Chain Transfer Agents In Polymerization Research Articles

RAFT Synthesis of Reactive Multifunctional Triblock‐Copolymers for Polyplex Formation

AbstractReversible addition–fragmentation chain transfer polymerization with a low‐temperature initiator can be used to synthesize multifunctional block copolymers for polyplex formation. Utilizing three methacrylate monomers (triethylene glycol methyl ether methacrylate (MEO3MA), pyridyldisulfideethyl methacrylate (PDSM), N,N‐dimethylethylenediamine methacrylate (DMAEMA)) and an azide bearing chain transfer agent for polymerization, the resulting triblock‐copolymers possess two orthogonally reactive functionalities (a block with reactive disulfide side chains and an azide end‐group) and two additional functional blocks for i) solubilization and ii) polyplex formation. Thereby, the MEO3MA block provides solubility in aqueous media and the DMAEMA block, having a tertiary amine in the side chain, allows polyplex formation with polyanionic biomacromolecules like DNA or RNA. Due to the reactive disulfide block the polyplexes can be (reversibly) crosslinked with dithiols. Because of the manifold of possibilities to modify the pDNApolyplexes, this polymers system is an interesting candidate for active‐targeting and codelivery approaches.

Synthesis and characterization of diethyl-dithiocarbamic acid 2-[4-(2-diethylthiocarbamoylsulfanyl-2-phenyl-acetyl)-2,5-dioxo-piperazin-1-yl]-2-oxo-1-phenyl-ethyl ester as new reversible addition-fragmentation chain transfer agent for polymerization of ethyl methacrylate

Diethyl-dithiocarbamic acid 2-[4-(2-diethylthiocarbamoylsulfanyl-2-phenyl-acetyl)-2,5-dioxo-piperazin-1-yl]-2-oxo-1-phenyl-ethyl ester as a novel di-functional reversible addition–fragmentation chain transfer (RAFT) agent was synthesized based on 2,5-diketopiperazine. The RAFT agent was designed based on the propagating core (R group) approach and characterized by 1H NMR, 13C NMR, FT-IR, elemental analysis, and melting point technique. Then, ethyl methacrylate was synthesized via free radical and RAFT polymerizations. To investigate the effect of the RAFT agent on the kinetic of polymerization, molecular weight, and polydispersity index (PDI) of polymers and also monomer conversion were monitored. Also, synthesized polymers were characterized by 1H NMR, 13C NMR, FT-IR, and TGA. Characterization analyses of synthesized RAFT agent were consistent with the structure. NMR and FTIR analyses confirmed end group incorporation of RAFT agent into polymer structure. According to results, poly(ethyl methacrylate) with low PDI (1.14) was obtained. Kinetic study indicated well-controlled polymerization of ethyl methacrylate by synthesized RAFT agent. TGA results showed that RAFT agent could reduce termination reactions and so reduce head-to-head bonds and chain-end unsaturation by keeping the concentration of radicals low enough.

Dispersion Reversible Chain Transfer Catalyzed Polymerization (Dispersion RTCP) of Methyl Methacrylate in Supercritical Carbon Dioxide: Pushing the Limit of Selectivity of Chain Transfer Agent

We demonstrated a dispersion reversible chain transfer catalyzed polymerization (dispersion RTCP) of methyl methacrylate (MMA) with 1-phenylethyl iodide (PE-I) as chain transfer agent and GeI4 as catalyst in supercritical carbon dioxide (scCO2), where the PE-I was known as noneffective chain transfer agent for polymerization of MMA in RTCP. The dispersion RTCP in scCO2 proceeded with control/livingness. On the other hand, in bulk system (bulk RTCP) and in dispersion iodine transfer polymerization (dispersion ITP) in scCO2 under the same conditions except for GeI4, no livingness was maintained. From these results, it was assumed that the reason for the living character in the dispersion RTCP in scCO2 is based on an accelerated reversible chain transfer reaction in scCO2. Based on the insight, when the dispersion RTCP of MMA was carried out at higher scCO2 pressure, poly(MMA) (PMMA) having a narrower molecular weight distribution was obtained because of the higher degree of PMMA plasticization by scCO2. Mor...

Effect of organosilicon chain-transfer agents on the heat resistance of vinyl polymers

The effect exerted on the resistance of polymers to thermal oxidation degradation by organosilicon hydrides used as chain-transfer agents in polymerization of styrene, methyl methacrylate, and vinyl acetate was examined.

Synthesis of Functional Inorganic−Organic Hybrid Polymers Based on Poly(silsesquioxanes) and Their Thin Film Properties

New stable and adherent coating materials have been synthesized on the basis of inorganic/organic hybrid polymers. As the inorganic part, different poly(silsesquioxanes) (PSSQ) have been functionalized to act as polymeric chain transfer agents (CTAs) for a reversible addition fragmentation chain transfer polymerization, thereby determining the starting point of a controlled radical polymerization of vinyl-type monomers. Using two different CTAs acrylates, we have successfully polymerized methacrylates and styrene under RAFT polymerization conditions. Different monomers were copolymerized in such an organic block to incorporate multiple functionalities. The variation of the block ratios and the secondary condensation behavior of the inorganic block were investigated. Finally, these materials were used as surface coating materials on silicon, glass, metal, and polymeric substrates. Successful surface functionalization was demonstrated by contact angle measurements. The stability of the film and the adhesion...

