtained from the study of the complex formation of BF30Et2 and the co-catalysts by 1H NMR. Molecular weight studies (using size-exclusion chromatography) indicated that the hydroxyl ion acted as a chain transfer reagent when the [OH] > [BF3]. A linear relationship was observed when the number average molecular weight was plotted against [oxetane] at constant [BF3:0H], and similarly a linear dependency was observed on the BF3:0H 1:1 adduct at constant oxetane concentration. Copolymerization of oxetane and THF was carried out using BF30Et2/ethanol system. The reactivity ratios were calculated as rOXT = 1.2 ± 0.30 and rTHF = 0.14 ± 0.03. These copolymers were random copolymers with no evidence of oligomer formation. The coordinated anionic catalyst, porphinato-aluminium chloride [(TPP)AICl], was used to produce a living polymerization of oxetane. An overall third-order kinetics was obtained, with a second-order with respect to the [(TPP)AICl] and a first-order with respect to the [oxetane] and a mechanism was postulated using these results. The stereochemistry of [(TPP)AlCl] catalyst was investigated using cyclohexene and cyclopentene oxide monomers, using extensive 1H NMR, 2-D COSY and decoupling NMR techniques it was concluded that [(TPP)AlCl] gave rise to stereoregular polymers.

Synthesis and characterization of diblock copolymer of butadiene and 2-ethyl-2-oxazoline

By mechanism-transformation (anionic --> cationic) polymerization, diblock copolymer of butadiene and 2-ethyl-2-oxazoline (PBd-b-PEOx) was synthesized in two steps. The first step is the polymerization of butadiene block capped with ethylene oxide and its tosylation; the second step is the cationic ring-opening polymerization of 2-ethyl-2-oxazoline. The products were characterized by various methods, such as IR, (HNMR)-H-1, DMA, TEM and SAXS. The results show that the obtained copolymers possess high molecular weight and narrow molecular weighs distribution, and that the content of 1,4-structure was controllable.

