RTCP

Figure 3.4.5 shows the protocol stack upon which the communication tools are based. The Internet protocols TCP and UDP in combination with RTP [902] are used for data transmission. The audio/video tools were developed for transmission over the Internet considering possible congestions thus, they realize an adaptive transmission where the transmission rate is adapted to currently available capacities [304], [465]. Both, the video and audio tool, use RTP for transmission and the capabilities of the corresponding RTCP... 

The video transmission tool is able to adapt to available capacities of the network by changing the video codec and/or the compression ratio before sending the data [304]. As shown in Fig. 3.45, this approach uses the Real-Time Transmission Protocol RTP for a connectionless data transmission without error handling. RTP also provides a control protocol named RTCP, by which the receiving party can give feedback information about the received data and the error ratio. The sending party uses this feedback information to... 

Reversible Chain Transfer Catalyzed Polymerization (RTCP) with Alcohol Catalysts... 

Alcohols (phenols, a vinyl alcohol, and an iodide derivative) worked as efficient catalysts for reversible chain transfer catalyzed polymerization (RTCP). Low-polydispersity (MJMn 1.2-1.3) polystyrenes and poly(methyl methaciylate)s with predicted molecular weights were obtained with a fairly high conversion. Attractive features of the alcohol catalysts include their high reactivity (a small amount being required), low or no toxicity, and low cost (cheapness). 

In RTCP, an effective activator radical (A ) undergoes no or little initiation (addition to monomer) but is still active enough to abstract iodine from Polymer-... 

Phenoxyl radicals (Ph-0 ) are known not to iiutiate radical polymerization in most cases (2) and may be RTCP catalysts if they can activate Polymer-I. Based on this idea, we attempted to use phenol derivatives as catalysts, thus extending the element of the catalyst to O (Figure 1). Notably, the phenols include common antioxidants for foods and resins and natural compounds such as vitamins (Figure 1). Their commonness (hence cheapness) and environmental safety may be highly attractive for practical applications. In this paper, we will present the results of the styrene and methyl methacrylate (MMA) polymerizations, along with a mechanistic study. 

As noted above, RTCP is supposed to involve the RT process. If RT exists, the catalyst radical (A in Scheme lb) is mediated and the propagating species is a free radical (Polymer in Scheme lb). Thus, we attempted to detect A by ESR and confirm the free radical nature from the tacticity of the product polymer in the styrene polymerizations with TI (deactivator) and BHT (precursor). 

Goto et al. [279] developed a process that they describe as reversible living chain transfer radical polymerization [278], where they us Ge, Sn, P, and N compounds iodides in the iodide mediated polymerizations." In this process, a compound such as GeLt is a chain transferring agent and the polymer-iodide is catalytically activated via a RFT process. They proposed that the new reversible activation process be referred to as RTCP [279]. The process can be illustrated by them as follows [279] ... 

The originally measured intermediary enthalpies of dilution were reduced by the authors to Am77a/(RTcp ) to get data which depend less on concentration (see also the next data sets below). 

In the RT process, P-X is activated by an activator A to produce polymer radical and deactivator XA. XA plays a chain transfer agent, and P-X plays a catalyst of activation via the RT process. This polymerization process, in which iodine is used as X and Ge, Sn, O, or N compound is used as RT catalyst, XA, is termed the RT-catalyzed polymerization (RTCP) [17]. 

All LRPs such as NMP, ATRP, RAFT, TERP, or RTCP have already been applied to surface-initiated polymerization by fixing dormant species or conventional radical initiators. For details, readers are referred to other relevant chapters. 

Goto, A., Tsujii, Y, and Fukuda, T. 2008. Reversible chain transfer catalyzed polymerization (RTCP) A new class of living radical polymerization. 2s1M L... 

RTCP is a simple and robust polymerization indudrng, like iodide-mediated polymerization, a monomer, an alkyl iodide as a dormant spedes (X=I), and a conventional radical initiator as a source of P", along with a catalyst such as Geld as a deactivator (AX). It is applicable to, for example, styrene, methacrylates, AN, and the rdevant functional monomers. Mechanistically, it is based on RT with a minor contribution of DT. 

For GeU, for example, in a typical RTCP condition with [GeU]/[PS-I] = 5 mM/80 mM = 0.0625, k a would be about 20 times larger than in the absence of GeU (iodide-mediated polymerization) (Figure 21). This explains why low-polydispersity polymers are obtainable in the GeU system from an early stage of polymerization. From the slope of the straight line in the plot, feda is determined to be 9.0 X This value is large and comparable to the... 

In the typical RTCP condition with [XA]/[P-X] = 0.0625, is about 13, 10, 5, and 3 times larger than in their absence for XA=SnU, NIS, p-tolyl-GeU, and PU, respectively. In all cases, feaci is so large as to give low-polydispersity polymers from an early stage of polymerization. Also noticeably, significantly... 

The feact values for TERP, SBRP, and BIRP systems 29-40 are also large enough to obtain low-polydispersity polymers. The feact largely depends on the central atoms (Te, Sb, and Bi) and substituents of the capping group and polymers, as noted in Section 3.05.8.1. The feact values for the RTCP systems 41-46 are also sufficiently large and depend on the catalysts and polymers, as noted in Section 3.05.8.2. 

The LRP field is stiU developing far more powerful and/or comprehensive techniques with wider and/or specific applicability, meeting new ideas such as TERP and RTCP. In this chapter, we have discussed the principles and fundamental aspects of LRP mainly on the basis of kinetic studies. This was because kinetic approaches have proved to provide precise, deep, and systematic imderstandings of LRP as well as conventional RP. The issues and references herein discussed and cited... 

Interestingly, it is possible to combine RTCP with RITP to obtain polymers in a more practical manner. Thus, low-polydispersity poly(MMA) (PDI s 1.2-1.4) has been prepared by RITP in the presence of nitrogen and phosphoms catalysts, enhancing the utility of RTCP. However, the real benefit of RTCP/RITP is still to be dearly demonsttated since low-polydispersity PMMA polymers are already reached by RTTP alone. 

Scheme 9 Reactions involved in RTCP with iodo-compounds (G-Z, catalyst G , activator G-I, deactivator).

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