Yiwen Pei

Polymerization-induced self-assembly: ethanolic RAFT dispersion polymerization of 2-phenylethyl methacrylate

Reversible addition-fragmentation chain transfer (RAFT) radical dispersion polymerization (RAFTDP) has been employed to polymerize 2-phenylethyl methacrylate (PEMA) using poly[2-(dimethylamino)ethyl methacrylate] (PDMAEMA) macromolecular chain transfer agents (macro-CTAs) of varying average degree of polymerization (n). RAFTDP of PEMA in ethanol at 70 °C with PDMAEMA macro-CTAs yields well-defined AB diblock copolymers that self-assemble in solution during polymerization leading to the formation of well-defined diblock copolymer nanostructures. A full morphology transition (from spheres to worms to vesicles) is observed with these formulations that is sensitive to (i) the target n of the solvophobic polyPEMA block, (ii) the total solids content at which the PEMA block copolymerization is performed and (iii) the target n of PDMAEMA as a macro-CTA. Finally, we demonstrate the ability to convert the PDMAEMA–PPEMA based nanoparticles to the corresponding sulfopropylbetaine analogues by the facile reaction of the DMAEMA residues with 1,3-propanesultone.

Thiol-reactive Passerini-methacrylates and polymorphic surface functional soft matter nanoparticles via ethanolic RAFT dispersion polymerization and post-synthesis modification

RAFT dispersion polymerization (RAFTDP) is used to prepare reactive nanoparticles via the incorporation of Passerini-derived methacrylic comonomers containing pentafluorophenyl (PFP) groups. Copolymerization of 2-(dimethylamino)ethyl methacrylate with a Passerini comonomer gives copolymers suitable as macro-CTAs for ethanolic RAFTDP of 3-phenylpropyl methacrylate. Reaction of the PFP residues with functional thiols offers an approach for preparing surface modified nanoparticles.

Microwave-assisted synthesis of block copolymer nanoparticles via RAFT with polymerization-induced self-assembly in methanol

A comparative study of microwave-assisted (MA) and conductive heating in RAFT dispersion polymerization formulations in MeOH that result in polymerization-induced self-assembly is detailed. A beneficial kinetic effect is seen in MA formulations, especially in lower concentration systems, with benzyl- and 2-phenylethyl methacrylate comonomers and poly[oligo(ethylene glycol) methyl ether methacrylate] macro-CTAs.

Synthesis of poly(stearyl methacrylate-b-3-phenylpropyl methacrylate) nanoparticles in n-octane and associated thermoreversible polymorphism

Poly(stearyl methacrylate) (PSMA) homopolymers with average degrees of polymerization (n) ranging from 18–30 have been prepared by homogeneous RAFT radical polymerization in toluene and subsequently employed as macro-chain transfer agents (CTAs) in non-polar RAFT dispersion formulations with 3-phenylpropyl methacrylate (PPMA) as the comonomer in n-octane at 70 °C. With PSMA18 or PSMA19 macro-CTAs in n-octane at 20 wt%, a series of PSMAx–PPPMAy block copolymers are readily accessible in situ that form the full range of common nanoparticle morphologies, with the complexity of the nano-objects increasing (spheres-to-worms-to-vesicles) with increasing n of the PPPMA block as clearly evidenced by transmission electron microscopy (TEM). An evaluation of the effect of total solids for the preparation of block copolymers of common composition indicated that polymerizations conducted at higher concentrations favoured the formation of nanoparticles with more complex morphologies. In the case of block copolymers prepared with a PSMA30 macro-CTA the only accessible morphology was spheres regardless of compositional asymmetry. However, the size of the spheres increased monotonically with increasing PPPMA block length. Formulations that yielded (essentially) pure worm phases, such as PSMA18-b-PPPMA71, formed physical gels at ambient temperature. Heating the physical gels to (or beyond) a critical temperature resulted in a macroscopic transformation to a free flowing solution. The fundamental reason for the transformation, as evidenced by TEM, was a morphological transition from worm to sphere nanoparticles facilitated, in part, by a change in solvation of the PPPMA core-forming block with increasing temperature. DLS analysis indicated that the morphology transitions were fully reversible.

Triply responsive soft matter nanoparticles based on poly[oligo(ethylene glycol) methyl ether methacrylate- block -3-phenylpropyl methacrylate] copolymers

The stimulus-responsive properties of soft matter nanoparticles based on poly[oligo(ethylene glycol) methyl ether methacrylate-block-3-phenylpropyl methacrylate] (p(OEGMA-block-PPMA)) copolymers in methanol and ethanol are described. Methanolic synthesis, with 4-cyanopentanoic acid dithiobenzoate as the RAFT mediating agent, facilitates simple access to nanoparticles exhibiting the full range of common morphologies (spheres, worms and vesicles) simply by varying the copolymer composition (fixed average degree of polymerization (n) of the pOEGMA macro-CTA for variable n of the pPPMA block). Interestingly, we demonstrate that p(OEGMAx-block-PPMAy) nanoparticles are able to elicit three types of response to externally applied stimuli. These materials possess two distinct, but complementary, reversible thermal responses – one that results in an order–order transition, i.e. a morphological change, while the second is a reversible order–disorder transition based on upper critical solution temperature (UCST)-type behaviour associated with the pOEGMA coronal chains in the nanoparticles. Finally, we report the first example where specific p(OEGMA-block-PPMA) nanoparticles are shown to be sensitive to addition of an organobase – a response that is accompanied by an order–order, worm-to-sphere, morphology transition.