Caracterização e transformação de Lenhosulfonatos de Eucalyptus globulus

Os lenhosulfonatos representam um sub-produto formado durante o cozimento ao sulfito ácido, sendo queimados para a regeneração da base e recuperação de energia. No entanto, os lenhosulfonatos são também considerados uma importante matéria-prima para a produção de vários produtos de valor acrescentado. Os objectivos principais deste trabalho foram contribuir para uma melhor compreensão sobre a caracterização química e estrutural dos lenhosulfonatos do Eucalyptus globulus, assim como, para complementar a informação disponível sobre a síntese e a caracterização estrutural e térmica de materiais poliméricos obtidos a partir de compostos modelo dos produtos de oxidação dos lenhosulfonatos. O licor de cozimento ao sulfito foi analisado em termos do teor de cinzas, extractáveis, compostos voláteis, açúcares e lenhosulfonatos. O teor de cinzas e açúcares no licor de cozimento é muito elevado, tendo sido necessário purificar o mesmo (2,8-13,8 % e 3,2-9,1 %, respectivamente). A análise dos açúcares mostrou uma quantidade considerável de pentoses, sendo o açúcar predominante a xilose. Os lenhosulfonatos foram purificados, isolados e caracterizados por química molhada (titulação potenciométrica e oxidação com permanganato), análise elementar, espectroscopia de ultravioleta/visível (UV/Vis), espectroscopia de infravermelho de transformada de Fourier (FTIR), espectroscopia de ressonância magnética nuclear de protão (RMN de 1H) e carbono (RMN de 13C), espectrometria de massa de ionização por electrospray (ESI-MS), cromatografia de permeação em gel (GPC), termogavimetria (TGA) e calorimetria diferencial de varrimento (DSC). Os lenhosulfonatos são constituídos principalmente por unidades S, são parcialmente sulfonados e possuem um peso molecular relativamente baixo (Mw = 1250-2400 Da). A ruptura das ligações β-O-4 e α-O-4 da lenhina do Eucalyptus globulus após cozimento ao sulfito ácido originam olígomeros de baixo peso molecular cuja estrutura foi elucidada por RMN 1D/2D e ESI-MS. A degradação térmica dos lenhosulfonatos apresentou dois máximos de degradação a 188-190ºC e a 315-380ºC. As curvas de DSC mostraram um pico endotérmico para temperaturas inferiores a 130ºC e um pico exotérmico a 300-500ºC. Os lenhosulfonatos foram despolimerizados na presença de oxigénio molecular em meio alcalino. Os produtos de oxidação principais foram o aldeído siríngico, a vanilina, o ácido vanílico e o ácido siríngico. A adição do catalisador (sal de cobre) promoveu a oxidação dos lenhosulfonatos aumentando o rendimento dos aldeídos aromáticos (< 50%). A presença de açúcares nos lenhosulfonatos teve um efeito negativo no rendimento dos produtos de oxidação principais. Alguns compostos modelo dos produtos de oxidação dos lenhosulfonatos foram polimerizados por poliadição (catiónica e radicalar) e policondensação. Os monómeros e os polímeros foram caracterizados por espectroscopia de infravermelho de transformada de Fourier e reflectância total atenuada (FTIR-ATR), RMN em solução e no estado sólido, UV/Vis no estado sólido, GPC, difracção de raios-X (XRD), TGA e DSC. Os compostos modelo estudados foram os estirenos metoxi-substituídos (p-metoxiestireno e 3,4-dimetoxiestireno) e os ácidos hidroxi aromáticos metoxi-substituídos (ácido vanílico e ácido siríngico). O 3,4-dimetoxiestireno foi ainda copolimerizado com o éter isobutil vinílico e os seus copolímeros foram desmetilados, assim como, o poli(p-metoxiestireno) e o poli(3,4-dimetoxiestireno). A polimerização catiónica do p-metoxiestireno e 3,4-dimetoxiestireno é mais rápida e mais completa do que a polimerização radicalar produzindo polímeros com pesos moleculares elevados. O poli(p-metoxiestireno) (Mw = 235000 Da) possui um peso molecular maior do que o poli(3,4-dimetoxiestireno) (Mw = 18800 Da). A estabilidade térmica e a temperatura de transição vítrea diminuiram com a presença do segundo grupo metoxilo. A desmetilação dos homopolímeros foi bem sucedida, tendo sido corroborada por FTIR-ATR e RMN. A policondensação do ácido siríngico foi dificultada pela presença do segundo grupo metoxilo, tendo sido necessário adicionar uma maior quantidade do agente de condensação devido a factores estéricos. O poli(ácido vanílico) e poli(ácido siríngico) são insolúveis na maior parte dos solventes orgânicos, sendo parcialmente solúveis em clorofórmio, ácido triflúoracético, 1,1,2,2- tetracloroetano, dimetilsulfóxido, tetrahidrofurano, N,N’-dimetilformamida e 1,1,1,3,3,3-hexaflúor-2-propanol. A estabilidade térmica diminuiu com a presença do segundo grupo metoxilo e os dois polímeros não exibiram temperatura de transição vítrea. O poli(ácido vanílico) e poli(ácido siríngico) apresentaram uma estrutura muito cristalina (grau de cristalinidade 70% e 50%, respectivamente). O segundo grupo metoxilo aumentou o valor da absorvância, mas a forma do espectro de UV/Vis foi similar. A polimerização catiónica do éter isobutil vinílico resultou na produção de um polímero muito viscoso com peso molecular elevado (Mw = 20400 Da). A degradação térmica do polímero ocorreu em várias gamas de temperatura e foi completa (0% de resíduo a 800ºC). A copolimerização catiónica do 3,4-dimetoxiestireno com o éter isobutil vinílico foi realizada com proporções diferentes 80:20, 50:50 e 20:80. Os copolímeros apresentaram uma viscosidade elevada e um peso molecular baixo (Mw = 2000-4000 Da) que aumentou com a quantidade de éter isobutil vinílico. A degradação térmica dos copolímeros ocorreu também em várias gamas de temperatura, sendo a sua degradação completa (0,9-1,5% de resíduo a 800ºC). A desmetilação dos copolímeros não foi bem sucedida, tendo sido confirmada por FTIR-ATR e RMN.

