Anton H. Hofman

Double-crystalline PLLA-b-PVDF-b-PLLA triblock copolymers : preparation and crystallization

Double-crystalline poly(L-lactide)-block-poly(vinylidene fluoride)-block-poly(L-lactide) (PLLA-b-PVDF-b-PLLA) triblock copolymers were successfully synthesized through ring opening polymerization of L-lactide and benzoyl peroxide initiated polymerization of vinylidene fluoride, followed by copper(I)-catalyzed azide–alkyne coupling of the functionalized PLLA and PVDF. Three triblock copolymers with different block ratios were prepared via this synthetic approach. The block copolymers were miscible in the melt, and an alternating crystalline lamellar nanostructure was formed upon crystallization from the homogeneous melt. Crystallization behavior of the PLLA component depends strongly on the block composition. The crystallization temperature of the lower temperature crystallizing PLLA block increased considerably with respect to its parent homopolymer for rather symmetric block copolymers, indicating a strong nucleation effect, while on the other hand asymmetric block copolymers with low PLLA content demonstrated a large decrease of crystallization temperature, due to a fractionated crystallization process. A confined crystallization mechanism for the PLLA blocks was suggested, indicated by the low degree of crystallization compared to the respective homopolymers, and confirmed by microstructure analysis performed during isothermal crystallization. Contrary to PLLA, crystallization of the higher temperature crystallizing PVDF component within the block copolymer was not influenced by the block composition and similar crystallization behavior was observed with respect to PVDF homopolymers.

Free-standing thermo-responsive nanoporous membranes from high molecular weight PS-PNIPAM block copolymers synthesized via RAFT polymerization

The incorporation of stimuli-responsive pores in nanoporous membranes is a promising approach to facilitate the cleaning process of the membranes. Here we present fully reversible thermo-responsive nanoporous membranes fabricated by self-assembly and non-solvent induced phase separation (SNIPS) of polystyrene-poly(N-isopropylacrylamide) (PS-PNIPAM) block copolymers. A variety of PS-PNIPAM block copolymers were synthesized by reversible addition–fragmentation chain transfer (RAFT) polymerization and the reaction conditions were optimized. The target copolymers featured: (1) a thermo-responsive PNIPAM block, (2) a majority PS fraction, and (3) a well-defined high molecular weight, which are requirements for successful fabrication of free-standing responsive membranes using SNIPS. The resulting membranes exhibited a worm-like cylindrical morphology with interconnected nanopores. The thermo-responsive character of the membranes was studied by measuring the permeability of the membranes as a function of temperature. The permeability was found to increase by almost 400% upon going from room temperature to 50 °C and this thermo-responsive character was fully reversible.

Poly(4-vinylpyridine)-block-poly(N-acryloylpiperidine) diblock copolymers: synthesis, self-assembly and interaction

Controlled radical polymerization of 4-vinylpyridine (4VP) and N-acryloylpiperidine (API) by the RAFT process allowed preparation of well-defined double hydrogen bond accepting P4VP-b-PAPI diblock copolymers. The miscibility of this new monomer pair was studied via a random copolymer blend approach and resulted in a Flory–Huggins interaction parameter χ4VP,API ≈ 0.03, which is higher than the commonly used styrene/MMA couple, but lower compared to styrene/isoprene. This value was found to support the bulk phase behavior of a series of diblock copolymers as evidenced by SAXS and TEM. Highly ordered structures, including cylinders, lamellae and spheres, were identified in these materials, even in diblocks of higher molecular weight and broader distribution, while a disordered morphology was indeed observed in a symmetric, low molecular weight analogue.

Hierarchical Layer Engineering Using Supramolecular Double-Comb Diblock Copolymers

Abstract The formation of unusual multilayered parallel lamellae‐in‐lamellae in symmetric supramolecular double‐comb diblock copolymers is presented. While keeping the concentration of surfactant fixed, the number of internal layers was found to increase with molecular weight M up to 34 for the largest block copolymer. The number of internal structures n was established to scale as M 0.67 and therefore enables easy design of such structures with great precision.

Highly Ordered Structure Formation in RAFT-Synthesized PtBOS-b-P4VP Diblock Copolymers

Linear poly(4-tert-butoxystyrene)-b-poly(4-vinylpyridine) (PtBOS-b-P4VP) diblock copolymers are synthesized using reversible addition-fragmentation chain transfer polymerization. The self-assembly of four different PtBOS-b-P4VP diblock copolymers is studied using small-angle X-ray scattering and transmission electron microscopy and a number of interesting observations are made. A tBOS62 -b-4VP28 diblock copolymer with a weight fraction P4VP of 0.21 shows a disordered morphology of P4VP spheres with liquid-like short-range order despite an estimated value of χN of the order of 50. Increasing the length of the 4VP block to tBOS62 -b-4VP199 results in a diblock copolymer with a weight fraction P4VP of 0.66. It forms a remarkably well-ordered lamellar structure. Likewise, a tBOS146 -b-4VP120 diblock copolymer with a weight fraction P4VP of 0.33 forms an extremely well-ordered hexagonal structure of P4VP cylinders. Increasing the P4VP block of this block copolymer to tBOS146 -b-4VP190 with a weight fraction P4VP of 0.44 results in a bicontinuous gyroid morphology despite the estimated strong segregation of χN≅150. These results are discussed in terms of the architectural dissimilarity of the two monomers, characterized by the presence of the large side group of PtBOS, and the previously reported value of the interaction parameter, χ≅0.39, for this polymer pair.

Hierarchical Self-Assembly of Supramolecular Double-Comb Triblock Terpolymers

Involving supramolecular chemistry in self-assembling block copolymer systems enables design of macromolecular architectures that are challenging to obtain through conventional all-covalent routes. In this work we present supramolecular double-comb triblock terpolymers in which both outer blocks are able to interact with a surfactant via hydrogen bonding and thereby form a comb-shaped architecture upon complexation. While the neat triblock terpolymer only formed a triple lamellar morphology, multiple hierarchical structures were observed in these supramolecular comb–coil–comb triblock terpolymers by simply adjusting the surfactant concentration. Structures included spheres on tetragonally packed cylinders-in-lamellae and spheres on double parallel lamellae-in-lamellae, as evidenced by electron microscopy and X-ray scattering. Incorporation of a middle coil block thus allowed an even higher macromolecular complexity than the previously reported double-comb diblock copolymers.

The Origin of Hierarchical Structure Formation in Highly Grafted Symmetric Supramolecular Double-Comb Diblock Copolymers

Involving supramolecular chemistry in self-assembling block copolymer systems enables design of complex macromolecular architectures that, in turn, could lead to complex phase behavior. It is an elegant route, as complicated and sensitive synthesis techniques can be avoided. Highly grafted double-comb diblock copolymers based on symmetric double hydrogen bond accepting poly(4-vinylpyridine)-block-poly(N-acryloylpiperidine) diblock copolymers and donating 3-nonadecylphenol amphiphiles are realized and studied systematically by changing the molecular weight of the copolymer. Double perpendicular lamellae-in-lamellae are formed in all complexes, independent of the copolymer molecular weight. Temperature-resolved measurements demonstrate that the supramolecular nature and ability to crystallize are responsible for the formation of such multiblock-like structures. Because of these driving forces and severe plasticization of the complexes in the liquid crystalline state, this supramolecular approach can be useful for steering self-assembly of both low- and high-molecular-weight block copolymer systems.