Modification of poly(lactic acid) via Olefin cross-metathesis

Poly(lactic acid), PLA, is a viable replacement to petroleum derived polymers due to its renewable feedstock, biodegradability and bioassimilability, yet improvements in its physical, thermal and mechanical properties are required before it can fully enter all commodity markets. This thesis investigates olefin cross-metathesis (CM) as a synthetic strategy to modify the properties of PLA. The use of novel lanthanide and actinide catalysts on the microstructure control of PLA are also explored. The Tebbe reagent was used in a new synthetic strategy to produce a novel olefin derivative of lactide (MML). Olefin CM of MML with hex-1-ene was successful but polymerisation pre- and post-CM was unsuccessful due to monomer instability. CM of another olefin derivative of lactide, 3-methylenated lactide (3-ML) was successful with aliphatic alkenes; hex-1-ene to dodec-1-ene. To overcome competing alcoholysis of the functionalised monomers, which prevented polymerisation, hydrogenation was used to remove the olefin entity followed by successful ring-opening polymerisation (ROP) to produce polymers of low glass-transition temperatures (Tg). Post-polymerisation CM on an olefin containing polymer P(β-heptenolactone) P(β-HL), with methyl acrylate and an epoxide, generated functionalised homopolymers with increased Tg’s. Co-polymerisation of lactide with β-HL generated novel gradient-copolymers. Olefin CM with 15 different cross-partners produced functionalised copolymers with different thermal properties. Based on this route a new methodology was created to introduce two unique functionalities into the polymer backbone by manipulation of the olefin reactivities. Finally, in a collaborative project, uranium and cerium catalysts, Me3SiOU(OArP)3 and Me3SiOCe(OArP)3 - designed out-with the group- were tested and compared as ROP catalysts for lactide. Both catalysts were active in living polymerisations of L-lactide and under immortal conditions the activity and rates of the catalysts were switched, accounted for by a change in the coordination sphere due to ligand displacement. ROP of rac-lactide using the uranium analogue produced heterotactic-biased PLA with a Pr = 0.79

Olefin cross metathesis and ring-closing metathesis in polymer chemistry

The use of olefin cross metathesis in preparing functional polymers, through either pre-functionalisation of monomers or post-polymerisation functionalisation is growing in both scope and breadth. The broad functional group tolerance of olefin metathesis offers a wealth of opportunities for introducing a broad range of functional groups into the polymer backbone, tuning polymer properties and expanding potential applications. Similarly, ring-closing metathesis offers the ability to tune the polymer macrostructure and microstructure to similar effect. In this review, we explore the importance of understanding selectivity in olefin cross metathesis in designing functional polymers, the manipulation of this reactivity to prepare (multi)functional polymers, and show how polymer systems can be constructed to favour ring closing and change backbone structure and properties

Do little embryos make big decisions? How maternal dietary protein restriction can permanently change an embryo's potential, affecting adult health

Periconceptional environment may influence embryo development, ultimately affecting adult health. Here, we review the rodent model of maternal low-protein diet specifically during the preimplantation period (Emb-LPD) with normal nutrition during subsequent gestation and postnatally. This model, studied mainly in the mouse, leads to cardiovascular, metabolic and behavioural disease in adult offspring, with females more susceptible. We evaluate the sequence of events from diet administration that may lead to adult disease. Emb-LPD changes maternal serum and/or uterine fluid metabolite composition, notably with reduced insulin and branched-chain amino acids. This is sensed by blastocysts through reduced mammalian target of rapamycin complex 1 signalling. Embryos respond by permanently changing the pattern of development of their extra-embryonic lineages, trophectoderm and primitive endoderm, to enhance maternal nutrient retrieval during subsequent gestation. These compensatory changes include stimulation in proliferation, endocytosis and cellular motility, and epigenetic mechanisms underlying them are being identified. Collectively, these responses act to protect fetal growth and likely contribute to offspring competitive fitness. However, the resulting growth adversely affects long-term health because perinatal weight positively correlates with adult disease risk. We argue that periconception environmental responses reflect developmental plasticity and 'decisions' made by embryos to optimise their own development, but with lasting consequences

Industrial Forest Product Quality: An Empirical Test of Garvin's Eight Quality Dimensions

A national sample of purchasing executives was asked to rate 26 product and dealer/manufacturer attributes on the basis of their importance in assessing office furniture quality. Attributes were selected a priori to represent eight quality dimensions—performance, features, reliability, conformance, durability, serviceability, aesthetics and perceived quality. Results of confirmatory factor analysis failed to support the eight dimensional structure. However, subsequent exploratory factor analysis utilizing raw and transformed rating scores supported the existence of most dimensions. Results also suggest the combining of performance and feature dimensions, adding an economic (price/value) dimension, and the existence of a strong association between service and perception of overall quality

Installing Multiple Functional Groups on Biodegradable Polyesters via Post-Polymerization Olefin Cross-Metathesis

Olefin cross-metathesis is an effective tool for the functionalization of biodegradable aliphatic polyesters through both pre- and post-polymerization of β-heptenolactone (βHL). Ring-opening polymerization of βHL accesses both homopolymers and novel copolymers, producing strong gradient copolymers with lactide. A total of 15 different alkene cross-partners ranging from type I to type III olefins are readily incorporated to produce polyesters with a range of functionalities, altering the thermal and chemical properties of the resulting polymers. A novel methodology was also developed to introduce two unique functionalities into the polymer backbone based on manipulation of cross-partner reactivity, showcasing the scope and versatility of olefin CM as a strategy for post-polymerization modification of polymers

Iron-Catalyzed Hydromagnesiation: Synthesis and Characterization of Benzylic Grignard Reagent Intermediate and Application in the Synthesis of Ibuprofen

Iron-catalyzed hydromagnesiation of styrene derivatives using ethylmagnesium bromide has been investigated for the synthesis of benzylic Grignard reagents. The benzylic Grignard reagent formed in the reaction was observed directly and its conformation in solution characterized by multinuclear and variable-temperature NMR spectroscopy. The Grignard reagent could be stored for at least 2 weeks without significant loss in activity. Hydromagnesiation of styrene in tetrahydrofuran gave a mixture of monoalkyl- and dialkylmagnesium species, (1-phenylethyl)­magnesium bromide (<b>2</b>; RMgBr) and bis­(1-phenylethyl)magnesium (<b>3</b>; R₂Mg), with the equilibrium between these species lying in favor of the dialkylmagnesium species. The thermodynamic parameters of alkyl exchange for the reaction MgBr₂ + R₂Mg (<b>3</b>)<b> ⇌</b> 2RMgBr (<b>2</b>) were quantified, with the enthalpy and entropy of formation of <b>2</b> from MgBr₂ and <b>3</b> calculated as 32 ± 7 and 0.10 ± 0.03 kJ mol^–1, respectively. This methodology was applied, on a 10 mmol scale, as the key step in the synthesis of ibuprofen, using sequential iron-catalyzed alkyl–aryl and aryl–vinyl cross-coupling reactions to give 4-isobutylstyrene, which following hydromagnesiation and reaction with CO₂ gave ibuprofen. Each step proceeded in excellent yield, at temperatures between 0 °C and room temperature, at atmospheric pressure. Inexpensive, nontoxic, and air- and moisture-stable iron­(III) acetylacetonate was used as the precatalyst in each step in combination with inexpensive amine ligands