Ethanolic RAFT Dispersion Polymerization of 2-(Naphthalen-2-yloxy)ethyl Methacrylate and 2-Phenoxyethyl Methacrylate with Poly[2-(dimethylamino)ethyl Methacrylate] Macro-Chain Transfer Agents

The ethanolic reversible addition-fragmentation chain transfer dispersion polymerization (RAFTDP), at 21 wt-%, of 2-(naphthalen-2-yloxy)ethyl methacrylate (NOEMA) and 2-phenoxyethyl methacrylate (POEMA) with a poly[2-(dimethylamino)ethyl methacrylate] macro-chain transfer agent (CTA) with an average degree of polymerization of 20 (PDMAEMA20) is described. DMAEMA20-b-NOEMAy (y = 20–125) block copolymers were readily prepared under dispersion conditions in ethanol at 70°C. However, the polymerization of NOEMA was not well controlled, with size exclusion chromatograms being distinctly bi or multimodal with measured dispersities . Though NOEMA copolymerization was not ideal, the resulting series of block copolymers did exhibit the anticipated full spectrum of nanoparticle morphologies (spheres, worms, and vesicles). Interestingly, these morphology transitions occurred over a relatively narrow range of block copolymer compositions. In the case of POEMA, copolymerization was also poorly controlled with 1.50 ≤ ĐM ≤ 1.83 for the series of DMAEMA20-b-POEMAy copolymers. In contrast to the NOEMA-based copolymers, the POEMA series only yielded nanoparticles with a spherical morphology whose size increased with increasing average degrees of polymerization of the POEMA block. Collectively, though both NOEMA and POEMA can be utilized in ethanolic RAFT dispersion polymerization formulations, these preliminary studies suggest that neither appears to be an ideal aryl methacrylate choice as comonomer, especially if the goal is to combine the synthesis of well-defined copolymers with efficient nanoparticle formation.

Synthesis and characterisation of non-ionic AB-diblock nanoparticles prepared by RAFT dispersion polymerization with polymerization-induced self-assembly

The synthesis and characterisation of soft matter nanoparticles based on AB diblock copolymers of oligo(ethylene glycol)methyl ether methacrylate (OEGMA) with 3-phenylpropyl methacrylate (PPMA) is described. Reversible addition–fragmentation chain transfer dispersion polymerization formulations that result in polymerization-induced self-assembly (RAFTDP-PISA) in methanol were utilized to access a range of poly(OEGMA-b-PPMA) (p(OEGMA-b-PPMA)) nanoparticles with the sphere-to-worm-to-vesicle order–order transitions being readily observed with increasing average degree of polymerization (n) of the pPPMA block for a fixed n of 28 for the pOEGMA block. Similarly the effect of total copolymer concentration on the resulting nanoparticle morphology is also demonstrated whereby we highlight how tuning of worm micelle diameters can be accomplished simply by varying the concentration of a formulation. The block copolymer nanoparticles were characterized by size exclusion chromatography (SEC), 1H NMR spectroscopy, transmission electron microscopy (TEM) and small angle X-ray scattering (SAXS). Additionally, we report the first examples utilizing 3D electron tomography and in situ atomic force microscopy (AFM) in methanol as convenient and powerful complementary techniques for the characterization of the resulting soft matter nano-objects with an emphasis on the direct visualization of worm nanoparticles.

Reactive Conjugated Polymers: Synthesis, Modification and Electrochemical Properties of Polypentafluorophenylacetylene (Co) Polymers

(Co)Polymers containing pentafluorophenylacetylene (F5 PA) have been prepared for the first time mediated by [Rh(nbd)Cl]2 /NEt3 to give materials with properties typical of poly(phenylacetylene)s prepared with this catalyst/co-catalyst combination. It is demonstrated that the F5 PA repeat units in these new (co)polymers serve as convenient reactive species for post-polymerization modification with thiols via para-fluoro aromatic nucleophilic substitution reactions to give an entirely new family of novel thioether-functional polyene materials accompanied by absorption maxima shifts of up to 130 nm. Finally, the electrochemical properties of these new fluorinated polyene materials are briefly examined and the distinct difference in behavior of the F5 PA homopolymer versus polyphenylacetylene, copolymers, and functional derivatives is highlighted.