Other homopolymers

7 an5-l,4-polyisoprene can be degraded by metathesis with ethene at 5 bar in toluene initiated by a tungsten carbene catalyst. The expected 2-methylhexa-1,5-diene is detected and the MW of the polymer is reduced from 2.5 x 10 to 10. The model compound squalene (16) is also degraded to the expected products eqn. (2) (Wagener 1991a). 

Poly(l-pentenylene) can be readily degraded with hex-2-ene to yield the expected C9, Cn, and Co products derived from single monomer units, together with C]4, C16, and Cjg products derived from pairs of monomer units (Ast 1970). 

Polynorbomene is more difficult to degrade. Ethene in the presence of a tungsten carbene catalyst does bring about some reduction in MW (factor of five) but no 1,3-divinylcyclopentane is detected (Wagener 1991a). This is another example of the protection against metathesis offered by substituents on the carbons adjacent to the double bonds, in this case in the form of cyclopentane rings. 

The polymer 17, prepared by the ADMET polymerization of neat diallyldi-phenylsilane using Mo(=CHCMe2Ph)(=NAr)[OCMe(CF3)2]2 (Anhaus 1991), can be degraded by diluting the living polymer solution with sufficient toluene. This gives a 30% yield of the tt cyclic dimer 18, which separates as a white precipitate. When this is isolated and placed in contact with further initiator, an equilibrium is established between the cyclic monomer 19 and the three cyclic dimers (cc ct ft = 73 21 6), eqn. (3) (Anhaus 1993). The formation of the tt cyclic dimer in the initial degradation of 17 is thus kinetically favoured. 

Polyphenylacetylene can be degraded by reaction with hept-l-ene in the presence of WCle (Severina 1987). Unsaturated polymers containing side-chain ester groups, and polymers of ambrettolide containing ester groups in the main chain have been successfully degraded by metathesis (Ast 1976b). 

Studies on the waste from PET bottles hydrolytically depolymerised in a high-pressure autoclave equipped with a stirrer concluded that the degree of degradation of PET increases as the particle size of PET decreases, reaching a maximum of 24.61 % at a size of 1 mm x 1 mm [a.396]. The rate constants of hydrolysis of PET were found to be greater at higher particle size, in contrast to lower particle size, if catalyst (lead acetate) is used. Further, 

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Blending of ionomers with other homopolymers is also one means of enhancing mechanical performance. Frequently, in ionomer/polymer blends, synergistic effects are realized and properties may be significantly increased over anticipated values based on the rule of mixtures. This area of study has not been extensively explored and the probability clearly exists that new materials and new blends, having even a greater degree of property enhancement, will become available in the near future. 

Similar computerized analysis can be carried out for other homopolymers where detailed fractionation/NMR data are available. The use of MIXCO methodology to analyze such data for polypropylene has been previously reported.(11) Note that although pairwise combinations of fractions were analyzed here, the methodology given here is general. In principle, the NMR data for three fractions (or even an array of fractions) can be treated at once. 

Similar calculations have been carried out for a variety of other homopolymer helices (Ooi et al., 1967 Scheraga et dl., 1966b, 1967b Scheraga, 1967a, c Yan et al., 1968), each of which has presented an interesting structural problem in polyamino acid chemistry. The energy contributions included in all of these calculations were torsional, nonbonded,... 

Functionalized polysiloxanes are attractive because, with only small modification of the polysiloxane properties (e.g. density, yield strength, etc.), they allow reduction in the interfacial tension thanks to better interactions with the other homopolymer. Two studies involving PB/PDMS and polyisoprene (PIP)/PDMS are of particular interest [19,20]. The PDMS end groups were either amine (-NH2) or acid (-COOH). It was first observed that the PB/PDMS-NH2 system exhibits a 30% reduction in interfacial tension compared to the equivalent PB/PDMS system. A preliminary reduction... 

Similar energy contour maps and the relative stabilities of right- and left-handed a helices have been computed for other homopolymers, and Table 1 compares the computed and observed preferred twists of a number of a-helical... 

