Covalent surface modification of medical grade PVC tubing was performed using copper-free azide-alkyne cycloaddition reactions to prepare anti-fouling surfaces. PVC azide surface was synthesized by nucleophilic substitution of labile chlorine with sodium azide in the presence of phase transfer catalyst in aqueous media to minimize loss of plasticizer. Electron-poor alkynes with different functionality (zwitterionic, polyethylene oxide, polyfluoro and quaternary amines) were synthesized and covalently attached to the PVC azide surface by thermal azide-alkyne cycloaddition reactions. The reaction progress was monitored by ATR-FTIR spectroscopy. Static contact angle, surface free energy, contact angle hysteresis and atomic force microscopic images were taken for each modified surface. Except for the C6F13 polyfluoro group, the other functional groups containing zwitterionic, polyethylene oxide and quaternary ammonium display hydrophilic properties with the initial SCA in the range of 35-80° due to the strong surface charges. All the modified PVC surfaces maintain their wetting properties against vigorous water rinsing for long period of time (over 60 minutes of sonication) confirming strong covalent bonding of the functional groups to the surface. The antifouling activity of these modified endotracheal tubing samples was evaluated by bacterial adherence assay using Pseudomonas aeruginosa, a gram-negative opportunistic and nosocomial pathogen. Although the adherence assays demonstrate that high polyfluoro (di-ester of C6F13) and long quaternary amine functionality samples slightly reduced P. aeruginosa adherence to endotracheal tubing, the inhibition was not as strong as expected. X-Ray Photoelectron Spectroscopy revealed a pre-existing silicone coating on the original commercial samples, dampening the effects of biofilm inhibition from the chemical modification procedures.

Poly(vinyl chloride) (PVC) is one of the most widely used thermoplastics; uses range from building materials, medical devices, toys, and sports equipment. Pure PVC is rigid and brittle. Typically, small molecule plasticizers are added to modify the flexibility and durability of PVC. The most common external plasticizers are phthalate esters. These small molecules leach out of the PVC matrix into the environment; when inhaled, absorbed, or ingested into the human body, phthalates and their metabolites pose a significant risk to human health. The most efficient way to prevent leaching of plasticizers is to covalently attach them to PVC. This is referred to as “internal plasticization.”

Two strategies have been used to achieve internal plasticization of PVC in this thesis. In the first strategy, thermal azide-alkyne Huisgen cycloaddition was utilized to attach electron-poor acetylenediamides using a branched glutamic acid linker to azidized PVC, incorporating four plasticizing moieties per attachment point. A systematic study incorporating either alkyl or triethylene glycol esters provided materials with varying degrees of plasticization, with depressed glass transition temperature (Tg) values ranging from −1 °C to 62 °C. Tg values of these internally plasticized PVC samples were shown to decrease with increasing chain length of the plasticizing ester. A branched internal plasticizer bearing a triethylene glycol ester had lower Tg values compared to that with a same length linear alkyl ester. Thermogravimetric analysis of PVC bearing internal plasticizers revealed that these branched internal plasticizers bearing alkyl ester chains are more thermally stable than similarity branched plasticizers bearing ethylene glycol esters. These internal tetra-plasticizers were synthesized and attached to PVC-azide in three simple synthetic steps.

In the second strategy, internal plasticization of PVC was achieved in one step using copper-mediated atom transfer radical polymerization (ATRP) to graft random n-butyl acrylate (BA) and 2-2-(2-ethoxyethoxy)ethyl acrylate (2EEA) copolymers from defect sites on the PVC chain. Five graft copolymers were made with different ratios of PBA and P2EEA; Tg values of these functionalized PVC polymers ranged from -28 °C to -50 °C. Single Tg values were observed for all polymers, indicating good compatibility between PVC and the grafted chains, with no evidence of microphase separation. Plasticization efficiency is higher for polyether P2EEA moieties compared with PBA components. The resultant PVC graft copolymers were thermally more stable compared to unmodified PVC. Increasing the reaction scale from 2 g to 14 g produced consistent and reproducible results, suggesting this method could be applicable on an industrial scale. Further optimizations of the ATRP conditions were carried out shortening the reaction time and varying the acrylate monomer to VC unit ratios. Nine different internally plasticized PVC graft copolymers with different weight percents of plasticizer spanning from 24% to 75% were prepared. A wide range of Tg values (-54 °C to 54 °C) were achieved, with Tg values below zero for samples with weight percent of plasticizer more than 50%. In summary, highly effective internal plasticization of PVC was accomplished by Cu-mediated ATRP in only one step. Whereas the azide-alkyne approach may be suffered from the potential danger in handling azides on large scale, the ATRP graft copolymerization approach is expected to be very attractive to industry, to afford internally plasticized PVC products with reliable and durable physical properties.

