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Vitrimers, which form a bridge between thermosets and thermoplastics, are a class of materials with promising opportunities for modern material innovations.

The thermal decomposition of different classes of RAFT/MADIX agents, namely dithioesters, trithiocarbonates, xanthates, and dithiocarbamates, were investigated through heating in solution. It was found that the decomposition behavior is complicated interplay of the effects of stabilizing Z-group and leaving R-group. The mechanism of the decomposition is mainly through three pathways, i.e., β-elimination, α-elimination, and homolysis of dithiocarbamate (particularly for universal RAFT agent). The most important pathway is the β-elimination of thiocarbonylthio compounds possessing β-hydrogen, leading to the formation unsaturated species. For the leaving group containing solely α-hydrogen, such as benzyl, α-elimination takes place, resulting in the formation of (E)-stilbene through a carbene intermediate. Homolysis occurs specifically in the case of a universal RAFT agent, in which a thiocarbonyl radical and an alkylthio radical are generated, finally forming thiolactone through a radical process. The stabilities of the RAFT/MADIX agents are investigated by measuring the apparent kinetics and activation energy of the thermal decomposition reactions. Both Z-group and R-group influence the stability of the agents through electronic and steric effects. Lone pair electron donating heteroatoms of Z-group show a remarkable stabilizing effect while electron withdrawing substituents, either in Z-or R-group, tends to destabilize the agent. In addition, bulkier or more β-hydrogens result in faster decomposition rate or lower decomposition temperature. Thus, the stability of the RAFT/MAIDX agents decreases in the order where R is (with identical Z = phenyl) ÀCH 2 Ph (5) > ÀPS (PS-RAFT 15) > ÀC(Me)HPh (2) > ÀC(Me) 2 C(dO)OC 2 H 5 (7) > ÀC(Me) 2 Ph(1) > ÀPMMA (PMMA-RAFT 16) > ÀC(Me) 2 CN (6). For those possessing identical leaving group such as 1-phenylethyl, the stability decreases in the order of O-ethyl (11) > ÀN(CH 2 CH 3 ) 2 (13) > ÀSCH(CH 3 )Ph (8) > ÀPh (2) > ÀCH 2 Ph (4) > ÀPhNO 2 (3). These results consort with the chain transfer acitivities measured by the CSIRO group and agree well with the ab initio theoretical results by Coote. In addition, the difference between thermal stabilities of the universal RAFT agents at neutral and protonated states has also been demonstrated.

Porous graphene monolith and porous composites of graphene oxide (GO) and silica were prepared by thermolytic cracking of graphene-coated, or GO/silica-coated polystyrene (PS) spheres. The spheres were synthesized through in situ precipitation polymerization of styrene using GO and poly (vinylpyrrolidone) as stabilizing agents. During polymerization, GO adsorbed to the surface of the PS particle due to its amphiphilicity as well as spontaneous grafting on GO basal plane. The GO-coated PS spheres were either reduced by hydrazine to graphene-coated PS spheres, or underwent a sol-gel reaction with tetraethyloxysilane (TEOS). These materials were finally subjected to thermolytic cracking in a thermogravimetry instrument or in a furnace under nitrogen up to 550 or 700 C, resulting in graphene-based porous materials in which the pores are surrounded by graphene or GO/silica walls. The factors affecting the specific surface area were discussed. The method may serve as a new approach to fabricate 3D graphene-based porous materials.

in the solid state. [38,45] In general, the terminal relaxation behavior of PBT vitrimers above the melting temperature was rarely observed at angular frequencies down to 10 −2 s −1 in the temperature range from 250 to 270 °C. [37,38,45] Considering that typical shear rates during injection molding are as high as 10 000 s −1 and the viscosity of PBT vitrimers can be up to 10 7 Pa s at 250 °C, these PBT vitrimers cannot be processed like neat PBT during the short residence times typical for extrusion and injection molding. [52] Here, we propose a controllable way to process PBT vitrimers (based on transesterification exchange reactions) via controlling the network formation with the help of protection-deprotection chemistry. In this way, we can overcome the relatively long relaxation times and high viscosities associated with PBT vitrimers and maintain the high production rates of final parts by injection molding as for neat PBT. The strategy is schematically shown in Scheme 1: pentaerythritol is first converted into 5,5-bis(hydroxymethyl)-2-phenyl-1,3-dioxane (BPO, melting point 135-137 °C) via benzaldehyde protection chemistry. [53] Subsequently, this diol is incorporated into the PBT backbone via solid-state (co)polymerization to form a linear copolyester in line with earlier work from our group on PBT modification in the solid state. [54][55][56][57][58][59][60] The linear polymer chain is then transformed into a network via deprotection of the benzal group to afford a linear polymer chain with pendent-free hydroxyl groups for further thermal transesterification of the linear copolyester catalyzed by the Zn(II) catalyst. If deprotection and subsequent cross-linking takes place during processing, we can combine an initial low viscosity with final vitrimer characteristics.Normally, the deprotection step to obtain the linear copolyester with pendent hydroxyl groups, as shown in Scheme 1, involves an acid-promoted deprotection of the benzal group at room temperature and an acid used often is trifluoroacetic acid (TFA). [53] Accidentally we discovered that compression molding of the linear copolyester with benzal protection groups resulted in a cross-linked material with vitrimer characteristics, even without deprotection with TFA. This observation is in contrast to results previously reported by Collard et al., [53] who obtained thermoset materials after incorporation of BPO into PBT and poly(ethylene terephthalate) (PET) and repeated subsequent cycling to 300 °C in differential scanning calorimetry (DSC). Driven by this intriguing result and its practical relevance, we investigated the in situ network formation in more Vitrimers Although the network dynamics and mechanical properties of poly(butylene terephthalate) vitrimers can to some extent be controlled via chemical and physical approaches, it remains a challenge to be able to process PBT vitrimers with the same processing conditions via, for example, injection molding as neat PBT. Here, it is shown that the use of protected pentaerythritol as a latent cross...