The matrix template effect

Monomer molecules with strongly polar substituents mutually associate and form complexes with the solvent and with their own polymer. All kinds of association cause changes in polymerization kinetics and sometimes even in the properties of the generated polymer. 

Kabanov et al. have studied the radical polymerization of acrylic acid in aqueous solutions [61] (see Chap. 4, Sect. 1.4). A crystaline, syndiotactic polymer was formed at pH 10.2-10.8. The kinetics of the photosensitized polymerization of acrylic acid was studied by Galperina et. al. [62]. They observed a strong solvent dependence for the rate constant of propagation. At 293 K, /Cp[mol dm s ] = 22 500 in water, 4 200 in formamide, and 500 in dimethylsulphoxide. 

Chapiro and Dulieu have established the dominant role of macromolecular associations from the reasons for the effects described [63], Acrylic acid associates by hydrogen bonds, yielding a cyclic dimer or an oligomer 

Solvents such as water, methanol, dioxan etc. stabilize the oligomeric associate. Hydrocarbons and their chlorinated derivatives do not associate with acrylic acid, and they shift equilibrium (28) to the left. The polymerization of an equilibriiun mixture of oligomers and dimers in polar complexing solvents is almost 20 times more rapid than the polymerization of dimers only [64]. Moreover, even with polymerization in bulk, it proceeds autocatalytically under these conditions. Oligomeric aggregates associate by hydrogen bonds on to the polymer matrix which is formed immediately after the start of the 

Polymerization on the matrix is 63 times more rapid than polymerization of dimers [64]. The product is a stereo block polymer of the syndiotactic and atactic polyacrylic acid configurations. When hydrocarbons or their chlorinated derivatives are used as solvent, the matrix effect does not occur. 

---