Functional Group Conversion

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Christopher N. Bowman - One of the best experts on this subject based on the ideXlab platform.

  • Vinyl sulfonamide based thermosetting composites via thiol-Michael polymerization.
    Dental materials : official publication of the Academy of Dental Materials, 2019
    Co-Authors: Jasmine Sinha, Jeffrey W. Stansbury, Parag K. Shah, Adam Dobson, Osamah Bankhar, Maciej Podgórski, Sheryl L. W. Zajdowicz, Abdulaziz Alotaibi, Christopher N. Bowman
    Abstract:

    Abstract Objective To assess the performance of thiol Michael photocurable composites based on ester-free thiols and vinyl sulfonamides of varying monomer structures and varied filler loadings and to contrast the properties of the prototype composites with conventional BisGMA-TEGDMA methacrylate composite. Methods Synthetic divinyl sulfonamides and ester-free tetraFunctional thiol monomers were utilized for thiol-Michael composite development with the incorporation of thiolated microfiller. Polymerization kinetics was investigated using FTIR spectroscopy. Resin viscosities were assessed with rheometry. Water uptake properties were assessed according to standardized methods. Thermomechanical properties were analyzed by dynamic mechanical analysis. Flexural modulus/strength and flexural toughness were measured on a universal testing machine in three-point bending testing mode. Results The vinyl sulfonamide-based thiol-Michael resin formulation demonstrated a wide range of viscosities with a significant increase in the Functional Group Conversion when compared to the BisGMA-TEGDMA system. The two different types of vinyl sulfonamide under investigation demonstrated significant differences towards the water sorption. Tertiary vinyl sulfonamide did not undergo visible swelling whereas the secondary vinyl sulfonamide composite swelled extensively in water. With the introduction of rigid monomer into the polymer matrix the glass transition temperature increased and so increased the toughness. Glassy thiol-Michael composites were obtained by ambient curing. Significance Employing the newly developed step-growth thiol-Michael resins in dental composites will provide structural uniformity, improved stability and lower water sorption.

  • Reduced shrinkage stress via photo-initiated copper(I)-catalyzed cycloaddition polymerizations of azide-alkyne resins
    Dental materials : official publication of the Academy of Dental Materials, 2016
    Co-Authors: Han Byul Song, Jeffrey W. Stansbury, Parag K. Shah, Nancy Sowan, Austin Baranek, Alexander Flores, Christopher N. Bowman
    Abstract:

    Abstract Objectives Polymerization shrinkage stress and factors involved in the stress development such as volumetric shrinkage and modulus were investigated in photo-CuAAC (photo-initiated copper(I)-catalyzed azide-alkyne cycloaddition) polymerization and compared with conventional BisGMA-based methacrylate polymerization for their use as alternative dental resins. Methods Tri-Functional alkyne and di-Functional azide monomers were synthesized for photo-CuAAC polymerization. Conversion kinetics, stress development and polymerization shrinkage were determined with FTIR spectroscopy, tensometery, and with a linometer, respectively, for CuAAC and BisGMA-based monomer mixtures using a camphorquinone/amine visible light photoinitiator system. Thermo-mechanical properties for the cured polymer matrices were characterized by dynamic mechanical analysis and in three-point bending on a universal testing machine. Polymerization kinetics, polymerization shrinkage stress, dynamic volumetric shrinkage, glass transition temperature (Tg), flexural modulus, flexural strength, and flexural toughness were compared between the two different resin systems. Results A glassy CuAAC polymer (Tg = 62 °C) exhibited 15–25% lower flexural modulus of 2.5 ± 0.2 GPa and flexural strength of 117 ± 8 MPa compared to BisGMA-based polymer (Tg = 160 °C) but showed considerably higher energy absorption around 7.1 MJ × m−3 without fracture when strained to 11% via three-point bend compared to the flexural toughness of 2.7 MJ × m−3 obtained from BisGMA-based polymer. In contrast to BisGMA-based polymers at 75% Functional Group Conversion, the CuAAC polymerization developed approximately three times lower shrinkage stress with the potential to achieve quantitative Conversion under ambient temperature photocuring conditions. Moreover, relatively equivalent dynamic volumetric shrinkage of around 6–7% was observed via both CuAAC and dimethacrylate polymerization, suggesting that the low shrinkage stress of CuAAC polymerization was due to delayed gelation along with slower rate of polymerization and the formation of a more compliant network structure. Significance CuAAC crosslinked networks possessed high toughness and low polymerization shrinkage stress with quantitative Conversion, which eliminated obstacles associated with BisGMA-based dental resins including limited Conversion, unreacted extractable moieties, brittle failure, and high shrinkage stress.

  • Stress Relaxation via Addition–Fragmentation Chain Transfer in High Tg, High Conversion Methacrylate-Based Systems
    Macromolecules, 2012
    Co-Authors: Hee-young Park, Christopher J. Kloxin, Ahmed S. Abuelyaman, Joel D. Oxman, Christopher N. Bowman
    Abstract:

    To reduce shrinkage stress which arises during the polymerization of cross-linked polymers, allyl sulfide Functional Groups were incorporated into methacrylate polymerizations to determine their effect on stress relaxation via addition–fragmentation chain transfer (AFCT). Additionally, stoichiometrically balanced thiol and allyl sulfide-containing norbornene monomers were incorporated into the methacrylate resin to maximize the overall Functional Group Conversion and promote AFCT while also enhancing the polymer’s mechanical properties. Shrinkage stress and reaction kinetics for each of the various Functional Groups were measured by tensometry and Fourier-transform infrared (FTIR) spectroscopy, respectively. The glass transition temperature (Tg) and elastic moduli (E′) were measured using dynamic mechanical analysis. When the allyl sulfide Functional Group was incorporated into dimethacrylates, the polymerization-induced shrinkage stress was not relieved as compared with analogous propyl sulfide-containin...

