Preparation of Microcapsules Using a Poly(2-(dimethylamino)ethyl methacrylate)‑b‑poly(benzyl methacrylate) Diblock Copolymer Emulsifier

TL;DR

This paper introduces a new diblock copolymer that efficiently stabilizes microcapsules with different structures and improves formulation efficiency.

Contribution

A novel PDMA–PBzMA diblock copolymer is proposed as an efficient emulsifier for microcapsule preparation.

Findings

The PDMA–PBzMA copolymer enables the creation of microcapsules with excellent colloidal stability and shell integrity.

PBzMA microcapsules showed exceptionally slow release of the hydrophobic model active pyrene.

The PBzMA shell matrix acts as the primary factor limiting the release rate of encapsulated species.

Abstract

Most encapsulation
techniques require suitable polymers or surfactants
to stabilize the microcapsule suspension. Typically, such stabilizers
are present in excess in the aqueous continuous phase. In this study,
the use of a poly­(2-(dimethylamino)­ethyl methacrylate)-poly­(benzyl
methacrylate) (PDMA–PBzMA) diblock copolymer is examined as
an efficient stabilizer for the preparation of three types of methacrylic
microcapsules with different morphologies. Unlike conventional water-soluble
stabilizers, this amphiphilic copolymer is dissolved directly in the
dispersed organic phase. This approach minimizes the amount of stabilizer
present in the aqueous continuous phase and hence maximizes the formulation
efficiency. This new PDMA–PBzMA stabilizer enables either poly­(benzyl
methacrylate) (PBzMA) or poly­(methyl methacrylate) (PMMA) microcapsules
to be prepared with excellent colloidal stability and shell integrity,
comparable to that previously achieved using poly­(vinyl alcohol).
Such formulations can produce (i) monolithic microcapsules,
(ii) oil-core microcapsules via internal phase separation,
or (iii) aqueous-core microcapsules via water-in-oil-in-water
(w
1/o/w
2) double emulsification. In particular, PBzMA microcapsules
exhibited an exceptionally slow release of the encapsulated hydrophobic
model active pyrene. Diffusivities of the encapsulated active species
on the order of 1 × 10–20 m2 s–1 were determined by fitting release data to appropriate
models assuming Fickian diffusion. For such microcapsules, the PBzMA
shell matrix acted as the primary release-rate-limiting factor. Given
that PDMA–PBzMA diblock copolymers can be conveniently prepared
via polymerization-induced self-assembly (PISA), this study highlights
their potential as a versatile, efficient stabilizer for a broad range
of microcapsule formulations.

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