Yes / Hydroxyapatite and fluorhydroxyapatite (F)HA nanoparticles were synthesised in the presence of branched poly(acrylic acid)s (PAA) synthesised via reversible addition–fragmentation chain transfer polymerisation and compared to those synthesised in the presence of linear PAA. Analysis of the resulting nanoparticles using Fourier transform infrared spectroscopy, powder X-ray diffraction and transition electron microscopy found that the polymer was included within the nanoparticle samples and affected their morphology with nanoparticles synthesised in the presence of branched PAA being more acicular and smaller overall.

Yes / Functional crosslinked hydrogels were prepared from 2-hydroxyethyl methacrylate (HEMA) and acrylic acid (AA). The acid monomer was incorporated both via copolymerization and chain extension of a branching, reversible addition–fragmentation chain-transfer agent incorporated into the crosslinked polymer gel. The hydrogels were intolerant to high levels of acidic copolymerization as the acrylic acid weakened the ethylene glycol dimethacrylate (EGDMA) crosslinked network. Hydrogels made from HEMA, EGDMA and a branching RAFT agent provide the network with loose-chain end functionality that can be retained for subsequent chain extension. Traditional methods of surface functionalization have the downside of potentially creating a high volume of homopolymerization in the solution. Branching RAFT comonomers act as versatile anchor sites by which additional polymerization chain extension reactions can be carried out. Acrylic acid grafted onto HEMA–EGDMA hydrogels showed higher mechanical strength than the equivalent statistical copolymer networks and was shown to have functionality as an electrostatic binder of cationic flocculants.

Bone undergoes constant turnover throughout life and has the capacity to regenerate itself. However, the repair of critical size defects, caused by bone diseases such as osteoporosis, can be more problematic. Therefore, there is a clinical need for a bone graft substitute that can be used at sites of surgical intervention to enhance bone regeneration. Poly(vinylphosphonic acid-co-acrylic acid) (PVPA-co-AA) has recently been identified as a potential candidate for use in bone tissue scaffolds. It is hypothesised that PVPA-co-AA can mimic the action of bisphosphonates – a class of drugs used in the treatment of osteoporosis – by binding to calcium ions from bone mineral surfaces. In this way, bisphosphonates can affect bone turnover by increasing the activity of osteoblasts and reducing osteoclast activity. Although PVPA-co-AA has been shown to improve bone formation, the mechanism of action has so far not been fully elucidated. Therefore, this work aims to understand the effect of copolymer composition on the properties of PVPA-co-AA, and thus to determine its effect on osteoblast adhesion and proliferation. PVPA-co-AA copolymers have been synthesised with a range of monomer feed ratios. It was found that a VPA content of 30 mol % led to the greatest calcium binding affinity of the copolymer and is thus expected to lead to enhanced bone formation and mineralisation of the matrix produced by osteoblast cells. The release profile of PVPA-co-AA from electrospun PCL scaffolds was investigated. It was shown that all of the PVPA-co-AA was released into aqueous media within 8 h of immersion. It was also found that the calcium chelation from osteogenic differentiation media significantly increased within the first 8 h. Therefore, it was concluded that PVPA-co-AA is released from the scaffolds, where it can then bind to calcium ions from the bone mineral surface to promote mineralisation, thus acting as a mimic of non-collagenous proteins, which are present in the extracellular matrix (ECM) of bone. Hydrogels of PVPA-co-AA have been produced and the effect of monomer feed ratio (0-50 mol % VPA) on the properties of the gels was explored. It was found that an increase in VPA content led to greater hydrogel swelling and increased porosities. Hydrogels that contained 30 and 50 mol % VPA were shown to have similar morphologies to the native ECM of bone. Rheological testing showed that hydrogels with higher VPA contents were more flexible and could be deformed to a large extent without permanent deformation of their structure. An increase in osteoblast adhesion and proliferation was observed for hydrogels with 30 and 50 mol % VPA content as well as superior cell spreading. Osteoblast cell metabolic activity also increased as a function of VPA content in the hydrogels. This work indicates that hydrogels of PVPA-co-AA, with VPA contents of 30 or 50 mol %, are ideal for use as bone tissue scaffolds. Furthermore, the mechanical and cell adhesion properties of the gels can be tuned by altering the copolymer composition. Finally, composite hydrogels of PVPA-co-AA and hydroxyapatite (HA) have been produced and investigated for their ability to remove fluoride ions from groundwater. It was found that the fluoride uptake ability of PVPA-HA hydrogels was significantly enhanced when compared with HA powder alone. Furthermore, the fluoride uptake was dependent on many factors, including pH, contact time and the presence of competing ions. It was possible to regenerate the hydrogel to remove the fluoride ions, and thus it was shown that the material can be used a number of times with only a slight reduction in its fluoride uptake capacity.

