Linear crystallinity

The physical properties of any polyisoprene depend not only on the microstmctural features but also on macro features such as molecular weight, crystallinity, linearity or branching of the polymer chains, and degree of cross-linking. For a polymer to be capable of crystallization, it must have long sequences where the stmcture is completely stereoregular. These stereoregular sequences must be linear stmctures composed exclusively of 1,4-, 1,2-, or 3,4-isoprene units. If the units are 1,4- then they must be either all cis or all trans. If 1,2- or 3,4- units are involved, they must be either syndiotactic or isotactic. In all cases, the monomer units must be linked in the head-to-tail manner (85). 

K. Kageyama, J.-i. Tamazawa and T. Aiola, Extrusion Polymerization Catalyzed Synthesis of Crystalline Linear Polyethylene Nanofibers Within a Mesoporous Silica, Science, 1999, 285, 2113. 

Figure 4.17 Schematic view of the chemical healing process in semi-crystalline linear polycondensates TR, transreactions AC, additional (post)condensation D, diffusion [87]. From Fakirov, S., J. Polym. Sci., Polym. Phys. Ed., 22,2095-2104 (1984), Copyright John Wiley Sons, Inc., 1984. Reprinted by permission of John Wiley Sons, Inc...

Space-filling models of amorphous and crystalline linear PE are given in Figures 5.3 and 5.4. 

Radiation-induced polymerization of crystalline tetroxocane gives a highly crystalline linear polymer in essentially 100% yield (63MI51900,68MI51901), and this has attracted some industrial attention. Tetroxocane also gives a crystalline polymer very rapidly under cationic conditions (boron trifluoride etherate catalyst) and the kinetics of the process have been studied <76MI51900>. 

Cinnamic acid derivative 36 crystallizes in the chiral space group P2t and gives the optically pure dimer 37 upon irradiation in the solid state [22], Chiral crystals of 38 gave, upon irradiation, the optically active dimer 39 of 90% ee, whereas the corresponding methyl ester gave a highly crystalline linear polymer through a typical [2 + 2] topochemical photopolymerization [23],... 

Parylene-C, the trade name of the film formed from the Union Carbide Corp. brand of dichloro-p-xylylene, is a vapor deposited film formed by the reaction shown in Figure 1. The solid dimer(I) is vaporized and pyrolyzed at 650° C to 750 C to the reactive olefinic monomer, chloro-p-xylylene(II), which polymerizes on cool surfaces in the low pressure deposition chamber to form the crystalline linear polymer poly(chloro-p-xylylene) (III) (5). 

Thus far we have considered the influence of the interphase in relation to the mechanical properties of semi-crystalline linear polymers, in particular for the case of UHMW-PE, i.e. its role in the drawability or in the welding of such materials. With the recent advent of synthesis routes to produce highly controlled model systems, the investigation of the interphase can be extended further. 

Some polymerisations do not continue in a linear fashion, and branching occurs, as shown in Fig. 1.7(a). When branching is prevalent, it can have a serious effect on properties. Thus the polymerisation of ethylene under high-pressure conditions gives a product that has so many side chains on each main chain that crystallisation is appreciably suppressed. This material is softer than the highly crystalline linear form from a catalytic low-pressure process. The two forms of polyethylene may be distinguished by a difference in density between them, the more crystalline material being denser. 

Already Kohlrausch (1943) has pointed out that linear paraffines shows a Raman band in the range 250. .. 400 cm the frequency of which decreases with increasing length of the chain. Schaufele and Shimanouchi (1967) have demonstrated that this longitudinal acoustical vibration can be observed in the Raman spectra of crystalline linear hydrocarbons as well as in polymers with folded chains. 

Also in 1967, Holm and Zienty announced in patent that crystalline linear polymers were obtained by photoirradiation of a number of crystalline dibenzylidenebenzene diacetonitrile derivatives6. In 1972, they published the results on the photopolymerization of dibenzylidenebenzene diacetonitrile in J. Polymer Science7 1. 

These results indicate that the polymerization readily affords a highly crystalline linear polymer in high yield as long as the polymerization temperature is sufficiently low to maintain the rigidity of the crystal lattice of the reactant. Since the monomer... 

