Crosslinks polymers and

Thermal expansion — as elasticity — depends directly upon the strength of the intermolecular forces in the material. Strongly bonded materials usually expand little when heated, whereas the expansion of weak materials may be a hundred times as large. This general trend is confirmed by Table 5.1. The coefficient of thermal expansion a was found to be lower in the crosslinked polymers and higher in the less crosslinked or thermoplastic materials as observed by Nielsen [1], In addition, Table 5.1 presents the Young s moduli E of the polymers at ambient temperatures as well as the products a2E. The values of oc2E are all close to 13.1 Pa K 2 with a coefficient of variation of 1.6%. 

Zeolite/polymer mixed-matrix membranes prepared from crosslinked polymers and surface-modified zeolite particles offered both outstanding separation properties and swelling resistance for some gas and vapor separations such as purification of natural gas. Hillock and coworkers reported that crosslinked mixed-matrix membranes prepared from modified SSZ-13 zeolite and 1,3-propane diol crosslinked polyimide (6FDA-DAM-DABA) synthesized from 2,2 -feis-(3,4-dicarboxyphenyl)hexafluoropropane dianhydride, p-dimethylaminobenzylamine-and 3,5-diaminobenzoic acid displayed high CO2/CH4 selectivities of up to 47 Barrer and CO2 permeabilities of up to 89 Barrer under mixed gas testing conditions [71]. Additionally, these crosslinked mixed-matrix membranes were resistant to CO2 plasticization up to 450 psia (3100kPa). 

The scope of the paper is to review the application of different NMR techniques, particularly the high resolution solid state methods, to crosslinked polymers and the potential of each particular technique in the investigation of network structure and dynamics at the molecular level. 

Although crosslinked polymers and polymer gels are not soluble, the spectra of swollen, low crosslink density networks exhibit reasonably narrow C-13 NMR line widths, sufficiently resolved to reveal details of microstructure 13S). Thus, recording the spectra under scalar low power decoupling yields characterization information and some dynamic measurements, concerning T, T2 (line widths) and nuclear Overhauser enhancement (NOE) for lightly crosslinked polymers. 

In a plastic the polymer chains can be either intertwined simply at random to form a three-dimensional pattern, or they can be linked together by chemical bonds. This latter type is called a crosslinked polymer, and it... 

Overcoming the current limitation faced by gas separation membranes may be accommodated by introducing two classes of materials that lie between conventional polymers and the high-performance molecular sieving materials. These two classes, illustrated in Fig. 11 and Fig. 12, respectively, are (i) crosslinked polymers and (ii) blends of molecular sieving domains in polymers, usually referred to as mixed matrix materials. Such materials... 

Since its first description in 1971 [35], gel-phase NMR was applied to peptide chemistry by Manatt and coworkers [36, 37], These authors used 13C NMR to determine the extent of chloromethylation of crosslinked polymers and 19F NMR to monitor protection-deprotection reactions. These two nuclei are the most commonly used in these types of studies, mainly because of their significant chemical shift dispersion, which can alleviate in part the resolution loss due to the non ideal linewidth obtained in the gel state. Apart from restricted molecular motion, that shortens T2 because of an efficient transverse relaxation, other sources of line-broadening derive from magnetic susceptibility variations within the sample (due to the physical heterogeneity of the system) and residual dipolar couplings. 

Polyurethane is a very common crosslinked polymer and many materials produced from it end up as waste. Given the quantity of material, recycling is a major problem. Cryogenic pulverization systems have been developed which can process PU foam to particles smaller than 1 mm (preferably <100 pm)/ " These particles are homogenized with polyol and then reacted with isocyanates to produce foam. This foam with 5% pulverized PU foam has a density equivalent to a similar foam produced without the recycled material. A further increase in filler content causes a density increase. Pulverized PU foam particles were also tried as a filler in natural rubber vulcanizates with good results. Figure 12.10 shows the effect of PU... 

The structures listed in Table 1.6 are divided into three categories Short sequences, Long sequences, and Networks. Within the first category a sequence of placement of individual CRU is considered, within the second the placement of long sequences of CRU defines the copolymer type, while to the third belong crosslinked networks, crosslinked polymers, and chemical-type interpenetrating polymer networks. The network is a crosslinked system in which macromolecules of polymer A are crosslinked by macromolecules of polymer B [Sperling, 1992]. The composition can be expressed as, e.g., Woc -co-poly(butadiene/styrene) (75 25 wt%), or gra/i-co-poly[isoprene/ (isoprene acrylonitrile)] (85 15 mole %). 

An interesting example of intra-polymeric catalysis is provided by the effect of polymer side chains on the aminolysis of polymer-bound nitrophenyl ester [41a], as illustrated in Fig. 10. Thus, apparent reactivity of the polymer-bound carbonyl groups is substantially increased by changing the polymer side chains from phenyl to methoxycarbonyl, and to dimethylamide. This type of intra-polymeric catalysis (shown schematically by species 9 in Fig. 11) assumes special significance in crosslinked polymers and solid phase synthesis. An important implication of this catalytic effect for polymer synthesis is that when an activated polymer intermediate (8) is not sufficiently reactive towards a given nucleophile, polymer reactivity can be enhanced by partial aminolysis with dimethyl-amine [25]. 

In this article, experimental results concerning the synthesis of ACECs, their properties, as well as the properties of ACECs-based crosslinked polymers and composites, are reviewed. The kinetics of the synthesis and curing of ACECs is considered only to the extent needed for the evaluation of the reactivity of different epoxy groups in ACECs and for the understanding of the formation processes of the crosslinked ACEC polymers. 

The DCPDO-based crosslinked polymers and composites exhibit similar mechanical strength and heat resistance in comparison with those prepared from UP-612, UP-632 and THIDO (Table 27). The increase in functionality of the diglycidyl ether or ester modifiers by the epoxidation of the cyclohexene ring results in a simultaneous increase in both mechanical strength and heat resistance... 

As for purely electro-optic polymers the electro-optic functionality can be achieved in a variety of different ways including guest/host systems, side-chain and main-chain polymers, crosslinked polymers and self-assembly approaches (36-38). In amorphous polymers, the NLO chromophores which have a permanent dipole moment are oriented with an electric field to induce electro-optic effects (39). Orientation of these dipoles leads not only to macroscopic electro-optic properties but also to birefringence (40). In the oriented gas model and for a poling field applied along the Z axis these two effects can be described by (39) ... 

V.Yu. Senichev in Synthesis and properties of crosslinked polymers and compositions on their basis. 

In highly crosslinked polymers and highly crystalline polymers the chains are held together by primary bonds and by crystalline forces. In both cases, forces are too strong to permit plasticizer to penetrate into the polymer. 

PLC elastomers are a special class of lightly crosslinked one-comb PLC which were first made by Finkelmann et al [69]. A permanently oriented PLC may be achieved by mechanical means by stretching a lightly crosslinked polymer, and the orientation is made permanent by further crosslinking in the distorted state. The crosslinks are attached to the backbone chains. The end product is crosslinked polydomain PLC which can be further aligned by drawing. 

Of the four repeat units, Monofunctional will make no polymer, Difimctional will make a linear polymer, Trifimctional will make a crosslinked polymer, and Tetrafimctional will make a crosslinked polymer if the reactions go to completion. 

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