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The synthesis and characterization of step-growth polymers with novel monomers provided materials with tailored properties for emerging technologies. Specifically, multiphase materials (i.e., microphase separated block copolymers) exploit the synergistic relationship of combining polymers with disparate thermal and mechanical properties. The introduction of intramolecular interactions such as hydrogen and ionic bonding into these polymers further tailored their properties for applications including elastomers, electromechanical transducers, and additive manufacturing (AM). A review of recent literature revealed the material properties required for polymeric materials in electromechanical transducers, which aided in the design of polymers for this application. An isocyanate-, catalyst-, and solvent-free approach facilitated the synthesis of segmented polyureas with tunable thermal and mechanical properties. These materials found use as high dielectric elastomers and water-soluble polymers for extrusion-based AM dependent on the backbone composition. Vat photopolymerization (VP) AM served as a technique to 3D printed novel unsaturated polyester resins (UPR). Incorporating a phosphonium ionic liquid as a reactive diluent replaced styrene and reduced the volatility of commonly used UPRs. VP successfully provided 3D structures from these UPRs that demonstrated limited ionic conductivities. An extensive review of the literature surrounding the structure-property relationships of charged block copolymers with varying architectures helped to inform the synthesis of novel, cationic step-growth polymers. The synthesis of a new phosphonium IL facilitated the synthesis of a segmented polyurethane containing a phosphonium-functionalized soft segment for the first time. This phosphonium polyurethane exhibited ionic conductivities comparable to literature examples of block copolymers used for ionic polymer transducers, which suggests that these materials may serve for this application as well. Carbonyldiimidazole provides a novel route towards synthesizing imidazolium ionenes with unique backbone structures. The coupling of poly(ethylene glycol) dibromides with a bis-carbonylimidazole monomer and a commercial aliphatic dibromide led to the formation of segmented imidazolium ionenes. These polymers exhibited significant atmospheric water uptake as well as water solubility. However, the physical properties of the materials suggested that the synthetic procedure resulted in low molecular weights. Suggested future work provides methods for circumventing this issue and proposes next steps for all the projects discussed herein. / Doctor of Philosophy / Emerging technologies require new polymeric materials with intentionally designed properties. Step-growth polymers such as polyesters, polyurethanes, and polyureas find use in many applications of our everyday lives. Although these materials have served mainly as commodity plastics historically, a reimagining of their syntheses and chemical structures makes them accessible for modern technologies. For example, applying green chemistry principles to the synthesis of polyureas resulted in a less toxic synthetic procedure. Polyureas synthesized through this method exhibited elastic properties comparable to classical polyureas and displayed high dielectric constants, which lend them towards use in dielectric elastomer actuators. This chemistry also allowed for the synthesis of water-soluble polyureas, which served as a material for low temperature extrusion additive manufacturing, colloquially known as 3D printing. Vat photopolymerization describes another type of 3D printing that involves the selective curing of liquid resins with light to form a 3D structure. Employing a reactive ionic liquid monomer with a commercially-relevant unsaturated polyester allowed for a nontoxic method of printing these materials, which also imparted ionic conductivity. Finally, the synthesis of positively charged polyurethanes and ionenes led to the production of ionically conductive materials that may find use in polymeric transducers.

