Aggregation states crystalline polymers

For a crystalline polymer, the melting temperature (Tm) may be observed for both the cyclic and the backbone in some cases. Poly(alkylene sebacate crown ether rotaxane)s 60 have two Tm values, those of the cyclic and the backbone [19, 111]. The crystallization of the crown ether on the backbone was attributed to aggregation enabled by the mobility of the crown ether along the backbone in solution or melt states. The crystallization process is driven by the tendency for these immiscible components to form their own separate phases to minimize interfacial energy. According to an X-ray diffraction study of polystyrene rotaxane)s 26... 

An important point in the science of conjugated polymers is the dependence of their optical properties as a response to their physical state (solution, aggregated, liquid crystalline, solid state, thermal treatment) [50]. Processable PPEs, particularly dialkoxy-PPEs, have been known since the early 1990s [1], and their spectroscopic behavior has been studied both in... 

It is now generally accepted that folding is universal for spontaneous, free crystallisation of flexible polymer chains. It was first of all found in crystallisation from very dilute solutions, but it is beyond doubt now, that also spherulites, the normal mode of crystallisation from the melt, are aggregates of platelike crystallites with folded chains, pervaded with amorphous material. "Extended chain crystallisation" only occurs under very special conditions in the case of flexible chains for rigid polymer chains it is the natural mode ("rigid rod-crystallisation" from the melt in case of thermotropic polymers, and from solution in case of the lyotropic liquid-crystalline polymers both of them show nematic ordering in the liquid state). 

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. 

Table 2.2.1. Heats of formation for a number of polymerization reactions generating carbon atoms chains [4]. The aggregation state for the monomer and for the polymer (ideal) are indicated as follows g = gas, I = liquid, c = solid crystalline, a = solid amorphous, s = solution.

The unordered (amorphous) state of aggregation in which the polymer chains also assume random conformations represents one extreme in the physical state of the polymer. This is the state that exists in such amorphous states as solution, melts, or some solids, the randomness being induced by thermal fluctuations. The other extreme is the case where the molecules are able to pack closely in perfect parallel alignment as is found in those polymers that exhibit fibrous behavior— that is, in those possessing a high degree of crystallinity and crystal orientation. In between these two extremes of amorphous and crystalline polymers there is a wide spectrum of polymeric materials with different degrees of crystallinity and amorphous character. These are called semicrystalline. 

The performance of polymer blends could be well represented by a Takayanagi model in which the relative values of /. and were related to the shape of the dispersed phase, e.g. /. = for homogeneous dispersions, and / > for dispersions in the form of elongated molecular aggregates. But for semi-crystalline polymers, with A and B representing amorphous and crystalline components, the dispersions were generally broader than predicted, suggesting that the unordered material was not identical with that in a completely amorphous state. 

The preparation of fully aromatic polyesters is mostly performed by melt condensation. Complex phase equilibriums and states of aggregation are formed in this manner. This is in most cases not easy to control under laboratory conditions. Example 4.5 describes a polyester that is easy to prepare under laboratory conditions and allows the observation of typical properties of some thermotropic liquid crystalline polymers. 

Crist B (2013) Chapter 3 structure of polycrystalline aggregates. In Piorkowska E, Rutledge G (eds) Handbook of polymer crystallization. Wiley, Hoboken de Rosa C, Auriemma F (2013) Crystals and crystallinity in polymers diffraction analysis of ordered and disordered crystals. Wiley, Hoboken Dettenmaier M, Fischer EW, Stamm M (1980) Calculation of small-angle neutrrai scattering by macromolecules in the semicrystalline state. Colloid Polym Sci 258(3) 343-349 Donald AM, Windle AH, Hanna S (2006) Liquid crystal polymers, 2nd edn. Cambridge University Press, Cambridge... 

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