Effects of ortho‐substituents on the living polymerization of phenylacetylenes by MoOCl₄‐based catalysts

Abstract

Polymerization of phenylacetylenes (PAS) having various ortho-substituents were examined by using MoOCI,-n-Bu,Sn-EtOH (mole ratio 1 : 1 : 1) as catalyst. Phenylacetylenes with no or sterically small ortho-substituents did not polymerize in a living fashion. On the other hand, in the polymerization of phenylacetylenes having medium-sized substituents (e. g., CH,, C1, Br, and iPr), the number-average molecular weights M, of polymers increased in direct proportion to monomer consumption, while the polydispersity ratios were 1,2-1,3, which is in favor of living polymerization. Further, monomers having bulky ortho-groups (CF, and Me,Ge) exhibited excellent living nature with small polydispersity ratios of = 1 , l . Thus, it is concluded that not the electronic but the steric effect of the ortho-substituent is important to achieve living polymerization.

Living Metathesis Polymerization of Several Substituted Acetylenes by MoOCl4–Et3Al–EtOH

“…Thus one can see that the MWD narrows with increase in the bulkiness of orthosubstituent. This tendency is the same as in previously developed systems such as toluene, 29 19 and MoOClcn-BuLi/anisole. 20 This means that steric effect of artha-substituents in phenylacetylene plays a vital role in achieving living polymerization by using Mo0Cl 4-based catalysts.…”

Living polymerization of substituted acetylenes

“…Although the initiation efficiencies of 8b ‐mediated polymerizations of ortho‐substituted phenylacetylenes were usually around 10%, initiation efficiencies as high as 20–30% were observed when ortho ‐(trialkylsilyl)methylene groups of different steric demands were used as substituents 81. Interestingly, 8b even effected the controlled polymerization of ( o ‐isopropylphenyl)acetylene,57 ( o ‐methylphenyl)acetylene,83 ( o ‐bromophenyl)acetylene,84 ( o ‐chlorophenyl)acetylene,57 and ( p ‐ n ‐butyl‐ o,o,m,m ‐tetrafluorophenyl)acetylene,85 which bear sterically less demanding ortho substituents (Table 1). A comparison of the polymerization results of 8b ‐derived poly(phenylacetylene)s having various ortho substituents57, 84 confirmed the observations reported from Percec's group 76.…”

“…Interestingly, 8b even effected the controlled polymerization of ( o ‐isopropylphenyl)acetylene,57 ( o ‐methylphenyl)acetylene,83 ( o ‐bromophenyl)acetylene,84 ( o ‐chlorophenyl)acetylene,57 and ( p ‐ n ‐butyl‐ o,o,m,m ‐tetrafluorophenyl)acetylene,85 which bear sterically less demanding ortho substituents (Table 1). A comparison of the polymerization results of 8b ‐derived poly(phenylacetylene)s having various ortho substituents57, 84 confirmed the observations reported from Percec's group 76. Hence, sterically demanding ortho substituents are believed to be indispensable to produce sterically crowded propagating species in which chain transfer and termination are prohibited because of steric hindrance.…”

“…Hence, sterically demanding ortho substituents are believed to be indispensable to produce sterically crowded propagating species in which chain transfer and termination are prohibited because of steric hindrance. Most notably, the electronic effect of ortho substituents hardly affected the living nature in the polymerizations of phenylacetylenes initiated by 8b 57, 84…”

Polymerization of aliphatic disubstituted acetylenes by MoOCl4-n-Bu4Sn-EtOH catalyst: Formation of polymers with narrow MWDs and confirmation of the living character

“…The living polymerization of substituted acetylenes has been achieved with Schrock carbenes, 1-5 MoOCl 4 -based ternary catalysts, 6 -8 and Rh catalysts. 9, 10 We have found that fairly many substituted acetylenes (e.g., 1-chloro-1-alkynes, 11 tert-butylacetylene, 12 and various ortho-substituted phenylacetylenes 13 ) polymerize in a living fashion in the presence of the MoOCl 4 -n-Bu 4 Sn-EtOH catalyst in a toluene solution. Except for 1-chloro-1-alkynes, however, there have been no examples of disubstituted acetylenes that polymerize in a living fashion with MoOCl 4 -based catalysts.…”