Copolymerization template effects

There are also reports of template effects on reactivity ratios in copolymerization. For example, Polowinski20S has reported that both kinetics and reactivity ratios in MMA-MAA copolymerization in benzene arc affected by the presence of a PVA template. 

A very interesting modification of the system was examined by Ferguson and McLeod. The authors replaced poly(vinyl pyrrolidone) with copolymers vinyl pyrrolidone-styrene or vinyl pyrrolidone-acrylamide. It was found that the mechanism of polymerization is the same as in the presence of homopolymer (PVP). However, the rate of polymerization decreases rapidly when vinyl pyrrolidone concentration in copolymer decreases. The concentration of vinyl pyrrolidone residues was kept equimolar to the concentration of acrylic acid. It was stressed that structure of template and, in the case of copolymeric template, sequence distribution of units play an important role in template effect. 

Copolymerization of methyl methacrylate with styrene in the presence of isotactic poly(methyl methacrylate) has been examined by O Driscoll and Capek. Copolymerization was carried out in acetone at O C and redox system benzoyl peroxide -dimethylaniline was used to initiate the polymerization process. Carrying out the process with various ratios of styrene to methyl methacrylate, it was found that the polymerization rate drops very quickly with the increase in styrene concentration. A very small amount of styrene destroys any template effect that it-poly(methyl methacrylate) exerts on the rate of the polymerization. Assuming, that the reactivity ratios are not changed by the template (ri = i2 = 0.5), the critical length of the sequence of methacrylic units is 10- 20. Complexation occurs only if longer sequences, composed of methacrylic... 

Belokon and co-workers (50,51) attributed their template effects (see "Distance Accuracy of Two Functional Groups") to the existence of cyclopolymerization, since polymers of low crosslinking also showed a good selectivity. What takes place is an intrachain reaction rather than an interchain one. Only in one case have we observed a similar behavior (23,49,52). In our case a cyclo-polymerization was proved by copolymerization of 3.4-0-isopropylidene-D-mannitol 1, 2,5,6-bis-O-[(4-vinylphenyl)... 

It was found that the composition and the distribution of units in copolymerization is controlled mainly by the propagation process. From this point of view, equations have been formulated (71) concerning how the reactivity ratios depend on the template concentration and individual reactivity rate constants of monomers taking part in the template copolymerization process. However, if long critical length is necessary for the adsorption of the growing macroradical onto the template, any template effect can be destroyed (72). 

It seems that the template effect can be pronounced only if interactions between at least one of the monomers is sufficiently strong. Examples of the systems in which one or both monomers were connected with the template by covalent bonds have been described (73-78). Copolymerization of multimonomers similar to the oligomers described by Kammerer with styrene leads to semiladder copolymers, and after hydrolysis to short-block copolsrmers (73). 

The template effects can be expressed as (1) kinetic effect -usually an enhancement of the reaction rate and change in kinetics equation (2) molecular effect - consisting of an influence of the template on the molecular weight and molecular weight distribution of daughter polymer (3) effect on tactidty -the daughter polymer can have the complementary stmcture to the stmcture of the template used and (4) in the case of template copolymerization, the template effect - deals with the composition and sequence distribution of units. 

For copolymerization of AA with MAA in the presence of PEG in toluene and in benzene, the template effect was described in Reference 73. Template copolymerization was carried out with the equimolar quantity of acid groups present in the reaction mixture and PEG units. For different molar ratios of MAA to AA, it was found that the relation proposed by Kelen-Ttidos equation was fulfilled. Reactivity ratios change from 2.12 and 0.42 (without the template) to 2.64 and 0.2 (with template) for toluene and 2.77 and 0.29 for benzene used as a solvent, respectively. 

This case was described by O Dtiscoll and Capek. Examining copolymerization of MMA with styrene in the presence of isotactic PMMA, it was found that a small amount of styrene destroys any template effect. 

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. 