Segmented copolymers are important polymers with attractive properties and wide applications. In this dissertation, segmented polyurethanes containing triptycene units and multiblock copolymers containing poly(arylene ether sulfone) (PAES) and poly(1,4-cyclohexyldimethylene terephthalate) (PCT) segments were synthesized and systematically studied. Investigation of the influence of the bulky triptycene structure on the morphologies and properties of segmented polyurethanes was carried out by using triptycene-1,4-hydroquinone bis(2-hydroxyethyl)ether (TD) as the chain extender. Segmented polyurethanes based on poly(tetramethylene glycol) (PTMG) of 1000 g/mol were synthesized using a two-step polymerization procedure. Hydroquinone bis(2-hydroxyethyl)ether (HQEE) was used for the purpose of comparison. Hard segments with different bulkiness and flexibility were prepared with hexamethylene diisocyanate (HDI) and 4,4'-methylenebis(phenyl isocyanate) (MDI), and HQEE or TD as chain extenders. The incorporation of bulky TD and less flexible MDI significantly inhibited hydrogen bonding based on the Fourier transform infrared (FTIR) results. In addition, the microphase separation was also disturbed by the bulky and less flexible hard segments with confirmation from tapping mode atomic force microscopy (AFM) and small angle X-ray scattering (SAXS). The flexible HDI can be used to overcome the bulkiness of triptycene, promote microphase separation, and enhance mechanical properties. Novel PTMG based soft segments containing triptycene units were also prepared with number average molecular weight (Mn) around 2500 g/mol. Then this soft segment was reacted with MDI and HQEE to prepare segmented polyurethanes. Soft segments such as hydroquinone (HQ) containing PTMG (Mn = 2100 g/mol), and pure PTMGs (Mn = 1000 and 2000 g/mol) were used for comparison. Differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) results demonstrated that triptycene units led to an increased glass transition temperature (Tg) and an elimination of the crystallization of the soft segments. The absence of strain hardening for the triptycene-containing sample suggested a suppressed strain induced crystallization of soft segments, which was also confirmed by the analysis of wide-angle X-ray diffraction (WAXD) on the films strained to 370 %. Crystallizable PCT segments were copolymerized with PAESs to enhance solvent resistance and mechanical properties. PAES oligomers (Mn = 2000 g/mol) were first synthesized, and then reacted with dimethyl terephthalate (DMT) and 1,4-cyclohexanedimethanol (CHDM). Weight percentages of PCT segments were gradually changed from 20 wt% to 80 wt%. With PCT content greater than 50 wt%, crystallinity was observed by DSC, DMA, and WAXD. The extent of crystallinity of the copolymers was dependent on the wt% of PCT. Furthermore, crystallization behavior of copolymers based on two CHDMs with different isomer ratios (cis/trans 30/70 and all trans) were studied. Due to their more symmetric structure, copolymers based on all trans CHDM exhibited a higher extent of crystallization. / Ph. D.

Considerações ambientais têm aumentado a pesquisa e o desenvolvimento de sistemas poliméricos aquosos para diversos tipos de aplicações, principalmente como revestimentos. Nesta dissertação, foram sintetizadas formulações não-poluentes à base de poliuretanos dispersos em água (PUDs), com 40% de teor de sólidos, na ausência de solventes orgânicos. Os monômeros empregados foram copolímeros em bloco à base de poli(glicol etilênico) e poli(glicol propilênico) (EG-b-PG), com teor de 25% de segmento hidrofílico EG, poli (glicol propilênico) (PPG), ácido dimetilolpropiônico (DMPA), diisocianato de isoforona (IPDI) e hidrazina (HYD), como extensor de cadeia. Foram variadas as razões entre o número de equivalente-grama de grupamentos isocianato e hidroxila (NCO/OH) e a proporção em equivalente-grama de PPG e dos copolímeros em bloco (EG-b-PG). Foi observado que a incorporação de altas quantidades de copolímero dificultou a síntese dos poliuretanos dispersos em água, levando à formação de géis. O tamanho médio de partícula e a viscosidade das dispersões foram determinados. Os filmes vazados a partir dessas dispersões foram avaliados quanto à capacidade de absorção de água, resistência mecânica, termogravimetria (TG), e caracterizados por espectroscopia na região do infravermelho (FTIR). As dispersões poliuretânicas produzidas se mostraram satisfatórias quando aplicadas como revestimento para madeira, metais e vidro / Environmental considerations are increasing the research and development of waterborne polymeric systems for many different applications, particularly as coatings. In this dissertation, non-polluting formulations based on waterborne polyurethanes (WPU), with 