Dithiocarbamate iniferter

In this work, a silane-derivatized dithiocarbamate iniferter was utilized to prepare PMAA brushes on Si/Si02 surfaces under UV irradiation. The combination of the photoiniferter-mediated photopolymerization with a UV-LED source appears to be ideally suited to the direct preparation of polyelectrolyte brushes with minimal free polymer formation during brash synthesis. Following characterization of the PMAA brushes by means of surface-analytical techniques, such as quartz crystal micro-balance with dissipation monitoring (QCM-D), spectroscopic ellipsometry, and static contact-angle measurements, the PMAA brushes were demonstrated to enhance aqueous lubrication of Si/ Si02 under low-contact-pressure conditions. 

Keywords Controlled Polymerization Living Radical Polymerization Iniferter Chain-End Structure Molecular Weight Control Block Copolymer Dithiocarbamate Disulfide Nitroxide Transition Metal Complex... 

Table 1. Classification and Applications of Iniferters with the Dithiocarbamate Group...

Living radical polymerizations have received considerable attention because they provide a convenient alternative for synthesizing block copolymers, polymers of narrow polydispersity and complex polymer structures (1-5). Because of their ability to initiate living free radical polymerizations, iniferters have been examined extensively after Otsu et al. (6) introduced them in 1982. In particular, dithiocarbamate derivatives have been studied more closely by several researchers. Lambrinos et al (7) have examined the molecular weight evolution during the polymerization of n-butyl acrylate using p-x ylylene bis(A,A-diethyl... 

Examples of surface functional derivatization by iniferter-based crossrecombination are shown below. A dithiocarbamated benzyl polymer surface was used as a model surface. When n-propyl N,N-diethyldithiocarbamate was used, XPS measurements showed that the complete loss of both N and S atoms but a marked increase in the C content of the surface was noticed. 

A polyhedron silsesquioxane ladder polymer containing polymerizable components was prepared in a three-step process to address this concern. The process initially entailed preparing the reversible addition-fragmentation transfer (RAFT) ladder iniferter, polysilsesquioxane dithiocarbamate. This intermediate was then polymerized with methyl methacrylate at ambient temperature by irradiating with ultraviolet (UV) light and poly(si Isesquioxane-g-methyl methacrylate) was obtained. 

The Inifer technique enables us to fulfil some requirements of polymer architecture even in some radical processes. An amplified form may be applied, the Iniferter variant, where the radical initiator simultaneously acts as a transfer and terminating agent. Otsu et al. used sulphides and disulphides (tetraethylthiuram disulphide, PhSSPh, Ph2S, PhCH2SSCH2Ph) [96] and carbamates (benzyl-A,A-diethyldithiocarbamate, p-xylylene-A,7V-diethyl-dithiocarbamate) [97] in the photopolymerization of methyl methacrylate and styrene, and phenylazotriphenylmethane in the polymerization of methyl methacrylate [98]. Living radical polymerizations yield polymers with defined end groups or the required block copolymers. 

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). 

Early attempts to realize the controlled radical polymerization of styrene involved the concept of reversible termination of growing polymer ehains by iniferters (initiation, trans/er, termination) [38]. These iniferters based on dithiocarbamates were the first species with photochemically labile C-S bonds. 

The adaptation of various controlled (free) radical polymerization methods to create polymer brushes that straddle interfaces and, as a result, modify surface properties has dramatically advanced the development of tailored soft interfaces. In this chapter, we have attempted to highlight commonalities among the various methods, as well as advantages of surface-initiated photoactivated IMP, which include facile spatial and temporal control and tolerance to thermally sensitive monomers or those with labile groups. Iniferters based on dithiocarbamate chemistry have been used to create... 

The tetrafunctional photoiniferter (DDC) was prepared by the reaction 1,2,4,5-tetrachloromethylbenzene with sodium JV,AT-diethyl-dithiocarbamate in ethanol at room temperature for about 24 hr and recrystallized from a benzene//i-hexane mixture (—1 1 v/v) the melting point is 125.5-126.3°C. Photopolymerization of MMA with the tetrafunctional iniferter (DDC) was compared with the bifunctional iniferter (XDC) and the monofunctional in-... 

Among the iniferters used, some compounds containing i, i r-diethyl-dithiocarbamate groups were found to be excellent photoiniferters of living radical polymerization. Otsu et al. [55] summarized these ideas and discussed some characteristics of the living radical polymerization with tetraethylthiuram disulfide (TD), benzyl JV,JV-diethyl-dithiocarbamate (BDC), / -xylene bis(iV,JV-diethyl-dithiocarbamate (XDC), and tetrakis(AT,iV-diethyl-dithiocarbamayl) benzene (DDC) as photoiniferters. 

Thiuram disulfides, described above as photoiniferters, can also act as thermal iniferters. The mechanism of the polymerization is the same and polymer chains are invariably end-capped at both ends with iniferter segments. The use of thiurams as thermal or photoiniferters for the preparation of block copolymers greatly depends on the quantum yield of dissociation. The synthesis of dithiocarbamate functional polymers by direct photolysis of the iniferters is limited due to the low quantum yield of dissociation, especially in the case of the thiuram disulfide (e.g., the quantum yield of dissociation (rf) of TD is 0.0025 in cyclohexane [81]). This very low value makes the photochemical dissociation much less attractive than the thermal one. It was suggested that better dithiocarbamate functionalization can be achieved by either thermal initiation with TD at 95°C or polymerization in the presence of AIBN as a thermal initiator and TD as a chain transfer agent. In the latter case, monofunctional or bifunctional TD-PSt were formed, depending on the mole ratio AIBN/TD. Interestingly, the quantum yield of BDC was found to be 0.06, which is 24 times higher than that of TD. Thus, BDC can be used both as a thermal initiator and as a photoiniferter [81]. 

Recently, Lambrinos et al. [101] observed some deviation from the proposed polymerization mechanism in iniferter systems. These authors pointed out the bimolecular termination leading to the deactivation of the iniferter site in the polymerization of n-butyl acrylate initiated by / -xylene bis(iV,iS -die-thyl-dithiocarbamate and claimed that the polymerization was not strictly living. Doi et al. [102] proposed a new two-cx)mponent iniferter system to prevent the deactivation of the iniferter site. In this system, BDC and TD act as an iniferter (or an initiator) and a chain transfer agent and/or a primary radical terminator, respectively. In the polymerization of methylacrylate (MA) with BDC bimolecular termination leading to the deactivation of the iniferter site occurred in preference to chain transfer to BDC and the dithio-carbamayl radical that produce the iniferter site, resulting in a deviation from... 

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