Oxygen diffusion in PAN homopolymer is very poor, due to the high molecular order. Again copolymerization helps to relieve the situation. Fig. 2 shows — for the cases of AN/Sty and AN/Butadiene copolymers — how the Oj-permeation increases with increasing comonomer content (experimental data of Salame ). The figure also includes the Oj-permeation of a number of other homopolymers (as 100% comonomer ). Assuming a similar type of dependence of the -permeation on the amount of the respective monomers M in a copolymer AN/M, the Oj... 

Other homopolymers of olefins are used in practice, a larger side chain typically leading to materials adequate to be used in adhesives, wax coatings, and elastomers. More frequently, practical applications are known for the copolymers of these compounds with ethylene or in synthetic rubbers with butadiene or with isoprene. The decomposition products of some of the homopolymeric olefins when heated in an inert atmosphere are indicated in Table 6.1.12. 

The majority of polymers are immiscible and, in bulk, they phase separate to form domains of varying sizes and shapes, depending on their relative volume fraction. This happens because of the very low entropy of mixing in the case of large polymeric molecules. Therefore, unless there is a large favorable enthalpic contribution, most polymers do not form molecularly miscible systems. The same is true for block copolymers, in which the length of each block exceeds a certain critical value. As mentioned earlier, block copolymers are systems wherein two (or more) different types of homopolymers are linked to each other at the chain end(s) diblock copolymers, represented as (A) -(B) , are systems in which two homopolymers are linked to each other at one end, while triblock copolymers, represented as (A)m-(B) -(C)p, are systems in which one central homopolymer block is linked at either end with two other homopolymers. The values m, n and p, represent the... 

Polyethylene is an example of a homopolymer, which is a polymer made up of only one type of monomer. Other homopolymers that are synthesized by the radical mechanism are Teflon, polytetraflnoroethylene (Figure 25.2) and poly(vinyl chloride) (PVC) ... 

Ternary blend using binary interaction model Gan et al. [18] found for certain copolymer compositions and volume fractions the ternary blend system of styrene acrylonitrile copolymer (SAN), polycarbonate (PC) homopolymer and polycaprolactone (PCL) was completely miscible. Develop the expression for binary interaction energy B for the ternary blend using binary interaction model. Is the intramolecular repulsion in the copolymer sufficient to drive miscibility with two other homopolymers without any common monomers ... 

In a block copolymer, the different homopolymer subunits are connected together in one chain. In contrast, a graft copolymer contains sections of one homopolymer that have been grafted onto a chain of the other homopolymer. Block copolymers and graft copolymers are formed by controlling the conditions under which polymerization occurs. 

These thermoplastics have properties which are superior to those of commodity plastics (namely, olefinics and styrenics). They go into a number of engineering applications and are termed engineering thermoplastics. Besides polyamides (nylons) and polyesters, some of the other homopolymers which fall into this category of engineering thermoplastics are the acrylics, acetals and polycarbonates. 

Figure 8 represents one of the c-nmr spectra of heteropolysaccharides consisting of 3-deoxygenated and non-deoxygenated (l->6)-a-D-gluco-pyranan units obtained via copolymerization of [6] and [10].All peaks were superimposable on peaks of one or the other homopolymers. The a-C-1 resonance of each structural unit was completely separated from the other, and the copolymer compositions could be estimated from their area ratios. In the benzylated precursors, some of the resonances were split into two peaks whose intensity varied with copolymer compositions. The splittings are due to diad sequences between the two crossover units. This is evidence of randomly distributed copolymers. These homo-and heteropolysaccharides will serve as a tool to investigate properties and functions. 

The polymerase activity of MoLV RTase, but not of AMV RTase, is almost completely blocked on sequences beyond an oligo(dA)jg insert in an M13 DNA template, whereas other homopolymers such as (dG)ig, (dT)ig, and (dC)j can be traversed without much difficulty (20). (This property of MoLV RTase is uniquely shared with HIV-1 RTase.)... 

Py-GC studies aimed at providing structural information have been conducted on a wide range of other homopolymers in recent years (see Table 1.3). 

When the crystallization is conducted over the complete accessible temperature range, i.e. from below the melting temperature to above the glass temperature, a more complex temperature dependence evolves. A typical example is given in Fig. 9.6 for natural rubber.(19) Here the time taken for half of the crystallization to develop is plotted as a function of the crystallization temperature. Many other homopolymers behave in a similar manner. This type of temperature dependence is not restricted to long chain polymers. It is also observed during the crystallization... 

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