Vinyl Acetate Radical Polymerization Kinetics Studies Otlaatla Monyatsi Pulsed-laser polymerization (PLP) combined with analysis of the resulting polymer molecular mass distribution (MMD) is used to measure the chain growth rate coefficient, kp, for radical polymerization of vinyl acetate (VAc). The measured value of kp significantly increases when the pulse repetition rate is increased from 100 Hz to 500 Hz. This behavior, not seen for other common monomers such as methyl methacrylate, styrene is an indication that secondary reactions are affecting the PLP-SEC analysis of VAc propagation. Combining an extensive PLP experimental study with simulation, the puzzling results can be attributed to the influence of headto-head addition (secondary reaction) on the rate of VAc chain growth. Simulations indicate that, while the PLP repetition rate dependence is explained by the presence of head-to-head propagation in the system, the data set could not be used to estimate the individual rate coefficients. Indeed, the mean value from all of the experimental results is considered as a reasonable estimation of the averaged kp value, with the best-fit Arrhenius parameters of ln (A/L mol 1 s 1 ) = 16.56±0.35 and E/R= 2508±108 K. Experiments (PLP) have also been performed with vinyl pivalate and vinyl benzoate to demonstrate the generality of this behavior for the vinyl ester family of monomers. In addition, batch polymerization experiments are performed to explore other kinetic features of VAc polymerization and also other vinyl esters monomers mentioned.
Modeling and Measurement of Aqueous Phase Non-Ionized Acrylic Acid/Acrylamide Copolymerization Calista Preusser Despite the importance of water soluble polymers for both consumer (e.g. anti-scalants in laundry detergents, thickening agents in cosmetics) and industrial (e.g. flocculants in mining and water treatment) applications, the kinetics of aqueous phase polymerizations are poorly understood relative to their organic counterparts. The modeling of aqueous phase polymerizations is complicated by the influence of monomer concentration and ph on rate coefficients and thus on resultant monomer conversion profiles and polymer molar masses. This work aims to capture these complexities in mechanistic models to describe the radical copolymerization of non-ionized acrylic acid (AA) and acrylamide (AM), to improve understanding and guide process and product development. Specialized pulsed-laser experiments have shown that AA and AM propagation and termination rate coefficients both decrease with increasing monomer concentration, such that the predicted polymerization rate should also decrease. The opposite trend, however, has been observed in our experimental data, with the rate of monomer conversion increasing with increasing monomer content in aqueous solution (Figure 1). This unexpected behavior can be attributed to the occurrence of backbiting reactions in both AA and AM. When this added complexity is introduced into the set of mechanisms used to represent the system, the model provides a good representation of the homopolymerization experimental data (Figure 1). We have extended the treatment to copolymerization, with both monomers susceptible to backbiting, and with rate coefficients functions of monomer concentrations and temperatures. The simulations are compared to experimental monomer conversion and composition data collected using an in-situ NMR technique 1 for temperatures between 40 and 70 o C and 5 to 40 wt% monomer at various monomer compositions. 1.0 0.8 Conversion 0.6 0.4 0.2 / 5 wt% AM / 20 wt% AM / 40 wt% AM 0.0 0 500 1000 1500 2000 2500 3000 3500 4000 Time (s) Figure 1 - Experimental and predicted conversion profiles at 40 o C, 0.22 wt% V-50 at 5, 20, and 40 wt% AM
Aqueous Copper(0)-Mediated Reversible Deactivation Radical Polymerization of 2-Hydroxyethyl Acrylate Mingmin Zhang A comparative analysis of reversible deactivation radical polymerization (RDRP) of 2-hydroxyethyl acrylate in D2O with Cu(0) wire-mediation and with two steps Cu(0) in situ -mediation is reported. Comparison with cross-linked gel formation in the former, in two steps Cu(0) in situ-mediated RDRP, no gel formation is observed throughout the reaction in different target degrees of polymerization (DPT=20 to 800). Effects of excess NaBr, reason of shoulder in molar mass distribution plots of P(HEA) at high molecular weight is discussed. Comparative kinetic studies with cannula transferring and with syringe transferring on different target degrees of polymerization and on variant temperatures are reported. Effects of using cannula transferring, syringe transferring and polymerization temperature increased from 0 to 22 are discussed. Based on mechanism understanding, a new synthesis solution is used to successfully synthesize well defined high molecular weight P(HEA) with fast polymerization rate using only ca. 250 ppm copper at room temperature in water under not very strictly oxygen-free condition.
