Effect on polymer chain

Hoeve.C.A.J., O Brien,M.K. Specific diluent effects on polymer chain dimensions. 

Islam MT, Vanapalli SA, Solmnon MJ (2004) Inertial effects on polymer chain scission in planar elongational cross-slot flow. Macrmnolecules 37 1023-1030... 

Hoeve, C. A. J. O Brien, M. K., Specific diluent effects on polymer chain dimensions. J. Polym. Sci. Part A General Papers 1963,1(6), 1947-1954. 

Lubricants are included in PVC compounds—especially rigids— to control fusion and metal release. There are two extremes of lubrication internal and external. External lubrication mainly facilitates metal release. Internal lubrication aids fusion and also has similar effect on polymer chains as plasticization however, much less internal lubricant is added than plasticizer. Real-life lubricants have a spectrum of properties between these two poles. 

As a class the aliphatic polyalkenamers have low values due to a combination of low chain stiffness and low interchain attraction. The presence of double bonds has the effect of increasing the flexibility of adjacent single bonds (see Chapter 4) and overall this leads to a reduction in. Thus in the sequence from polydecenamer down to polypentenamer an increase in the double bond concentration leads to a lowering of Tg. On the other hand the Tg of polybutenamer, i.e. poly butadiene, is somewhat higher than that of polypentenamer, presumably because the proportion of stiff links, i.e. double bonds, becomes sufficiently high to override the flexibilising effect on adjacent chains. Consequently the polypentenamers have the lowest Tg values known for hydrocarbon polymers (cis- -114°C, trans- -97°C). 

One of the most dramatic examples of a solvent effect on propagation taken from the early literature is for vinyl acetate polymerization.78,79 Kamachi el al.n reported a ca. 80-fold reduction in kp (30aC) on shifting from ethyl acetate to benzonilrile solvent (Table 8.1). Effects on polymer structure were also reported. Hatada ef a m conducted a H NMR study on the structure of the PVAc formed in various solvents. They found that PVAc (M n 20000) produced in ethyl acetate solvent has 0.7 branches/chain while that formed in aromatic solvents is essentially unbranched. 

Kraus, J., Muller-Buschbaum, P., Kuhlmann, T., Schubert, D. W. and Stamm, M. (2000) Confinement effects on the chain conformation in thin polymer films. Europhys. Lett., 49, 210-216. 

As discussed extensively in this chapter, most of the surprising properties of polyelectrolyte dynamics are due to the coupling of counterion dynamics with polymer dynamics. But, there is no adequate understanding of how much of the counterions are mobile and how much are effectively condensed on polymer chain backbone. Theoretical attempts [77, 78] on counterion condensation need to be extended to concentrated poly electrolyte solutions. 

Li, Y., Chung, T.S., Cao, C., and Kulprathipanja, S. (2005) The effects of polymer chain rigidification, zeolite pore size and pore blockage on polyethersul-fone (PES)-zeolite A mixed matrix membranes./. Memhr. Sci., 260, 45-55. 

Initial photooxidation and several other factors will diminish the molecular weight of polymers thereby releasing low molecular weight portions of pol3nneric chains which eventually can be biodegraded. The total environmental effect on polymers is therefore put together by... 

In some specific cases, dissolved macromolecules take up the shape predicted by the above theories of isolated chain molecules. In general, however, the interaction between solvent molecules and macromolecules has significant effects on the chain dimensions. In poor solvents, the interactions between polymer segments and solvent molecules are not that much different from those between different chain segments. Hence, the coil dimensions tend towards those of an unperturbed chain if the dimension of the unperturbed coil is identical to that in solution, the solution conditions are called conditions (ff solvent, temper-... 

Figure 4.11 Effect of polymer chain entanglements on melt viscosity. From Z. Tadmor and C. G. Gogos, Principles of Polymer Processing, Copyright 1979 by John Wiley Sons, Inc. This material is used by permission of John Wiley Sons, Inc.

A ternary system consisting of two polymer species of the same kind having different molecular weights and a solvent is the simplest case of polydisperse polymer solutions. Therefore, it is a prototype for investigating polydispersity effects on polymer solution properties. In 1978, Abe and Flory [74] studied theoretically the phase behavior in ternary solutions of rodlike polymers using the Flory lattice theory [3], Subsequently, ternary phase diagrams have been measured for several stiff-chain polymer solution systems, and work [6,17] has been done to improve the Abe-Flory theory. 

The effect on the chain configuration of the polymers was just as drastic. t-Butylmagnesium bromide in toluene solution at 230 produced a polymer of steric triad composition i h s 1 1 1 if initiated at the melting point of toluene, and i h s s 99 0 1 if initator solution at 230 was mixed with monomer solution at 230 K. 

The importance of polymer solution thermodynamics in the present context will become evident when we discuss polymer-induced forces in Section 13.6. For the present, in order to illustrate the above point, we may consider a very highly simplified picture of some of the possible effects of polymer chains on a dispersion, as depicted in Figure 13.11. 

Methyl branching also occurs in the preparation of many polymers. Ordinarily methyl branches are present in only trace amounts, barely detectable by the most sensitive 13C-NMR(69), and they have no effect on polymer properties. But if the polymerization is carried out at atmospheric pressure or less, methyl branching becomes much more common (69). It may originate from isomerizarion at the active site. This isomerization is probably not favored but does occur very rarely (Scheme 2). Low pressure decreases the propagation rate, allowing each chain to spend more time around the active site, thus increasing the probability of such side reactions. Internal... 

In Fig. 21 we show the dependency of qedj)/qefi for a chain of length N=72,f=l, for the values =1, 0.5, 0.25. Qualitatively the curve for = looks the same as the one in Fig. 18. For smaller the end effect vanishes, since both the number of annealing counterions and the strength of the electric field decrease strongly. In Fig. 22, we can observe the dependency of the end-effect on polymer concentration and added salt, which should be similar since in both cases the Debye length changes. In the first three cases, the... 

Other reactions may be taken into consideration, with an effect on polymer structure, namely the formation of short- and long-chain branches. A complete list of reactions in S-PVC polymerization may be found in Kiparissides et al. [5]. On the above basis kinetic equations may be written. To keep it simple the chain transfer, back-biting and inhibition reactions are disregarded, while termination is considered to occur only by disproportionation. The elementary reaction rates for initiator decomposition and free radicals generation are as follows ... 

Polyethylene is known as one of the typical polymers which crosslink under the influence of ionizing radiation. The radiation-induced crosslinking (the formation of C-C covalent bonds between polymer chains) of polyethylene has long attracted the interest of a large number of research workers, because this polymer has the most simple chemical structure for the fundamental study of radiation effects on polymers, and also because the irradiation with ionizing radiation is a practically important means of modifying the mechanical and thermal properties of polyethylene. 

DP is the average number of monomer (or repeat) units per polymer chain and so is directly related to molecular weight (or viscosity). This relationship shows that we must have control over variables that have a significant effect on propagation, chain transfer, and termination to achieve the desired polymer properties. What are these variables They are the same as those we have discussed throughout this chapter temperature, reactant monomer concentrations, concentrations of chain transfer agents or other impurities that affect polymerization, initiator or catalyst concentration, residence time, etc. 

Figure 20.10. Effect of polymer chain branching on shear and extensional viscosities of (a) branched LDPE (low-density polyethylene) melts, and (b) dough.

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