40% solids content, were synthesized in the absence of organic solvents. The monomers (polyols) employed were block copolymers of ethylene glycol and propylene glycol (EG-b-PG), with 25% of EG hydrophilic segments, poly(propylene glycol) (PPG), dimethylolpropionic acid (DMPA), isophorone diisocyanate (IPDI) and hydrazine (HYD), as chain extender. The ratio between the number of equivalent-grams of isocyanate and hydroxyl groups (NCO/OH) and the ratio between the equivalent-grams of PPG and (EG-b-PG) were varied. It was observed that the incorporation of high quantities of the copolymer resulted in gels instead of dispersions. The average particle size and the viscosity of the resins were determined. Thermal and mechanical resistances and water absorption of cast films produced from the dispersions were evaluated. The chemical structure of the chains was characterized by infrared spectroscopy (FTIR). The waterborne polyurethanes showed to be suitable as coatings for wood, metals and glass

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Neste trabalho foram sintetizados nanocompósitos à base de poliuretanos em dispersão aquosa (NWPUs) e argilas hidrofílicas do tipo montimorilonita (MMT) de natureza sódica e cálcica. Os monômeros empregados na síntese foram: poli(glicol propilênico) (PPG); copolímero em bloco à base de poli(glicol etilênico) e poli(glicol propilênico) (EG-b-PG), com teor de 7% de EG; ácido dimetilolpropiônico (DMPA) e diisocianato de isoforona (IPDI). Os NWPUs tiveram as argilas, previamente deslaminadas em água e incorporadas à formulação no momento da dispersão do prepolímero. Dispersões aquosas (WPUs), sem a presença de argila, foram sintetizadas como base, nas quais foram variadas a razão NCO/OH e a proporção de copolímero em relação ao PPG. Nas formulações NWPUs, foram variados também o teor de argila em relação à massa de prepolímero e o tipo de argila sódica e cálcica. As dispersões foram avaliadas, quanto ao teor de sólidos totais, tamanho médio de partícula e viscosidade. Os filmes vazados a partir das dispersões foram caracterizados por espectrometria na região do infravermelho (FTIR), difração de raios-x (XRD) e microscopia eletrônica de varredura (SEM). A resistência térmica dos filmes foi determinada por termogravimetria (TG) e a resistência mecânica dos filmes foi avaliada por ensaios mecânicos em dinamômetro. O grau de absorção de água dos filmes também foi determinado. A formação de nanocompósitos à base de água foi confirmada pela ausência do pico de XRD, característico das argilas empregadas na maioria dos filmes analisados. As micrografias obtidas por SEM confirmam uma dispersão homogênea das argilas na matriz poliuretânica. Os filmes à base de nanocompósitos (NWPUs) apresentaram propriedades superiores às apresentadas por aqueles obtidos a partir das dispersões sem argilas (WPUs). Os revestimentos formados a partir da aplicação das dispersões aderiram à maioria dos substratos testados (metal, vidro, madeira e papel) formando superfícies homogêneas / In this work nanocomposites (NWPUs) based on waterborne polyurethanes and hydrophilic montimorillonite clays (MMT) were synthesized. Polypropyleneglycol (PPG), poly(ethylene glycol-b-propylene glycol) (EG-b-PG) containing 7% of ethylene glycol (EG), dimethylolpropionic acid (DMPA) and isophorone diisocyanate (IPDI) were employed in polyurethane synthesis. The NWPUs were prepared with calys previously exfoliated in water, and were added at the moment of dispersion. Different formulations were obtained from WPUs, without clays, by varying the NCO/OH ratio, and the proportions of PPG and EG-b-PG. For NWPUs formation was varied the content of clays with different cations (Na+ and Ca+2). The properties of the dispersions were evaluated in terms of their solid content, particle size and viscosity. The cast films obtained were characterized by infrared spectrometry (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM). The thermal stability of the films was evaluated by thermogravimetry (TG) and mechanical properties in a dynamometry. X-ray diffraction and scanning electron microscopy examinations were determined confirming the nanocomposite formation. NWPUs films showed improved properties in comparison with WPUs Coatings obtained by the application of the dispersions in substrates as wood, metals, paper and glass were homogeneous and showed good adherence