Doctor of Philosophy / The kinetics of electrosterically stabilized emulsion systems was studied. The aim of this was to understand the impact that steric and electrosteric stabilizers have on the kinetics of particle growth and particle formation in the area of emulsion polymerization. The well-established mechanisms that govern these processes for emulsions stabilized by conventional low molecular weight surfactants were used as a reference point for comparative purposes. Model latexes were synthesized that comprised of a poly(styrene) core stabilized by a corona of poly(acrylic acid). The advent of successful controlled radical polymerization techniques in heterogeneous media (via RAFT polymerization) allowed for latexes to be synthesized under molecular weight control. For the first time, the degree of polymerization of the stabilizing block on the particle surface was able to be controlled and verified experimentally using mass spectrometry techniques. Three latexes were made with different average degrees of polymerization of the stabilizing block; five, ten and twenty monomer units respectively. A methodology was developed to remove the RAFT functionality from the polymer chains present in the emulsion while retaining the desired particle morphology. Oxidation with tertbutylhydroperoxide (TBHP) was proven to be successful at eliminating the living character provided by the thiocarbonyl end-group. Extensive dialysis and cleaning of the latex was performed to ensure no residual TBHP or reaction by-products remained. Latexes with poly(styrene) cores were chosen for this work as poly(n-butyl acrylate) latexes were shown to be influenced by chain transfer to polymer, providing an additional kinetic complication. The three electrosterically stabilized emulsions were used as seed latexes in carefully designed kinetic experiments to measure the rate of polymerization as a function of time. Two independent techniques (chemically initiated dilatometry and γ-relaxation dilatometry) were used to measure the rate coefficients of radical entry (ρ) and exit (k) in these systems – the two parameters that essentially govern the rate of particle growth. The latexes were chosen such that they satisfied ‘zero-one’ conditions (i.e. that any given latex particle contains at most one growing radical at any given time) in order to simplify data analysis. Three different chemical initiators were used, each yielding a radical with a different electric charge. Results from γ-relaxation experiments demonstrated that the three electrosterically stabilized latexes gave very long relaxation times when removed from the radiation source, ultimately yielding very small k values. These values were up to a factor of 10 smaller than that predicted by the ‘transfer-diffusion’ model for exit for particles of that size. This reduction was attributed to a ‘restricted diffusion’ effect, where the exiting monomeric radical has to diffuse through a dense layer of polymer on the particle surface, where its mobility will be restricted. Modification of the Smoluchowski equation for diffusion-controlled adsorption/desorption to account for this postulate led to the development of a model that gave excellent semi-quantitative agreement with experiment. Chemically initiated dilatometric experiments (using three different types of initiator) gave the unusual result of very low reaction rates and low steady-state values of 'nbar', the average number of radicals per particle. Using the standard kinetic equations for styrene-based systems (where it is assumed that an exited monomeric radical undergoes re-entry), this led to the calculation of impossibly small values of the entry rate coefficient ρ (far below any background or ‘thermal’polymerization rate). However upon removing the assumption of re-entry and assuming that exited radicals undergo termination, the obtained values of ρ were in almost perfect agreement with the values predicted from the ‘control by aqueous phase growth’ entry mechanism. This unexpected result was attributed to chemical reaction with the poly(acrylic acid) stabilizers through chain transfer to polymer (via hydrogen-atom abstraction). This postulate was verified by separate experiments that demonstrated that poly(acrylic acid) could act as a reasonably efficient chain transfer agent for styrene polymerization. The addition of poly(acrylic acid) to the aqueous phase of a conventionally stabilized emulsion also led to the rate reduction seen previously. NMR experiments demonstrated the existence of poly(acrylic acid-graft-styrene), which could only be formed through termination of a poly(styrene) chain with a poly(acrylic acid) chain bearing a mid-chain radical (as the product of a chain transfer reaction). These additional terms of transfer and termination were included in the governing kinetic equations of emulsion systems (the Smith-Ewart equations) to develop a model to account for the behaviour of electrosterically stabilized latexes. The ultimate fate of an exiting radical was now shown to be a competition between fates; successful desorption into the aqueous phase, or chemical reaction (through transfer or termination) within the hairy layer. These additional terms were shown to significantly reduce the theoretical value of nbar, and were in excellent agreement with experiment. For small electrosterically stabilized particles with a densely packed ‘hairy layer,’ it was seen that transfer/termination is the dominant loss mechanism as opposed to desorption. The developed model showed that as the particle size was increased, the dominant loss mechanism once again became successful desorption into the aqueous phase. The model was shown to give excellent agreement with experimental data from ‘uncontrolled’ emulsion systems. To explain the highly unusual secondary nucleation behaviour seen in systems such as these, it was postulated that beta-scission of a poly(acrylic acid) chain bearing a mid-chain radical is an important mechanistic step in the nucleation mechanisms of these systems. Modelling (both steady-state and time-dependent) gave good agreement with experiment with a minimal number of adjustable parameters. Theory (and supporting experimental evidence) demonstrated that this nucleation mechanism is only significant at high particle numbers; under other conditions the well-known ‘homogeneous nucleation’ mechanism is once again dominant.

