29 июня, 2015 
Malyar The formation of more energetically stable free radicals during propagation can result in orientation of the monomer molecule since the more stable free radical will normally be formed on the substituted side of the C=C bond, where resonance stabilisation is more likely.
In the case of ionic polymerisation, electrostatic interaction has a major influence, and occurs as a result of attraction between a polymeric ion and the permanent dipole on the monomer. In free radical polymerisation the effect of electrostatic forces are not as clearly defined. Since free radicals are in effect neutral, attack on either side of the C=C bond is possible from an electrostatic point of view. However, it is suggested from experimental evidence that attack on a terminal olefine is almost exclusively at the CH2 side of the C=C bond, as shown below:
R-CH=CH2+CCI3————— ► RCH = CH2CCI3
Figure 1 -55
In the case of the steric and energy state factors it is well known that the stability of the free radical will increase with the degree of substitution.
R3C > R2CH > RCH2 > CH3
increasing stability
Figure 1-56
The stability also increases with the polarisation of the substituent in direct relationship to the ability to delocalise electrons.
The stability of the free radicals is possibly the greatest influence on the orientation of the repeating unit in a polymer chain.
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