Cyclopolymerization of bifunctional monomers is an effective method of chirality induction. Optically active vinyl homopolymers and copolymers have been synthesized by using optically active distyrenic monomers (41) based on a readily removable chiral template moiety. Free-radical copolymerization of 41a with styrene and removal of the chiral template moiety from the obtained copolymer led to polystyrene, which showed optical activity ([Oc]365 -0.5-3.5°) (Scheme 11.6) [84], The optical activity was explained in terms of chiral (S,S)-diad units generated in the polymer chain through cyclopolymerization of 41a [85], Several different bifunctional monomers have been synthesized and used for this type of copolymerization [86-90]. 

There are two processes by which the bulk imprinted polymers are formed covalent imprinting and noncovalent imprinting. In the former, the template molecule is first covalently functionalized with the monomer, and then copolymerized with the pure monomer. After that the covalent bond is broken and the template molecule is removed by extraction. In order to facilitate the extraction step, a so-called porogenic solvent is used. It effectively swells the polymer matrix. 

In contrast to these approaches based on nonspecific interactions, Zhang and coworkers described a molecularly imprinted hydrogel based on the ther-moresponsive PNIPAM [184], This hydrogel was prepared by copolymerization of a metal chelate monomer iV-(4-vinyl)-benzyl iminodiacetic acid, which formed a coordination complex with the template protein in the presence of Cu ions, A-isopropylacrylamide, acrylamide, and IV.lV-methylenebisacrylamide as crosslinker. The interaction of the imprinted thermoresponsive hydrogel with the protein could be switched between coordination effects and electrostatic attraction by addition or omission of Cu ions. Furthermore, this imprinted hydrogel allowed switching of lysozyme adsorption by changing the temperature. 

Piletsky et al. [81] had found that using a coated hydrogen abstraction photoinitiator (see Scheme 4e) very thin MIP films, which were covalently anchored and covered the entire surface of the base material, could be synthesized by a photo-initiated cross-linking graft copolymerization. This approach had been first explored with benzophenone as photo-initiator and a membrane from polypropylene as support. MIP synthesis and recognition were possible in/from water, and significantly less cross-linker than with bulk preparations was necessary to obtain the highest template specificity. Both effects were explained by a contribution of the soUd polymer support to the stabilization of the imprinted sites. The approach is very flexible because no premodification is necessary. 

In an early approach towards MIP-based sensors using capacitance measurement, thin MIP membranes were prepared by in situ polymerization of MAA/ EDMA and then sandwiched as a sensing layer in afield effect device a capacitance decrease was observed due to specific binding of the template L-phenylalanine anilide [103]. Recently, two promising alternative approaches towards ultrathin MIP films for capacitive sensors had been reported electropolymerization of phenol for imprinting of phenylalanine [74], and photo-initiated graft copolymerization of AMPS/MBAA for imprinting of desmetryn [82] and creatinine [83] (cf Sections III.C.2, III.C.3). 

MIP catalysts. Efendiev etal. have performed seminal research in which the oxidation of ethylbenzene to acetophenone was studied (Scheme I4).36a,37 Having copolymerized the diethyl ester of vinylphosphonic acid with acrylic acid, the resulting polymer was then functionalized with Co(II) complexes, while the template was added. A series of polymers were prepared in which the template was the substrate, an analog of the intermediate, or the product itself. Cross-linking of the prearranged polymer was effected using /V,/V-methylenebis(acrylamide), and a control polymer was prepared which did not contain imprinted sites. The substrate-imprinted polymer displayed a catalytic... 

Pegylated hematin was developed as an effective biomimetic catalyst for polymerization of various anihnes [56]. PEG modified hematin, a biomimetic catalyst, was used in the synthesis of PEDOT and PPYR at the presence of SPS template [57]. The polymerization was carried out in an aqueous solution at pH 1.0. The polymers were electrochemically active. Conductivity was measured as 10 S/cm for PEDOT and 10 S/cm for PPYR. The conductivity was substantially improved by the copolymerization of PEDOT and PPYR and was found to be in the range of O.l-l.O S/cm. 

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