Poly(acrylic acid) (PAA) was grafted onto both termini of Pluronic F87 (PEO₆₇-PPO₃₉-PEO₆₇) via atom transfer radical polymerization to produce a novel muco-adhesive block copolymer PAA₈₀-b-F₈₇-b-PAA₈₀. It was observed that PAA₈₀-F₈₇-PAA₈₀ forms stable complexes with weakly basic anti-cancer drug, Doxorubicin. Thermodynamic changes due to the drug binding to the copolymer were assessed at different pH by isothermal titration calorimetry (ITC). The formation of the polymer/drug complexes was studied by turbidimetric titration and dynamic light scattering. Doxorubicin and PAA-b-F87-b-PAA block copolymer are found to interact strongly in aqueous solution via non-covalent interactions over a wide pH range. At pH>4.35, drug binding is due to electrostatic interactions. Hydrogen-bond also plays a role in the stabilization of the PAA₈₀-F₈₇-PAA₈₀/DOX complex. At pH 7.4 (α=0.8), the size and stability of polymer/drug complex depend strongly on the doxorubicin concentration. When CDOX <0.13mM, the PAA₈₀-F₈₇-PAA₈₀ copolymer forms stable inter-chain complexes with DOX (110 ~ 150 nm). When CDOX >0.13mM, as suggested by the light scattering result, the reorganization of the polymer/drug complex is believed to occur. With further addition of DOX (CDOX >0.34mM), sharp increase in the turbidity indicates the formation of large aggregates, followed by phase separation. The onset of a sharp enthalpy increase corresponds to the formation of a stoichiometric complex. / Singapore-MIT Alliance (SMA)

BACKGROUND: There is an increased need to replace materials derived from fossil sources by renewables. Sugar-cane derived carbohydrates are very abundant in Brazil and are the cheapest sugars available in the market, with more than 400 million tons of sugarcane processed in the year 2007. The objective of this work was to study the preparation of sugar acrylates from free sugars and free acrylic acid, thus avoiding the previous preparation of protected sugar derivatives, such as glycosides, or activated acrylates, such as vinyl acrylate. RESULTS: Lipase catalyzed esterification of three mono- and two disaccharides with acrylic acid, in the presence or absence of molecular sieves was investigated. The reactions were monitored by high-performance liquid chromatography (HPLC) and the products were analyzed by matrix-assisted laser desorption ionization–time of flight (MALDI-TOF) mass spectrometry. The main products are mono- and diacrylates, while higher esters are formed as minor products. The highest conversion to sugar acrylates was observed for the D-glucose and D-fructose, followed by D-xylose and D-maltose. Molecular sieves had no pronounced effect on the conversion CONCLUSIONS: A feasible method is described to produce and to characterize sugar acrylates, including those containing more than two acrylate groups. The process for production of these higher esters could potentially be optimized further to produce molecules for cross-linking in acrylate polymerization and other applications. The direct enzymatic esterification of free carbohydrates with acrylic acid is unprecedented.

Citrate-coated gadolinium trifluoride (Cit-GdF3) and poly(acrylic acid)-coated nanoparticles (PAA-GdF3 NPs) were synthesized, the former reproduced from literature (though using more refined conditions), the latter through a new, two-step, ligand exchange method. Diamagnetic nanoparticle analogs (Cit-YF3 NPs) were prepared to investigate citrate interactions with the nanoparticle surface using NMR. Citrate was found to bind in numerous conformations, with a total of between 29 – 46 % bound at 0 ºC. Exchange studies revealed short residence lifetimes of one and twelve seconds respectively for bound and free forms of citrate (0 ºC), perhaps explaining the colloidal instability of these nanoparticles. PAA-GdF3 NPs were synthesized by first producing their Cit-GdF3 counterparts, and then exchanging citrate for PAA. The impetus behind this latter synthesis was the relative enhancement in stability and relaxivity attainable by these nanoparticles. The displacement of citrate by PAA was verified using diffusion NMR studies.

