Mesomorphic precursor phase

More recently, Strobl [18] has stimulated a discussion by arguing that in all processes of polymer crystallization, a mesomorphic precursor phase is first formed before the crystalline phase. Blocks of this mesomorphic state then attach to the growth front, as sketched in Fig. 1.5. This model, inspired by the observation of the hexatic phase in short n-alkanes [19, 20], is actively contested by the polymer community. Whether such mesomorphic phases are stable intermediates before the formation of the crystalline phase and whether a critical chain stiffness is required for such mesomorphic phases are being discussed. Several laboratories worldwide are pursuing experiments to explore this aspect of poljmer crj talUzation. 

Other ortV o-metallated pyridazine complexes (134, where R = -Me, -CH2CI2) were reported by Guang et For n = m= Q, the free ligand showed a SmA phase (Cr 79 SmA 102 I), as did the /i-Cl precursor complex (Cr 163 SmA 212 I) and the chloro- and bromoacetates (Cr 160 SmA 185 I and Cr 160 SmA 174 I, respectively) the simple /i-acetato complex was non-mesomorphic at all chain lengths reported. The lower symmetry complexes ( = 6, m= 10) were mesomorphic for the chloro- but not the bromoacetate, and a more extensive series where n was fixed as 10 and m was varied from 6 to 12 showed enantiotropic SmA phases for all except that with m = i>. 

Similarly, smectic mesophases were obtained in heteronuclear or/ o-palladated imine complexes based on various non-mesomorphic enaminoketone ligands ((263) to (265), Figure 104). The precursor chloro-bridged complex was also mesomorphic, showing an SmA phase between 238 and 248°C. ... 

The eleven examples of TABLE 4 based on electron-donor compounds of family 3b show that induction processes starting from either non-mesomorphic or nematic discotic precursors can indeed give the ( intermediate kind of) stable colunmar nematic phase including the three known cases of chiral nematic phases. Unfortunately, for application purposes the temperature ranges of the nematic phases of the intermolecular electron donor-acceptor complexes (TABLE 4) may be much too high ... 

This collection contains one platinum and four palladium organyls (7a and 7b-7e, respectively) as well as an azacyclic cobalt(II) complex (8). Whereas the five pure metal organyls 7a-7e meh between 73 and 96°C and show only a monotropic No phase, the cobah(II) compound 8 does exhibit the Ncoi phase enantiotropically at lower temperatures, between 30 and 60°C. The metal-free precursor ligand of 8 is not mesomorphic [63] ... 

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