<p>U ovoj doktorskoj disertaciji je ispitan uticaj montmorilonita i<br />termoplastičnih segmentiranih poliuretana na kinetiku reakcija<br />umrežavanja, strukturu i svojstva funkcionalnih hibridnih<br />materijala na osnovu epoksidnih smola. Pripremljene su dve<br />serije uzoraka hibridnih materijala: prva na osnovu epoksidne<br />smole sa različitim sadržajem organski modifikovanog<br />montmorilonita (0, 1, 3, 5 i 10 mas.%) umrežene sa<br />umreživačem Jeffamine D-230; druga serija je sintetisana na<br />osnovu epoksidne smole, sa različitim sadržajem (10, 15 i 20<br />mas.%) termoplastičnog poliuretanskog elastomera sa<br />različitim sadržajem tvrdih segmenata (20, 25 i 30 mas.%)<br />sintetisanih na osnovu alifatičnog polikarbonatnog diola i<br />heksametilendiizocijanata i produživača lanca butandiola, kao<br />i katalizatora dibutiltin dilaurata; kao i bez dodatog elastomera<br />umrežene sa diaminom Jeffamine D-2000. Umrežavanje<br />reaktivnih sistema sa projektovanim sirovinskim sastavom je<br />praćeno diferencijalnom skenirajućom kalorimetrijom (DSC).<br />Modeli izokonverzije primenjeni su da se ustanovi da li<br />dodatak punila utiče na reakciju umrežavanja hibridnih<br />materijala. Sintetisani materijali su analizirani dinamičkomehaničkom<br />analizom (DMA), mikroskopijom atomskih sila<br />(AFM), kao i TG-DSC i TG-MS metodama i određena su<br />mehanička svojstva (zatezna čvrstoća, prekidno izduženje i<br />tvrdoća po &Scaron;oru A). Epoksidni materijal sa 10 mas.% organski<br />modifikovanog montmorilonita ima značajno niže vrednosti<br />energija aktivacije za definisane stepene reagovanja, čime je<br />potvrđen katalitički efekat gline sa slojevitom strukturom kada<br />je prisutna u reakcionoj sme&scaron;i u dovoljnoj količini. Uticaj<br />otežane difuzije pri kraju reakcije je izraženiji u prisustvu<br />montmorilonita, čime je pokazano da njegovo prisustvo utiče<br />na ceo mehanizam umrežavanja. Utvrđeno je da na vrednosti<br />G&#39;, pored udela montmorilonita, utiče i stepen dispergovanja<br />čestica unutar polimerne matrice. Zaključeno je da dodatak<br />punila do 3 mas. % utiče povoljno na ispitana mehanička<br />svojstva, dok pri sadržaju od 5 i 10 mas. % dolazi do<br />aglomeracije čestica punila, &scaron;to negativno utiče na ispitana<br />svojstva, osim tvrdoće, koja se povećava linearno sa dodatkom<br />punila montmorilonita. Na osnovu rezultata TG analize<br />zaključeno je da je sa porastom udela montmorilonita u<br />epoksidnoj matrici termička stabilnost uzoraka ispitivanih u<br />atmosferi vazduha neznatno pobolj&scaron;ana, dok u inertnoj<br />atmosferi nema uticaja na termičku stabilnost, niti na<br />mehanizam raspada hibridnih materijala na osnovu epoksidnih<br />smola sa različitim udelima montmorilonita. Kod sistema kod<br />kojih je dodavan termoplastični poliuretanski elastomer,<br />zaključeno je da pri većem sadržaju segmentiranih poliuretana<br />u epoksidnoj matrici (10 i 15 mas.%) proces umrežavanja<br />započinje na nižim temperaturama i maksimalna brzina se<br />ostvaruje na nižim temperaturama, a najveća vrednost<br />promena ukupne entalpije reakcije umrežavanja je određena za<br />hibridni materijal sa poliuretanom koji u svojoj strukturi ima<br />30 mas.% tvrdih segmenata. Zatezna čvrstoća hibridnih<br />materijala raste sa porastom udela tvrdih segmenata u strukturi<br />poliuretana, kao i sa porastom masenog udela poliuretanskog<br />elastomera u epoksidnoj matrici. Dodatkom termoplastičnih<br />segmentiranih poliuretana značajno je povećano prekidno<br />izduženje epoksidnih smola. Sa porastom udela tvrdih<br />segmenata kod poliuretana dodatih u istom masenom procentu<br />u epoksidnu matricu, tvrdoća raste. Ustanovljeno je da na<br />konačna svojstva hibridnih materijala utiče izbor polaznih<br />komponenti, način ume&scaron;avanja punila u matricu i uslovi pri<br />kojima se vr&scaron;i umrežavanje. Zaključeno je da je dobro<br />poznavanje kinetičkih parametara reakcije umrežavanja važno<br />za pravilan odabir optimalnih uslova za proizvodnju i preradu<br />hibridnih materijala u industrijskim uslovima.</p> / <p>In this thesis the influence of clay fillers and thermoplastic<br />segmented polyurethanes on the curing kinetics, structure and<br />properties of functional hybrid materials based on epoxy resins<br />was assessed. Two sets of hybrid material samples were<br />prepared. First type of samples was based on epoxy resin with<br />a different content of organically modified montmorillonite (0,<br />1, 3, 5 and 10 wt. %) and crosslinking with hardener Jeffamine<br />D-230. Second type of samples was based on epoxy resin,<br />having different content (10, 15 and 20 wt. %) of thermoplastic<br />segmented polyurethane with different content of hard<br />segments (20, 25 and 30 wt. %) based on aliphatic<br />polycarbonate macrodiols and hexamethylene diisocyanate,<br />with chain extender 1,4-butanediol and the catalyst, dibutyltin<br />dilaurate, and also a sample without added elastomeric<br />polyurethane and crosslinking with hardener Jeffamine D-<br />2000. The curing of the hybrid materials based on epoxy resins<br />systems were investigated by non-isothermal differential<br />scanning calorimetry (DSC). The kinetic study by<br />isoconversion models has been carried out using data from<br />DSC. The synthesized materials were analyzed by dynamicmechanical<br />analysis (DMA), atomic force microscopy (AFM)<br />as well as TG-DSC and TG-MS methods and mechanical<br />properties (tensile strength, elongation and hardness at Shore<br />A) were determined. Epoxy based hybrid material with 10 wt.