Toughening of vinylester–urethane hybrid resins through functionalized polymers

Abstract

Liquid nitrile rubber, hyperbranched polyester, and core/shell rubber particles of various functionality, namely, vinyl, carboxyl, and epoxy, were added up to 20 wt % to a bisphenol-A-based vinylester-urethane hybrid (VEUH) resin to improve its toughness. The toughness was characterized by the fracture toughness (K c ) and energy (G c ) determined on compact tensile (CT) specimens at ambient temperature. Toughness improvement in VEUH was mostly achieved when the modifiers reacted with the secondary hydroxyl groups of the bismethacryloxy vinyl ester resin and with the isocyanate of the polyisocyanate compound, instead of participating in the free-radical crosslinking via styrene copolymerization. Thus, incorporation of carboxyl-terminated liquid nitrile rubber (CTBN) yielded the highest toughness upgrade with at least a 20 wt % modifier content. It was, however, accompanied by a reduction in both the stiffness and glass transition temperature (T g ) of the VEUH resin. Albeit functionalized (epoxy and vinyl, respectively) hyperbranched polymers were less efficient toughness modifiers than was CTBN, they showed no adverse effect on the stiffness and T g . Use of core/shell modifiers did not result in toughness improvement. The above changes in the toughness response were traced to the morphology assessed by dynamic mechanical thermal analysis (DMTA) and fractographic inspection of the fracture surface of broken CT specimens.

Toughness response of vinylester/epoxy‐based thermosets of interpenetrating network structure as a function of the epoxy resin formulation: Effects of the cyclohexylene linkage

“…Note that in the neat VE this peak is marginal. 23 Therefore, the onset of the ␤-relaxation should be related to the EP network. Based on analogies (discussed later) with linear amorphous copolyesters with cyclohexylenedimethylene units along the macromolecular chain, the key parameter of the ␤-transition can be identified: conformational transitions of the cyclohexylene rings.…”

Synthesis of the first hyperbranched polyorganoethoxysilsesquioxanes and their chemical transformations to functional core–shell nanogel systems

“…H NMR spectra were obtained with a Bruker AC‐250 (250.13 MHz; Germany). Chemical shifts are reported in ppm and referenced to residual nondeuterated solvent frequencies ( δ = 7.25 ppm).…”

“…As a result of possessing a number of unique physical and chemical properties, hyperbranched polymers have currently found a broad range of applications. For example, they have been utilized as additives to polymeric structural materials in order to improve the physical–mechanical characteristics, in the creation of metal–organic nanocomposites and nanoporous materials, and in the improvement of the processability of various polymeric material manufacturing processes . Moreover, all by themselves, hyperbranched polymers appear to be effective in the creation of special polymer coatings .…”

Modifications and applications of hyperbranched aliphatic polyesters based on dimethylolpropionic acid

“…Furthermore, Boltorn ® U2 with vinyl, Boltorn ® E1 with epoxy groups, liquid nitrile rubber and core–shell rubber particles of various functionality were added up to 20wt% to a bisphenol A‐based vinylester‐urethane hybrid resin for its toughening 144. Toughness improvement in the hybrid resin was achieved when the modifiers reacted with the secondary hydroxyl groups of the bismethacryloxy vinyl ester resin and with the isocyanate of the polyisocyanate compound, instead of participating in the free radical crosslinking via styrene copolymerization 145…”