Nitroxides have played a vital role in many areas in chemistry, due to their persistent radical nature, and facile redox properties. In this thesis, nitroxides are used to quench the fluorescence of organic fluorophores and quantum dots, as well as to prepare end-functionalized polymers using nitroxide mediated radical polymerization (NMRP).

Quantum dot (QD) fluorescence is effectively quenched by binding to functionalized nitroxides. The association constants and fluorescence quenching of CdSe QDs with nitroxides bearing a ligand coordinated to the QD surface have been examined using electron paramagnetic resonance and fluorescence spectroscopy. Quenching of QD fluorescence is dependent on the distance between the radical and the QD, and the binding affinity. The quenched fluorescence is restored when the surface-bound nitroxide is converted to a hydroxylamine by a mild reducing agent, or trapped by a carbon radical to form an alkoxyamine. A fluorescence quenching mechanism is proposed.

The phenomenon of fluorescence quenching was extended to organic fluorophores. Nitroxides were synthesized bearing a tethered photosensitive species that undergo photocleavage to form a radical, which is then intramolecularly trapped by the nitroxide. When a fluorescent tag is appended to these nitroxides, the fluorescence is restored upon photoexcitation. A profluorescent nitroxide sensor of mild reductants was also developed, which undergo cyclization upon formation of the hydroxylamine. Unlike existing methodologies, this sensor is non-reversible since it cannot be reoxidized in the presence of oxygen.

Thiol-derivatized N-alkoxyamines, functionalized with a free thiol, disulfide, or trityl-protected thiol group were synthesized and employed in NMRP. Deprotection of the trityl group and mild oxidation provided disulfide linked polystyrene of double the molecular weight. Reduction of this polystyrene, followed by trapping with N-phenylmaleimide (NPM) resulted in a NPM-protected thiol terminated polystyrene with the same molecular weight as prior to oxidation.

A series of novel 8-amino BODIPY profluorescent nitroxides and the corresponding N-ethoxyamine derivatives were synthesized with varying substitution and molecular geometries. Single crystal X-ray diffraction data for the three 8-amino BODIPY nitroxides were obtained. UV-Vis absorption and emission data for the profluorescent nitroxides and 8-amino BODIPY N-ethoxyamine derivatives were examined to assess the utility of these compounds as fluorescent probes.

Poly(vinyl chloride) (PVC) is one of the most utilized thermoplastics on Earth. However, PVC by itself is brittle and not readily processable. This material reached the success of its worldwide demand because of phthalates, a cost-effective additive (emollient) that imparts flexibility and resistivity towards weathering, temperature extremes and electrical conductivity. The use of phthalates as plastic emollients is widespread, representing approximately three quarters of all plasticizers globally, with applications ranging from industrial to consumer products. The pervasive utilization of low molecular weight blended phthalates as emollients inevitably leads to leaching, contamination and exposure. Phthalates and their metabolites have displayed negative effects on various organs and act as potent endocrine disrupting chemicals that cause deleterious pre- and postnatal developmental effects, notably in males. Bans of phthalates by the European Union and the United States in children’s articles have spurred the development of less toxic PVC plasticizer alternatives.

Branched and linear non-migratory internal plasticizers attached to PVC by a pendant triazole linkage were synthesized. Copper-free azide-alkyne thermal cycloaddition was employed to covalently bind triazole-based phthalate mimics to poly(vinyl chloride) (PVC). To systematically investigate the effect of plasticizer structure on glass transition temperature, several architectural motifs were explored. Free volume theory was considered when designing many of these internal plasticizers: hexyl-tethers were utilized to generate additional space between the triazole-phthalate mimic and the polymer backbone. Miscibility of these triazole-plasticizers in PVC is important: variation of the ester moieties on the triazole possessing alkyl and/or poly(ethylene oxide) (PEO) chains produced a wide range of glass transition temperatures (Tg): from anti-plasticizing 96 °C, to highly efficient plasticized materials exhibiting Tg values as low as -42 °C.

Triazole methyl esters directly appended to PVC displays an inherent anti-plasticization effect originating from the aromatic ring, which diminishes with increasing molecular weight and branching of the alkyl ester chains. Introduction of a flexible hexyl tether to the secondary triazole group acts as additional molecular weight and branching, further lowering Tg values. Attachment of two hexyl tethered secondary triazoles follows this trend by enforcing another branch point and increasing molecular weight. Utilization of PEO esters in all architectural types significantly enhances Tg depressions, with longer PEO chains exhibiting remarkable results. Single PEO triazole esters readily prepared from propiolic esters using low-cost, commercially available materials combine excellent plasticization with straightforward synthesis, making these non-migratory internal plasticizers extremely attractive for industrial applications.