Citrate-coated gadolinium trifluoride (Cit-GdF3) and poly(acrylic acid)-coated nanoparticles (PAA-GdF3 NPs) were synthesized, the former reproduced from literature (though using more refined conditions), the latter through a new, two-step, ligand exchange method. Diamagnetic nanoparticle analogs (Cit-YF3 NPs) were prepared to investigate citrate interactions with the nanoparticle surface using NMR. Citrate was found to bind in numerous conformations, with a total of between 29 – 46 % bound at 0 ºC. Exchange studies revealed short residence lifetimes of one and twelve seconds respectively for bound and free forms of citrate (0 ºC), perhaps explaining the colloidal instability of these nanoparticles. PAA-GdF3 NPs were synthesized by first producing their Cit-GdF3 counterparts, and then exchanging citrate for PAA. The impetus behind this latter synthesis was the relative enhancement in stability and relaxivity attainable by these nanoparticles. The displacement of citrate by PAA was verified using diffusion NMR studies.

Surface grafting and modification of poly(acrylic acid) (PAA) were performed on nylon 6,6 carpet fibers to achieve permanent stain and soil resistance. PAA was grafted to nylon and modified with 1H, 1H-pentadecafluorooctyl amine (PDFOA) using an amidation agent, 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium chloride (DMTMM). The first goal was to optimize acrylamide modification of PAA in solution. Aqueous reactions with taurine, hydroxyethyl amine, and butyl amine progressed ~100%, while PDFOA reactions in MeOH progressed ~80%. Reaction products precipitated at 77% butyl or 52% PDFOA acrylamide contents. The second goal was to optimize the PAA grafting process. First, PAA was adsorbed onto nylon 6,6 films. Next, DMTMM initiated grafting of adsorbed PAA. PAA surface coverage was ~78%, determined by contact angle analysis of the top 0.1-1 nm and x-ray photoelectron spectroscopy (XPS) analysis of the top 3-10 nm. The third goal was to modify PAA grafted nylon films with butyl amine and PDFOA. Randomly methylated beta-cyclodextrin (RAMEB) solubilized PDFOA in water. Contact angle detected ~ 100% surface reaction for each amine, while XPS detected ~77% butyl amine (H2O) and ~50% for PDFOA (MeOH or H2O pH=7) reactions. In H2O pH=12, the PDFOA reaction progressed ~89%, perhaps due to greater efficiency, access and solubility. The fourth goal was to perform surface depth profiling via angle-resolved XPS analysis (ARXPS). The PAA surface coverage from contact angle and XPS was confirmed. Further, adsorbed PAA was thicker than grafted PAA, supporting the theory that PAA adsorption occurs in thick layers onto nylon followed by DMTMM-activated spreading and grafting of thinner PAA layers across the surface. The PDFOA reaction in MeOH produced a highly fluorinated but thin exterior and an unreacted PAA interior. The PDFOA reaction in H2O pH=12 produced a completely fluorinated exterior and highly fluorinated interior. Thus surface modification levels from contact angle and XPS were confirmed. The final goal was to PAA-graft and PDFOA-modify nylon 6,6 fabrics and carpets. PDFOA modification achieved significant water and oil repellency. Stainblocking was slightly improved for ionized PAA-g-nylon and greatly improved for PDFOA-modified PAA-g-nylon. However, traditional stainblockers may be necessary to completely prevent dye penetration into carpet tufts.

In this study, pH-sensitive poly(acrylamide-co-acrylic acid) hydrogels were synthesized as controlled release systems in the presence of N,N-methylene bisacrylamide as crosslinker and ammonium persulfate as initiator. A set of hydrogels were used in the form they were prepared. One set of hydrogels were prepared as porous networks by incorporating sodium chloride into the reaction medium and then leaching of it after the completion of polymerization reaction. Two sets of hydrogels were modified by argon-plasma at different discharge powers. Hydrogels were characterized by 13C-NMR, XPS, SEM, ATR-FTIR, ESR as well as equilibrium degree of swelling (EDS) and contact angle measurements. Prepared hydrogels were loaded with a model antibiotic, ciprofloxacin-HCl (CPFX), and in-vitro release of CPFX from hydrogel matrices were examined in buffer solutions of varying pH values. There are two factors determining the release rates of CPFX / one is the pH-dependent solubility of CPFX and the other is EDS of the hydrogel samples. For porous samples drug loading and release rates were higher when compared to the control samples and CPFX solubility dominated over release kinetics. Plasma treatment resulted in prolonged release rates in acidic medium.