Template Copolymerization

Borovik et al. [70] prepared a highly crosslinked polymeric porous material containing Co-salen units 38 (Figme 13) by template copolymerization method. The authors reported that as the cross-linking degree increases from 5 % to 50 %, the catalyst become more efficient in terms of reactivity, possibly due to the improved proximity of metal centers that work in cooperation. Unfortunately low enantioselectivity for the product epoxide was observed (<42 % ee) while the ee for concomitantly produced diol did not go above 86%. Reusability of the catalyst containing 50 mol% template showed consistent activity and enantioselectivity for three consecutive recycle experiments. 

Deviations are also observed in some copolymerizations where the copolymer formed is poorly soluble in the reaction medium [Pichot and Pham, 1979 Pichot et al., 1979 Suggate, 1978, 1979]. Under these conditions, altered copolymer compositions are observed if one of the monomers is preferentially adsorbed by the copolymer. Thus for methyl methacrylate (M1 )-/V-vinylcarbazole (M2) copolymerization, r — 1.80, r2 = 0.06 in benzene but r — 0.57, > 2 0.75 in methanol [Ledwith et al., 1979]. The propagating copolymer chains are completely soluble in benzene but are microheterogeneous in methanol. /V-vinylcarba-zole (NVC) is preferentially adsorbed by the copolymer compared to methyl methacrylate. The comonomer composition in the domain of the propagating radical sites (trapped in the precipitating copolymer) is richer in NVC than the comonomer feed composition in the bulk solution. NVC enters the copolymer to a greater extent than expected on the basis of feed composition. Similar results occur in template copolymerization (Sec. 3-10d-2), where two monomers undergo copolymerization in the presence of a polymer. Thus, acrylic acid-2-hydroxyethylmethacrylate copolymerization in the presence of poly(V-vinylpyrrolidone) results in increased incorporation of acrylic acid [Rainaldi et al., 2000]. 

The synthesis of biopolymers in vivo leads to macromolecules with a defined sequence of units. This effect is very important for living organisms and is different in comparison with random copolymerization in which sequences of units are distributed according to stochastic rules. On the other hand, the predicted sequence of units can be achieved by a set of successive reactions of respective monomer molecule addition. In template copolymerization, the interaction between comonomers and the template could pre-arrange monomer units defining sequence distribution in the macromolecular product. 

There is far less information in the scientific literature about template copolymerization than about template homopolymerization. As in the case of template homopolymerization, template copolymerization can be realized according to different types of reaction stepwise (template polycondensation), copolyaddition, radical or ionic polymerization, ring-opening copolymerization, etc. 

The conclusion can be drawn that in template copolymerization reactivity ratios depend on the nature and concentration of the template used. Template controls composition and sequence distribution of monomer units in copolymers obtained. 

COPOLYMERIZATION WITHOUT MULTIMONOMERS The second case of template copolymerization deals with the systems in which at least one comonomer is interacting with the template by intermolecular forces, such as hydrogen bonding, dipole-dipole interaction, etc. 

Table 5.5 Template copolymerization of methacrylic acid, MA, with styrene (S), acrylic acid, AA, or methyl methacrylate, MM. Template PEG 20,000. solventdoluene...

Template copolymerization seems to be applied to the synthesis of copolymers with unconventional sequences of units. As it was shown, by copolymerization of styrene with oligomers prepared from p-cresyl-formaldehyde resin esterified by methacrylic or acrylic acid - short ladder-type blocks can be introduced to the macromolecule. After hydrolysis, copolymer with blocks of acrylic or methacrylic acid groups can be obtained. Number of groups in the block corresponds to the number of units in oligomeric multimonomer. Such copolymers cannot be obtained by the conventional copolymerization. 

IR spectrometry is a convenient method of examination of template copolymerization and polymerization kinetics. For instance, IR spectroscopy was applied in order to examine kinetics of template polymerization of multiacrylate according to the reaction ... 

Borovik and co-workers (29-31) developed porous organic materials for reversible binding of CO, O2, and NO by means of gas chemical coordination to the metal centers. For immobihzation of metal centers, templated copolymerization was employed (Fig. 7). Material 14, for example, contained immobilized four-coordinate Co(II) centers, and the cobalt concentration ranged from 180 to 230 mol g with an average pore diameter of 25 A (31). Polymer 14 bound NO in toluene solution and even on the air-solid interphase, but was relatively inert toward other biologically important gases O2, CO2, and CO. Nitric oxide could be slowly released from 14 under ambient conditions. For example, after 30 days 80% of NO was lost. Heating the sample accelerated the gas release. 

Moreover, efficiency of phase inversion imprinting can be improved with pre-forming complex of monomer-template (Table 2) in copolymerization [70]. The THO-acrylic acid or methacrylic acid precomplex monomer was copolymerized with acrylonitrile in DMSO. The resultant viscous solution contents were used for phase inversion in water after template copolymerization. Template copolymers can improve binding capacity of THO. From H-NMR analysis, this is due to tailor-made modification of a copolymer backbone for the template molecule. Also, comparison was made between copolymers of acrylic acid and methacrylic acid in THO selectivity of the imprinted polymers. Presence of the methacryl methyl group is more efficient in the tailor-made structure of the THO template. 

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