<br />% of the organically modified montmorillonite has<br />significantly lower activation energy values for the defined<br />reaction rates, thereby confirming the catalytic effect of the<br />clay with the layered structure when present in the reaction<br />mixture in sufficient quantity. The diffusion effects at the end<br />of the reaction are more pronounced in the presence of<br />montmorillonite, which indicates that its presence affects the<br />entire curing mechanism. It was found that G&#39;, along with<br />montmorillonite content, is affected by the degree of particle<br />dispersion inside the polymer matrix. It was concluded that the<br />addition of montmorillonite up to 3 wt. % improves<br />investigated mechanical properties, while the samples with 5<br />and 10 wt. % of montmorillonite resulted in agglomeration of<br />the filler particles, which negatively influenced the<br />investigated properties, except for the hardness which<br />increases linearly with the addition of montmorillonite. TG<br />analysis shows that the increase of montmorillonite content in<br />the epoxy matrix slightly improves the thermal stability in the<br />air, while in the inert atmosphere there is no influence on the<br />thermal stability nor on the mechanism of the decomposition<br />of epoxy based hybrid materials. In the system with a<br />thermoplastic polyurethane filler, it was concluded that hybrid<br />materials with a higher content of segmented polyurethane (10<br />and 15 wt. %), curing process starts at lower temperatures and<br />the maximum speed is achieved at lower temperatures and the<br />highest value of changes in total enthalpy of the crosslinking<br />reaction is determined for the epoxy hybrid material with<br />polyurethanes containing 30 wt. % of hard segments. Tensile<br />strength of hybrid materials increases with the increase of hard<br />segments content in the polyurethane elastomer as well as with<br />the increase of polyurethane content in the epoxy matrix. The<br />addition of thermoplastic segmented polyurethanes<br />significantly increased the elongation at break of prepared<br />epoxy resins hybrid materials. The increase of the hard<br />segments content in polyurethane, in the same ratio, improves<br />hardness of epoxy based hybrid material. It was concluded that<br />the final properties of hybrid materials are influenced by the<br />selection of initial compounds, methods of processing and the<br />curing conditions. It was concluded, as well that knowing the<br />kinetic parameters of curing reaction is important for the<br />proper selection of optimal parameters for production and<br />processing of hybrid materials in industrial conditions.</p>

In this work, hyperbranched aromatic polyesters-polyphenols based on 4,4-bis(4’ hydroxy¬phenyl)pentanoic acid (BHPPA) were prepared and, according to the authors knowledge, for the first time tested as precursors for polyurethane bulk resins and coatings. Comparison of poly-BHPPA with competing products The materials prepared in this work show better properties than their aliphatic polyester-polyol analoga based on 2,2-bis-(hydroxymethyl)propanoic acid (BHMPA). Especially, the solubility of poly-BHPPA in organic solvents is better and poly-BHPPAs also do not tend to microphase separation during their reaction with isocyanates, in contrast to poly-BHMPAs. The poly-BHPPA and the polyurethane networks made from them display higher Tg values than analogous poly- BHMPA compounds. Because of the high Tg of the reacting and final systems, curing must occur at elevated temperatures (90°C) in order to avoid undercure. The lower reactivity of phenolic OH groups prevents the reaction from being too fast at that temperature. A drawback of the polyurethanes based on the aromatic polyesters-polyols prepared is the lower thermal stability of their urethane bonds, if compared to aliphatic urethanes. An interesting possibility for future investigations would be the modification of the BHPPA monomer in order to change the OH functionality from phenolic to aliphatic OH, e.g. by replacement of the phenolic OH by hydroxymethyl or hydroxyethyl groups (requires a strong modification of the monomer synthesis) or simpler by reacting the phenolic OH of BHPPA with a suitable reagent like oxirane, which would lead to groups