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This Thesis describes the synthesis and characterisation of new Group 2 tetrahydroborate, alkoxide and organohydroborate complexes and their uses as catalysts for the living ROP and immortal ring-opening polymerisation (iROP) of &epsilon;- caprolactone and rac-lactide. <strong>Chapter One</strong> introduces cyclic esters and possible mechanistic pathways leading to polyesters by ROP. Living and immortal ROP, including their kinetic characteristics are discussed. An overview of ROP from an industrial perspective is also given. <strong>Chapter Two</strong> describes the synthesis and characterisation of a new series of Group 2 tetrahydroborate complexes supported by a 3-methyl, 5-tert-butyl tris(pyrazolyl)hydroborate ligand. Their activities towards the ROP of &epsilon;-caprolactone are presented. Detailed mechanistic studies using spectroscopic techniques are discussed and a new mechanism is proposed. <strong>Chapter Three</strong> describes the ROP of rac-lactide using the Group 2 tetrahydroborate complexes introduced in Chapter Two, including their mechanistic studies. <strong>Chapter Four</strong> introduces the new immortal ROP using trialkyl borate and organoborane derivatives as chain-transfer agents (CTAs). The immortal ROP of &epsilon;- caprolactone and rac-lactide using Group 2 initiators with trialkyl borates/organoboranes as CTAs from either in situ generation or external addition is discussed. Possible immortal ROP pathways using this new class of CTAs are illustrated. <strong>Chapter Five</strong> details the synthesis and characterisation of a new series of Group 2 organohydroborate complexes. The &epsilon;-caprolactone and rac-lactide ROP activity shown by the complexes presented is discussed and compared with those obtained from the corresponding tetrahydroborate analogues. <strong>Chapter Six</strong> contains experimental details and characterising data for the new complexes reported in this Thesis. <strong>CD Appendix</strong> contains .CIF files for all the new crystallographically-characterised complexes.

Aluminium salen and aluminium salan complexes are excellent catalysts for the ring-opening polymerisation of lactide. This thesis studied their efficacy in the polymerisation of novel monomers and their ability to build new macrostructures. Aluminium salen and aluminium salan complexes were tested as catalysts for ring-opening polymerisation of common aliphatic monomers where controlled polymer synthesis has not yet been achieved with similar systems. Excellent control over molecular weight and dispersity was achieved for β-caprolactone polymerisation, with high molecular weights accessible. Immortal polymerisation could also be performed with an extremely high level of chain transfer agent (up to 100 equivalents) and the highest monomer turnover (10000 monomer equivalents) with aluminium salen catalysts to date. Addition of functional groups to the monomer was also studied; the effect of steric bulk in polymerisation of methylsubstituted derivatives was significant. Protected alcohol functionalities can also be introduced into easily synthesised homopolymers and copolymers. The first example of synthesising a polyester with aromatic functionality within the polymer backbone via polymerisation of cyclic ester monomers was studied with an aluminium salen catalyst. 2,3-Dihydro-5H-1,4-benzodioxepin-5-one polymerisation was facile and proceeded under mild conditions. The resulting polymer could be depolymerised back to starting monomer with the same aluminium salen catalyst under dilute conditions. Random, AB diblock and ABA triblock copolymers were readily synthesised with L-lactide and β-butyrolactone as comonomers. Block copolymers with β-butyrolactone could also be selectively depolymerised, to give poly(3-hydroxybutyrate) homopolymers. Attempted polymerisation of a range of other aromatic monomers was unsuccessful due to addition of steric bulk, changing orientation of the monomer ester bond or decreasing the ring size. Synthesis of homopolymer and ABA triblock copolymers with L-lactide and alkyl-substituted β-lactones was investigated. Homopolymerisation of all alkyl-substituted β-lactones resulted in well controlled polymer, with rate decreasing as alkyl-substituent length increased. A sequential addition of monomers method with β-butyrolactone, β-valerolactone and β-heptanolactone was employed for copolymer synthesis. Copolymers synthesised from β-butyrolactone and β-valerolactone resulted in tunable glass transition and melting temperatures. Copolymers synthesised from β-heptanolactone resulted in thermoplastic elastomers exhibiting microphase separation, supported by differential scanning calorimetry and small-angle X-ray scattering. Finally, optimisation of in situ generated carbonylation catalysts was studied. Optimisation of literature complexes allowed for synthesis of β-valerolactone, β- heptanolactone, β-tridecalactone, 4-chloro-β-butyrolactone and β-6-heptenolactone on relatively large scales under much easier experimental protocols. Additionally, tuning of ortho-phenylene bridged salen ligand framework gave to structure-activity relationships. Using this optimised catalyst system, 4-chloro-β-butyrolactone and β- 6-heptenolactone were prepared and used in ring opening polymerisation. Well controlled and efficient polymerisation of 4-chloro-β-butyrolactone was easily achieved with aluminium salen and salan catalysts. Homopolymers and block copolymers with poly(ethylene glycol) and β-6-heptenolactone were readily synthesised.

