Understanding the CDSA of poly(lactide) containing triblock copolymers

Abstract

Crystallisation-driven self-assembly (CDSA) has become an extremely valuable technique in the preparation of well-defined nanostructures using diblock copolymers. The use of triblock copolymers is considerably less well-known on account of more complex syntheses and assembly methods despite the functional advantages provided by a third block. Herein, we show the simple preparation of well-defined tuneable 1D and 2D structures based on poly(lactide) triblock copolymers of different block ratios synthesised by ring-opening polymerisation (ROP) and reversible addition-fragmentation chain transfer (RAFT) polymerisation, where a phase diagram based on a novel unimer solubility approach is proposed. Using a series of poly(L-lactide)-b-poly(N,N-dimethylacrylamide) (PLLA-b-PDMA) diblock copolymers and PDMA-b-PLLA-b-PDMA triblock copolymers with different core/corona ratios, single solvent CDSA processes revealed that comparatively hydrophilic polymers were liable to achieve 2D platelets, while the less hydrophilic counterparts yield 'transition state' wide cylinders and pure 1D cylinders. The length of crystalline core block is also shown to play an important role in fixed corona/core ratio systems, where a longer core block is prone to form cylindrical structures due to a lack of overall solubility, whereas a shorter block forms platelets. Importantly, this approach reveals contrary results to conventional theories, which state that longer solvophilic blocks relative to the core-forming block should favour more curved core/corona interfaces. Our morphological transitions are shown in both di-and tri-block copolymer systems, showing the generalisation of these assembly methods towards promising methodologies for the rational design of PLLA-based nanocarriers in the biomedical realm.

Thermoreversible crystallization-driven aggregation of diblock copolymer nanoparticles in mineral oil

“… 21 Furthermore, PDMAC–PLLA–PDMAC triblock copolymers formed either diamond-shaped lamellae or cylindrical micelles of varying length in dilute methanolic solution. 22 Similarly, Lecommandoux and co-workers 23 reported the 1D fusion of spherical diblock copolymer micelles to form fibres on prolonged heating at 65 °C in water, with wide-angle X-ray scattering (WAXS) studies indicating the gradual formation of crystalline cores. There have also been several reports of CDSA formulations utilizing poly(ε-caprolactone) core-forming blocks.…”

Toward Uniform Nanofibers with a π-Conjugated Core: Optimizing the “Living” Crystallization-Driven Self-Assembly of Diblock Copolymers with a Poly(3-octylthiophene) Core-Forming Block

“…For example, BCPs with a crystallizable poly(ferrocenyldimethylsilane) 23 core-forming block form fiber-like micelles for a range of block ratios from 1:3 to 1:20. 23,24 The formation of fiber-like micelles with crystalline cores has also been achieved for other BCPs with crystallisable core-forming blocks, such as PE, [25][26][27][28] PEO, 29 polycaprolactone, [30][31][32] poly(L-lactic acid), [33][34][35][36][37][38] poly(3-hexylthiophene), [39][40][41][42][43][44][45] poly(3-heptylselenophene), 46 oligo-and poly(phenylene-vinylene), [47][48][49] and poly(dialkylfluorene). [50][51][52] Moreover, in an expanding number of cases the formation of low dispersity 1D fibers with length control can be achieved by a method termed "living" crystallization-driven self-assembly (CDSA).…”

Recent progress in block copolymer crystallization

“…Cylindrical micelles were more prominent when the w PS increased. Yu et al . studied the assembly behavior of PDMA copolymers with PLLA as the crystalline block, PDMA‐ b ‐PLLA‐ b ‐PDMA.…”

“…A phase diagram based on the size (DP = degree of polymerization) and weight fraction of PLLA is also included. (Reproduced from with permission from The Royal Society of Chemistry)…”