A new amphiphilic diblock copolymer prepared via polymerization-induced self-assembly forms spheres, worms, vesicles or lamellae in aqueous solution on adjusting the temperature.

A near-monodisperse monohydroxy-terminated polydimethylsiloxane (PDMS; mean degree of polymerization = 66) was esterified using a carboxylic acid-functionalized trithiocarbonate to yield a PDMS66 precursor with a mean degree of functionality of 92 ± 5 % as determined by 1 H NMR spectroscopy. This PDMS66 precursor was then chain-extended in turn using nine different methacrylic monomers in a low-viscosity silicone oil (decamethylcyclopentasiloxane, D5). Depending on the monomer type, such PISA syntheses proceeded via either RAFT dispersion polymerization or RAFT emulsion polymerization. In each case the target DP of the core-forming block was fixed at 200 and the copolymer concentration was 25 % w/w. Transmission electron microscopy studies indicated that kinetically-trapped spheres were obtained in almost all cases. The only exception was 2-(dimethylamino)ethyl methacrylate (DMA), which enabled access to spheres, worm or vesicles. This striking difference is attributed to the relatively low glass transition temperature for this latter block. A phase diagram was constructed for a series of PDMS66-PDMAx nano-objects by systematically increasing the PDMA target DP from 20 to 220 and varying the copolymer concentration between 10 and 30 % w/w. Higher copolymer concentrations were required to access a pure worm phase, whereas only spheres, vesicles or mixed phases were accessible at lower copolymer concentrations. Gel permeation chromatography studies indicated a linear evolution of number-average molecular weight (Mn) with PDMA DP while dispersities remained below 1.39, suggesting relatively well-controlled RAFT polymerizations. Small angle x-ray scattering (SAXS) was used to characterize selected examples of spheres, worms and vesicles. PDMS66-PDMA100-112 worms synthesized at 25-30 % w/w formed freestanding gels at 20 °C. Oscillatory rheology studies performed on a 30 % w/w PDMS-PDMA105 worm dispersion indicated a storage modulus (gel strength) of 1057 Pa and a critical gelation concentration (CGC) of 12 % w/w. Finally, PDMS66-PDMAx worms could also be prepared in n-dodecane, hexamethyldisiloxane or octamethylcyclosiloxane. Rotational rheometry studies indicate that such worms are efficient viscosity modifiers for these non-polar oils.

It is shown that hydroxyl functionality is required to induce stasis in human embryonic stem cell colonies immersed within wholly synthetic block copolymer worm gels with comparable storage moduli. Thus gel softness does not appear to be an essential parameter for stasis induction.

This is a repository copy of Effect of core cross-linking on the physical properties of poly(dimethylsiloxane)-based diblock copolymer worms prepared in silicone oil.

Reversible addition-fragmentation chain transfer (RAFT) solution polymerization of 3-[tris(trimethylsilyloxy)silyl] propyl methacrylate (SiMA) was conducted in toluene in order to prepare three PSiMA precursors with mean degrees of polymerization (DP) of 12, 13 or 15. Each precursor was then chain-extended in turn via RAFT dispersion polymerization of benzyl methacrylate (BzMA) in a low-viscosity silicone oil (decamethylcyclopentasiloxane, D5). 1 H NMR studies confirmed that such polymerizations were relatively fast, with more than 99 % BzMA conversion being achieved within 100 min at 90°C. Moreover, GPC analysis indicated that these polymerizations were well-controlled, with dispersities remaining below 1.25 when targeting PBzMA DPs up to 200. A phase diagram was constructed at a constant copolymer concentration of 20% w/w. When the PSiMA 15 stabilizer was utilized, only spherical micelles were accessible as determined by transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS) studies. Nevertheless, these spheres exhibited narrow size distributions and tunable intensityaverage diameters ranging between 19 and 49 nm, as determined by dynamic light scattering (DLS). In contrast, spheres, worms or vesicles could be prepared depending on the target PBzMA DP when utilizing the relatively short PSiMA 12 precursor. Moreover, each of these nano-objects could be obtained at copolymer concentrations as low as 5% w/w. To obtain more detailed structural information, these spheres, worms and vesicles were further characterized by small-angle X-ray scattering (SAXS). PSiMA 12-PBzMA 55 worms formed reasonably transparent free-standing gels when prepared at copolymer concentrations as low as 5% w/w and exhibited an elastic modulus (G') of 90 Pa at 25°C as judged by oscillatory rheology studies. Finally, broadening of the molecular weight distribution was observed during the long-term storage of PSiMA-PBzMA dispersions at ambient temperature. We tentatively suggest that this instability is related to hydroxyl impurities in the SiMA, which leads to crosslinking side-reactions. This problem also causes incipient flocculation of the spheres and worms during long-term storage of such dispersions.

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We report that polymerization-induced self-assembly (PISA) can be used to prepare lyotropic phases comprising diblockc opolymer nano-objects in non-polar media. RAFT dispersion polymerization of benzyl methacrylate (BzMA) at 90 8 8Cusing atrithiocarbonate-capped hydrogenated polybutadiene (PhBD) steric stabilizer blocki nn -dodecane produces either spheres or worms that exhibit long-range order at 40 % w/w solids.N MR studies enable calculation of instantaneous copolymer compositions for eachp hase during the BzMA polymerization. As the PBzMA chains growl onger when targeting PhBD 80 -PBzMA 40 ,t ime-resolved small-angle X-ray scattering reveals intermediate body-centered cubic (BCC) and hexagonally close-packed (HCP) sphere phases prior to formation of af inal hexagonal cylinder phase (HEX). The HEX phase is lost on serial dilution and the aligned cylinders eventually form disordered flexible worms.T he HEX phase undergoes an order-disordert ransition on heating to 150 8 8C and apure HCP phase forms on cooling to 20 8 8C.

We report that polymerization-induced self-assembly (PISA) can be used to prepare lyotropic phases comprising diblockc opolymer nano-objects in non-polar media. RAFT dispersion polymerization of benzyl methacrylate (BzMA) at 90 8 8Cusing atrithiocarbonate-capped hydrogenated polybutadiene (PhBD) steric stabilizer blocki nn -dodecane produces either spheres or worms that exhibit long-range order at 40 % w/w solids.N MR studies enable calculation of instantaneous copolymer compositions for eachp hase during the BzMA polymerization. As the PBzMA chains growl onger when targeting PhBD 80 -PBzMA 40 ,t ime-resolved small-angle X-ray scattering reveals intermediate body-centered cubic (BCC) and hexagonally close-packed (HCP) sphere phases prior to formation of af inal hexagonal cylinder phase (HEX). The HEX phase is lost on serial dilution and the aligned cylinders eventually form disordered flexible worms.T he HEX phase undergoes an order-disordert ransition on heating to 150 8 8C and apure HCP phase forms on cooling to 20 8 8C.