Reversible Addition-fragmentation Chain Transfer Chemistry Research Articles

Reduction of molar mass loss and enhancement of thermal and rheological properties of recycled poly(lactic acid) by using chain extenders obtained from RAFT chemistry

The synthesis of block copolymers of glycidyl methacrylate (G), styrene (S) and acrylonitrile (AN) (represented as GS-SAN) by reversible addition–fragmentation chain transfer (RAFT) polymerization, with well-defined average molar masses and epoxy functionalities, and evaluation of their performance as macromolecular chain extenders for recycled poly(lactic acid) (rPLA), is reported. The introduction of the GS-SAN chain extenders during the extrusion processing of rPLA leads to recovery of molar mass as well improvement of thermal stability and rheological properties, compared to recycled unmodified PLA. Differential scanning calorimetry (DSC) results revealed a reduction in cold crystallization temperature and an increase in the degree of crystallinity of chain extended rPLA. Increasing epoxide content in the synthesized block copolymers leads to increased degrees of crystallinity. The rheological study revealed that the GS-SAN copolymers allowed significant increases in modulus, strength and complex viscosity of chain extended rPLA, indicating that better mechanical performance and processability were obtained. These increases become more pronounced as the concentration of reactive epoxy functional group is increased.

Fusing Light-Induced Step-Growth Processes with RAFT Chemistry for Segmented Copolymer Synthesis: A Synergetic Experimental and Kinetic Modeling Study

We pioneer the synthesis of well-defined high molar mass segmented copolymers, employing a unique combination of step-growth and reversible addition–fragmentation chain transfer (RAFT) polymerization. The step-growth precursor polymer is obtained via the ambient temperature UV-light-induced Diels–Alder reaction of 6′-(propane-1,3-diylbis(oxy))bis(2-methylbenzaldehyde) (AA monomer) and di(isopropionic ethyl ester fumarate) trithiocarbonate (BB monomer). Unconventional off-stoichiometric conditions (r = [AA]0:[BB]0 = 1.5–1.75) are employed to ensure a sufficiently high incorporation of BB in the step-growth product (1200 ≤ Mn/g mol–1 ≤ 3950). The optimum r value is based on a detailed product distribution analysis, comparing experimental and bivariate kinetic Monte Carlo generated data, using a scheme of over 200 reactions. The analysis highlights the unexpected occurrence of AA homopolymerization and the ligation of the resulting AA segments at higher reaction times. The precursor step-growth polymer is su...

The RAFT Alliance, a Global Community Promoting Innovation

Reversible addition–fragmentation chain transfer (RAFT) chemistry was first published in 1998 by CSIRO scientists Ezio Rizzardo, Graeme Moad, and San Thang.[1] RAFT is a powerful polymerization technology for the synthesis of tailor-made polymers with predetermined molecular weights, with narrow polydispersities, and with highly complex architectures.[2] Continued research into fundamental RAFT chemistry has seen the development of intellectual property in the order of some 300 patents,[3] all based upon the original[4] patent from CSIRO, Australia’s national research organization. Key developments of the RAFT technology, such as end-group removal,[5–8] microgel synthesis,[9] and aqueous polymerization,[10,11] have been integral to the development of innovative applications. These include coatings with improved pigment dispersions,[12] lubricants to improve fuel economy,[13] and spatially controlled drug conjugates.[14] There is an ever-increasing demand for technical and commercial information to support the applications of RAFT in industry. At CSIRO, we have initiated the RAFT Alliance; a community of scientists and business professionals with shared research or commercial interests in RAFT (Fig. 1). The RAFT Alliance was launched at the inaugural

Reversible Addition Fragmentation Chain Transfer (RAFT) and Hetero-Diels−Alder Chemistry as a Convenient Conjugation Tool for Access to Complex Macromolecular Designs

The combination of RAFT chemistry and the hetero-Diels−Alder (HDA) cycloaddition was successfully utilized in the synthesis of poly(styrene) (PS) star polymers with up to 4 arms. This variant of the “coupling onto” method of star polymer synthesis was investigated for two different RAFT end groups (diethoxyphosphoryldithioformate and pyridin-2-yldithioformate) and coupling agents bearing 2, 3, or 4 diene functional groups. When a diethoxyphosphoryldithioformate terminated polymer was reacted with the 2-, 3-, and 4-fold functionalized coupling agents, the yields of 2-arm star, 3-arm star, and 4-arm star polymers were 81%, 77%, and 65%, respectively, and when a pyridin-2-yldithioformate terminated polymer was reacted with the same coupling agents, the yields of 2-arm star, 3-arm star and 4-arm star polymers were 91%, 86% and 82% respectively. The HDA coupling reaction was monitored via UV/vis spectroscopy from the perspective of the RAFT end group as well as by 1H NMR spectroscopy from the perspective of the diene functionality. The results of these investigations indicated that the phosphoryldiethoxydithioformate terminated polymer achieves 92% conversion within a 24 h time frame and the pyridin-2-yldithioformate terminated polymer achieves 96% conversion in 10 h. The 4-arm star polymers were also subjected to high-temperature environments, and GPC measurements indicated that complete cleavage of all 4 arms from the core was achieved in 24 h at 160 °C.

RAFT Synthesis of Branched Acrylic Copolymers

We report the synthesis of branched acrylic copolymers based on 2-hydroxypropyl acrylate using reversible addition fragmentation chain transfer (RAFT) polymerization in tert-butanol at 80 °C. Three branching comonomers were investigated in this study: ethylene glycol diacrylate, bisphenol A ethoxylated diacrylate and a disulfide-based diacrylate. The latter comonomer allows chemical degradation of the branched acrylic copolymers to produce thiol-functionalized primary chains. Gel permeation chromatography analysis of these degraded copolymer chains indicated low polydispersities (Mw/Mn < 1.22), which confirmed that the living character of the RAFT chemistry was retained under branching conditions. RAFT allows significantly more than one branching agent per primary chain to be used in the copolymerization without causing gelation. This result was obtained with all three branching comonomers and differs from the near-ideal copolymerizations previously reported for the ATRP synthesis of branched methacrylic...

RAFT Chemistry and Huisgen 1,3-Dipolar Cycloaddition: A Route to Block Copolymers of Vinyl Acetate and 6-O-Methacryloyl Mannose?

The present communication explores a novel avenue to glycopolymer-block-poly(vinyl acetate) polymers by a combination of reversible addition fragmentation chain transfer (RAFT) chemistry and Huisgen 1,3-dipolar cycloaddition (i.e., so-called ‘click’ chemistry) under mild reaction conditions. Such block copolymers are—because of the strongly disparate reactivity of the two monomers—otherwise not obtainable. Poly(vinyl acetate) that has an azide end group (Mn 6800 g mol–1, PDI 1.15) was treated with poly(6-O-methacryloyl mannose) (Mn 7600 g mol–1, PDI 1.11) in the presence of 1,8-diaza[5,4,0]bicycloundec-7-ene and copper(i) iodide. The resulting poly(vinyl acetate)-block-poly(6-O-methacryloyl mannose) had a number-average molecular weight of 15400 g mol–1 and a PDI of 1.48, which indicates that while the cycloaddition had occurred the resulting polymer distribution featured a considerable width. The resulting slightly amphiphilic block copolymer was subsequently investigated with regard to its self-assembly in aqueous solution. Dynamic light scattering studies indicated a hydrodynamic diameter of close to 200 nm. Transmission electron microscopy studies indicate the formation of rods as well as spheres with transitions between these two phases. However, the segregation between core and shell in the spheres is not pronounced; such behaviour is expected for weakly amphiphilic block copolymers.