like O-CH2-CH2-OH in the place of the phenolic OH. Such a BHPPA modification should in turn yield modified “poly-BHPPA” polycondensates, which would combine the advantages of poly-BHPPA with those of aliphatic OH precursors of polyurethanes. Poly-BHPPA synthesis Hyperbranched polymers of the 4,4-bis-(4’-hydroxyphenyl)pentanoic acid (BHPPA) were synthesized successfully by the catalyzed (by dibutyltin diacetate) polycondensation of BHPPA. The products obtained were oligomers with number average molecular weight ranging from 1800 to 3400 g/mol (polymerization degree of ca. 6 to 12), displaying a first moment of functionality in the range 7 to 14. Such products were good OH precursors for the preparation of polyurethane coatings, because higher functional polymers would gel at low conversions. The analysis of the functional groups (determination of acid and hydroxyl numbers) and the 1H-NMR and the 13C-NMR spectroscopy were found to be good methods for the determination of molecular weights. The polydispersity of the poly-BHPPA products was in the range 3.5 to 6. Their degree of branching was found to be in the range 0.36 to 0.47. Poly-BHPPA containing aliphatic polyols as core monomers were also prepared successfully. Difunctional and trifunctional core monomers usually reached a full conversion of their OH groups, while the tetra- and hexafunctional core monomers were converted only to 89%. In all these products however, a considerable amount, usually even a majority, of the polymer molecules were core free. The poly-BHPPA products prepared displayed relatively high glass transition temperatures, in the range of 84°C to 114°C, obviously due to interactions between the phenol groups and to hydrogen bridging. The thermal stability of these products was also high, with decomposition occurring near 350°C (at a heating rate of 10°C / min) Kinetics investigations of the poly-BHPPA reactivity towards isocyanates The poly-BHPPA are polyphenols and were expectedly found to react significantly slower with isocyanates than aliphatic alcohols. The reactivity of poly BHPPA was also found to be somewhat lower than that of the monofunctional, low molar-mass 4 ethylphenol. Hexamethylene diisocyanate trimer, Desmodur N3300, was found to be more reactive than hexamethylene diisocyanate (HDI) or butyl isocyanate in all experiments, possibly due to a substitution effect. The substitution effect can be explained by a change of microenvironment caused by conversion of isocyanate group and OH group into urethane groups. The reactions of low-molecular-mass alcohols or phenols with low molecular weight isocyanates followed well the 2nd order kinetics, while the reactions of poly-BHPPA with isocyanates show deviations from ideal 2nd order kinetics at higher conversions. All the kinetics experiments were carried out under catalysis by dibutyltin dilaurate. This catalyst inhibits the undesired reaction of isocyanate groups with moisture. It was also found that the catalysis was necessary to reach reasonable curing times for poly-BHPPA based polyurethane networks. The uncatalyzed systems reacted extremely slowly. Preparation of polyurethane networks from poly-BHPPA The poly BHPPA products prepared were used successfully as OH functional precursors of polyurethane networks. The networks prepared contained only very low sol fractions. Acetone and also ethylene diglycol dimethylether (diglyme) were found to be good swelling solvents for the networks prepared, while methyl propyl ketone was a much poorer solvent and aromatic compounds like toluene or xylene practically did not swell the poly BHPPA based polyurethanes. The networks prepared contain a relatively high amount of cyclic bonds, 40 to 50% in the finally cured state, which is an expected result for systems with precursors of high functionality and with small distances between the functional groups. The temperature of glass transition (Tg) of the networks prepared (ranging from 68°C to 126°C) depends of the poly BHPPA precursor used: it increases with increasing molecular mass and with increasing core functionality. The choice of the isocyanate crosslinker also influences Tg: the networks made from HDI show higher Tg values, than networks made from the same poly BHPPA but crosslinked with Desmodur N3300 (Tri HDI). The urethane bonds in the networks prepared start to decompose near 140°C. The easier degradation of PU with aromatic urethane bonds is a disadvantage in comparison with aliphatic polyurethanes, whose decomposition starts at 200°C. The surfaces of polyurethane coatings prepared are smooth, displaying a roughness of ca. 20-25 nm, and relatively hydrophilic: the contact angle with water was found to be near 80°. The prepared networks are also relatively hard, possessing the Shore D hardness of 70.

