Publications (5)6.5 Total impact

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    B Starr · E Burts · J.R Upson · J.S Riffle
    [Show abstract] [Hide abstract] ABSTRACT: Dimethacrylate matrix resins and composites are becoming increasingly important in structural and coating components in the development of civil infrastructure. Service lives in excess of 50 years in outdoor environments are desirable for these materials. Aliphatic matrix resins derived from cycloaliphatic epoxies and dicarboxylic acids are under investigation as a means of obtaining coatings and fiber reinforced composites with such extreme durability to sunlight. The cycloaliphatic backbone shows reduced ultraviolet adsorption relative to bisphenol-A/epichlorohydrin resins. A series of new dimethacrylate resins and networks were prepared with 800 and 1200 g/mol oligomers and different concentrations of methyl methacrylate as the reactive diluent. Their thermal and mechanical properties have been compared to the bisphenol-A/epichlorohydrin-based dimethacrylate resins, which have either styrene or methyl methacrylate as the reactive diluent. The molecular weight between crosslinks was controlled by both the oligomer molecular weight as well as the amount of the reactive diluent to tailor network properties. The aliphatic networks exhibit glass transition temperatures ranging from ≈93–115°C with the higher Tgs associated with lower molecular weight oligomers and higher network densities. The aliphatic networks, in general, also have lower fracture toughness and higher hardness values as compared to networks prepared from bisphenol-A/epichlorohydrin oligomers. The fracture toughness, K1C, increases with the percentage of methacrylate diluent due to the increase in the molecular weight between crosslinks. However, networks cured with styrene as the reactive diluent show the reverse trend in fracture toughness.
    Preview · Article · Oct 2001 · Polymer
  • [Show abstract] [Hide abstract] ABSTRACT: The influence of vinyl ester/styrene network structure on thermal and mechanical properties was investigated. The crosslink density of the resins was altered by changing the molecular weight of the vinyl ester oligomer and by varying the amount of styrene used during the crosslinking reaction leading to variations in both the physical network structure and the chemical composition of the polymeric networks. The glass transition temperatures of the network polymers were found to increase systematically with increasing crosslink density without the additional influence of the chemical composition as determined from both differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). The breadth of the glass transition regions increased with crosslink density for the DSC data, but the breadth assessed from the DMA data did not vary significantly for the network materials. A secondary relaxation was observed for the materials using DMA, and this relaxation did not appear to be significantly affected by changes in either the crosslink density or the composition of the network. Cooperativity studies involving time–temperature scaling of dynamic mechanical data in the glass formation temperature region were also conducted. The degree of segmental cooperativity at Tg appeared to be primarily influenced by the chemical composition of the networks. These issues dealing with the structure of the networks provided insight into the associated fracture properties in the glassy state (ambient temperature). Specifically, an empirically based linear correlation was found between the fracture toughness of the networks and the cooperative domain size at the glass transition temperature normalized by the crosslink density. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 917–927, 2001
    No preview · Article · May 2001 · Journal of Applied Polymer Science
  • [Show abstract] [Hide abstract] ABSTRACT: One of the major classes of polymer matrix resins under consideration for structural composite applications in the infrastructure and construction industries is theso-called "vinyl esters." These are comprised of low molecular weight poly (hydroxyether) oligomers with methacrylate endgroups diluted with styrene monomer. The methacrylate oligomeric endgroups co-cure with the styrene in free radical copolymerization to yield thermoset networks. Selected properties of such resins and resultant networks where the molecular weights of the poly(hydroxyether) oligomers have been varied from 700 to 1200 g/mole and the concentration of styrene has been systematically changed are presented. In general, both the glass transition temperatures and fracture toughness of the fully cured networks increased as the styrene was decreased in each oligomer series with different molecular weights. As expected, the volume contraction upon cure also decreased significantly as styrene was decreased, and thus residual cure stresses may be reduced in fiber reinforced composites. The resistance to crack propagation was significantly improved for networks prepared with the 1200 Mn dimethacrylate oligomer relative to those from the 700 g/mole material. Crosslink densities were estimated from measurements of the rubbery moduli at Tg + 40°C and relationships between network density, chemical composition and properties are discussed.
    No preview · Article · Sep 2000 · Journal of Composite Materials
  • L.A. Harris · E. Burts · J.S. Riffle
    [Show abstract] [Hide abstract] ABSTRACT: A series of dimethacrylate resins and networks have been prepared comprised of methacrylate terminated poly(propylene oxide), a bisphenol A based dimethacrylate and styrene. These rubber modified dimethacrylates (vinyl esters) may be ideal for coatings, toughened matrix resins for fiber reinforced composites, bridge deck wear surface resins and structural adhesives. Networks were cured via free radical copolymerization at various temperatures and their morphologies were investigated by DMA and TEM analyses. Cloud point analysis confirmed a LCST. The resins cured at high temperatures phase separated during cure, while those cured at low temperatures did not. The single phase networks, room temperature cured with a postcure, produced higher fracture toughness values then the phase separated networks. FTIR analysis confirmed significant conversion of the room temperature cured resins. Adhesive strengths of the networks to aluminum, steel, and a vinyl ester/E-glass composite were measured. In general, adhesives with the appropriate viscosities exhibited structural strength on all substrates. Interestingly, an adhesive resin containing the 700 g/mole vinyl ester oligomer when reacted following two different room temperature cure schedules, 1) 25 °C for one week with no postcure, and 2) 25 °C for 16 hours followed by a one hour post cure at 100 °C, both exhibited good adhesion (approximately 2000 psi) on composite and aluminum.
    No preview · Article · Jan 2000
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