This review focuses on the structural control in thin films of regioregular poly(3-hexylthiophene) (P3HT), a workhorse among conjugated semiconducting polymers. It highlights the correlation existing between processing conditions and the resulting structures formed in thin films and in solution. Particular emphasis is put on the control of nucleation, crystallinity and orientation. P3HT can generate a large palette of morphologies in thin films including crystalline nanofibrils, spherulites, interconnected semicrystalline morphologies and nanostructured fibers, depending on the elaboration method and on the macromolecular parameters of the polymer. Effective means developed in the recent literature to control orientation of crystalline domains in thin films, especially by using epitaxial crystallization and controlled nucleation conditions are emphasized. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 49: 1218–1233, 2011

https://www.onlinelibrary.wiley.com/doi/pdf/10.1002/polb.22310

Structure and morphology control in thin films of regioregular poly(3‐hexylthiophene)

A critical assessment of unbalanced surface stresses as the mechanical origin of twisting and scrolling of polymer crystals

A previous work reported that the polymorphic crystallization behavior of isotactic polypropylene (iPP) can be efficiently tuned by the combination of controlling the melt structure (i.e., creation of an ordered structure by tuning the fusion temperature Tf by self-nucleation) and the addition of the α-/β-dual-selective nucleation agent (dual-selective β-NA, tradename WBG-II). In this study, we further investigated the impact of isothermal treatment on the polymorphic behavior and the isothermal crystallization kinetics of a β-iPP sample with different melt structures by differential scanning calorimetry (DSC). The results of isothermal crystallization kinetics study illustrated that as Tf decreased gradually from Region I to Region II and Region III, two sharp increases of the crystallization rate took place at the transition temperatures of Region II, showing that the enhancement of β-phase crystallization took place in a certain crystallization rate window. The calculation of the Avrami exponent n revealed that the two-dimensional growth of crystallites with instantaneous nucleation took place before and after the occurrence of the synergetic effect between the ordered structures and the dual-selective β-NA (when Tf ≥ 168 °C). Moreover, it was found that the occurrence of the synergetic effect in the fusion temperature range of Region II can evidently enhance the βc of the sample: by tuning the fusion temperature Tf and the isothermal crystallization temperature Tc, the relative percentage of β-phase (βc) of the single β-iPP sample with only 0.03 wt.% β-NA can be efficiently tuned in the wide βc range of 0 %–95.0 %; meanwhile, the sensitivity of βc to the isothermal crystallization temperature Tc was reduced.

Isothermal crystallization behavior of β-nucleated isotactic polypropylene with different melt structures

Wide-angle X-ray diffraction (WAXD) was used to investigate the effects of shear on the crystallization behavior of polypropylene (PP) with β-nucleating agent. The melt was subjected to shear at the shear rate from 0.5 to 60 s-1 for 5 s with a CSS450 shear stage. For the PP with low content of the additive, the formation mechanism of the β crystals is almost the same as that of pure isotactic polypropylene (iPP), viz., shear induces. Otherwise, for the samples with high content of the additive, the formation mechanism of the β form are nucleating agent induces. The results clearly show that shear restrains the formation of high β phase for the melt with additive.

Influence of Shear on Crystallization Behavior of the β Phase in Isotactic Polypropylene with β-Nucleating Agent

The frustrated structure of poly(l-lactide)

Isotactic polypropylene, β-phase: a study in frustration

Epitaxial crystallization and crystalline polymorphism of poly(1-butene): form I

The spontaneous phase II to phase I crystal-crystal transformation of polybutene-1 was investigated by electron diffraction and bright- and dark-field imaging of solution and thinfilm grown single crystals. Whole single crystals were observed to transform with a single phase II to phase I orientational relationship and, in the case of multiple orientations, the transformed areas were not dependent on growth sectors. These results do not support the views of Holland and Miller of a “twinned” phase II to I transformation determined by growth sectors but are consistent with a transformation scheme introduced by Fujiwara. Nucleation and growth of the transformation are further discussed.

Phase II to phase I crystal transformation in polybutene-1 single crystals: a reinvestigation

Epitaxial crystallization and crystalline polymorphism of poly(1-butene) : forms III and II

Three-dimensional electron diffraction intensity data from form (III) of isotactic poly(1-butene) have been collected by tilting solution- and epitaxially grown thin microcrystals. The orthorhombic space group is P2 1 2 1 2 1 with cell constants a= 12.38, b= 8.88 and c= 7.56 A, the latter being the chain repeat. The crystal structure was determined by direct methods, employing the tangent formula (QTAN) and initially 106 phase values were found for 125 unique observed reflections. Refinement by Fourier techniques gave a structure very similar to that proposed in an earlier powder X-ray diffraction study

S. Kopp

Papers

Isotactic polypropylene, β-phase: a study in frustration

Epitaxial crystallization and crystalline polymorphism of poly(1-butene): form I

Phase II to phase I crystal transformation in polybutene-1 single crystals: a reinvestigation

Epitaxial crystallization and crystalline polymorphism of poly(1-butene) : forms III and II

Direct determination of polymer crystal structures by electron crystallography ‒ isotactic poly(1-butene), form (III)