This Thesis describes the synthesis and characterisation of new Group 2, Group 3 and lanthanide amide, alkyl, halide, borohydride and alkoxide complexes, and their uses as catalysts for the living ROP and immortal ring-opening polymerisation (iROP) of rac-, L, D- and meso-lactide. <strong>Chapter One</strong> introduces cyclic esters and possible mechanistic pathways leading to polyesters by ROP. Living and immortal ROP, including their kinetic characteristics are discussed. An overview of ROP from an industrial perspective and a literature review are also given. <strong>Chapter Two</strong> describes the synthesis and characterisation of a new series of magnesium and zinc amide, alkyl, halide, borohydride and alkoxide complexes supported by a carbazole-bis(dimethyloxazoline) ligand. Their activities towards the ROP of rac-, L- and meso-lactide are presented. Detailed mechanistic studies using spectroscopic techniques are discussed and a new mechanism is proposed. <strong>Chapter Three</strong> describes the synthesis and characterisation of a new series of calcium, strontium, yttrium, lanthanum and samarium amide, alkyl, halide, borohydride and alkoxide complexes supported by a carbazole-bis(dimethyloxazoline) ligand. Their activities towards the ROP of rac-, L- and meso-lactide are presented. Detailed mechanistic studies using spectroscopic techniques are discussed. <strong>Chapter Four</strong> describes the synthesis and characterisation of a new series of magnesium, calcium, strontium, yttrium, lanthanum and samarium amide, halide and borohydride complexes supported by a chiral carbazole-bis(isopropyloxazoline) ligand. Their activities towards the ROP of rac-, L-, D- and meso-lactide are presented. <strong>Chapter Five</strong> contains experimental details and characterising data for the new complexes reported in this Thesis. <strong>CD Appendix</strong> contains .CIF files for all the new crystallographically-characterised complexes.

Yes / In this work we report a facile method to prepare a fluorescence active self-healable hydrogel via incorporation of fluorescence responsive ionic block copolymers (BCPs). Ionic block copolymers were prepared via a combined effect of ring opening polymerization (ROP) of ε-caprolactone and xanthate mediated reversible addition–fragmentation chain transfer (RAFT) polymerization. Here polycaprolactone (PCL) was modified with xanthate to prepare a PCL based macro-RAFT agent and then it was utilized to prepare block copolymers with cationic poly(2-(methacryloyloxy)ethyltrimethyl ammonium chloride) (PCL-b-PMTAC) and anionic poly(sodium 4-vinylbenzenesulfonate) (PCL-b-PSS). During the block formation, the cationic segments were randomly copolymerized with a trace amount of fluorescein O-acrylate (FA) (acceptor) whereas the anionic segments were randomly copolymerized with a trace amount of 9-anthryl methylmethacrylate (AMMA) (donor) to make both the segments fluorescent. The block copolymers form micelles in a DMF : water mixture (1 : 4 volume ratio). The ionic interaction of two BCPs was monitored via Förster resonance energy transfer (FRET) and zeta potential measurements. The oppositely charged BCPs were incorporated into a polyacrylamide (PAAm) based hydrogel that demonstrated self-healing behavior and is also highly fluorescent. / IIT Kharagpur and MRC (MR/N501888/2)

This Thesis describes the use of alkaline earth and rare earth complexes bearing phenolate ligands as catalysts in the amine-initiated, immortal ring opening polymerisation (ROP) of cyclic esters. Mechanistic elucidation was performed and two propagation pathways are presented. Chapter One introduces cyclic esters and catalytic routes to polyesters by ROP. Common techniques for polymer characterisation are described and an overview of relevant phenolate-supported ROP catalysts is given. Reversible chain transfer in ROP is also discussed. Chapter Two describes the synthesis and characterisation of zwitterionic Group 3 complexes bearing bis(phenolate)-amino ligands and the development of the amine-initiated, immortal ROP methodology using this class of catalyst. Detailed studies into the ROP of rac-lactide using amines and a zwitterionic yttrium complex are presented and the mechanism of amine-initiated, immortal ROP was derived. Chapter Three documents further amine-initiated, immortal ROP studies using a zwitterionic yttrium complex as the catalyst. The preparation of multiarm polymers is described and further investigations using the cyclic esters, ε-caprolactone and rac-β-butyrolactone are presented. Chapter Four describes the use of Group 2 and lanthanide phenolate complexes in the amine-initiated ROP of rac-lactide. Bulk polymerisation studies revealed the generality of the amine-initiated, immortal ROP methodology and an alternative propagation pathway was derived from mechanistic studies. Chapter Five details the synthesis and characterisation of Group 3 amide complexes supported by phenolate-amino ligands. Each complex was screened for ROP capability and amine co-initiators were employed. Chapter Six contains experimental details and characterisation data for the new complexes and polymer products described in this Thesis. CD Appendix contains crystallography .cif files, supporting information for each Chapter and spreadsheets containing polymerisation data.

