Cleavage of macromolecular RAFT chain transfer agents by sodium azide during characterization by aqueous GPC

Accurate and reliable analysis of polymers by GPC is vital in the field of controlled radical polymerisation. Often, water-soluble polymers are analysed by aqueous gel permeation chromatography (GPC) in a solvent containing dilute sodium azide as an anti-microbial agent. Previous reports have shown that sodium azide at high concentration is able to remove terminal CTA groups from polymer chains, producing thiol-terminated polymers. This study demonstrates that GPC sample preparation of RAFT polymers in aqueous solvents containing dilute (200 ppm) sodium azide can cause significant changes in the measured molecular weight distribution. These changes occur within hours of dissolving the polymer sample and are shown to be due to cleavage of the CTA in the polymer chain together with disulfide coupling of the resulting polymeric thiols. The extent to which this occurs is strongly dependent on the CTA attached to the polymer; an almost 10-fold difference in the rate of CTA removal is observed between different RAFT agents. The by-product of the reaction between sodium azide and RAFT polymers is also investigated and shown to be an unstable thiatriazole-functionalised Z group. The thiatriazole then degrades further to form a nitrile-functionalised Z group, N2 and elemental sulfur

Ultra-fast aqueous polymerisation of acrylamides by high power visible light direct photoactivation RAFT polymerisation

The effect of visible LED power (λmax = 402 nm, 451 nm) on kinetics and control of direct photoactivation RAFT polymerisations of acrylamide and dimethylacrylamide are investigated. By increasing power supplied to the LEDs from 6 to 208 W, the polymerisation time required to reach >85% conversion is reduced from 12 hours to 11 minutes for acrylamide. Similar conversions are shown to be obtainable in 5 minutes for dimethylacrylamide, all without any exogenous photoinitiator or catalyst. This increase in polymerisation rate is attributed to an increase in both photon flux and a coincident increase in polymerisation temperature at higher light intensities. With both 402 nm and 451 nm LEDs exciting the same n → π* electronic transition, little difference in rate of polymerisation is seen between the two light sources. Minimal reduction in polymerisation control is observed at high irradiation intensity for acrylamide, while an increased production of low molecular weight dead chains is observed for dimethylacrylamide. This is shown to be mitigated by controlling the polymerisation temperature to 17 °C which caused both a reduction in low molecular weight tailing and an increased polymerisation time. Visible light direct photoactivation RAFT is also shown to have application in the synthesis of ultra-high molecular weight acrylamide polymers (Mn > 1 000 000 g mol−1)

5,7,12,14-tetramethyldibenzo[b,i]-1,4,8,11-tetraazacyclotetradecine-nickel(II) : ester derivatives and supramolecular complexes with ionic substrates

Abstract not availabl

5,7,12,14-tetramethyldibenzo[b,i]-1,4,8,11-tetraazacyclotetradecine-nickel(II) : ester derivatives and supramolecular complexes with ionic substrates

Abstract not availabl

Optimizing the photochromic performance of naphthopyrans in a rigid host matrix using poly(dimethylsiloxane) conjugation

A series of methoxy substituted 2,2-diaryl-2H-naphthopyran photochromic dyes were assembled incorporating hydroxy functionality to allow their subsequent attachment to flexible poly(dimethylsiloxane) oligomers. The photochromic performance of the generated PDMS-naphthopyran conjugates was studied in a thermoset host matrix and compared to non-conjugated, electronically equivalent control dyes. Both coloration and decoloration speeds were found to be greatly improved with critical T-1/2 decoloration times reduced by 42-80%. The extent of solution-like performance provided by PDMS conjugation in the rigid host was examined with reference to the fade performance of control dyes in solution, and found to range from 20 to 90%. These measures are believed to be influenced by the electronic nature and steric interactions of the photochromic dyes

Photochromic Polymer Conjugates: The Importance of Macromolecular Architecture in Controlling Switching Speed within a Polymer Matrix

Naphthopyran-poly(n-butyl acrylate) conjugates with different geometries were assembled using ATRP. First, within a rigid lens matrix, all investigation of the photochromic behavior of various poly(n-butyl acrylate), p(n-BA), homopolymers showed that midplacement of a single dye moiety, made possible using a Y-branching difunctional photochromic initiator, gave superior fade kinetics per chain length of conjugated polymer compared to end-functionalized homopolymers. Furthermore, having the dye pendant from the chain opposed to directly within the chain was also found to be advantageous. Fading kinetics became faster when chain length was increased, except in the case of linear random copolymers made by copolymerization of n-butyl acrylate with a naphthopyran acrylate. A gradient copolymer made with a nonphotochromic difunctional initiator and a naphthopyran methacrylate displayed Superior kinetics. Films consisting or ABA triblock copolymers, incorporating the photochromic in the middle of a sort p(n-BA) section, gave slower switching speeds compared to lens samples, with responses that were highly tunable and dependent on the amount of soft section inhabited by the photochromic moiety

Low-distortion holographic data storage media using free-radical ring-opening polymerization

Holographic data storage, due to its potential to increase capacity beyond one terabyte per disk, is tipped to be one of the next generation optical data storage technologies. Polymer-based systems are leading candidates due to their high dynamic range, high sensitivities, are flexible and easy production, and yet polymerization-shrinkage-induced distortion is a major hurdle for its reliable use. In this paper, a new free radical polymerization holographic recording monomers, is proposed and demonstrated. The percentage of volume shrinkage is measured to be 0.002%, with refractive index (RI) contrast of (1.01 +/- 0.5) x 10(-3). The measured volume shrinkage is, to the authors' best knowledge, the best reported so far in the literature. Other parameters such as sensitivity, dynamic range, and dark reaction properties are also measured, where the values can be optimized with high RI functional groups without sacrificing the low shrinkage

Light-induced RAFT single unit monomer insertion in aqueous solution—toward sequence-controlled polymers

\u3cp\u3eFirst report on the sequential, visible light-initiated, single unit monomer insertion (SUMI) of N,N-dimethylacrylamide (DMAm) into the reversible addition fragmentation chain transfer (RAFT) agent, 4-((((2-carboxyethyl)thio)carbonothioyl)thio)-4-cyanopentanoic acid (CTA\u3csub\u3e1\u3c/sub\u3e), in aqueous solution is provided. The specificity for SUMI over formation of higher oligomers and/or RAFT agent-derived by-products is higher for longer irradiation wavelengths. Red light provides the cleanest product (selective SUMI), showing a linear pseudo-first order kinetic profile to high (>80%) conversion, but also the slowest reaction rate. Blue light provides a relatively rapid reaction, but also gives some by-products (<2%) and the kinetic profile displays a conversion plateau at >65% conversion. Higher specificity with red light is attributed to CTA\u3csub\u3e1\u3c/sub\u3e absorbing at longer wavelengths than the SUMI product, which allows selective excitation of CTA\u3csub\u3e1\u3c/sub\u3e. The use of a higher reaction temperature (65 °C vs ambient) results in a higher reaction rate and a reduction in oligomer formation.\u3c/p\u3