In this work, a new polyurethane (PU) chain extender was developed to incorporate a Glycine-Leucine (Gly-Leu) dipeptide, the cleavage site of several matrix metalloproteinases. PUs were synthesized with either the Gly-Leu-based chain extender (Gly-Leu PU) or a phenylalanine-based chain extender (Phe PU). Both PUs had high molecular weight averages (Mw > 125,000 g/mol) and were phase segregated, semi-crystalline polymers (Tm ~ 42°C) with a low soft segment glass transition temperature (Tg < -50°C). Uniaxial tensile testing of PU films revealed that the polymers could withstand high ultimate tensile strengths (~ 8-13 MPa) and were flexible with breaking strains of ~ 870-910% but the two PUs exhibited a significant difference in mechanical properties. The Phe and Gly-Leu PUs were electrospun into porous scaffolds for degradation and cell-based studies. Fibrous Phe and Gly-Leu PU scaffolds were formed with randomly organized fibers and an average fiber diameter of approximately 3.6 µm. In addition, the Phe PU was electrospun into scaffolds of varying architecture to investigate how fiber alignment affects the orientation response of cardiac cells. To achieve this, the Phe PU was electrospun into aligned and unaligned scaffolds and the physical, thermal, and mechanical properties of the scaffolds were investigated. The degradation of the Phe and Gly-Leu PU scaffolds was investigated in the presence of active MMP-1, active MMP-9, and a buffer solution over 28 days to test MMP-mediated and passive hydrolysis of the PUs. Mass loss and structural assessment suggested that neither PU experienced significant hydrolysis to observe degradation over the course of the experiment. In cell-based studies, Phe and Gly-Leu PU scaffolds successfully supported a high density of viable and adherent mouse embryonic fibroblasts (MEFs) out to at least 28 days. Culturing murine embryonic stem cell-derived cardiomyocytes (mESCDCs) alone and with MEFs on aligned and unaligned Phe PU scaffolds revealed both architectures supported adherent and functionally contractile cells. Importantly, fiber alignment and coculture with MEFs improved the organization and differentiation of mESCDCs suggesting these two parameters are important for developing engineered myocardial constructs using mESCDCs and PU scaffolds.

In this work, a new polyurethane (PU) chain extender was developed to incorporate a Glycine-Leucine (Gly-Leu) dipeptide, the cleavage site of several matrix metalloproteinases. PUs were synthesized with either the Gly-Leu-based chain extender (Gly-Leu PU) or a phenylalanine-based chain extender (Phe PU). Both PUs had high molecular weight averages (Mw > 125,000 g/mol) and were phase segregated, semi-crystalline polymers (Tm ~ 42°C) with a low soft segment glass transition temperature (Tg < -50°C). Uniaxial tensile testing of PU films revealed that the polymers could withstand high ultimate tensile strengths (~ 8-13 MPa) and were flexible with breaking strains of ~ 870-910% but the two PUs exhibited a significant difference in mechanical properties. The Phe and Gly-Leu PUs were electrospun into porous scaffolds for degradation and cell-based studies. Fibrous Phe and Gly-Leu PU scaffolds were formed with randomly organized fibers and an average fiber diameter of approximately 3.6 µm. In addition, the Phe PU was electrospun into scaffolds of varying architecture to investigate how fiber alignment affects the orientation response of cardiac cells. To achieve this, the Phe PU was electrospun into aligned and unaligned scaffolds and the physical, thermal, and mechanical properties of the scaffolds were investigated. The degradation of the Phe and Gly-Leu PU scaffolds was investigated in the presence of active MMP-1, active MMP-9, and a buffer solution over 28 days to test MMP-mediated and passive hydrolysis of the PUs. Mass loss and structural assessment suggested that neither PU experienced significant hydrolysis to observe degradation over the course of the experiment. In cell-based studies, Phe and Gly-Leu PU scaffolds successfully supported a high density of viable and adherent mouse embryonic fibroblasts (MEFs) out to at least 28 days. Culturing murine embryonic stem cell-derived cardiomyocytes (mESCDCs) alone and with MEFs on aligned and unaligned Phe PU scaffolds revealed both architectures supported adherent and functionally contractile cells. Importantly, fiber alignment and coculture with MEFs improved the organization and differentiation of mESCDCs suggesting these two parameters are important for developing engineered myocardial constructs using mESCDCs and PU scaffolds.