A Organização Mundial da Saúde (OMS) relata o câncer como uma das principais causas de morte no mundo. O câncer de próstata é o segundo tipo de câncer mais prevalente em homens, com cerca de 1,1 milhão de casos diagnosticados em 2012. Braquiterapia com iodo-125 é uma método de radioterapia que consiste na introdução de sementes com material radioativo no interior do órgão a ser tratado. As sementes de iodo-125 podem ser inseridas soltas ou em cordas poliméricas bioabsorvíveis, mais comumente o poli(ácido lático-co-ácido glicólico) (PLGA). A função do polímero é reduzir a possibilidade de migração das sementes, o que poderia ser prejudicial para órgãos e tecidos saudáveis. De modo a reduzir os custos do tratamento, a síntese dos dímeros L-lactídeo e glicolídeo, para posterior utilização para preparação do PLGA, por meio da polimerização por abertura de anel, é proposta neste trabalho. Adicionalmente, propõe-se a utilização do amino-alcóxido tris(fenolato) de zircônio (IV) como alternativa ao usual octanoato de estanho (SnOct2), uma vez que a toxicidade do estanho permanece como obstáculo na produção do PLGA para aplicações biomédicas. Embora o iniciador de zircônio seja mais lento do que o SnOct2, massas molares relativamente elevadas foram obtidas quando razões monômero/iniciador (M/I) de 1000/1 (24 h), e 5000/1 (48 h) foram utilizadas. Considerando que as unidades glicolila (GA) são mais reativas do que as unidades lactila (LA), tempos longos de reação são necessários para atingir uma razão LA/GA próxima do objetivo do trabalho (85/15). O grau de racemização também depende do iniciador utilizado. As reações de polimerização realizadas com o iniciador de zircônio mostraram um maior grau de racemização, quando comparadas com aquelas realizadas com o SnOct2. Também foi observado um ligeiro aumento na racemização com o tempo. Considerando os resultados obtidos na síntese e purificação dos dímeros, e na síntese do PLGA em condições semelhantes às industriais, foi possível preparar o polímero de alta massa molar com um custo dezenas de vezes inferior ao custo do PLGA no mercado internacional. Os efeitos da radiação gama no PLGA também foram estudados. Doses normalmente aplicadas para esterilizar materiais para aplicações biomédicas foram empregadas: 10, 18, 25 e 50 kGy. A massa molar de todas as amostras irradiadas diminuiu de uma forma proporcional à dose até 56% de perda para 10 kGy e 72% para 50 kGy porém, são menos pronunciadas para doses mais elevadas. Alterações nas propriedades térmicas, tais como temperatura de fusão, temperatura de transição vítrea e a entalpia de cristalização e fusão foram também observadas após a irradiação. / The World Health Organization (WHO), reports cancer a leading cause of death worldwide. Prostate cancer is the second most common cancer in men, with 1.1 million diagnoses in 2012. Brachytherapy is a method of radiotherapy where encapsulated radioactive sources (seeds) are placed inside or very close to the area requiring treatment. Iodine-125 seeds can be inserted loose or stranded in bioresorbable materials most commonly poly(lactic-co-glycolic) acid (PLGA). The main function of the polymer is to reduce the possibility of seeds migration, which could potentially harm healthy organs and tissues. In order to reduce the cost of the treatment, we propose in this work the synthesis of L-lactide and glycolide dimers, for the production of PLGA using the ring-opening polimerisation route. Additionally, we also propose the use of a Zr (IV) amine tris(phenolate) alkoxide initiator as an alternative to the usual SnOct2, which is still considered an unsolved problem for biomedical applications due to its toxicity. Although the zirconium alkoxide initiator is less active and slower than SnOct2, relatively high molecular weights were obtained at a temperature of 130°C, for a monomer to initiator ratio of 1000/1 (24 h), and 5000/1, in 48 h. Since glycolyl units are more reactive than lactyl counterpart, longer reaction times are needed to achieve a LA/GA ratio closer to the initial (85/15). The degree of racemisation of the polymer depended upon the initiator used. The reactions carried out with the zirconium initiator showed a higher degree of racemisation when compared to those carried out with SnOct2. A modest increase in the degree of racemisation with time was also observed. Considering the results obtained for the synthesis and purification of the dimers, and for the synthesis of PLGA under industrial-like conditions, we concluded that it was possible to produce a high molecular weight polymer that costs far less than the usual price of PLGA on the market. The effects of gamma radiation on PLGA were also studied. We used doses commonly applied to sterilise materials for biomedical applications: 10, 18, 25 and 50 kGy. All irradiated samples showed a reduction in the molecular weight in a dose dependent fashion - up to 56% loss for 10 kGy and 72% for 50 kGy - but these reductions were less pronounced for higher doses. Changes in thermal properties, such as melting point, glass transition temperature and enthalpy of crystallisation and fusion were also observed after irradiation.