Noves aproximacions a la síntesi i caracterització de poliglicols al·lílics, polihidrosiloxans i surfactants copolimèrics. Avaluació d'aquests surfactants en formulacions de poliuretà

Els polímers són una sèrie de compostos que troben un ampli ventall d'aplicacions en la indústria actual. Un exemple són les espumes de poliuretà, estructures de tipus cel·lular obtingudes mitjançant la reacció química entre compostos de tipus isocianat i compostos de tipus poliol (polièters amb diferent nombre de grups hidroxil). És imprescindible l'ús d'additius d'estructura tensioactiva (surfactants de silicona) per estabilitzar el procés d'espumació i per proporcionar una estructura cel·lular ordenada i homogènia en mida i distribució. La síntesis i caracterització de les molècules precursores (polihidrosiloxans i polièters al·lílics), l'estudi de la reacció d'hidrosililació com a via d'obtenció dels diferents surfactants per reacció d'addició entre els polihidrosiloxans i els polièters al·lílics i la caracterització i avaluació en formulacions comercials de poliuretà dels surfactants sintetitzats han constituït els objectius del present treball. MEMÒRIA La Tesi Doctoral ha estat presentada seguint el següent esquema: CAPÍTOL I. INTRODUCCIÓ A LA QUÍMICA DEL POLIURETÀ. Es presenten els principis de la química del poliuretà, fent esment dels recents avenços en la síntesis i caracterització d'aquests compostos polimèrics, així com un apartat concret centrat en els surfactants de silicona. Es presenten les estructures habituals d'aquests compostos comercials i es detallen les reaccions de síntesi i les característiques físiques que aquests compostos proporcionen a les espumes de poliuretà. CAPÍTOL II. OBJECTIUS. 1.- Síntesis y caracterització d'una àmplia gamma de poliglicols al·lílics i de polihidrosiloxans amb grups hidrur reactius, ambdós precursors d'estructures polimèriques de tipus surfactant. 2.- Estudi de la reacció d'hidrosililació com a via de formació d'enllaços Si-C no hidrolitzables, mitjançant la reacció d'addició entre els substrats al·lílics insaturats i els polisiloxans amb grups hidrur reactius. 3.- Caracterització de les estructures polimèriques de tipus surfactant sintetitzades i avaluació d'aquestes en formulacions de poliuretà, a fi de relacionar l'estructura química d'aquests oligómers amb els efectes físics que originen en l'espuma de poliuretà. CAPÍTOL III. SÍNTESI I CARACTERITZACIÓ DE SUBSTRATS AL·LÍLICS INSATURATS DE TIPUS POLIGLICOL. S'han caracteritzat per HPLC-UV una sèrie de polietilenglicols comercials. S'ha estudiat la reacció de derivatització al·lílica sobre els grups hidroxil dels polièters comercials (PEG, PPG i copolímers PEG-PPG) i s'han caracteritzat exhaustivament els productes sintetitzats (1H,13C-RMN, GC, GC-MS, FTIR, ESI-MS, HPLC-UV). S'ha iniciat un estudi de polimerització aniònica sobre nous epòxids amb un punt de diversitat molecular, sintetitzant-se i caracteritzant-se els corresponents nous polièters obtinguts. CAPÍTOL IV. SÍNTESI I CARACTERITZACIÓ DE POLIHIDROSILOXANS REACTIUS. S'estudia la síntesis de polihidrosiloxans amb grups hidrur reactius, mitjançant la reacció de polimerització aniònica d'obertura d'anell ("AROP, anionic ring opening polimerization") i mitjançant la reacció de polimerització per equilibració catiònica. Es presenta una caracterització exhaustiva dels productes sintetitzats i es descriu la naturalesa de la microestructura polimèrica a partir de la distribució bivariant dels copolímers PDMS-co-PHMS (poli(dimetilsiloxà)-co-poli(hidrometilsiloxà)). CAPÍTOL V. ESTUDI SISTEMÀTIC DE LA REACCIÓ D'HIDROSILILACIÓ. S'ha estudiat la reacció d'hidrosililació amb la finalitat de sintetitzar estructures copolimèriques poliglicol-polisiloxà a partir de la reacció de polisiloxans hidrur reactius i polièters al·lílics. S'han provat diferents catalitzadors (Pt/C 5%, cat. de Speier i cat. de Karstedt), s'han sintetitzat diferents estructures tensoactives (lineals i ramificades) i s'ha modelitzat les diferents reaccions secundàries observades, per presentar un estudi mecanístic de la reacció d'hidrosililació aplicada a la síntesis de molècules d'elevat PM a partir de la reacció entre substrats al·lílics insaturats i polihidrosiloxans. CAPÍTOL VI. AVALUACIÓ DELS SURFACTANTS EN FORMULACIONS DE POLIURETÀ. S'ha estudiat la idoneïtat dels surfactants de silicona sintetitzats en diferents formulacions de poliuretà comercials. S'ha relacionat el comportament físic d'aquests surfactants en les espumes de poliuretà amb la seva estructura química a partir de l'anàlisi per microscòpia electrònica de rastreig. CAPÍTOL VII. CONCLUSIONS. S'han esposat les conclusions extretes de cada capítol.

