Disulfides chain transfer

Latex products are manufactured in an identical fashion as the dry polymers described earlier. One major exception is that the primary and auxiUaiy surfactants used in latex manufacture are not destroyed prior to shipment to the end user. Molecular weight control is identical with mercaptan, organic halides, and xanthogen disulfides chain-transfer agents typically used. Copolymerizations are conducted with the same variety of comonomers that include... 

Cha.in-Tra.nsferAgents. The most commonly employed chain-transfer agents ia emulsion polymerisation are mercaptans, disulfides, carbon tetrabromide, and carbon tetrachloride. They are added to control the molecular weight of a polymer, by transferring a propagating radical to the chain transfer agent AX (63) ... 

Other radical reactions not covered in this chapter are mentioned in the chapters that follow. These include additions to systems other than carbon-carbon double bonds [e.g. additions to aromatic systems (Section 3.4.2.2.1) and strained ring systems (Section 4.4.2)], transfer of heteroatoms [eg. chain transfer to disulfides (Section 6.2.2.2) and halocarbons (Section 6.2.2.4)] or groups of atoms [eg. in RAFT polymerization (Section 9.5.3)], and radical-radical reactions involving heteroatom-centered radicals or metal complexes [e g. in inhibition (Sections 3.5.2 and 5.3), NMP (Section 9.3.6) and ATRP (Section 9.4)]. 

Aliphatic disulfides 4 are not particularly reactive in chain transfer towards MMA and S (Table 6.3). However, they appear to be ideal transfer agents (Cu 1.0) for VAc polymerizations. 

Since the dithiocarbatnyl end groups 8 are thermally stable but pholochemically labile at usual polymerization temperatures, only photo-initiated polymerizations have the potential to show living characteristics. However, various disulfides, for example, 9 and 10, have been used to prepare end-functional polymers37 and block copolymers38 by irreversible chain transfer in non-living thermally-initiated polymerization (Section 7.5.1). 

Nair et al. studied the kinetics of the polymerization of MMA at 60-95 °C using N,1SP-diethyl-NjW-di(hydroxyethyl)thiuram disulfide (30a) as the thermal in-iferter [142]. The dependence of the iniferter concentration on the polymerization rate was examined. The chain transfer constant of the propagating radical of MMA to 30a was determined to be 0.23-0.46 at 60-95 °C, resulting in the activation energy of 37.6 kj/mol for the chain transfer. Other derivatives 30b-30d were also prepared and used to derive telechelic polymers with the terminal phosphorus, amino, and other functional aromatic groups [143-145]. Thermal polymerization was also investigated with the end-functional poly(St) and poly(MMA) which were prepared using the iniferter 13 [146]. 

The amine-terminated poly(EA) was prepared by the chain transfer polymerization of EA in the presence of the salt of aminomercaptan, followed by the reaction with carbon disulfide to give the polymeric iniferter 31. The polymerizations of St and MMA with 31 provided the triblock copolymers, poly(EA)-block-poly(St)-fcfoc/c-poly(EA) and poly(E A)-Woc/c-poly(MMA)-fcfoc/c-poly(EA), respectively, as shown in Eq. (29) [ 147] ... 

In this study, molecular weight of the produced polymers will not be tracked over the course of the reaction. Thus, in order to simplify the model, chain transfer mechanisms will not be considered, along with side reactions, such as the production of carbon disulfide. Each of these reactions, as well as the molecular weight, plays a significant role in the iniferter polymerizations however, to simplify the system, it is essential to examine only the core reactions which contribute significantly to the mechanism. 

Dinaburg, V. A., and A. A. Vansheidt Meicaptans and disulfides as chain transfer agents in thermal polymerization of styrene. Zhur. Obschei Khim. 24, 840 (1954). 

The most widely used chain transfer agents are compounds with one relatively weak bond like this thiols, disulfides, CCI4, or CBr4, but even hydrogen and... 

The mechanistic principle of the chain transfer exploiting functionalized transfer agents was used for the synthesis of polymer bound CB AO, attached to the polymer chain via the sulfur atom. Weinstein [73, 74] used phenolic and aminic thiols 79, 81 and disulfides 80, 82 as generators of thiyls during free-radical bulk or emulsion copolymerization of butadiene or isoprene with styrene. Systems formed can be considered as bifunctional physically persistent stabiUzers combining CB and HD fiinctions. 

Dithiocarbamate-iunctionalized polymers of styrene and MMA at both ends are prepared [148] by thermal free radical initiation with tetraethylthiuram disulfide which is known [146] to behave as initiator, chain transfer agent and terminator (iniferter). Successive photolysis of the terminal dithiocarbamate end groups, in the presence of another vinyl monomer, allows one to obtain three-block cc lymers (Scheme 43). 

Telechelic oligobutadiene can be prepared Ity emulsion polymerization in the presence of dialkylxanthogen disulfides as chain transfer agents [172]. 

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