Poly monomer reactivities

Monomer Reactivity. The poly(amic acid) groups are formed by nucleophilic substitution by an amino group at a carbonyl carbon of an anhydride group. Therefore, the electrophilicity of the dianhydride is expected to be one of the most important parameters used to determine the reaction rate. There is a close relationship between the reaction rates and the electron affinities, of dianhydrides (12). These were independendy deterrnined by polarography. Stmctures and electron affinities of various dianhydrides are shown in Table 1. 

In addition, however, several minor but important side reactions concurrently proceed with the main reaction. These side reactions may become significant under certain conditions, particularly when the main reaction is slow because of low monomer reactivities or low concentrations. The principal pathways involved in the formation of poly(amic acid) are as shown in Eigure 1. 

The relative reactivity of the macromonomer in copolymerization with a common comonomer, A, can be assessed by l/rA=kAB/kAA> i-e-> the rate constant of propagation of macromonomer B relative to that of the monomer A toward a common poly-A radical. In summarizing a number of monomer reactivity ratios in solution copolymerization systems reported so far [3,31,40], it appears reasonable to say that the reactivities of macromonomers are similar to those of the corresponding small monomers, i.e., they are largely determined by the nature of their polymerizing end-group, i.e., essentially by their chemical reactivity. 

Radical copolymerization of OVE with AN was carried out using AIBN in acetonitrile at 60 C for lOh. Poly(OVE-co-AN) was identified by an FT-IR spectrometer. The FT-IR spectrum of poly(OVE-co-AN) exhibited characteristic peaks of cyclic carbonate C=0 band at 1790 cm, ether C-0 band at 1720 cm and CN band at 2250 cm. In order to estimate the monomer reactivity ratio for the copolymer, the copolymer composition was calculated by... 

Ethylene is used in a considerable number of copolymers. Some of these are binary copolymers, but copolymers of three or even four components also are known. As indicated in Section 2.3, specific monomer reactivity ratios are required for generating a copolymer. However, this requirement is satisfied for a number of monomers. Some common copolymers of polyethylene are indicated in Table 6.1.3. Some of the copolymers listed in Table 6.1.3 are a/f-copolymers. They behave during pyrolysis as homopolymers. More details regarding pyrolysis of several a/f-copolymers are given further in this section for poly(propylene-a/f-ethylene), in Section 6.3 for poly(ethylene-a/f-chlorotrifiuoroethylene), and in Section 6.9 for poly(ethylene-a/f-maleic anhydride). The copolymers in which the backbone chain contains atoms different from carbon, such as oxygen or sulfur, are discussed in sections dedicated to polymers containing that particular atom in the backbone. 

In principle, for a successful crossover reaction in the sequential monomer addition process, the monomers have to be added from the more reactive monomer (more nucleophilic) to the less reactive monomer (e.g., VE>aMeSt>St>IB). The monomer reactivity order in cationic polymerization is based on the electron-donating ability of the pendant groups of the vinylic double bond. However, this is not sufficient, and in most of the cases tuning of the Lewis acidity is also required. The synthesis of poly(a-methylstyrene)-l7-polyisobutylene (PaMeSt-l -PlB) is a characteristic example (Scheme 13). 

Monomers that yield radicals in which the unpaired electron is extensively delocalized have ground state structures that are themselves resonance stabilized. The important factor is the relative stability of the product radical, however, because a single electron is more easily delocalized than one in a C=C double bond. Thus resonance stabilization causes as increase in monomer reactivity and a decrease in reactivity of the resulting polymer radical. Styrene is more reactive toward polymerization than vinyl acetate, for example, and the propagation rate in the former polymerization is much slower than in the radical synthesis of poly(vinyl acetate). 

Studies of the copolymerizations of 1,1-diphenylethylene and dienes showed rather different behavior compared with the copolymerizations of styrene and 1,1-diphenylethylene [125, 133-136]. The monomer reactivity ratios for copolymerizations of dienes with DPE are shown in Table 7. When butadiene was copolymerized with 1,1-diphenylethylene in benzene at 40 °C with -butyl-lithium as initiator, the monomer reactivity ratio for butadiene, ri, was 54 this means that the addition of butadiene to the butadienyl anion is 54 times faster than addition of 1,1-diphenylethylene to the butadienyl anion [133]. This unreactivity of poly(butadienyl)lithium towards addition to DPE was also observed in studies of end-capping of poly(butadienyl)lithium with DPE in hydrocarbon solution (see Sect.3.3) [109, 111]. Because of this unfavorable monomer reactivity ratio, few DPE units would be incorporated into the co-... 

It was anticipated that the copolymerization of substituted 1,1-dipheny-lethylenes with dienes such as butadiene and isoprene would be complicated by the very unfavorable monomer reactivity ratio for the addition of poly(-dienyl)lithium compounds to 1,1-diphenylethylene [133, 134]. Yuki and Oka-moto [133, 134] calculated values of ri=54 and ri=29 in hydrocarbon solutions for the copolymerization of 1,1-diphenylethylene (M2) with butadiene (Mi) and isoprene (Mi), respectively. Although the corresponding values in THE are ri(butadiene)=0.13 and ri(isoprene)=0.12, this would not be an acceptable solution since THE is known to form polymers with high 1,2-microstructures [3]. Anionic copolymerizations of butadiene (Mi) with excess l-(4-dimethyla-mino-phenyl)-l-phenylethylene (M2) were conducted in benzene at room temperature for 24-48 h using scc-butyllithium as initiator [189]. Anisole, triethy-lamine and ferf-butyl methyl ether were added in ratios of [B]/[RLi]=60, 20, 30, respectively, to promote copolymerization and minimize 1,2-enchainment in the polybutadiene units. Narrow molecular weight distribution copolymers with Mn=14xl0 to 32x10 (Mw/Mn=1.02-1.03) and 8, 12, and 30 amine... 

Investigation of Monomer Reactivity in Poly(aryl ether) Synthesis Utilizing NMR Spectroscopy... 

We felt it would be informative to find a spectroscopic probe that would allow the evaluation of a large number of potential monomers in regards to their ability to undergo these S Ar-type polymerization reactions. Work performed in the preparation of poly(aryl ether triazoles) (8) and poly(aryl ether quinoxalines) (9) indicated that NMR could be used as a sensitive and convenient probe of a monomers ability to undergo transformation under standard S Ar conditions. Early results of the use of NMR in the evaluation of monomer reactivity has been reported (19,20). 

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