  • Temperature Dependent Stress Relaxation in a Model Diels–Alder Network
    Australian Journal of Chemistry, 2011
    Co-Authors: Richard J. Sheridan, Brian J. Adzima, Christopher N. Bowman
    Abstract:

    The effect of temperature on the complex shear modulus (G*(ω)) of a model reversible covalent network formed by the Diels–Alder reaction was studied. The gel temperature of 119°C and the Functional Group Conversion at this temperature were determined by the Winter–Chambon criterion. The complex modulus of the cross-linked network was measured from 110°C to 121°C, near the gel temperature, to determine the frequency ranges over which stress relaxation could occur. The crossover time was found to have a strong dependence on temperature (Ea ∼ 260 kJ mol–1); greater than would be expected from a typical thermally-activated retro-Diels–Alder process. Low frequency scaling of G*(ω) over the experimental frequency and temperature range was interpreted to be a result of the existence of a distribution of transient clusters in these thermoreversible covalent gels.

  • Stress Relaxation by Addition−Fragmentation Chain Transfer in Highly Cross-Linked Thiol−Yne Networks
    Macromolecules, 2010
    Co-Authors: Hee-young Park, Christopher J. Kloxin, Timothy F. Scott, Christopher N. Bowman
    Abstract:

    Radical mediated addition-fragmentation chain transfer of mid-chain allyl sulfide Functional Groups was utilized to reduce polymerization-induced shrinkage stress in thiol-yne step-growth photopolymerization reactions. In previous studies, the addition-fragmentation of allyl sulfide during the polymerization of a step-growth thiol-ene network demonstrated reduced polymerization stress; however, the glass transition temperature of the material was well below room temperature (~ -20°C). Many applications require super-ambient glass transition temperatures, such as microelectronics and dental materials. Polymerization reactions utilizing thiol-yne Functional Groups have many of the advantageous attributes of the thiol-ene-based materials, such as possessing a delayed gel-point, resistant to oxygen inhibition, and fast reaction kinetics, while also possessing a high glass transition temperature. Here we incorporate allyl sulfide Functional Groups into a highly crosslinked thiol-yne network to reduce polymerization-induced shrinkage stress. Simultaneous shrinkage stress and Functional Group Conversion measurements were performed during polymerization using a cantilever-type tensometer coupled with a FTIR spectrometer. The resulting networks were highly crosslinked, possessed super-ambient glass transition temperatures, and exhibited significantly reduced polymerization-induced shrinkage stress when compared with analogous propyl sulfide-containing materials that are incapable of addition-fragmentation.

Guoxin Wang - One of the best experts on this subject based on the ideXlab platform.

Hak-fun Chow - One of the best experts on this subject based on the ideXlab platform.

Tsai-ming Chung - One of the best experts on this subject based on the ideXlab platform.

  • Isotactic Polypropylene-Based Stereoregular Diblock Copolymers: Syntheses and Self-Assembly
    Macromolecules, 2008
    Co-Authors: Jing-chung Kuo, Wen-fu Lin, Jing-cherng Tsai, Tzu-chung Wang, Tsai-ming Chung
    Abstract:

    The preparation of polyolefin-based stereoregular diblock copolymers (BCPs) by postpolymerization of hydroxy-capped isotactic polypropylene (iPP) led to the successful generation of a series of structurally well-defined iPP-based stereoregular BCPs for self-organizing into various nanostructures. The hydroxy-capped iPP prepolymer was synthesized by using ansa-metallocene catalysts to mediate the selective chain transfer to alkylaluminums during isospecific polymerization of propylene, leading to the production of alkylaluminum end-capped iPP as the preliminary product. Subsequently, in-situ O2/H2O2 treatment of the resulting aluminum-capped iPP led to the successful preparation of hydroxy-capped iPP. The terminal hydroxyl end Group of the iPP-based prepolymer was allowed to undergo tosylation reaction that led to the production of tosyl Group end-capped iPP with a quantitative Functional Group Conversion ratio. Subsequently, coupling the tosyl Group end-capped iPP with living anionic poly(2-vinylpyridine)...

  • Syntheses of Polyolefin-Based Stereoregular Diblock Copolymers for Self-Assembled Nanostructures
    Journal of Polymer Science Part A: Polymer Chemistry, 2008
    Co-Authors: Wen-fu Lin, Jing-cherng Tsai, Ting-jui Hsiao, Tsai-ming Chung
    Abstract:

    The preparation of polyolefin-based stereoregular diblock copolymers by postpolymerization of ethenyl-capped syndiotactic polypropylene-based propylene/norbornene copolymer (sPP-based P-N copolymer) led to the successful generation of a structurally uniform stereoregular diblock copolymer for self-assembly studies. The ethenyl-capped prepolymer was prepared by conducting propylene/norbornene copolymerization in the presence of Me2C(Cp)(Flu)ZrCl2/MAO. Ozonolysis of ethenyl-capped sPP-based P-N copolymer provided the formyl Group end-capped, end-Functionalized prepolymer with a quantitative Functional Group Conversion ratio. Subsequently, connecting the formyl end-Group of the stereoregular prepolymer by coupling with living anionic polystyrene resulted in the high yield production of stereoregular diblock copolymer (sPP-based P-N-block-polystyrene), which is difficult to prepare by other methods. The resulting stereoregular diblock copolymer possesses precise chemical architecture to self-organize into consistent nanostructures as evidenced by transmission electron microscopy and small angle X-ray scattering. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4843–4856, 2008

Chi-wing Leung - One of the best experts on this subject based on the ideXlab platform.

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