Polymer network chemical networks

In interpenetrating polymer networks, chemical crosslinking and phase separation and their timing affect properties. Fumed silica, alumina, and carbon fiber were used in a network developed Ifom polyurethane and polycslcracrylalc. The presence of fillers affected many properties. Conversion rates were higher in the presence of fillers. Also, microphase separation was affected. As a result of these two changes the filled material was unrecognizable from the unfilled material. 

LG Chemical Polifil RTP M.A. Polymers Plastics Fina Polymers LG Chemical Network ... 

H. L. Frisch, K. C. Frisch, and D. Klempner, Interpenetrating Polymer Networks, Chemical Properties of Crosslinked Polymers, in Chemistry and Properties of Crosslinked Polymers S. S. Labana, ed.. Academic, New York (1977). Review of Polyurethane SINs. 

Polymers with the mechanical and chemical properties we have discussed in this section are called elastomers. In the next couple of sections we shall examine the thermodynamic basis for elasticity and then apply these ideas to cross-linked polymer networks. 

Chemical analyses reveal that measurable amounts of uranyl ion are actually present in Pu(IV) polymers grown in mixtures of Pu(IV) and uranyl nitrate suggesting that uranyl ion is being taken up in the polymer network and consequently hampers the growth through a chain termination process as suggested in Fig. 3. The uranyl serves to terminate active sites because it does not typically form extensive polymeric aggregates as does Pu(IV) instead it tends only to dimerize and, at most, tri-merize (4). 

An interpenetrating polymer network (IPN) is defined as a material comprising two or more networks which are at least partly interlaced on a molecular scale, hut not covalently bonded to each other. These networks caimot he separated unless chemical bonds are broken. Two possible methods exist for preparing them, as follows ... 

Radio-chemical graft copolymerization with good efficiency on halogenated polyolefins has been carried out by contacting the substrate with monomer (styrene) vapor [158,159]. Interpenetrating polymer network (IPN) could be made by grafting the monomers on preirradiated substrates... 

The Flory principle is one of two assumptions underlying an ideal kinetic model of any process of the synthesis or chemical modification of polymers. The second assumption is associated with ignoring any reactions between reactive centers belonging to one and the same molecule. Clearly, in the absence of such intramolecular reactions, molecular graphs of all the components of a reaction system will contain no cycles. The last affirmation concerns sol molecules only. As for the gel the cyclization reaction between reactive centers of a polymer network is quite admissible in the framework of an ideal model. 

Thermoset polymers (sometimes called network polymers) can be formed from either monomers or low MW macromers that have a functionality of three or more (only one of the reagents requires this), or a pre-formed polymer by extensive crosslinking (also called curing or vulcanisation this latter term is only applied when sulfur is the vulcanising or crosslinking agent.) The crosslinks involve the formation of chemical bonds — covalent (e.g., carbon-carbon bonds) or ionic bonds. 

Comments on Calculated Data. In several studies (13,18,19), G ax has been found to equal, or possibly be somewhat less than, the plateau modulus, G j, of a high molecular weight polymer whose chemical composition is the same as that of the network chains. Although G j for amorphous PPO has not been reported, it can be estimated from Zc, the number of chain atoms per molecule above which the viscosity increases approximately with the 3.4 power of Z. This quantity has been reported (25,26) to be about 400. As the chain atoms between entanglements is commonly about Zc/2, it follows that the molecular weight between entanglement loci is about 3900, and thus G j [ = (p/Me)RT] is about 0.65 MPa at 30°C. 

The initial drying of currently applied alkyd paints is accomplished by evaporation of solvent (physical drying). Subsequently, the eventual curing of the alkyd paint is completed by the formation of a polymer network, which is mainly formed by chemical crosslinks (oxidative drying) but in some cases also physical interactions between the fatty acid side chains occur, such as crystallization or proton-bridge formation [129]. Efficient network formation is crucial in the formation of dry films with good mechanical properties. Due to the presence of unsaturated units in the investigated LOFA- and TOFA-PHA bin-... 

Silicone co-polymer networks and IPNs have recently been reviewed.321 The development of IPNs is briefly described, and the definitions of the main (non-exclusive) classes of the IPNs are cited. Examples of latex IPNs, simultaneous and sequential IPNs, semi-IPNs, and thermoplastic IPNs are provided. The use of silicone-silicone IPNs in studies of model silicone networks is also illustrated. Networks in which siloxane and non-siloxane components are connected via chemical bonds are considered co-polymer networks, although some other names have been applied to such networks. Today, some of the examples in this category should, perhaps, be discussed as organic-inorganic hybrids, or nanocomposites. Silicone IPNs are discussed in almost all of the major references dealing with IPNs.322-324 Silicone IPNs are also briefly discussed in some other, previously cited, reviews.291,306... 

Bokobza, L. Clement, F. Monnerie, L. Lapersonne, P. In Chemical and Physical Networks, Formation and Control Properties Nijenhuis, K., Mijs, W. J., Eds. The Wiley Polymer Networks Group Review Series, Wiley New York, 1998 Vol. 1, 321. 

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