Poly self-nucleation

In addition to the nucleating agents discussed in Section 18.4, many other materials have been found to be effective. Whilst the nylons may be self-nucleating, partieularly if there is some unmelted crystal structure, seeding with higher melting point polymers can be effective. Thus nylon 66 and poly(ethylene terephthalate) are reported to be especially attractive for nylon 6. 

The technique of self-nucleation can be very useful to study the nucleation and crystallization of block copolymers that are able to crystallize [29,97-103]. Previous works have shown that domain II or the exclusive self-nucleation domain disappears for systems where the crystallizable block [PE, PEO or poly(e-caprolactone), PCL] was strongly confined into small isolated MDs [29,97-101]. The need for a very large number of nuclei in order to nucleate crystals in every confined MD (e.g., of the order of 1016 nuclei cm 3 in the case of confined spheres) implies that the amount of material that needs to be left unmolten is so large that domain II disappears and annealing will always occur to a fraction of the polymer when self-nucleation is finally attained at lower Ts. This is a direct result of the extremely high number density of MDs that need to be self-nucleated when the crystallizable block is confined within small isolated MDs. Although this effect has been mainly studied in ABC triblock copolymers and will be discussed in Sect. 6.3, it has also been reported in PS-fc-PEO diblock copolymers [29,99]. 

The quantitative influence of self-nucleation is shown in Fig. 3.66 for the case of crystallization of poly-l-butene with crystal form 11 when followed by dilatometry. 

Muller AJ, Albueme J, Marquez L, Raquez JM, Degee P, Dubois P, Hobbs J, Hamley IW. Self-nucleation and crystallization kinetics of double crystalline poly(p-dioxanone)-b-poly(c-caprolactone) diblock copolymers. Faraday Discuss 2005 128 231-252. 

In contrast to the PE-6-PS block copolymers, when PE is covalently bonded to poly(ethylene-alt-propyl-ene) (PEP), a strong diluent effect is observed upon PE crystallization, and in the extreme case of EnEPgg, fractionated crystallization was also observed for the PE block. Additionally, the difference between being bonded to a rubbery block or bonded to a glassy block was studied by successive self-nucleation and annealing (SSA). The results showed that the dilution effect of... 

The use of ordered supramolecular assemblies, such as micelles, monolayers, vesicles, inverted micelles, and lyotropic liquid crystalline systems, allows for the controlled nucleation of inorganic materials on molecular templates with well-defined structure and surface chemistry. Poly(propyleneimine) dendrimers modified with long aliphatic chains are a new class of amphiphiles which display a variety of aggregation states due to their conformational flexibility [38]. In the presence of octadecylamine, poly(propyleneimine) dendrimers modified with long alkyl chains self-assemble to form remarkably rigid and well-defined aggregates. When the aggregate dispersion was injected into a supersaturated... 

SCH Schwalm, D., Richter, D., Wight, P.J., Symon, C., Fetters, L.J., and Lin, M., Self-assembhng behavior in decane solution of potential wax crystal nucleators based on poly(co-oleGns), Macromo/ecu/es, 35, 861, 2002. 

Of relevance to this section, Reculusa et al. also recently demonstrated that the addition of a small amount (only 1.5 pmole/m ) of a monomethylether mono methylmethacrylate poly(ethylene oxide) macromonomer (structure 9, Table 4.5) allowed the direct self-assembly of nanometric polystyrene latex particles on the surface of submicronic sihca particles through an in-situ nucleation and growth process (Fig. 4.12) [102]. The two sets of particles were assembled in a raspberry-like morphology via the formation of hydrogen bonds at the interface of the inorganic and organic coUoids. The size and shape of the assembly can be easily controlled by varying the sizes and stoichiometries of the colloidal components (Fig. 4.13). 

Schwahn, D. Richter, D., Wright, P.J. Symon, C. Fetters, L.J. Lin, M (2002a). Self-Assembling Behaviour in Decane Solution of Potential Wax Crystal Nucleators Based on Poly(co-01efins). Macromolecules, Vol.35, No.3, pp.861-870, ISSN 0024-9297 Schwahn, D. Richter, D. Lin, M. Fetters, L.J. (2002b). Cocrystallization of a Poly(Ethylene-Butene) Random Copolymer with C-24 in n-Decane. Macromolecules, Vol.35, No.9, pp.3762-3768, ISSN 0024-9297... 

Dibenzylidene sorbitol exists in the form of fibrils and usually acts as an effective nucleating agent to facilitate crystallization of poly-(olefin)s during manufacturing (12). In particular, when the dibenzylidene sorbitol concentration reaches a critical value, the fibrils will self-organize into a three-dimensional network when there is a decrease of temperature, but before crystallization takes place. The network of the fibrils may facilitate the subsequent process of nu-cleation and crystallization growth. An oriented deformation of the dibenzylidene sorbitol network could act as a template for anisotropic crystallization of PP, which then results in a high lamellar orientation level. 

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