The biodegradability and when functionalised biocompatibility of aliphatic polycarbonates (APCs) makes them an attractive class of materials for biomedical applications such as tissue engineering scaffolds and drug-delivery carriers. One route to accessing a wide-range of well-defined and functional APCs is the controlled ring-opening polymerisation (ROP) of cyclic carbonates. In turn, these would ideally be prepared by the direct coupling of CO2 with diols to give water as the only by-product. In this way, the combination of CO2 and sugar-derived diols draws upon two natural renewable building blocks for the construction of polycarbonates that are anticipated to show good biocompatibility properties. Chapter 2 develops a simple and mild alternative to the traditional use of phosgene derivatives for the synthesis of six-membered cyclic carbonates from 1,3-diols and CO2. DFT calculations highlighted the need to lower both the CO2-insertion and ring-closing kinetic barriers to cyclic carbonate formation. Organic superbase, 1,8- diazabicyclo[5.4.0]undec-7-ene (DBU) enabled the formation of carbonate species at 1 atm CO2 pressure whereas, the introduction of a leaving group strategy lowered the cyclisation barrier. Mechanistic considerations suggested a kinetic preference for ring- closing via a nucleophilic addition-elimination pathway rather than a SN2-like intramolecular cyclisation. Chapter 3 applies the procedure with CO2 to the preparation of a novel monomer from natural sugar, ᴅ-mannose. ROP was carried out via an organocatalytic approach and a preference for head-tail linkages in the polycarbonate backbone indicated by NMR spectroscopy and supported by DFT calculations. Chapter 4 utilises CO2 to invert the natural stereochemistry of sugars and create a thymidine-based monomer. The thermodynamic parameters of the ROP with 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) catalyst are determined and the properties of the polycarbonates investigated to include preliminary cell attachment studies. Finally, chapter 5 details the synthesis of cyclic carbonates from 2- deoxy-ᴅ-ribose and the investigation into the different ROP behaviour of the α- and β- anomers. The ability to tune the polymer properties through copolymerisation with trimethylene carbonate (TMC) is also discussed.

This Thesis describes the activity and mechanism of alkaline earth organohydroborate, tetrahydroborate and alkoxide catalysts for the ring-opening polymerisation (ROP) of cyclic esters including rac-, L-, D- and meso-lactide (LA), and rac-β-butyrolactone (rac-BBL). <b>Chapter One</b> introduces cyclic esters and general mechanisms for their ROP to give polyesters. Living and immortal ROP, an overview of stereocontrolled ROP, and determination of polylactide (PLA) stereosequences are given. Various techniques for polymer characterisations are also described. <b>Chapter Two</b> describes the activity and mechanism of heavy alkaline earth organohydroborate complexes for the ROP of LA. The synthesis and characterisation of alkaline earth alkoxide complexes serving as model species are also described, together with their activities for the ROP of LA. <b>Chapter Three</b> describes the activity and mechanism of a cyclic organohydroborate calcium complex for the ROP of LA. The role of borinic esters as chain transfer agents in the ROP of rac-LA is also discussed. <b>Chapter Four</b> describes the activity and mechanism of heavy alkaline earth tetrahydroborate complexes for the ROP of LA. The immortal ROP of rac-LA using heavy alkaline earth alkoxide complexes and borate esters as chain transfer agents is discussed. <b>Chapter Five</b> describes the activity and mechanism of alkaline earth organohydroborate, tetrahydroborate and alkoxide complexes for the ROP of rac-BBL. <b>Chapter Six</b> presents experimental procedures and characterising data for new complexes reported.