An alternative strategy to post-polymerization direct modification of PVC to obtain internally plasticized materials involves the copolymerization of vinyl chloride monomer (VCM) with a monomer functionalized with a triazole-phthalate mimic. Electron-rich vinyl acetate monomers with an appended triazole-plasticizer were synthesized for this purpose. Copolymerizations with the vinyl acetate triazole monomers and VCM were largely unsuccessful. It was envisaged that an acrylate derivative should remedy the low reactivity of these vinyl acetate monomers. An acrylate incorporating a hexyl-tethered triazole-phthalate mimic served two purposes: 1) generate space between the triazole and polymerizing vinyl group to prevent monomer deactivation and, 2) enhance the plasticization efficiency of the triazole.

AbstractChemical Modification of Polyvinyl Chloride: Internal Plasticization and Chemical Degradation Patrick Skelly Polyvinyl Chloride (PVC) is the third most-produced plastic in the world. It is found in construction materials, pipes that contain our drinking water, toys, furniture, clothing, credit cards, medical tubing and blood bags. Because of the sheer quantity of PVC in the world, it is important to make it as safe as possible. Health concerns over additives to PVC can add up over a lifetime of exposure to household products. Environmental concerns over the degradation of PVC also add up with millions of tons entering the waste stream every year. This dissertation addresses two aspects of chemical modification of PVC with regards to these health and environmental concerns. The first aspect is the internal plasticization of PVC, replacing migratory plasticizers that can enter the body. The second is controlled chemical degradation of PVC, working towards the goal of harvesting PVC waste as a carbon resource. The first chapter is a review article about internal plasticization: covalently bonding plasticizers to PVC. A comprehensive review of this field was previously lacking. Literature from 1936 to 2021 is reviewed and categorized by method of attachment, either nucleophilic substitution or graft-from polymerization. A perspective is given on the types of structures and syntheses used in successful internal plasticizers. With the continued goal of internal plasticization, the second chapter is an experimental study of the metal-free azide-alkyne cycloaddition, a reaction well-suited for attaching plasticizers to PVC. To more effectively use this reaction, the effect of different electron-withdrawing groups was studied. A range of alkynes were synthesized and their rates compared by competition experiments. The most reactive alkyne contained a sulfone group and an ester group, and reacted 2100 times faster than the least reactive, containing a phenyl substituent and an ester. Phenyl- and nitrophenyl- substituents surprisingly decreased the reactivity of the alkynes instead of increasing it. DFT calculations of reaction energies, orbital energies, distortion-interaction parameters, and bond indices were performed to help explain the reactivity trends. The third chapter addresses the chemical degradation of PVC. A method was developed to eliminate chloride from PVC using hydroxide base, and then cleave the all-carbon backbone using olefin metathesis of the newly-created double bonds. Addition of allyl alcohol to the elimination step allows the incorporation of allyl side chains, which more easily attach to the metathesis catalyst and incorporate it into the main chain by a ring-closing metathesis reaction. Over 20x reduction in molecular weight is observed, demonstrating repeated cleavage of the polymer chain. By adding an external alkene to the reaction, a diene with the corresponding substituents is successfully created, indicating some incorporation of PVC carbons into a new chemical product.

Three novel fluorinated alkoxyamines were synthesized for nitroxide-mediated precipitation polymerization (NMP) of styrene in supercritical carbon dioxide. The polymerizations were conducted in supercritical carbon dioxide without excess free nitroxide to allow for a detailed study on nitroxide partitioning. The addition of a fluorinated moiety allowed for increased partitioning relative to the parent nitroxide into supercritical carbon dioxide. The loss of control over the polymerization due to nitroxide partitioning did not have a significant influence on the polymerization rate. Synthesis of polyfluorinated macroinitiators by atom transfer radical polymerization (ATRP) of fluorinated monomers was explored but thwarted due to a lack of solubility. The increased fluorine content due to polymerization of fluorinated monomers would have allowed direct control over the quantity of fluorine added to the macroinitiator and potentially influenced the quantity of nitroxide partitioning.

Synthesis of styrene, acetate, and acrylate derivatives bearing the 1,2,3-triazole-4,5-

dicarboxylate moiety through Cu-free Huisgen 1,3-dipolar cycloadditions are presented.

Following synthesis, the monomers were copolymerized with styrene and n-butyl

acrylate via nitroxide mediated radical polymerization (NMP) methodology to afford

these triazole macroplasticizers to act as phthalate mimics. The copolymers were then

blended in 20%, 40%, and 60% synthetic copolymer – PVC ratios to be analyzed by

differential scanning calorimetry (DSC). These macroplasticizers provide the opportunity

for further elaboration and could become an effective replacement for common phthalate

plasticizers.