Precise Synthesis and Thin Film Self-Assembly of PLLA-b-PS Bottlebrush Block Copolymers

Abstract

The ability of bottlebrush block copolymers (BBCPs) to self-assemble into ordered large periodic structures could greatly expand the scope of photonic and membrane technologies. In this paper, we describe a two-step synthesis of poly(l-lactide)-b-polystyrene (PLLA-b-PS) BBCPs and their rapid thin-film self-assembly. PLLA chains were grown from exo-5-norbornene-2-methanol via ring-opening polymerization (ROP) of l-lactide to produce norbornene-terminated PLLA. Norbonene-terminated PS was prepared using anionic polymerization followed by a termination reaction with exo-5-norbornene-2-carbonyl chloride. PLLA-b-PS BBCPs were prepared from these two norbornenyl macromonomers by a one-pot sequential ring opening metathesis polymerization (ROMP). PLLA-b-PS BBCPs thin-films exhibited cylindrical and lamellar morphologies depending on the relative block volume fractions, with domain sizes of 46–58 nm and periodicities of 70–102 nm. Additionally, nanoporous templates were produced by the selective etching of PLLA blocks from ordered structures. The findings described in this work provide further insight into the controlled synthesis of BBCPs leading to various possible morphologies for applications requiring large periodicities. Moreover, the rapid thin film patterning strategy demonstrated (>5 min) highlights the advantages of using PLLA-b-PS BBCP materials beyond their linear BCP analogues in terms of both dimensions achievable and reduced processing time.

Water-Stable Thin-Film Nanostructures from Amphiphilic Cationic Bottlebrush Block Copolymers by Grafting-through Ring-Opening Metathesis Polymerization

“…Morphological changes for PS 17 - b -PDMH films were observed as f PDMH increased from about 0.58 to about 0.73, influencing the molecular packing shapes and interfacial curvatures (Figure B top and middle rows and Figures S6A and S7A). Other researchers have demonstrated that BBCPs can phase-separate into lamellar, cylindrical, or spherical morphologies, which are dependent upon the block compositions and polymer side-chain lengths. , Our BBCP films appeared to show lamellar and cylindrical morphologies for the films with f PDMH values of 0.58 and 0.73, respectively; however, definitive assignments require future scattering experiments . Due to nonselective CHCl 3 used to cast the films and no preferential interfacial interaction between the individual block and glass surface, the self-assembled orientation exhibited perpendicular features to the surfaces. , This indicates that a balance exists between the interaction of the sterically hindered polymer brushes and the surface or the air interfaces .…”

“…13,37 Our BBCP films appeared to show lamellar and cylindrical morphologies for the films with f PDMH values of 0.58 and 0.73, respectively; however, definitive assignments require future scattering experiments. 38 Due to nonselective CHCl 3 used to cast the films and no preferential interfacial interaction between the individual block and glass surface, the self-assembled orientation exhibited perpendicular features to the surfaces. 26,39 This indicates that a balance exists between the interaction of the sterically hindered polymer brushes and the surface or the air interfaces.…”

“… a Obtained from radial power spectral density function analysis of four different AFM phase images over two different analyzed regions on the thin films and then reported as an average ± standard deviation of the four AFM phase images. b Estimated by AFM phase images of casted BBCP films as determined by comparison to the similar phase-separated shapes and patterns for the BBCP in ref . L = perpendicular lamellae and C = perpendicular cylinder. …”

Synthesis and Thermal Analysis of Non-Covalent PS-b-SC-b-P2VP Triblock Terpolymers via Polylactide Stereocomplexation

“…In the case of the diblock copolymers, the T g values of PS and P2VP blocks cannot be observed, indicating that the PS/P2VP (amorphous blocks) and PLLA/PDLA (crystalline blocks) are miscible in the melt [50,51]. The PLLA/PDLA crystallites are well organized (as proved by the distinct ∆H m ) and limit the mobility of the amorphous blocks [50]. In addition, for PS 6.2 -b-PDLA 7.1 (Figure 4c), the T g of PS overlaps with the exothermic peaks from the cold-crystallization temperature (T cc ) of PLA.…”

“…The T g values of the amorphous PS 6.2 -OH and P2VP 5.2 -OH precursors are observed to be 92.3 • C and 93.6 • C (Table 2), respectively. In the case of the diblock copolymers, the T g values of PS and P2VP blocks cannot be observed, indicating that the PS/P2VP (amorphous blocks) and PLLA/PDLA (crystalline blocks) are miscible in the melt [50,51]. The PLLA/PDLA crystallites are well organized (as proved by the distinct ∆H m ) and limit the mobility of the amorphous blocks [50].…”