Advanced Polymer Nanoparticles from Ring-opening Metathesis Polymerization (ROMP) in Aqueous Phase Aaron (Chunyang) Zhu Polymer nanoparticles are well known for their large-volume applications such as coatings, paints, adhesives, and sealants. Yet current state-of-the-art technology including radical-initiated emulsion polymerization only works with a limited number of monomers like styrene and acrylates. Meanwhile, ring-opening metathesis polymerization (ROMP) has been tactfully applied to prepare a range of high-value functionalized polymers with unique backbones and properties, but note that this method currently only works in volatile organic solvents. Here we combine both techniques via developing an emulsion or miniemulsion polymerization process based on ring opening metathesis polymerization (ROMP) in order to synthesize well-defined polymer nanoparticles (latexes) in aqueous dispersions. Our approach focuses on the modification of ROMP catalyst which is typically employed in organic solvents; and the introduction of PEG-tagged ligands into the structure of catalyst suggests that the modified catalyst is considerably stable and reactive in water phase. Further, ROMP-based polymers including functionalized polynorbornene and polybutadiene can be obtained by using a general protocol of miniemulsion polymerization. Thus it is believed that our approach will achieve three important objectives: (1) enabling the preparation of nanoparticles via ROMP method, which is currently impossible; (2) eliminating the use of large amount of volatile organic compounds (VOCs); and (3) improving the efficiency and lower the cost of manufacturing process.
Hydrogen atom transfer and vinyltriethoxysilane grafting reactions of poly(isobutylene-co-isoprene) Christopher Twigg Peroxides such as Bis(1-methyl-1-phenylethyl) peroxide, referred to as DCP, are commonly used to improve polyolefin properties by modifying their chemical structure. This includes cross-linking the polymer backbone to give thermoset products, as well as grafting of trialoxysilanes such as vinyltriethoxysilane to produce reactive derivatives for use in adhesive and composite formulations. The challenge is applying traditional solvent-free processing methods to poly(isobutylene) (PIB) and poly(isobutylene-co-isoprene) (IIR) copolymers with small diene contents. Given the low reactivity of PIB as a hydrogen atom donor, radical graft modification yields are well below those of many other polymers of commercial interest such as polyethylene. IIR materials containing higher amounts of isoprene provide greater macroradical yields, however, while hydrogen atom abstraction is expected to increase cross-linking potential, radical addition to vinyl monomers is less favourable. The higher abstraction efficiency of high isoprene materials may not improve the radical grafting yields involving vinyltrialkoxysilane. Vinyltriethoxysilane grafting yields were established for PIB and IIR with sequentially higher diene concentrations. Additionally, knowledge of the regioselectivity of hydrogen atom abstraction is needed to understand the implications for polymer modification chemistry. A well-established radical trapping nitroxyl (2,2,6,6-tetramethyl-1-piperidinyloxy) was used to trap radicals formed by the hydrogen abstraction of DCP from the IIR model compound 2,2,8,8-pentamethyl-4-nonene. Stable alkoxyamines were formed and the reaction mixture s composition reflected the radical population and alkoxyamine structures established by initial hydrogen atom transfer, thereby giving an indication of hydrogen atom abstraction efficiency and regioselectivity from IIR.
Synthesis, Kinetics, and Biomedical Applications of Nanoparticles from Degradable Macromers Thomas Rooney Semi-batch radical emulsion polymerization is used to produce nanoparticles (NPs) with tunable dimension, hydrophobicity, and degradation from copolymerization of novel poly(ɛ-caprolactone) (PCL) or poly(lactide) (PLA) based macromonomers with PEGylated 2-hydroxyethyl methacrylate (HEMA-PEG) in a surfactant-free process. Macromonomers include a vinyl end-group amenable to radical polymerization, degradable CL or LA units with tunable length, and a terminal end-group with alkyl, hydroxyl, carboxyl, or fixed cationic charge functionality. NP final properties, such as degradation, are controlled by the number of degradable units in the macromonomer as well as the identity of the terminal functionality. Thus, the pulsed-laser polymerization (PLP) technique is employed to study the copolymerization kinetics for this family of macromonomers. Copolymer microstructure, functional group placement, and rate data are used to better understand NP performance during in vitro and in vivo anti-cancer drug delivery therapies.
