In this thesis, I describe experiments that provide a new and deeper understanding of factors that affect polymer diffusion in acrylic latex films. This is the step that leads to the growth of mechanical properties of these films. Polymer diffusion was studied by fluorescence resonance energy transfer (FRET) in films prepared from dye-labeled latex particles. Poly(n-butyl acrylate-co-methyl methacrylate) [P(BA-MMA)] was chosen for the study of copolymer composition on the polymer diffusion rate. Four sets of P(BA-MMA) copolymers were prepared from various weight ratios of BA/MMA. Polymer diffusion was monitored as a function of annealing temperature, and apparent diffusion coefficients (Dapp) were calculated from the FRET data, using a simple diffusion model. The temperature dependence of polymer dynamics (G’, G”) obtained by linear rheology measurements is in good agreement with the temperature dependence of Dapp. Increasing the BA content of the copolymer led to an apparent increase in long-chain branching, which is reflected in both the time dependence of Dapp and in the dynamic moduli measurements. To study the effect of branching on polymer diffusion rates, latex particles comprised of branched poly(n-butyl methacrylate) (PBMA) were prepared. The degree of branching was controlled by adding various amounts of bisphenol A dimethacrylate as a branching agent, plus 1-dodecanethiol as a chain transfer agent to prevent gel formation and to control the polymer molecular weight. The results of rheology (G’, G”) measurements are consistent with the absence of entanglement in these polymers. After correcting for the effects of Tg, by comparing results at a constant T- Tg, ET data show that the PBMA with the highest degree of branching had the highest diffusivity. In a separate set of experiments I tested the effect of incorporating the highly branched PBMA (HB-PBMA) into P(BA-MMA) dispersions to examine its influence on polymer diffusion in the latex films. Three different approaches were taken to combine these different polymers: latex blends, using HB-PBMA seeds in the synthesis of P(BA-MMA) by semicontinuous emulsion polymerization, and dissolving HB-PBMA in the mixture of BA and MMA for latex particles prepared by miniemulsion polymerization. ET studies indicate that HB-PBMA significantly enhances polymer diffusion rate, comparable with TexanolTM, a volatile organic coalescing agent. Tensile tests show that the films containing HB-PBMA have significant higher mechanical properties than the films containing TexanolTM.

In this thesis, I describe experiments that provide a new and deeper understanding of factors that affect polymer diffusion in acrylic latex films. This is the step that leads to the growth of mechanical properties of these films. Polymer diffusion was studied by fluorescence resonance energy transfer (FRET) in films prepared from dye-labeled latex particles. Poly(n-butyl acrylate-co-methyl methacrylate) [P(BA-MMA)] was chosen for the study of copolymer composition on the polymer diffusion rate. Four sets of P(BA-MMA) copolymers were prepared from various weight ratios of BA/MMA. Polymer diffusion was monitored as a function of annealing temperature, and apparent diffusion coefficients (Dapp) were calculated from the FRET data, using a simple diffusion model. The temperature dependence of polymer dynamics (G’, G”) obtained by linear rheology measurements is in good agreement with the temperature dependence of Dapp. Increasing the BA content of the copolymer led to an apparent increase in long-chain branching, which is reflected in both the time dependence of Dapp and in the dynamic moduli measurements. To study the effect of branching on polymer diffusion rates, latex particles comprised of branched poly(n-butyl methacrylate) (PBMA) were prepared. The degree of branching was controlled by adding various amounts of bisphenol A dimethacrylate as a branching agent, plus 1-dodecanethiol as a chain transfer agent to prevent gel formation and to control the polymer molecular weight. The results of rheology (G’, G”) measurements are consistent with the absence of entanglement in these polymers. After correcting for the effects of Tg, by comparing results at a constant T- Tg, ET data show that the PBMA with the highest degree of branching had the highest diffusivity. In a separate set of experiments I tested the effect of incorporating the highly branched PBMA (HB-PBMA) into P(BA-MMA) dispersions to examine its influence on polymer diffusion in the latex films. Three different approaches were taken to combine these different polymers: latex blends, using HB-PBMA seeds in the synthesis of P(BA-MMA) by semicontinuous emulsion polymerization, and dissolving HB-PBMA in the mixture of BA and MMA for latex particles prepared by miniemulsion polymerization. ET studies indicate that HB-PBMA significantly enhances polymer diffusion rate, comparable with TexanolTM, a volatile organic coalescing agent. Tensile tests show that the films containing HB-PBMA have significant higher mechanical properties than the films containing TexanolTM.

