Flexible chain linear polymers

The thermodynamic chain rigidity along with the potential barriers of inter-and intramolecular interactions control the temperature of the -transition. For a large number of flexible-chain linear polymers, the regular relationships for Qfi s (0.3 + 0.05) Ec i,S + Qo and, according to the Arrhenius equation, for Tf = Qp(kJ mole )/(0.25-0.019 Igv) were demonstrated using DSC [112, 114]. 

Therefore, for highly flexible polymers, metal complex dimerization occurs either in a single chain (linear polymer) or in the chain site between the crosslinked knots. It was reported that a ratio of mononuclear and binuclear complexes of Cu with polymeric acids depends on the degree of neutralization of the latter low charge density provides binuclear complexes and monomer formation as the charge density increases. 

Both polymers are linear with a flexible chain backbone and are thus both thermoplastic. Both the structures shown Figure 19.4) are regular and since there is no question of tacticity arising both polymers are capable of crystallisation. In the case of both materials polymerisation conditions may lead to structures which slightly impede crystallisation with the polyethylenes this is due to a branching mechanism, whilst with the polyacetals this may be due to copolymerisation. 

At present, it is known that the structures of the ECC type (Figs 3 and 21) can be obtained in principle for all linear crystallizable polymers. However, in practice, ECC does not occur although, as follows from the preceding considerations, the formation of linear single crystals of macroscopic size (100% ECC) is not forbidden for any fundamental thermodynamic or thermokinetic reasons60,65). It should be noted that the attained tenacities of rigid- and flexible-chain polymer fibers are almost identical. The reasons for a relatively low tenacity of fibers from rigid-chain polymers and for the adequacy of the model in Fig. 21 a have been analyzed in detail in Ref. 65. 

The reason for the low intrinsic viscosities in solution is that dendrimers exist as tightly packed balls. This is by contrast with linear polymers, which tend to form flexible coils. The effect of this difference is that, whereas polymer solutions tend to be of high viscosity, dendrimer solutions are of very low viscosity. In fact, as dendrimers are prepared, their intrinsic viscosity increases as far as the addition of the fourth monomer unit to growing branches (the so-called fourth generation), but this is the maximum value that the viscosity reaches, and as the side chains grow beyond that, the viscosity decreases. 

The polymer we consider here is a semi-flexible chain which has some bending stiffness (Eq. 3). We first estimated the chain conformation in the melt. The calculated mean-square end-to-end distance R2n between atoms n-bond apart has shown that the chains have an ideal Gaussian conformation R2 is a linear function of n (see Fig. 35 given later). The value of R2 for n = 100... 

If R is a polymeric ester, or ether, of molecular weight 1000-3000 a flexible elastic material will result. By reacting MDI and active hydrogen components (polyether/ester and a short chain glycol) in equivalent stoichiometric quantities, a linear polymer with virtually no crosslinks is obtained. 

The wall-PRISM theory has also been implemented for binary polymer blends. For blends of stiff and flexible chains the theory predicts that the stiffer chains are found preferentially in the immediate vicinity of the surface [60]. This prediction is in agreement with computer simulations for the same system [59,60]. For blends of linear and star polymers [101] the theory predicts that the linear polymers are in excess in the immediate vicinity of the surface, but the star polymers are in excess at other distances. Therefore, if one looks at the integral of the difference between the density profiles of the two components, the star polymers segregate to the surface in an integrated sense, from purely entropic effects. 

It should also be noted that ternary and higher order polymer-polymer interactions persist in the theta condition. In fact, the three-parameter theoretical treatment of flexible chains in the theta state shows that in real polymers with finite units, the theta point corresponds to the cancellation of effective binary interactions which include both two body and fundamentally repulsive three body terms [26]. This causes a shift of the theta point and an increase of the chain mean size, with respect to Eq. (2). However, the power-law dependence, Eq. (3), is still valid. The RG calculations in the theta (tricritical) state [26] show that size effect deviations from this law are only manifested in linear chains through logarithmic corrections, in agreement with the previous arguments sketched by de Gennes [16]. The presence of these corrections in the macroscopic properties of experimental samples of linear chains is very difficult to detect. 

Most linear polymers have a flexible chain in which every monomer unit is able to assume more than one low energy conformation by rotation around single... 

AS is very rare for a polymerization process. The only other reported instances of positive AS values are those for the polymerizations of the cyclic octamers of sulfur and selenium and cyclic carbonate oligomers (Sec. 7-5c) [Brunelle et al., 1989]. All other polymerizations involve a decrease in entropy because of the decreased disorder for a polymer relative to its monomer. The positive AS values for the cyclic siloxane, S, and Se probably result from the high degree of flexibility of the linear polymer chains due to the large-sized atoms that they contain. This flexibility leads to greater degrees of freedom in the linear polymer compared to the cyclic monomer. 

Many copolymers are said to be internally plastidzed because of the flexibilization brought about by the presence of a second repeating unit in the polymer chain. In contrast. DOP and other liquid plastidzers are said to be external plastidzers. The presence of bulky pendant groups on the polymer increases segmental motion, and the flexibility of the polymer increases as the size of the pendant group increases. However, linear pendant groups with more than 10 carbon atoms reduce flexibility because of side chain crystallization. 

Then there are flexible linear polymers which curl up in solution to give a random cell. If the chain is stiff, such as in cellulose or in DNA, the coil becomes highly expanded. 

The linkage of conventional low molar mass Lc s to a linear polymer main chain via a flexible spacer provides a method to realize systematically the liquid crystalline state in linear polymers. Above the glass transition temperature Tg the polymer main chain can be assumed to exhibit, at least in the nematic state, an almost free motion of the chain segments, causing a tendency towards a statistical chain conformation. Due to their mobility, the polymer main chains are able to diffuse past each other, which is a condition to obtain the liquid state. Therefore such polymers can be classified as liquids of high viscosity10O). 

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