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Crystal Engineering of Self-Assembled Diblock Copolymers with a Crystalline Core-Forming Block

Final Report Summary - CESADIC (Crystal Engineering of Self-Assembled Diblock Copolymers with a Crystalline Core-Forming Block)


Work carried out and results:

The milestones / work plan for one year were as follows:

1. influence of the type of corona-forming block on the growth rate, the morphology of PFS core-forming micelles;
2. PFS crystallisation and crystal orientation under 2D cylindrical confinement on the nanoscale.

The research has progressed on schedule.

1. Eight well-defined metal-containing poly (ferrocenyl dimethylsilane) based block copolymers with three different kinds of corona-forming block and identical ratios of corona to core-forming block length were successfully synthesised (PI324-b-PFS37, PI508-b-PFS66, PI835-b-PFS121, PFS41-b-PDMS238, PFS72-b-PDMS390, PFS44-b-P2VP257, PFS75-b-P2VP454, PFS102-b-P2VP625). Based on both TEM and DLS results, the following conclusions were made. First, growth rates of three different PFS-based diblock copolymers (PI-b-PFS, PFS-b-PDMS, PFS-b-P2VP) were similar when samples possessed N PFS = 44 and N corona/ N core =6.0. Second, the difference of the growth rate and two different micelle morphologies (cylinder and sphere) can be observed in hexane (or n-decane) in three asymmetric PI-b-PFS samples.

2. Two different polystyrene-b-poly (ferrocenyl dimethylsilane) (PS-b-PFS) diblock copolymers having cylindrical morphology were synthesised for investigating the crystalline behavior of metal-containing polymers (metallopolymers) in confined environment. From two-dimensional (2D) WAXD results, the crystallisation of PFS blocks can take place under glassy PS cylindrical environment on the nanoscale. By a combination of simultaneous 2D SAXS and WAXD techniques, the relationship between PFS crystal orientation and the (Tc) via the preparation of a large sample (on the order of millimeters) with a uniformly-oriented cylindrical phase structures was established.

The milestones / work plan for year 2 were as follows:

1. the influence of molecular weight and solvent selectivity on the self-assembly of asymmetric Poly(ferrocenyldimethylsilane-b-2-vinylpyridine) diblock copolymers with a shorter crystallisable core-forming metalloblock;
2. collaborative work on Poly(ferrocenylsilane) based diblock copolymers;
3. reporting of results in international journals and conferences.

1. Three well-defined poly (ferrocenyl dimethylsilane-b-2 vinyl pyridine) diblock copolymers with similar block ratios (r = NP2VP/NPFS = circa 6.0 ± 0.1) but different overall molecular weights, were synthesised (PFSx-b-P2VP6x) for studies of their solution self-assembly behavior as a function of molecular weight and the ratio of common to selective solvent. Four interesting results were observed and analysed. First, a decrease in the rate of micellar transition from the spheres formed initially (with amorphous PFS cores) into cylinders (with crystalline cores) was detected with an increase in molecular weight in isopropanol. This trend can be explained by a decrease in the rate of crystallisation for the PFS core-forming block as the chain length increased. Second, spheres, cylinders and also platelets were subsequently formed from the same asymmetric PFSx-b-P2VP6x sample in iPrOH/THF mixed solvent as the THF content was increased. A change of the growth of crystalline PFS core from 1 D to 2 D, caused by the improvement of solvent quality, for both the corona and core-forming blocks might explain this micellar sphere-cylinder-platelet transition. Third, electron diffraction results indicated that the spherical micelles were amorphous, but the crystalline core of the cylindrical micelles existed in an approximate single crystalline state. Thus, the one-dimensional (1D) growth of a lamellar PFS single crystal within a confined cylindrical micellar environment appears to provide the driving force for the crystallisation-driven self-assembly process in which spheres are transformed into cylinders. Four, the platelet micelles were found to be polycrystalline and consisted of crystalline PFS lamellae sandwiched between two glassy coronal P2VP layers. The formation of lenticular rather than regular, rectangular platelets was attributed to a poisoning effect whereby the interference of long P2VP coronal blocks in the growth of rectangular PFS single crystalline core creates defects in the crystal growth fronts.

2. Collaborations with other researchers on other projects in Prof. Ian Manners' group involving synthesis, characterisation and self-assembly of functional diblock copolymers with a metalloblock, were necessary. With Dr Rumman Ahmed, the synthesis, structure, and characterisation of novel redox-active mesomorphic complexes from the ionic self-assembly of cationic polyferrocenylsilane polyelectrolytes and anionic surfactants, was investigated. Together with Dr Siti Fairus Mohd Yusoff, unique lenticular platelet micelles formed by Poly (ferrocenyldimethylsilane-block-2-vinylpyridine) with a short crystallisable PFS core-forming block was observed, and a mechanism was proposed successfully for the formation of these lenticular platelet micelles.

3. Some of the work have been published in international journals, and also presented in conferences as oral presentation (95th Canadian Chemistry Conference and Exhibition, Calgary, AB, Canada 2012; 12th Eurasia Conference on Chemical Sciences, Corfu, Greece 2012; 242nd ACS National Meeting, Denver, United States of America (USA), 2011).

Conclusions:

The results based on these crystalline-coil poly(ferrocenyldimethylsilane) based diblock copolymers have been well explained from the viewpoint of polymer crystallisation. The crystallisation-driven self-assembly process of other diblock copolymers including one crystallisable core-forming block such as polythiophene, PPV and polylactide in solution could be easily understood based on accumulated knowledge coming from this PFS based diblock copolymers. The design of new functional hybrid materials with different architectures was achieved through a crystallisation-driven self-assembly process. Some results have been published in some of the best scientific journals and a number of manuscripts are being prepared for high reputed journals (Macromolecules, Soft Matters, J. Am. Chem. Soc.).

The fellowship has provided Dr Ming-Siao Hsiao with a tremendous boost with regard to research expertise. As a result, the fellowship has helped him to learn precise synthesis techniques (the synthesis of metal-containing polymer and anionic polymerisation). The training and experience gained while working with one of the world leaders in polymer science and nanoscience (Prof. Ian Manners) during the Marie Curie fellowship, will be crucial to his independent academic career in the future. On his return to Taiwan, there are good possibilities for long term collaborative research to develop the new area emerged through this Marie Curie programme, thus providing an excellent means of engagement between the Taiwan and European scientific communities.