This thesis describes the design and synthesis of homopolymers and copolymers for tuning surface properties of colloidal semiconductor quantum dots (QDs), and directing QD self-assembly to create well-defined 3D structures in which the spatial organization of QDs and other functional materials (e.g. conjugated polymers) is properly controlled. A common feature of all of the polymers described in this thesis is that they contain multiple pendant anchoring groups such as tertiary amines, pyridines and acrylic acids, which bind strongly to QD surfaces as multidentate ligands. This thesis starts by describing a quantitative analytical method based on size exclusion chromatography (SEC) to characterize the interaction of poly(2-N,N-dimethylaminoethyl methacrylate) (PDMA) with TOPO-coated CdSe QDs. In addition, the separation of polymer-bound QDs from excess free polymer can be scaled up by preparative high-performance liquid chromatography. The second part of this thesis explores a method to disperse CdSe and core/shell CdSe/ZnS QDs into water using a poly(ethylene glycol-b-N,N-dimethylaminoethyl methacrylate) (PEG–b–PDMA) diblock copolymer. Alternatively, statistical copolymers, such as poly(oligoethyleneglycol)-co-PDMA (POEG-co-PDMA) and poly(N,N-dimethylacrylamide)-based statistical copolymers carrying pendant pyridine or imidazole groups play the same role as PEG–b–PDMA for dispersion of the QDs into water. The third part of this thesis describes the synthesis and characterization of a water-soluble pH-responsive PDMA-grafted polythiophene (denoted as PT-g-PDMA). The relatively rigid and extended conformation of the polythiophene backbones provides new opportunity for studying the correlation of between optical responses of conjugated polymers and their conformational transitions. In addition, the favorable interaction between the PDMA arms of PT-g-PDMA and CdSe nanorods allows enhanced interface-compatibility of the nanorods with the polythiophene backbone. The last part of this thesis presents a straightforward and versatile approach to achieving nanoscale co-organization of colloidal QDs (e.g. CdSe, CdSe/ZnS core/shell or PbS QDs) with conjugated polymers (e.g. poly(3-hexylthiphene)) by using polymer micelles of poly(styrene-b-4-vinylpyridine) as the structural motif. The spatially defined organization allows photoinduced excited state interaction between the QDs and poly(3-hexylthiphene) at the micellar interface, reminiscent of structures of light harvesting complexes in nature. This strategy is also applicable to other morphologies of polymer self-assemblies, such as poly(styrene-b-acrylic acid) (PS-b-PAA) vesicles.

This thesis describes a study of various aspects of chemical reactions conducted in microfluidic reactors. (i) In the first project, we proposed the application of the 'internal trigger' approach to multi-step microfluidic polymerization reactions conducted in droplets, namely, polyaddition and polycondensation. We hypothesized and experimentally established that heat generated in the exothermic free radical polymerization of an acrylate monomer triggers the polycondensation of the urethane oligomer. As a result, we synthesized monodispersed poly(acrylate/urethane) microparticles with an interpenetrating polymer network structure. (ii) In the second project, we developed a multiple modular microfluidic reactor with the purpose of increasing productivity in microfluidic synthesis. Compared to the productivity of the single microfluidic reactor < 1g/hr, we synthesized poly(N-isopropylacrylamide) particles at a productivity of approximately 50g/hr with a CV < 5%. We analyzed and addressed several challenges of this process, such as the fidelity in the fabrication of microfluidic reactors, crosstalk between individual reactors sharing a common liquid supply, and coalescence of droplets. (iii) We developed an integrated microfluidic reactor comprising four parallel individual reactors to study the effect of geometry and surface energy of the microchannels on the emulsification process. We spontaneously generated droplets with different volumes by integrating individual droplet generators in parallel with varying geometry. This approach is important in studies of the effect of droplet surface and volume on chemical reactions, and in the studies of diffusion-controlled processes. (iv) We conducted a microfluidic study of the reversible binding of CO2 to secondary amines in the process that mediates solvent polarity switch. We studied reaction rates and CO2 uptake by generating plugs of gaseous a CO2 and monitoring the change in their dimensions. We also demonstrated fast screening of reaction conditions, as well as the ability to reverse the reaction in situ.

