Heterogeneous polymeric material

A. Yakovlev, O. Ruban, in Heterogenic Polymeric Materials, Naukova Dumka, Kiev, p. 23 (1973). 

FTSs are widdy used to investigate self-assembly and phase behavior of heterogeneous polymeric materials, particularly block copolymers. Fredrickson and coworkers have shown that this approach can be extended in various ways, for example, for systems with external stresses and for charged polymers. One of the main advantages of the field-theoretic methods is that any arbitrary morphology can be described... 

V.P. Privalko in Heterogeneous Polymeric Materials (Russ.), Naukova Dumka, Kiev,... 

When polymer blends and alloys are considered, a problem arises for the application of the principle of temperature-time superposition to the systems consisting of two and more phases. A variant of this superposition has been proposed for such materials [175]. The main feature of the temperature-time reduction in this case is the dependence of the reduction coefficient on the variables—temperature and time. The expression for the reduction coefficient may be obtained via the Taylor expansion of the relaxation function with respect to variable t and T. Phase-separated IPNs relate to thermorheologically complicated materials, hi principle, in these systems two different mechanisms of relaxation exist, each of them being characterized by its own temperature coefficient. Because of this, the application of traditional temperature-frequency superposition to IPNs is restricted. However, even in those cases when this approach is not entirely vahd, it may be used for approximate calculations. Thus, the apphcation of the temperature-time superposition to heterogeneous polymeric materials shows that the method may be very valuable for prediction of the viscoelastic properties, in spite of the necessity of further developing the theory. 

The results disoissed above indicate that in heterogeneous polymeric materials, in accordance with general physico-chemical principles stated in section 1, the viscoelastic properties of a polymeric matrix are strongly dependent on the type of heterogeneity and on the nature of the interphase interactions. In all cases the changes in molecular mobility and structure of the polymer in the boundary layer close to... 

Biomass is a complex substance made up of many organic species combined into a heterogeneous polymeric material. Although the actual structure of biomass cannot be defined, portions of it can be related to the structure of known organic compounds. These structures include carbohydrates (cellulose andhemicelluloses, approximately... 

Application to heterogeneous polymer solids, and elastic composites, is presented in the Section 7 (Gusev, Suter), which is followed by a summary and the outlook for the various methods reviewed here. It will be apparent to the reader that this review thus assembles several building blocks for the difficult task to bridge the gaps from the atomistic to the macroscopic scales in space and times for the simulation of polymeric materials. Integrating these building blocks into one coherent framework still is not fully solved and a matter of current research. 

State-of-the-art polymeric materials possess property distributions in more than one parameter of molecular heterogeneity. Copolymers, for example, are distributed in molar mass and chemical composition, while telechelics and macromonomers are distributed frequently in molar mass and functionality. It is obvious that n independent properties require n-dimensional analytical methods for accurate (independent) characterization of the different structural parameters. 

The advantages that heterogeneous catalysts have is that they are easily separable from the product, and can be recycled. A number of studies have been conducted in which ligands have been attached or bound to polymeric material to provide an immobilized ligand, and these include polyacrylate and silica [27], polyurea [28], polythiourea [29], polyether [30, 31] and dendritic [32] systems. Upon metal coordination, the immobilized catalysts have retained most of the activity and selectivity, but they now provide the advantage of simple separation and recycling. For exam-... 

The group of ion-selective electrodes with fixed ion-exchange sites includes systems with various membrane structures. The membranes are either homogeneous (single crystals, pressed pellets, sintered materials) or heterogeneous, set in an inactive skeleton of various polymeric materials. Important electrode materials include silver halides, silver and divalent metal chalcogenides, lanthanum trifluoride and various glassy materials. Here, the latter will be surveyed only briefly, for the sake of completeness. 

HMX composite propellants are composed of crystalline HMX particles and polymeric materials, and so their physical structures are heterogeneous. On the other hand, nitropolymer propellants are composed of mixtures of nitrate esters such as NC and NG, and their physical structures are homogeneous. Moreover, HMX pro-... 

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