Preparing Artificial Polymer Latexes Using Switchable Hydrophilicity Solvents Xin Su The most latexes are prepared using emulsion polymerization and the latex contains polymer nanoparticles as the dispersed phase. However, emulsion polymerization typically cannot be used for condensation, ionic or Ziegler-Natta polymerization. Our group has been developing CO2-switchable technology such as switchable-hydrophilicity solvents (SHS) and switchable water (SW). SHS are solvents that can be switched reversibly between a hydrophilic and hydrophobic state by the addition and removal of CO2 gas. SW is an aqueous solution of switchable ionic strength controlled by the addition and removal of CO2 gas. Based on CO2-switchable technology, we have developed new methods for the preparation of latexes from solid polymer. Polymer resin is first dissolved in SHS. This polymer solution is then blended with an aqueous surfactant solution in a high shear emulsification apparatus. The resulting intermediate product is a highly diluted emulsion with dispersed droplets of polymer dissolved in the CO2-switchable solvent. After sparging with CO2, the protonated SHS diffuses into the aqueous phase and behaves as SW. The polymer remains in the droplets, and the polymer particles can be readily isolated. This approach allows the preparation of artificial polymer latexes from a wide range of polymer resins, without requiring expensive and energy intensive solvent handling steps.
Polymerization induced self-assembly of alginate based amphiphilic graft copolymers synthesized by copper(0)-catalyzed living radical polymerization Vitaliy Kapishon Alginate-based amphiphilic graft copolymers were synthesized by copper(0)-catalyzed living radical polymerization (Cu(0)C- LRP), forming stable micelles during polymerization induced self-assembly (PISA). First, alginate macroinitiator was prepared by partial depolymerization of native alginate, solubility modification and attachment of initiator. Depolymerized low molecular weight alginate (~12,000 g/mol) was modified with tetrabutylammonium enabling miscibility in anhydrous organic solvents, followed by initiator attachment via esterification yielding a macroinitiator with a degree of substitution of 0.02, or 1-2 initiator groups per alginate chain. Then, methyl methacrylate was polymerized from the alginate macroinitiator in mixtures of water and methanol forming polymethyl methacrylate grafts, prior to self-assembly, of ~75,000 g/mol and polydispersity of 1.2. PISA of the amphiphilic graft-copolymer resulted in the formation of micelles with diameters of 50-300 nm characterized by light scattering and electron microscopy. As the first reported case of LRP from alginate, this work introduces a synthetic route to a preparation of alginate-based hybrid polymers with a precise macromolecular architecture and desired functionalities. The intended application in the present study is the preparation of micelles for drug-delivery, however LRP from alginate can also be applied in the field of biomaterials to the improvement of alginate-based hydrogel systems such as nano- and micro-hydrogel particles, islet encapsulation materials, hydrogel implants and topical applications. Such modified alginates can also improve the function and application of native alginates in food and agricultural applications.
Polymer selection for two-phase partitioning bioreactors Stuart Bacon A number of commodity and specialty chemicals are commercially produced by bacteria or yeast through fermentation, including ethanol, butanol, organic acids, natural flavours and pharmaceuticals. In industrial settings, it is common for the microbes to produce so much of the desired product that it starts harming them, known as end-product inhibition. A solution to this problem is to introduce an absorptive polymer phase into the bioreactor to selectively remove and concentrate the desired molecule. The methodology behind the rational selection of said polymers will be the main focus of this talk. Specifically, I will focus on how certain polymer properties (molecular weight, Tg, Tm, crystallinity and thermodynamic affinity) affect the absorption of target molecules from the aqueous fermentation broth.