Polystyrene (PS) is an important commodity polymer. In its most commonly used form, PS is a high molecular weight linear polymer, typically produced through free-radical polymerization, which is a well understood and robust process. This process produces a high molecular weight, clear thermoplastic that is hard, rigid and has good thermal and melt flow properties for use in moldings, extrusions and films. However, polystyrene produced through the free radical process has a very broad molecular weight distribution, which can lead to poor performance in some applications. To this end, nitroxide-mediated radical polymerization (NMRP) can synthesize materials with a much more consistently defined molecular architecture as well as relatively low polydispersity than other methods. NMRP involves radical polymerization in the presence of a nitroxide mediator. This mediator is usually of the form of a stable radical which can bind to and disable the growing polymer chain. This will “tie up” some of the free radicals forming a dynamic equilibrium between active and dormant species, through a reversible coupling process. NMRP can be conducted through one of two different processes: (1) The bimolecular process, which can be initiated with a conventional peroxide initiator (i.e. BPO) but in the presence of a stable nitroxide radical (i.e. TEMPO), which is a stable radical that can reversibly bind with the growing polymer radical chain, and (2) The unimolecular process, where nitroxyl ether is introduced to the system, which then degrades to create both the initiator and mediator radicals. Based on previous research in the group, which included experimental investigations with both unimolecular and bimolecular NMRP under various conditions, it was possible to build on an earlier model and come up with an improved detailed mechanistic model. Additionally, it was seen that certain parameters in the model had little impact on the overall model performance, which suggested that their removal would be appropriate, also serving to reduce the complexity of the model. Comparisons of model predictions with experimental data both from within the group and the general literature were performed and trends verified. Further work was done on the development of an additionally reduced model, and on the testing of these different levels of model complexity with data. The aim of this analysis was to develop a model to capture the key process responses in a simple and easy to implement manner with comparable accuracy to the complete models. Due to its lower complexity, this substantially reduced model would me a much likelier candidate for use in on-line applications. Application of these different model levels to the model-based D-optimal design of experiments was then pursued, with results compared to those generated by a parallel Bayesian design project conducted within the group. Additional work was done using a different optimality criterion, targeted at reducing the amount of parameter correlation that may be seen in D-optimal designs. Finally, conclusions and recommendations for future work were made, including a detailed explanation of how a model similar to the ones described in this paper could be used in the optimal selection of sensors and design of experiments.

Polystyrene (PS) is an important commodity polymer. In its most commonly used form, PS is a high molecular weight linear polymer, typically produced through free-radical polymerization, which is a well understood and robust process. This process produces a high molecular weight, clear thermoplastic that is hard, rigid and has good thermal and melt flow properties for use in moldings, extrusions and films. However, polystyrene produced through the free radical process has a very broad molecular weight distribution, which can lead to poor performance in some applications. To this end, nitroxide-mediated radical polymerization (NMRP) can synthesize materials with a much more consistently defined molecular architecture as well as relatively low polydispersity than other methods. NMRP involves radical polymerization in the presence of a nitroxide mediator. This mediator is usually of the form of a stable radical which can bind to and disable the growing polymer chain. This will “tie up” some of the free radicals forming a dynamic equilibrium between active and dormant species, through a reversible coupling process. NMRP can be conducted through one of two different processes: (1) The bimolecular process, which can be initiated with a conventional peroxide initiator (i.e. BPO) but in the presence of a stable nitroxide radical (i.e. TEMPO), which is a stable radical that can reversibly bind with the growing polymer radical chain, and (2) The unimolecular process, where nitroxyl ether is introduced to the system, which then degrades to create both the initiator and mediator radicals. Based on previous research in the group, which included experimental investigations with both unimolecular and bimolecular NMRP under various conditions, it was possible to build on an earlier model and come up with an improved detailed mechanistic model. Additionally, it was seen that certain parameters in the model had little impact on the overall model performance, which suggested that their removal would be appropriate, also serving to reduce the complexity of the model. Comparisons of model predictions with experimental data both from within the group and the general literature were performed and trends verified. Further work was done on the development of an additionally reduced model, and on the testing of these different levels of model complexity with data. The aim of this analysis was to develop a model to capture the key process responses in a simple and easy to implement manner with comparable accuracy to the complete models. Due to its lower complexity, this substantially reduced model would me a much likelier candidate for use in on-line applications. Application of these different model levels to the model-based D-optimal design of experiments was then pursued, with results compared to those generated by a parallel Bayesian design project conducted within the group. Additional work was done using a different optimality criterion, targeted at reducing the amount of parameter correlation that may be seen in D-optimal designs. Finally, conclusions and recommendations for future work were made, including a detailed explanation of how a model similar to the ones described in this paper could be used in the optimal selection of sensors and design of experiments.

