Polypropylene oxide networks

The equilibrium shear modulus of two similar polyurethane elastomers is shown to depend on both the concentration of elastically active chains, vc, and topological interactions between such chains (trapped entanglements). The elastomers were carefully prepared in different ways from the same amounts of toluene-2,4-diisocyanate, a polypropylene oxide) (PPO) triol, a dihydroxy-terminated PPO, and a monohydroxy PPO in small amount. Provided the network junctions do not fluctuate significantly, the modulus of both elastomers can be expressed as c( 1 + ve/vc)RT, the average value of vth>c being 0.61. The quantity vc equals TeG ax/RT, where TeG ax is the contribution of the topological interactions to the modulus. Both vc and Te were calculated from the sol fraction and the initial formulation. Discussed briefly is the dependence of the ultimate tensile properties on extension rate. 

Reaction-induced phase separation is certainly also the reason for which an inhomogeneous structure is observed for photocured polyurethane acrylate networks based on polypropylene oxide (Barbeau et al., 1999). TEM analysis demonstrates the presence of inhomogeneities on the length scale of 10-200 nm, mostly constituted by clusters of small hard units (the diacrylated diisocyanate) connected by polyacrylate chains. In addition, a suborganization of the reacted diisocyanate hard segments inside the polyurethane acrylate matrix is revealed by SAXS measurements. Post-reaction increases the crosslink density inside the hard domains. The bimodal shape of the dynamic mechanical relaxation spectra corroborates the presence of a two-phase structure. 

Figure 10.1 Temperature dependence of the H T2 relaxation time of well-defined end-linked (PPO) networks with narrow molecular mass distributions between chemical crosslinks [44], The molecular mass of network chains (in g/mol) is shown in this figure. The temperature dependence of a linear, high-molecular-mass polypropylene oxide) prepared from a polypropylene glycol precursor (with a molecular mass of 4000 g/mol) using a chain extender with a chemical structure similar to that of the crosslinker is shown for comparison. The synthesis of the model networks has been...

As a result of increase in molecular weight of prepolymer from 1400 (SPU-1) to 2100 (SPU-4) or partial replacement of MOCA by polypropylene oxide diol (SPU-2) the amount of hard segments and common density of network decreased. But the equilibrium swelling in plasticizers increases (Table 10.15). The SPU modulus of elasticity decreases. The increase in the number of oxygen atoms in a polyether chain (SPU-4) results in decreased swelling in less polar plasticizers (TO, DOS, DOP). The elasticity modulus of the material in these plasticizers varies slightly. A large value for polyurethane SPU-5... 

Another proof for incorporation of the originally present antioxidant into an oxidized polypropylene was provided by 14C-labelled Ionox 330. The structures XC and LXXXV (R = polypropylene residue) were proposed for the reaction product123. It is, however, more probable that the transformation products of tris-phenolic antioxidant are bonded to the polypropylene skeleton in a simpler way for steric reasons than under formation of a polymer network. 

Swollen elastomers have domains of solvent between the network chains that may also he considered pores. fhermoporometry is useful to characterize the pore size and size distribution in such gels. Examples include natural ruhher, - styrene-divinylhenzenepolymers, poly(ethylene oxide),polyethylene and polypropylene, and ethylene-propylene-diene polymers and cis-polycyclo-octene. ... 

Polymer/fullerene [Ceol nanocomposites can be considered environmentally friendly alternatives to some traditional flame retardants. The presence of Ceo can markedly delay thermal oxidative degradation and reduce the flammability of polypropylene at very low loadings. It can decrease the heat release rate of polymeric materials by trapping the free radicals created through thermal degradation and combustion, and subsequently forming three-dimensional gelled networks. This network can increase the melt viscosity and consequently slow down combustion. Furthermore, the incorporation of Qo does not affect the physical properties of the polymer. 

SEM has been used extensively in morphological studies on polymers. Polymers studied include epoxy resin-polyaniline composites [3], polyoxyethylene [15], polypropylene-polycaprolactone blends [16], polydimethylsiloxane-co-ethylene oxide [17], PET fibres [18], polyurethane/polybutylmethacrylate polymer networks [19], methylacrylate-co-cellulose [20], styrene-butadiene copoylmer [21], Nylon 6-ethylene vinyl alcohol [22] and propylene-calcium carbonate or talc composites [23]. 

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