This thesis presents a preparation of porous polymer materials. The first half of this thesis focuses on the microfluidic synthesis of macroporous copolymer microparticles. Macroporous copolymer microparticles have a broad range of applications such as ion exchange resins and sorbents, catalyst supports, and carriers of biologically active species. Many of these applications require precise control of the dimensions of microparticles in the range from 50 to 100 μm and predetermined size of pores. First, this thesis reports semicontinuous photoinitiated microfluidic synthesis of macroporous copolymer microparticles with the designated dimensions and a range of internal structures. A synthesis of macroporous polymer microparticles under certain conditions produces microparticles with a smooth nonporous “skin” layer. This effect limits the applications of porous microbeads by preventing solute molecules to permeate the dense particle surface and reach particle’s porous interior. Second, this thesis reports a straightforward method that was used to suppress the formation of the “skin” on the surface of macroporous copolymers. The second half of this thesis focuses on the synthesis and applications of porous polymer hybrid materials (PHM). PHMs carrying inorganic nanoparticles on the surface of pores have important applications in chemical and biological sensing, in chromatography and in heterogeneous catalysis. Particularly, this thesis describes the results of the experimental study of the preparation of PHM carrying gold nanorods (NRs) on the surface of pores. The material was prepared by utilizing two effects occurring concurrently: the photoinitiated polymerization induced phase separation in the polymer–solvent mixture and the migration of the NRs to the interface between the polymer and the porogen solvent. We show that the enrichment of the interface with the NRs is enhanced at high polymerization rates leading to rapid phase separation. By contrast, a more rapid increase in viscosity achieved at high polymerization rates does not have a significant effect on the segregation of NRs to the surface of the pores. Finally,the PHM coated with gold nanorods was utilized for the simultaneous detection of different analytes using surface enhanced Raman scattering (SERS) spectroscopy and fluorescence microscopy.

This thesis describes the design and synthesis of homopolymers and copolymers for tuning surface properties of colloidal semiconductor quantum dots (QDs), and directing QD self-assembly to create well-defined 3D structures in which the spatial organization of QDs and other functional materials (e.g. conjugated polymers) is properly controlled. A common feature of all of the polymers described in this thesis is that they contain multiple pendant anchoring groups such as tertiary amines, pyridines and acrylic acids, which bind strongly to QD surfaces as multidentate ligands. This thesis starts by describing a quantitative analytical method based on size exclusion chromatography (SEC) to characterize the interaction of poly(2-N,N-dimethylaminoethyl methacrylate) (PDMA) with TOPO-coated CdSe QDs. In addition, the separation of polymer-bound QDs from excess free polymer can be scaled up by preparative high-performance liquid chromatography. The second part of this thesis explores a method to disperse CdSe and core/shell CdSe/ZnS QDs into water using a poly(ethylene glycol-b-N,N-dimethylaminoethyl methacrylate) (PEG–b–PDMA) diblock copolymer. Alternatively, statistical copolymers, such as poly(oligoethyleneglycol)-co-PDMA (POEG-co-PDMA) and poly(N,N-dimethylacrylamide)-based statistical copolymers carrying pendant pyridine or imidazole groups play the same role as PEG–b–PDMA for dispersion of the QDs into water. The third part of this thesis describes the synthesis and characterization of a water-soluble pH-responsive PDMA-grafted polythiophene (denoted as PT-g-PDMA). The relatively rigid and extended conformation of the polythiophene backbones provides new opportunity for studying the correlation of between optical responses of conjugated polymers and their conformational transitions. In addition, the favorable interaction between the PDMA arms of PT-g-PDMA and CdSe nanorods allows enhanced interface-compatibility of the nanorods with the polythiophene backbone. The last part of this thesis presents a straightforward and versatile approach to achieving nanoscale co-organization of colloidal QDs (e.g. CdSe, CdSe/ZnS core/shell or PbS QDs) with conjugated polymers (e.g. poly(3-hexylthiphene)) by using polymer micelles of poly(styrene-b-4-vinylpyridine) as the structural motif. The spatially defined organization allows photoinduced excited state interaction between the QDs and poly(3-hexylthiphene) at the micellar interface, reminiscent of structures of light harvesting complexes in nature. This strategy is also applicable to other morphologies of polymer self-assemblies, such as poly(styrene-b-acrylic acid) (PS-b-PAA) vesicles.

This thesis describes a study of various aspects of chemical reactions conducted in microfluidic reactors. (i) In the first project, we proposed the application of the 'internal trigger' approach to multi-step microfluidic polymerization reactions conducted in droplets, namely, polyaddition and polycondensation. We hypothesized and experimentally established that heat generated in the exothermic free radical polymerization of an acrylate monomer triggers the polycondensation of the urethane oligomer. As a result, we synthesized monodispersed poly(acrylate/urethane) microparticles with an interpenetrating polymer network structure. (ii) In the second project, we developed a multiple modular microfluidic reactor with the purpose of increasing productivity in microfluidic synthesis. Compared to the productivity of the single microfluidic reactor < 1g/hr, we synthesized poly(N-isopropylacrylamide) particles at a productivity of approximately 50g/hr with a CV < 5%. We analyzed and addressed several challenges of this process, such as the fidelity in the fabrication of microfluidic reactors, crosstalk between individual reactors sharing a common liquid supply, and coalescence of droplets. (iii) We developed an integrated microfluidic reactor comprising four parallel individual reactors to study the effect of geometry and surface energy of the microchannels on the emulsification process. We spontaneously generated droplets with different volumes by integrating individual droplet generators in parallel with varying geometry. This approach is important in studies of the effect of droplet surface and volume on chemical reactions, and in the studies of diffusion-controlled processes. (iv) We conducted a microfluidic study of the reversible binding of CO2 to secondary amines in the process that mediates solvent polarity switch. We studied reaction rates and CO2 uptake by generating plugs of gaseous a CO2 and monitoring the change in their dimensions. We also demonstrated fast screening of reaction conditions, as well as the ability to reverse the reaction in situ.