This thesis has as its principal goal the development of sustainable pressure-sensitive adhesives (PSAs). To that end, we examined polymer reaction engineering practices and polymer formulations through the lens of the 12 Principles of Green Chemistry. To begin with, we employed emulsion polymerization as our polymer synthesis method because of its use of water instead of hazardous solvents. We also replaced various petroleum-based components with bio-based alternatives (e.g., starch, cellulose nanocrystals), thereby reducing synthesis hazards, increasing product safety and increasing the amount of sustainably sourced raw materials in the PSA. However, changing the synthetic method as well as key components in the formulation presented significant challenges to maintaining PSA performance. This thesis illustrates the challenging path taken towards developing a fully renewable PSA. PSAs should display a specific balance of adhesion and cohesion. Typically, petroleum-based additives (which are often hazardous/toxic) such as tackifiers, cross-linkers, chain transfer agents and rheology modifiers are added to tailor latex properties to fit the intended application. However, because of their inherently opposing effects, an additive used to increase adhesion will weaken the cohesive forces of the polymer, and vice versa. Cellulose nanocrystals (CNCs) are sustainable nanomaterials that have been shown to be effective to resolve the adhesion/cohesion conundrum. In the first part of this project, we developed a new technique to increase CNC loading in emulsion-based PSA formulations beyond the 1-2% limits previously encountered due to high latex viscosity, colloidal instability, and poor film properties. The higher CNC loadings were shown to continuously improve shear strength but resulted in eventual decreases to tack and peel strength. In the second part of this project, we replaced the sulfated CNCs with carboxylated CNCs (cCNCs), which are produced by a process using a “greener” catalyst (i.e., hydrogen peroxide instead of sulfuric acid). The cCNCs’ carboxylate surface groups interacted strongly with the polymer matrix, ultimately leading to catastrophic coagulation. The interactions between cCNCs and other standard latex components were studied and through the creative manipulation of the emulsion polymerization process, a reproducible method to incorporate the cCNCs in a seeded semi-batch reaction yielded stable, high-quality latexes. In the third part of this project, the effect of the cCNCs on the adhesive properties of the nanocomposite latex films was studied and compared to the effects of the sulfated CNCs. AFM imaging revealed that cCNCs interact with latex particles and each other; thus, omitting ultrasonication at the preparation stage was shown to preserve these interactions and lead to greater property enhancements. In the fourth part of this project, starch nanoparticles (SNPs) were used to displace some of the petroleum-based monomer in the production of core-shell (SNP cores, acrylic shell) latexes. SNPs are renewably sourced, inexpensive, and biodegradable. The challenge of locating the SNPs into the particle cores was overcome by crosslinking the SNPs using a food grade cross-linker (sodium trimetaphosphate) and functionalizing them using a sugar-based monomer (EcoMer™). To tune the PSA properties to rival a range of commercial tapes, a method to incorporate CNCs to the SNP-latexes in situ was developed. In addition, because monomers such as 2-octyl acrylate (2OA), styrene, and acrylic acid can be bio-sourced, they were selected as the acrylic shell monomers to encapsulate the SNPs in the nanocomposite latexes. Due to supply chain challenges, n-octyl acrylate was used as a model monomer for 2OA to produce latexes with ~80% bio-content that rivaled commercial Post-It™ notes, masking tapes, and duct tapes. After addressing the sustainability of the polymerization method and polymer components, we posed the question: what are the effects of using renewably sourced and bio-sourced materials on the end-of-life of the PSAs? Because the infrastructure for biodegradation studies at the lab scale via composting does not exist in Canada (to our knowledge), we designed an in-house aerobic composting set-up consisting of a series of bioreactors and sensors capable of measuring the aerobic biodegradability of our polymers in a simulated composting environment. Although not fully tested, the composting setup was designed, and its construction was begun. Steps to complete the construction and validate its operation are detailed. The path towards sustainability is often long and complex. In this four-year study, the re-design of an adhesive synthesis process using a more sustainable approach, emulsion polymerization, along with an 80% bio-sourced formulation required significant corrective measures. Overcoming the technical challenges required mustering all the polymer reaction engineering tools at our disposal. Despite the time and effort required, achieving a more sustainable process is indeed within our grasp.

Independent control of the surface and bulk properties is advantageous for many applications such as adhesives, release coatings, and antimicrobial films. Traditional methods for achieving independent control typically require multiple processing steps such as wet-on-wet or wet-on-dry coating methods. Independent control over the surface properties can achieved in a single step utilizing the temporal and spatial control inherent to photopolymerization. Specifically, a co-photopolymerization of monomers with different reactivities in the presence of a light gradient is capable of producing a polymer film with a surface chemistry that differs from the bulk chemistry. The light gradient, produced via the concentration of photoinitiator in the formulation, results in a reaction gradient through the film with the higher rates of reaction occurring in the high light intensity regions of the film. The preferentially reacting monomer adds at a greater rate in the high light intensity regions resulting in non-uniform consumption yielding a concentration gradient. Consequently, diffusion of the preferentially reacting monomer from the bulk to the surface of the film and a counter-diffusion of the other monomer from the surface to the bulk of the film occurs from the non-uniform monomer consumption thus producing a film with a concentration gradient through the depth of the film with the preferentially reacting monomer enriching the high light intensity regions. A variety of kinetic differences capable of producing a stratified film will be presented including inherent monomer reactivity, number of functional groups per monomer, oxygen inhibition, thiol-ene chemistry, and Norrish type two initiation. Additionally, parameters that control the degree of stratification, such as methods of varying polymerization rate and the light gradient, will be examined. Changes in surface properties (such as contact angle, surface hardness, adhesion) and bulk properties (such as mechanical properties measured by dynamic mechanical analysis and polymer swelling) are studied as a function of stratification. Finally, a mathematical model which describes and predicts the production of stratified films via photopolymerization is presented. Photopolymerization allows for a facile, single step method of generating stratified films with controllable surface chemistries.