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Order-Order Morphological Transitions for Dual Stimulus Responsive Diblock Copolymer Vesicles.

ABSTRACT: A series of non-ionic poly(glycerol monomethacrylate)-poly(2-hydroxypropyl methacrylate) (PGMA-PHPMA) diblock copolymer vesicles has been prepared by reversible addition-fragmentation chain transfer (RAFT) aqueous dispersion polymerization of HPMA at 70 °C at low pH using a carboxylic acid-based chain transfer agent. The degree of polymerization (DP) of the PGMA block was fixed at 43, and the DP of the PHPMA block was systematically varied from 175 to 250 in order to target vesicle phase space. Based on our recent work describing the analogous PGMA-PHPMA diblock copolymer worms [Lovett J. R.; Angew. Chem.2015, 54, 1279-1283], such diblock copolymer vesicles were expected to undergo an order-order morphological transition via ionization of the carboxylic acid end-group on switching the solution pH. Indeed, irreversible vesicle-to-sphere and vesicle-to-worm transitions were observed for PHPMA DPs of 175 and 200, respectively, as judged by turbidimetry, transmission electron microscopy (TEM), and dynamic light scattering (DLS) studies. However, such morphological transitions are surprisingly slow, with relatively long time scales (hours) being required at 20 °C. Moreover, no order-order morphological transitions were observed for vesicles comprising longer membrane-forming blocks (e.g., PGMA₄₃-PHPMA_225-250) on raising the pH from pH 3.5 to pH 6.0. However, in such cases the application of a dual stimulus comprising the same pH switch immediately followed by cooling from 20 to 5 °C, induces an irreversible vesicle-to-sphere transition. Finally, TEM and DLS studies conducted in the presence of 100 mM KCl demonstrated that the pH-responsive behavior arising from end-group ionization could be suppressed in the presence of added electrolyte. This is because charge screening suppresses the subtle change in the packing parameter required to drive the morphological transition.

SUBMITTER: Lovett JR

PROVIDER: S-EPMC4762544 | biostudies-literature | 2016 Feb

REPOSITORIES: biostudies-literature

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Order-Order Morphological Transitions for Dual Stimulus Responsive Diblock Copolymer Vesicles.

Lovett Joseph R JR Warren Nicholas J NJ Armes Steven P SP Smallridge Mark J MJ Cracknell Robert B RB

Macromolecules 20160128 3

A series of non-ionic poly(glycerol monomethacrylate)-poly(2-hydroxypropyl methacrylate) (PGMA-PHPMA) diblock copolymer vesicles has been prepared by reversible addition-fragmentation chain transfer (RAFT) aqueous dispersion polymerization of HPMA at 70 °C at low pH using a carboxylic acid-based chain transfer agent. The degree of polymerization (DP) of the PGMA block was fixed at 43, and the DP of the PHPMA block was systematically varied from 175 to 250 in order to target vesicle phase space. ...[more]

PMID: 26937051

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Project description:Dynamic covalent chemistry is exploited to drive morphological order-order transitions to achieve the controlled release of a model payload (e.g., silica nanoparticles) encapsulated within block copolymer vesicles. More specifically, poly(glycerol monomethacrylate)-poly(2-hydroxypropyl methacrylate) (PGMA-PHPMA) diblock copolymer vesicles were prepared via aqueous polymerization-induced self-assembly in either the presence or absence of silica nanoparticles. Addition of 3-aminophenylboronic acid (APBA) to such vesicles results in specific binding of this reagent to some of the pendent cis-diol groups on the hydrophilic PGMA chains to form phenylboronate ester bonds in mildly alkaline aqueous solution (pH ? 10). This leads to a subtle increase in the effective volume fraction of this stabilizer block, which in turn causes a reduction in the packing parameter and hence induces a vesicle-to-worm (or vesicle-to-sphere) morphological transition. The evolution in copolymer morphology (and the associated sol-gel transitions) was monitored using dynamic light scattering, transmission electron microscopy, oscillatory rheology, and small-angle X-ray scattering. In contrast to the literature, in situ release of encapsulated silica nanoparticles is achieved via vesicle dissociation at room temperature; moreover, the rate of release can be fine-tuned by varying the solution pH and/or the APBA concentration. Furthermore, this strategy also works (i) for relatively thick-walled vesicles that do not normally exhibit stimulus-responsive behavior and (ii) in the presence of added salt. This novel molecular recognition strategy to trigger morphological transitions via dynamic covalent chemistry offers considerable scope for the design of new stimulus-responsive copolymer vesicles (and hydrogels) for targeted delivery and controlled release of cargoes. In particular, the conditions used in this new approach are relevant to liquid laundry formulations, whereby enzymes require protection to prevent their deactivation by bleach.

Dataset Information

Order-Order Morphological Transitions for Dual Stimulus Responsive Diblock Copolymer Vesicles.

Publications

Order-Order Morphological Transitions for Dual Stimulus Responsive Diblock Copolymer Vesicles.

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