Livingness of polymerization

Following on from the above, various methods have been described to test and/or rank the livingness of polymerization processes." Ul7 20 All of these tests have limitations.. The following list paraphrases a set of criteria for living polymerization set out by Quirk and Lee11 who also critically assessed their applicability primarily in the context of living anionic polymerization. 

According to their recent reports [11], 5 provides livingness of polymerization for styrene (ST) and methyl methacrylic acid (MA). Irrespective of the type of monomer, the initiator efficiency / was over 0.9, and the polydis-persity index, Mw/Mn (Mw weight-average molecular weight, Mn number-average molecular weight), was close to unity (approximately 1.2). The polymerization rate was very low (on the order of an hour), i.e., a very slow... 

Livingness of Polymerization in Processes Initiated with Multivalent Metal Alkoxides... 

The polymerization of ethylene oxide (epoxyethane, EO) with 17 also proceeded by irradiation with visible light. For example, the polymerization with the mole ratio [EO]o/[17]o of 190 in benzene at room temperature, where the monomer conversion after 205 min was very low (<2%, determined by H NMR) in the dark, proceeded to 97% conversion in only 80 min under irradiation. The Mn of the polymer, as estimated from the GPC chromatogram, was 8700, which is in excellent agreement with the expected value of 8100 provided that the numbers of the molecules of the produced polymer and 17 (X=SPr) are equal [81]. The Mw/Mn of the polymer (1.05) was close to unity, indicating the livingness of the visible Hght induced polymerization of EO initiated with (NMTPP)ZnSPr (17). 

There are several ways in which block copolymers can be made. The three main methods are (1) sequential addition of monomers, (2) the preparation of a functionalized polymer followed by the use of the functionalized polymer as a macroinitiator or chain-stopper for initiation or termination of polymerization of the second monomer, and (3) use of a multiple-headed initiator. The purity of the block copolymers produced in these processes is dependent upon the livingness (lack of side reactions that lead to termination) of the chemistry used to make them. If the integrity of the chain-ends is maintained throughout the polymerization because all possible termination mechanisms are absent or eliminated, then pure block copolymers can be produced. If, however, impurities get into the process or if there are side reactions that lead to chain termination, the resulting block copolymers are contaminated with some homopolymer. Depending upon the application, some contamination of homopolymer in the block copolymer may be acceptable. 

The V(acac)3-mediated hompolymerization of ethylene is not living and the polydisper-sity index is quite high (2.0). Nevertheless, ethylene can be successfully copolymerized with propylene while maintaining the livingness of the process. Moreover, the enolate ligated vanadium is a catalyst for the living polymerization of 1,5-hexadiene and copolymerization with propylene. It must be noted that polymerization of 1,5-hexadiene is a route to a polymer that combines constitutive 1,3-cyclopentylenemethylene units (2 ) and vinyltetramethylene units. Therefore, pendant unsaturations are available for further functionalization. 

Consistently, Anderson and coworkers showed that the polymerization of MMA in THF at —78 °C is living when initiated by DPHLi (10), which is nothing but the model of the diphenylalkyl anion (9) of the PS macroinitiator used in the synthesis of PS-fcZock-PMMA (equation 21). It must be noted that DPHLi (10) results from the direct addition of DPE (8) to n-Buli (equation 22)". The molecular weight of PMMA is predetermined by the monomer-to-initiator molar ratio and the MMA conversion. The polydispersity index is low (1.04 < Mw/Mn < 1.16). The livingness of this polymerization was confirmed by the successful resumption of the polymerization of lauryl methacrylate (LMA), and formation of the parent PMMA-fc/ock-PLMA diblocks. The anionic polymerization of MMA in THF at —78°C is thus living , provided that sterically hindered initiators are used. 

The livingness of the polymer is also easily calculated because the number of dead chains is practically equal to the number of the released persistent species, which is known from eq 18. Further, the analytical solutions provide conditions for the rate constants that should allow a successful living and controlled polymerization.17 First, we may want the concentration fraction of the dead polymer products [P]/[I]o at the large monomer conversion of 90% to... 

Livingness of the Microflow System-controlled Cationic Polymerization... 

In Section 9.4.1 we discussed ideal living polymerization. Let us examine the livingness of the microflow system-controlled cationic polymerization here. 

How to enhance livingness of CRP systems withont sacrificing the polymerization rate. 

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