Both bis(l,5-cyclooctadiene)nickel(0) and bis(acrylonitrile)nickel(0) catalyze the polymerization of allene to highly crystalline linear polymers (451). With compounds such as tri-o-tolyl phosphite, bis(acrylo-nitrile)nickel in hydrocarbon catalyzes the cyclodimerization of butadiene to 1,5-cyclooctadiene, whereas in alcohols it catalyzes the... 

In most non-crystalline linear polymers described to date, the relaxation mechanism (in the absence of such extraneous factors as degradation) is the simple molecular flow, or the a mechanism. Exceptions have been found, for instance in the case of the polysulfides (4,54,56,57) or pol5mrethanes (57) in which far above the gla transition temperature a ixmd interchange mechanism was observed. For a number of reasons (which will be described below), it is of interest to study viscoelasticity of polymers which are subject to both mechanisms, i. e., a and (as bond-interchange will be called due to the intrinsically chemical nature of the reaction), particularly if both mechanisms occur with comparable relaxation times. Among the benefits of such a study, particularly in the case of the ionic inorganic polymers would be ... 

The large group of phenol-formaldehyde, urea-formaldehyde, and melamine-formaldehyde polymers are also prepared by carbonyl-addition-substitution reactions. Their final crosslinking reaction occurs in the solid state, however, the polymers are amorphous. Crystalline linear polymers have been obtained using parasubstituted phenols. But up to now only relatively low molecular weight polymers have been prepared (5). 

This is the first example of topochemical copolymerization in which the copolymer formation is completely substantiated on the basis of direct evidence from spectroscopic and preparative techniques. The same mixed crystal is also obtained through crystal-crystal contact by simple grinding of two monomers with an amalgamator. Irradiation of the resulting mixed crystal gives a crystalline linear copolymer (rjjnh = 0.6 dlg" ) having the same structure. 

As shown in Table 12.2, thermoplastic matrices such as polyethersulphone (PES) and polyetheretherketone (PEEK) absorb much less moisture than the advanced epoxies. PEEK is an example of a partially crystalline linear polymer with very low moisture absorption. Thermoplastics which are relatively nonpolar and absorb low... 

Kageyama, K. Tamazawa, J. Aida. T. Extrusion polymerization Catalyzed synthesis of crystalline linear polyethylene nanofibers within a mesoporous silica. Science 1999. 285, 2113. 

The higher efficiency of the modification for extruded iPP when compared to biaxially oriented iPP was explained by different susceptibility to oxidation due to different crystallinity. Linear dependence of either PC of the surface energy or hydroperoxide concentration of modified iPP on current density was observed. A decrease in the exposition time of iPP foil resulted in lower modification effect. The sensitivity on exposition time was more pronounced for extruded iPP. Aging of modified PP foil leads to a significant drop in surface energy during first 24 hours for extruded iPP, while for biaxially oriented iPP the decrease was small. An increase of the mechanical work of adhesion was observed if temperature of auto-adhesive joints rised. The observed decrease of hydroperoxide concentration after a destruction of the auto-adhesive joints is in accordance with the previous data. 

A preformed linear polymer (in molten, solution, or emulsion states), or A polymer network, physically (e.g., semi crystalline linear polymer) or chemically (e.g., thermosets, elastomers) cross-linked. 

A eommon feature in such arrangements is the presence of a ID H-bonded ribbons. This particular organisation resembles the photopolymerisation of diolefins named four-center type polymerisations, where each reactive double bonds can independently react, leading to crystalline linear high organic polymer (Scheme 20). 

Fig. 6.1 Illustration of the characteristic deformation of non-crystalline linear polymers as a function of temperature under a small external stress. The characteristic glass, rubber and fluid states are separated by the glass-rubber transition Tg and the rubber-fluid transitimi Tf, respectively. The dashed lines are drawn to guide the eyes...

FIGURE 5.21 Chain configurations in crystalline linear polyphosphates. (Adapted from M.T. Averbuch-Pouchot, A. Durif, and U. Schuelke, IC, 33,1091, 1996.)... 

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