With alternating rigid and flexible

Thermotropic liquid crystalline polymers with alternating rigid and flexible units along the backbone are a class of polymers which have been studied extensively over the years. The rigid units are usually aromatic moieties connected to each other by a variety of functional groups while the flexible units are most commonly methylene or... 

The urethane systems used in this application are essentially casting systems. In these, prepolymers are reacted with low molecular weight glycols or diamines to give chain-extended copolymer with alternating rigid and flexible segments. 

Yoon, D. Y, and Flory, P. J., Conformational rearrangement in the nematic phase of a polymer comprising rigid and flexible sequences in alternating succession II. Theoretical results and comparison with experiments, MRSSymp. Proc., (Adams, W. W, Eby, R. K., and McLemore, D. E., Eds.) 134, 11-19 (1989). 

The brief information reported indicated the great variety of the reactions of synthesis of regular LC polymers. The variations of the conditions of conducting the reactions are limited by the requirement of chemical stability of the polymer chain, however. In synthesis of irregular LC polymers (with irregular alternation of rigid and flexible fragments), this restriction is practically eliminated. 

June et al. (12) used TST as an alternative method to investigate Xe diffusion in silicalite. Interactions between the zeolite oxygen atoms and the Xe atoms were modeled with a 6-12 Lennard-Jones function, with potential parameters similar to those used in previous MD simulations (11). Simulations were performed with both a rigid and a flexible zeolite lattice, and those that included flexibility of the zeolite framework employed a harmonic term to describe the motion of the zeolite atoms, with a force constant and bond length data taken from previous simulations (26). 

Unlike the cyclic catenanes, rotaxanes are simpler species originally proposed by Wasserman and first demonstrated by Harrison [77], In these systems a cyclic molecule is threaded on a rigid or flexible molecular axle, attracted by complementary binding sites, to form a pseudorotaxane. Under normal entropically driven supramolecular chemistry the cyclic component would eventually slip off one or other end of the central axle, however, it can be kept in place if both ends of the axle react with bulky groups while the macrocycle is still threaded. Alternatively a macrocycle can be formed around an axle molecule that already possesses bulky termini, as shown in Fig. 1.22. Either method leads to an entanglement in which the cycle species can move along the thread without ever coming off. 

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