Rigid-rod monomers

Other, rigid-rod monomers can be incorporated into PET, to increase chain stiffness, and therefore the Tg (Figure 6.5). A prime example of such a rigid copolyester is a multi-ring poly(ethylene terephthalate-imide) [43], As was the case with the polyesteramides of Gaymans, the imide-containing diol monomer, A,A-bis[p-(2-hydroxyethoxycarbonyl)phenyl]-biphenyl-3,3,4,4-tetracarboxy-diimide, was preformed prior to polycondensation, where this monomer is free... 

Melissaris and co-workers [46] have studied various novel p-ethynyl-substituted rigid rod monomers by DSC, TG and TG-FTIR and identified the main decomposition products. Void-free neat resin mouldings were made by compression moulding the monomers followed by heating. 

If a diacid is mixed with the glycidyl terminated rigid rod monomer the reaction is much slower. The resulting cured material will exhibit a smectic phase with high values of isotropization enthalpy. If stressed above Tg, the smectic planes will orient, and macroscopically this implies a transition from an opaque state to a transparent state for the anisotropic film. The oriented polymer will relax back to the unoriented state if heated above Tg. No double peak exotherm can be observed by DSC analysis, since at the reaction temperature the forming thermoset is above its isotropization temperature. 

The adsorption of diatomic or dimeric molecules on a suitable cold crystalline surface can be quite realistically considered in terms of the dimer model in which dimers are represented by rigid rods which occupy the bonds (and associated terminal sites) of a plane lattice to the exclusion of other dimers. The partition function of a planar lattice of AT sites filled with jV dimers can be calculated exactly.7 Now if a single dimer is removed from the lattice, one is left with two monomers or holes which may separate. The equilibrium correlation between the two monomers, however, is appreciable. As in the case of Ising models, the correlation functions for particular directions of monomer-monomer separation can be expressed exactly in terms of a Toeplitz determinant.8 Although the structure of the basic generating functions is more complex than Eq. (12), the corresponding determinant for one direction has been reduced to an equally simple form.9 One discovers that the correlations decay asymptotically only as 1 /r1/2. 

Although rigid-rod poly(p-phenyleneterephthalamide) analogues having alkyl side chains did not contain cyclic polymers, the polycondensation of silylated m-phenylenediamine and aliphatic dicarboxyhc acid chloride afforded cyclic polyamides predominantly (Scheme 49) [187]. Furthermore, cyclic polymers were also produced in polycondensations for polyesters, poly(ether ketone)s, polyimides, and polyurethanes [183]. These examples are the products in polycondensation of AB monomers or in A2 + B2 polycondensations, but cyclization of oligomer and polymer was also confirmed in polycondensation of AB2 monomers [ 188-195] and in A2 + B3 [ 196-202] and A2 + B4 polycondensations [203-206], which afford hyperbranched polymers. 

Fig. 13 Constitutional adaptation to the environment in the hydrophobically-driven component selection on formation of a rigid rod dynamer from amphiphilic monomers. Polycondensation occurs in aqueous solution with preferential incorporation of the monomer presenting the largest hydrophobic area. Selectivity is progressively lost in solutions containing increasing amounts of organic solvent, acetonitrile...

X-ray crystallographic studies during the course of the reaction have demonstrated that the reaction is a typical topochemical process involving a direct rearrangement of the monomer crystal to the polymer crystal having an extended rigid rod-like structure. By x-ray analysis and DSC on the thermal depolymerization of the polymer crystal, a reversible topochemical process has been demonstrated for monomer and polymer crystals. 

The intention of this brief survey has been to demonstrate that besides the "classical" aspects of isotropic polymer solutions and the amorphous or partially crystalline state of polymers, a broad variety of anisotropic structures exist, which can be induced by definable primary structures of the macromolecules. Rigid rod-like macromolecules give rise to nematic or smectic organization, while amphiphilic monomer units or amphiphilic and incompatible chain segments cause ordered micellar-like aggregation in solution or bulk. The outstanding features of these systems are determined by their super-molecular structure rather than by the chemistry of the macromolecules. The anisotropic phase structures or ordered incompatible microphases offer new properties and aspects for application. 

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