Class I polymers

Class II polymers—random copolymers—fit less neatly into crystal lattices. Melting points are depressed, and the degree of crystallization is reduced. (A few special exceptions exist, in which the two monomer units are sufficiently matched in geometry that they can interchangeably occupy sites in a common lattice.) Because vitrification does not involve fitting into a crystal lattice, the glass temperatures of copolymers are not depressed by the chain irregularity. Consequently, random copolymers do not follow the T i(-Tg correlation characteristic of Class I polymers (3). 

Synthetic polyisoprene, prepared by free-radical polymerization of isoprene monomer, is a copolymer of six structurally distinct kinds of isoprene chain units. Unlike natural rubber, which is a regularly repeating Class I structure (cis-1,4), such synthetic polyisoprene does not crystallize. On the other hand, by the use of the appropriate stereospecific catalyst, isoprene monomer can be converted to a regular Class I polymer with the same structure as natural rubber (. ... 

FIGURE 1.15 Tja and as functions of composition for random copolymers composed of two Class-I polymers. 

A Class-I polymer is injection molded from the hot melt into a cold metal mold. As it cools in the mold the material structure will vary across the mold. Sketch the structure that results at room temperature (Troom) if Tg where is the glass transition temperature. 

The chemistry and technology of this class of polymer may be considered as an extension to those of the polysulphones, particularly insofar as there are strong parallels in preparative methods. The two polymer classes also have strong structural similarities with polysulphones containing the structure (I) and the polyetherketones the structure (II) of Figure 21.6. 

Within the past several years, we have examined the synthesis and reactions of several classes of polymers related to PECH. We have adopted three simple approaches to the preparation of polymeric substrates more reactive than PECH toward nucleophilic substitution. We have i). removed the 8-branch point by extension of the side chain, ii). replaced the chloride leaving group by a more reactive bromide and iii). replaced the backbone oxygen atom by a sulfur atom that offers substantial anchimeric assistance to nucleophilic... 

Polymer gels and ionomers. Another class of polymer electrolytes are those in which the ion transport is conditioned by the presence of a low-molecular-weight solvent in the polymer. The most simple case is the so-called gel polymer electrolyte, in which the intrinsically insulating polymer (agar, poly(vinylchloride), poly(vinylidene fluoride), etc.) is swollen with an aqueous or aprotic liquid electrolyte solution. The polymer host acts here only as a passive support of the liquid electrolyte solution, i.e. ions are transported essentially in a liquid medium. Swelling of the polymer by the solvent is described by the volume fraction of the pure polymer in the gel (Fp). The diffusion coefficient of ions in the gel (Dp) is related to that in the pure solvent (D0) according to the equation ... 

Polymers in which the quarternary nitrogen atom is part of a five- or six-membered ring comprise the second class of polymers. The ring forms part of the polymer backbone as indicated by the second and third polymer repeat units given in Table I. The member of this class cited in several patents is poly(diallyldimethyl-ammonium chloride) abbreviated poly(DMDAAC). 

Associated with the class of polymer particles n(t,i)dx in the polymer reactor is a physical property p(t,x) (e.g. diameter or area of particles of class (t,x), etc.). Then, a total property Pit) (e.g. total particle diameter in the reactor at time t) can be obtained by summing (integrating) p(t,x) over all classes of particles in the reactor vessel, viz ... 

Fig. 7 Persistence length P is plotted vs. the chain diameter D both for polymers giving Class I and for polymers giving Class II mesophases. (From ref [11], see also Table 1). Reproduced with permission from [11]. Copyright 2004 Am Chem Soc...

Geometrical and flexibility data pertaining to the same polymers are also given in Table 1, namely the persistence length and the average chain-to-chain interaxial distance D. The first five polymers in Table 1 have D values smaller than 6 A, unlike all the following polymers (i.e., no. 6 to 19 in Table 1, Class II). This is a consequence of the relatively bulky substituents carried by Class II polymer chains. For some of the polymers in Table 1 the C0o and P literature values are widely scattered or unavailable. In those cases lower-limit values of P from experimentally determined geometrical parameters, are predicted from our model by suitable interpolation and reported within parentheses. 

As an extension of the perspective of micelle formation by amphiphihc block copolymers the following part will focus on two other types of polymers. The micellar structures that will discussed are (i) micelles and inverse micelles based on a hyperbranched polymers and (ii) polysoaps, that are copolymers composed of hy-drophihc and amphiphihc or hydrophobic monomers. Whereas the first class of polymers is stiU very new and only few examples exist of the synthesis and appH-cation of such stracture in catalysis, the synthesis and aggregation characteristics of polysoaps has already been intensively discussed in the hterature. 

---