In situ photopolymerization of a gel ionic liquid electrolyte in the presence of iodine and its use in dye sensitized solar cells

We report for the first time an in situ photopolymerization of model co-monomers, 2-hydroxyethyl methacrylate (HEMA) and tetra (ethylene glycol) diacrylate (TEGDA), in an IL electrolyte containing I₂ for DSSCs. TiO₂ nanoparticles were used as the photo-initiator and co-gelator in a charge transfer polymerization reaction. The gel-IL polymer obtained was characterized in terms of the diffusion properties of the electrolyte. Preliminary results from DSSCs assembled using the gel-IL electrolyte showed energy conversion efficiency of 3.9% at 1 sun (AM1.5) and 5.0% at 0.39 sun illumination.

Ceramic Crucible Corrosion by Heavy Metal Oxide Glasses, Part I: Phenomenological Study

Heavy metal oxide (HMO) glasses have received special attention due to their optical, electrical and magnetic properties. The problem with these glasses is their corrosive nature. In this work, three ceramic crucibles (Al 2O 3, SnO 2 and ZrO 2) were tested in the melting of the system 40 PbO-35 BiO 1.5-25 GaO 1.5 (cation-%). After glass melting, crucibles were transversally cut and analyzed by scanning electronic microscopy (SEM), coupled to microanalysis by energy dispersive spectroscopy (EDS). Results indicated that zirconia crucibles presented the highest corrosion, probably due to its smallest grain size. Tin oxide crucibles presented a low corrosion with small penetration of the glass into the crucible. This way, these crucibles are an interesting alternative to melt corrosive glasses in instead of gold or platinum crucibles. It is important to emphasize the lower cost of tin oxide crucibles, compared to gold or platinum ones.

Electrooptic proprieties of layer-by-layer films of a azobenzene containing copolymer

The methacrylic copolymer functionalized with the azo chromophore 4-[N-ethyl-N-(2-hydroxiethyl)]-amino-2′-chloro-4-nitroazobenzene (MMADR13), in its polyelectrolyte form, can be used to fabricate thin films by the layer-by-layer (LbL) technique just if one alternates this anionic polyelectrolyte with a cationic polyelectrolyte such as poly(allylamine hydrochloride) (PAH). Since PAH does not present any particular optical functionality, the main final film feature will came from the side chain DR13 azo-chromophore group due to its large nonlinear optical properties and photoisomerization capabilities. This work reports the electrooptic activity of MMADR13/DR13 LBL films, which arises from the high hiperpolarizability about the azo side chain group.