Molecular exchange in spherical diblock copolymer colloids synthesised by polymerisation-induced self-assembly

Gregory N Smith,Isabelle Grillo,James E Hallett

doi:10.1016/j.jcis.2020.06.022

Abstract

To study molecular exchange between colloids requires the preparation of suitably labelled species. Deuterium isotopic labelling has been used to prepare two chemically identical yet isotopically distinguishable poly(lauryl methacrylate)-poly(methyl methacrylate) (PLMA-PMMA) diblock copolymer colloids by polymerisation-induced self-assembly (PISA) directly in an alkane solvent. Molecular exchange should be detectable by performing small-angle neutron scattering (SANS) measurements on the dispersions. SANS measurements were performed on fully hydrogenous PLMA39-PMMA57 and deuterated core PLMA39-P(MMA-d8)57 colloids. They were mixed in equal amounts and heated to determine if molecular exchange occurred. PISA syntheses are often thermally initiated, and diblock copolymers self-assemble at elevated temperature, making this an important parameter to study. Experimental data for the mixture were compared to predicted curves for exchanged and non-exchanged colloids. The scattering of a mixture of fully hydrogenous and deuterated core copolymers does not disappear upon molecular exchange, due to the remaining contrast between the stabiliser and the core and solvent even after the cores fully exchange. By simultaneously fitting the SANS data from dispersions before mixing and using these parameters to constrain fitting the SANS data of mixtures, the molecular exchange between diblock copolymer micelles upon heating is clearly observed.

Highlights

Significant insight has been gained into the self-assembly of block copolymers [1,2,3,4,5,6,7,8,9,10] through the use of molecular exchange, a long-studied topic in colloid science [11,12,13,14,15]
The difference between the fully hydrogenous and deuterated core polymer micelles is in contrast to previous experiments on fully-deuterated diblock copolymer micelles [22], as the diblock copolymers used in this study are only core-deuterated
By using isotopically-labelled diblock copolymers and smallangle neutron scattering, we have shown that diblock copolymer micelles synthesised by polymerisationinduced self-assembly (PISA) undergo molecular exchange

Summary

Introduction

Significant insight has been gained into the self-assembly of block copolymers [1,2,3,4,5,6,7,8,9,10] through the use of molecular exchange, a long-studied topic in colloid science [11,12,13,14,15]. While many of the previous reports using deuterium isotopic labelling to study the exchange between polymer micelles have revealed very interesting aspects of the process, they rely on post-polymerisation methods to prepare colloids [1,3,6,21,22] These numerous examples of the application of small-angle neutron scattering (SANS) to the study of the self-assembly and molecular exchange of block copolymers demonstrate the value of this technique [1,2,3,4,5,6,7,8,9,10,21,22]. Gaining a better understanding of this exchange process for particles synthesised by PISA is what we set out to understand

Methods

Results

Conclusion