New oil modified acrylic polymer for pH sensitive drug release:experimental results and statistical analysis

We report results of an experimental study, complemented by detailed statistical analysis of the experimental data, on the development of a more effective control method of drug delivery using a pH sensitive acrylic polymer. New copolymers based on acrylic acid and fatty acid are constructed from dodecyl castor oil and a tercopolymer based on methyl methacrylate, acrylic acid and acryl amide were prepared using this new approach. Water swelling characteristics of fatty acid, acrylic acid copolymer and tercopolymer respectively in acid and alkali solutions have been studied by a step-change method. The antibiotic drug cephalosporin and paracetamol have also been incorporated into the polymer blend through dissolution with the release of the antibiotic drug being evaluated in bacterial stain media and buffer solution. Our results show that the rate of release of paracetamol getss affected by the pH factor and also by the nature of polymer blend. Our experimental data have later been statistically analyzed to quantify the precise nature of polymer decay rates on the pH density of the relevant polymer solvents. The time evolution of the polymer decay rates indicate a marked transition from a linear to a strictly non-linear regime depending on the whether the chosen sample is a general copolymer (linear) or a tercopolymer (non-linear). Non-linear data extrapolation techniques have been used to make probabilistic predictions about the variation in weight percentages of retained polymers at all future times, thereby quantifying the degree of efficacy of the new method of drug delivery.

Design, synthesis and thermal behaviour of a series of well-defined clickable and triggerable sulfonate polymers

In the printing industry, the exploitation of triggerable materials that can have their surface properties altered on application of a post-deposition external stimulus has been crucial for the production of robust layers and patterns. To this end, herein, a series of clickable poly(R-alkyl p-styrene sulfonate) homopolymers, with systematically varied thermally-labile protecting groups, has been synthesised via reversible addition-fragmentation chain transfer (RAFT) polymerisation. The polymer range has been designed to offer varied post-deposition thermal treatment to switch them from hydrophobic to hydrophilic. Suitable RAFT conditions have been identified to produce well-defined homopolymers (Đ, Mw/Mn < 1.11 in all cases) at high monomer conversions (>80% for all but one monomer) with controllable molar mass. Poly(p-styrene sulfonate) with an isobutyl protecting group has been shown to be the most readily thermolysed polymer that remains stable at room temperature, and was thus investigated further by incorporation into a diblock copolymer, P3HT-b-PiBSS, by click chemistry. The strategy for preparation of thermal modifiable block copolymers exploiting R-protected p-styrene sulfonates and azide-alkyne click chemistry presented herein allows the design of new, roll-to-roll processable materials for potential application in the printing industry, particularly organic electronics.

Kinetic studies of the photopolymerisation of acrylamide in aqueous solution:effects of bromoform as a Chain transfer agent

The effects of adding bromoform (CHBr3) as a potential chain transfer agent in the photopolymerisation of acrylamide (AM) in aqueous solution have been studied both in terms of influencing the rate of polymerisation and the molecular weight of the polyacrylamide (PAM) formed. Using 4,4′-azo-bis(4-cyanopentanoic acid) (ACPA) as photoinitiator, two different CHBr3 concentrations as chain transfer agent were compared: 0.5 and 2.0 mol % (relative to AM), the higher of which was determined by the limit of CHBr3 water solubility. The results showed that CHBr3 was an effective chain transfer agent that could regulate the molecular weight of the PAM formed without seriously affecting the polymerisation rate. It is concluded that chain transfer to CHBr3occurs by both Br and H atom transfer although Br transfer is the more favoured due to the weaker C-Br bond. Furthermore, Br transfer leads to Br-terminated chains in which the terminal C-Br bond can re-dissociate leading to re-initiation and re-propagation of the same chain, thereby maintaining the polymerisation rate. Continuing studies into how this mechanism can be exploited in order to synthesize water-soluble block copolymers of potential biomedical importance are currently in progress.

Biomimetic synthetic lubricants (Biosurfactants)

Poly(styrene-co-maleic anhydride) (PSMA) based copolymers are known to undergo conformational transition in response to environmental stimuli. This smart behaviour makes it possible to mimic the behaviour of native apoproteins. The primary aim of this study was to develop a better understanding of the structure-property relationships of various PSMA-based copolymers sought. The work undertaken in this thesis has revealed that the responsive behaviour of PSMA-based copolymers can be tailored by varying the molecular weight, hydrophobic (styrene) and hydrophilic (maleic acid) balance, and more so in the presence of additional hydrophobic, mono-partial ester moieties. Novel hydrophilic and hydrophobic synthetic surfactant protein analogues have successfully been prepared. These novel lipid solubilising agents possess a broad range of HLB (hydrophilic-lipophilic balance) values that have been estimated. NMR spectroscopy was utilised to confirm the structures for PSMA-based copolymers sought and proved useful in furthering understanding of the structure-property relationships of PSMA-based copolymers. The association of PSMA with the polar phospholipid, 2-dilauryl-sn-glycero-3- phosphocholine (DLPC) produces polymer-lipid complexes analogous to lipoprotein assemblies present in the blood plasma. NMR analysis reveals that the PSMA-based copolymers are not perfectly alternating. Regio-irregular structures, atactic and random monomer sequence distribution have been identified for all materials studied. Novel lipid solubilising agents (polyanionic surfactants) have successfully been synthesised from a broad range of PSMA-based copolymers with desired estimated HLB values that interact with polar phospholipids (DLPC/DPPC) uniquely. Very low static and dynamic surface tensions have been observed via the du Noϋy ring method and Langmuir techniques and correlate well with the estimated HLB values. Synthetic protein-lipid analogues have been successfully synthesised, that mimic the unique surface properties of native biological lubricants without the use of solvents. The novel PSMA-DLPC complexes have successfully been combined with hyaluronan (hyaluronic acid, HA). Today, the employment of HA is economically feasible, because it is readily available from bacterial fermentation processes in a thermally stable form - HyaCare®. The work undertaken in this thesis highlights the usage of HA in biolubrication applications and how this can be optimised and thus justified by carefully selecting the biological source, concentration, molecular weight, purity and most importantly by combining it with compatible boundary lubricating agents (polar phospholipids). Experimental evidence supports the belief that the combined HA and PSMA-DLPC complexes provide a balance of rheological, biotribological and surface properties that are composition dependent, and show competitive advantage as novel synthetic biological lubricants (biosurfactants).

Effects of substituents in polyvinylcarbazole structures on their optical properties

Absorption, photoluminescence, and photoluminescence excitation spectra of solutions and thin films of N-vinylcarbazole polymers and copolymers with various substituents directly on the carbazole moiety and on the polymer chain were studied comprehensively. Polymers that were used previously to develop polymer composites with polymethine dyes having photosensitivity over a broad spectral range including the visible and near-IR regions were selected for the studies.