Thermoplastic semi-interpenetrating

Certain thermoplastic polyimides possess excellent resistances to high temperatures and chemicals, with Tgs ranging from 217 to 371 °C. Certain polyimides also exhibit excellent toughness and dielectric properties. The melt blending process of polyimides with other thermoplastic polymers is difficult due to polyimides high Tg, high melt viscosities, and incompatibility. A solution process is used, therefore, to achieve a semi-interpenetrating polyimide network... 

During the same period, commercialization of thermoplastic starch polymer blends was pursued by Novamont, a division of the Ferruzzi Group of Italy.162-172 Their products, marketed under the trade name Mater-Bi, are typically comprised of at least 60% starch or natural additive and hydrophilic, biodegradable synthetic polymers.64,165 It is stated that these blends form interpenetrated or semi-interpenetrated structures at the molecular level. Properties of typical commercial formulations have properties similar to those in the range of low- and high-density PE. Blends of Mater-Bi products with biodegradable polyesters have been claimed for use as water impervious films.173... 

An increase in heat deflection temperature of some thermoplastic polymers can be achieved by the addition of polyfunctional aromatic cyanates (BPA/DC in particular) and trimerization catalysts. A rigid network is formed as a resul t of the cyanate trimerization. The polymer material consists of a linear polymer and a crosslinked network and belongs to the class of semi-IPNs (semi-interpenetrating Polymer Networks) the corresponding classification is given in [34-37]. 

Hybrid versions of silicone-thermoplastic semi-IPNs have been developed (19). A hybrid interpenetrating network is one in which the cross-linked network is formed by the reaction of two polymers with structurally distinct backbones. Hydride-functionalized siloxanes can be reacted with organic polymers with pendant unsaturated groups such as polybutadienes (5) in the presence of platinum catalysts. Compared with the polysiloxane semi-IPNs discussed earlier, the hydride IPNs tend to maintain mechanical and morphologically derived properties, whereas properties associated with siloxanes are diminished. The probable importance of this technology is in cost-effective ways to induce thermoset characteristics in thermoplastic elastomers. 

A commercial blend consisting of a thermoplastic polyamide (PA-6 or PA-66) and 5-25 wt% of a crosslinkable silicone, which forms a semi-interpenetrating network (semi-IPN) upon curing, has been offered under the trade name of Rim-... 

B) Thermoset-thermoplastic blends and semi-interpenetrating networks (Semi-IPN)... 

PI (thermoplastic/ thermoset and semi-interpenetrating networks) 6.0 - 60.0 92Jan... 

Polysulfones have been made from acetylene-terminated sulfone monomers (Fig. 3.51), and cured graphite-fiber laminates have shown Tg = 300°C and good mechanical properties at 170°C before and after heat and humid aging. Semi-interpenetrating polymer networks with linear thermoplastic polysulfones showed promise of combining the heat deflection temperature and solvent-resistance of the thermoset polymer with the impact resistance of the thermoplastic. 

The idea behind semi-interpenetrating networks (semi-lPN s) is to combine the processabiity of thermoplastics with the high temperature performance of crosslinked thermosetting materials. Such mixtures should possess the desirable features of both types of materials. The majority of semi-IPN s contain continuous phases and the components are immiscible at the molecular level. 

A commercial grade of high-impact (notched Izod > 900 J/m) POM resin (Delrin 100 ST, DuPont) is believed to be a blend of POM with >30 wt% of a thermoplastic poly(ester-urethane) elastomer derived from poly(l, 4-butane adipate) diol and methylene-bis-(4,4 -diphenyl diisocyanate) (MDl) (Hexman 1989). This blend is reported to have a cocontinuous or semi-interpenetrating network of the elastomer in a matrix of the polyacetal (Flexman et al. 1990). The toughening effect in such a blend of IPN-type morphology was interpreted to occur partly through a rubber band mechanism by which the fracture energy is absorbed. The bands of rubbery domains were believed to span the crack and participate in the deformation process. 

The chemical and/or physical interaction between the silane-treated natural fibers and the polymer matrix is an important factor for improving the mechanical properties of biocomposites. Physical mixing of silane-treated natural fibers with thermoplastic resins can enhance the fiber-matrix interaction through in-termolecular entanglement or acid-base interaction [56]. In this case, limited improvement in the mechanical properties may be expected. The mechanical properties may be marginally increased by the increased wettability and the uniform dispersion of silane-treated natural fibers into the thermoplastic matrices [71]. The molecular chains may be interdiffused into the natural fiber surfaces, forming a (semi)interpenetrating polymer network [65, 72]. 

Interpenetrating network (IPN) A combination of two polymers into a stable interpenetrating network. In a true IPN each polymer is cross-linked to itself, but not to the other, and the two polymers interpenetrate each other. In a semi-lPN, only one of the polymers is cross-linked the other is linear and by itself would be a thermoplastic. The purpose of producing IPN is to improve strength, stiffness, and chemical resistance of certain polymeric systems. 

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