This thesis presents a preparation of porous polymer materials. The first half of this thesis focuses on the microfluidic synthesis of macroporous copolymer microparticles. Macroporous copolymer microparticles have a broad range of applications such as ion exchange resins and sorbents, catalyst supports, and carriers of biologically active species. Many of these applications require precise control of the dimensions of microparticles in the range from 50 to 100 μm and predetermined size of pores. First, this thesis reports semicontinuous photoinitiated microfluidic synthesis of macroporous copolymer microparticles with the designated dimensions and a range of internal structures. A synthesis of macroporous polymer microparticles under certain conditions produces microparticles with a smooth nonporous “skin” layer. This effect limits the applications of porous microbeads by preventing solute molecules to permeate the dense particle surface and reach particle’s porous interior. Second, this thesis reports a straightforward method that was used to suppress the formation of the “skin” on the surface of macroporous copolymers. The second half of this thesis focuses on the synthesis and applications of porous polymer hybrid materials (PHM). PHMs carrying inorganic nanoparticles on the surface of pores have important applications in chemical and biological sensing, in chromatography and in heterogeneous catalysis. Particularly, this thesis describes the results of the experimental study of the preparation of PHM carrying gold nanorods (NRs) on the surface of pores. The material was prepared by utilizing two effects occurring concurrently: the photoinitiated polymerization induced phase separation in the polymer–solvent mixture and the migration of the NRs to the interface between the polymer and the porogen solvent. We show that the enrichment of the interface with the NRs is enhanced at high polymerization rates leading to rapid phase separation. By contrast, a more rapid increase in viscosity achieved at high polymerization rates does not have a significant effect on the segregation of NRs to the surface of the pores. Finally,the PHM coated with gold nanorods was utilized for the simultaneous detection of different analytes using surface enhanced Raman scattering (SERS) spectroscopy and fluorescence microscopy.

Bead foam technology with a double crystal-melting peak structure has been well established for polyolefins. The double crystal melting peak structure, which is required in the molding stage of the bead foams, generates a strong sintering among the foamed beads and maintains the overall foam structure. In this research, despite the PLA’s poor foaming behavior and its slow crystallization kinetics, we successfully developed expanded PLA (EPLA) bead foams with double crystal melting peak structure and the inter-bead sintering behavior was verified through steam chest molding. For this purpose, the generation and evolution of double crystal melting peak structure in different PLA materials is simulated in a high-pressure differential scanning calorimeter (HP-DSC). The simulation results shows that the formation of double crystal melting peak with different peak ratios can be controlled by varying the processing parameters (i.e., saturation pressure, temperature, and time) during the saturation. The PLA bead foams characterization showed that the high melting temperature crystals generated during the saturation and the low melting temperature crystals formed during the cooling and foaming can significantly affect the foaming behavior of PLA bead foams. Moreover, the crystallization kinetics of different PLA materials are systematically investigated in presence of dissolved gas. It is shown that the different crystallization kinetics (i.e., crystal nucleation and growth rate) that can be induced at various gas pressures can significantly influence the PLA’s foaming behavior (i.e., cell nucleation and expansion behavior).

Bead foam technology with a double crystal-melting peak structure has been well established for polyolefins. The double crystal melting peak structure, which is required in the molding stage of the bead foams, generates a strong sintering among the foamed beads and maintains the overall foam structure. In this research, despite the PLA’s poor foaming behavior and its slow crystallization kinetics, we successfully developed expanded PLA (EPLA) bead foams with double crystal melting peak structure and the inter-bead sintering behavior was verified through steam chest molding. For this purpose, the generation and evolution of double crystal melting peak structure in different PLA materials is simulated in a high-pressure differential scanning calorimeter (HP-DSC). The simulation results shows that the formation of double crystal melting peak with different peak ratios can be controlled by varying the processing parameters (i.e., saturation pressure, temperature, and time) during the saturation. The PLA bead foams characterization showed that the high melting temperature crystals generated during the saturation and the low melting temperature crystals formed during the cooling and foaming can significantly affect the foaming behavior of PLA bead foams. Moreover, the crystallization kinetics of different PLA materials are systematically investigated in presence of dissolved gas. It is shown that the different crystallization kinetics (i.e., crystal nucleation and growth rate) that can be induced at various gas pressures can significantly influence the PLA’s foaming behavior (i.e., cell nucleation and expansion behavior).