Controlled radical polymerization of styrene and n-butyl acrylate mediated by trithiocarbonates

The free-radical bulk homopolymerization of styrene and n-butyl acrylate at 80°C mediated by dibenzyl trithiocarbonate, poly(styryl) trithiocarbonate, or poly(n-butyl acrylate) trithiocarbonate as reversible addition-fragmentation chain-transfer agents has been studied. It has been shown that the use of low-and high-molecular-mass reversible addition-fragmentation chain-transfer agents makes it possible to efficiently control the molecular-mass characteristics of polymers. In the case of styrene, the rate of polymerization slightly depends on the concentration of the addition-fragmentation chain-transfer agent. In contrast, for the polymerization of n-butyl acrylate, the rate significantly decreases with the concentration of the chain-transfer agent. Formation of radical intermediates during the polymerization of styrene and n-butyl acrylate mediated by trithiocarbonates has been studied by ESR spectroscopy. It has been demonstrated that the polymeric chain-transfer agents are efficient for the synthesis of block copolymers with the controlled block length.

Thiols as chain transfer agents in free radical polymerization in aqueous solution

The behavior of thiophenol and aliphatic thiols of different structure as chain transfer agents in the polymerization of acrylamide and 1-vinyl-2-pyrrolidone in aqueous solution at 25 °C was studied. Addition of millimolar concentrations of thiols to acrylamide polymerization reduced notably the polymer molecular weights, without change of the polymerization rate. Measurements at different pH showed that the reactive species towards the macroradicals is the protonated –SH group. Chain transfer constants, determined from Mayo plots, are only slightly dependent on the thiol structure. Aliphatic thiols and thiophenol react at similar rates. The selectivity is opposite for acrylamide (electron acceptor) and 1-vinyl-2-pyrrolidone (electron donor), pointing to significant charge transfer contributions. The reactions rates of these sulfur compounds with the electrophilic DPPH radical showed higher selectivity, and are not related with the chain transfer constants measured for the acrylamide macroradicals. These results are explained in terms of the different factors that control the reactivity of thiols with macroradicals.

Influence of thionoesters on the degree of polymerization of styrene, methyl acrylate, methyl methacrylate and vinyl acetate

AbstractThe aromatic thionoester 3 (benzyl thionobenzoate) was an effective chain transfer agent in polymerizations of styrene (Cx = 1,0) and methyl acrylate (Cx = 1,2) at 60°C. This activity was close to the ideal for obtaining narrow molecular‐weight distributions in batch polymerizations. The thionoester 3 showed no activity in polymerizations of methyl methacrylate, but was too reactive to be useful in vinyl acetate polymerizations. Ring‐substituted thionoesters 9‐11 and 14 and 1H NMR spectroscopy of the resulting polymers were used to establish the type and quantity of end‐groups. The thionoester 12 was used to produce low‐molecular‐weight polystyrene that was terminated at one end with a hydroxy group and at the other end by a thioloester moiety.

Functional polypropylene blend compatibilizers

AbstractSolid phase dispersants, often referred to as blend compatibilizers, are the key components of high‐value‐in‐use polypropylene blends with unusual property combinations. In multiphase polypropylene blends, functional blend compatibilizers enhance the dispersion of incompatible polymeric blend components, in particular of polar polymers, fibers or fillers, and improve the interfacial adhesion between polymer matrix and dispersed phases. Some of the major synthetic routes to functional polypropylene blend compatibilizers are discussed. A novel range of monofunctional polypropylenes containing a variety of functional endgroups, e.g., anhydrides, esters, amines, carboxylic acids, silanes, boranes, alcohols, and thiols, has been derived from mono‐olefin‐terminated polypropylenes. These olefinic polypropylene intermediates have been prepared with soluble metallocene catalysts which give excellent control of polypropylene molecular weight, molecular weight distribution, microstructure, and olefinic endgroups. Thiol‐terminated isotactic polypropylenes have been used as polymeric chain transfer agents in styrene and styrene/acrylonitrile polymerization to form novel polypropylene‐block‐polystyrene and polypropylene‐block‐poly(styrene‐co‐acrylonitrile) block copolymers. In the case of poly(styrene‐co‐acrylonitrile) blends with polypropylene morphological studies demonstrate the efficiency of propylene block copolymer blend compatibilizers.

P-Bromophenacyldimethylsulphonium Ylide as a Chain Transfer Agent for Polymerization of N-Vinylpyrrolidone and Methyl Methacrylate

p-Bromophenacyldimethylsulphonium Ylide as a Chain Transfer Agent for Polymerization of N-Vinylpyrrolidone and Methyl Methacrylate