Template polymerization with acrylic acids

A similar procedure was described by Eboatu and Ferguson. An object of analysis was the complex obtained by template polymerization of acrylic acid in the presence of poly(vinyl pyrrolidone). The polycomplex was dispersed in dry benzene and treated with diazomethane. The insoluble portion was filtered. The filtrate containing poly(methyl acrylate) was concentrated and finally dried. The insoluble fraction was scrubbed with methanol to extract polyCvinyl pyrrolidone). The residue was further washed with methanol and then dried. These three portions were characterized by IR spectroscopy. It was found that only about 70% separation of the complex is achieved. The occurrence of inseparable portion is attributed to a graft copolymer formation. For the separated... 

Another complexation technique was reported by Chuang et al. [145], who prepared PEC particles by templating polymerization of acrylic acid in the presence of CHT at various monomolar ratios (0.2/1.1 to 1.0/1.1). Hollow CHT/PAC particles were formed with sizes of around 200 nm, which varied with the pH of the medium, and zeta-potentials of around 25 mV. The release of doxycycline (DOC) incorporated by various feeding processes was found to last for up to 8 days. 

From this equation, it is clear that concentration of the solvent, S, influences a number of sites on the template which are occupied by the monomer, M. As the result of monomer units association with the template, the orientation of the substrate takes place and some special type of structure can be created. The structures, in which the monomer is aligned in a regular manner on the polymer template, were described by Chapiro in the case of polymerization of acrylic acid and acrylonitrile and details are described below. The ordered structure increases concentration of monomer at the reaction site, affects distances between pre-oriented monomer molecules, and changes a steric hindrance. This change in structure leads to the change in the kinetics of the polymerization reaction and it is responsible for stereo-control of the propagation step. 

As published by Ferguson and Shah and independently by Bamford and Shiiki, polyethylene imine can be used as template for polymerization of acrylic acid. It was found that polyethylene imine forms water insoluble complex with polyacrylic acid. Polymerization was carried out at 31 C, using potassium persulphate as an initiator. The polymerization was followed by turbimetry and bromometric titration. During polymerization, the precipitation takes place, however, at GO C, degradation of the com-... 

The polycomplexes obtained by template polymerization of methacrylic acid or acrylic acid in the presence of poly(N,N,N, N - tetramethyl-N-p-xylene-ethylenediammonium dichloride) were used for spinning of fine fibers 5 to 50 pm in diameter. The fibers are soluble in water but become stable after thermal treatment at about 80°C. The polycomplex with regular structure, obtained by template polymerization, is expected to be of considerable interest for textile industry. 

Another technique which is used to follow the extent of template polymerization vs. time is turbidimetry. Two types of measurements can be used here. The first is based on the determination of passed light intensity, the second on the determination of scattered light intensity. The former was used in many papers by Ferguson and co-workers for studies on polymerization of acrylic acid in aqueous solution in the presence of many homopolymers used as templates as well as for application of copolymers with interacting and non-interacting groups. This measurement was also used for studying com-... 

It has been attempted to perform template polymer syntheses without using biological sources. Concepts focus on the formation of a complex between monomer molecules and a present macromolecule [4,480], This way the monomer will get preorganized and the polymerization is supposed to follow a zip mechanism controlled by the length and the configuration of the template polymer, offering replication of the molecular weight and control of the stereo structure. Polymerization of acrylic acid in the presence of poly(ethyleneimine), N-vinylimidazole/ poly(methacrylic acid) or acrylonitrile with poly(vinylacetate) have been described [469,470,471,472,473]. Recently the preparation of solid polyelectrolyte complexes from chitosan and sodium-styrenesulfonate has been reported [481]. 

Spontaneous polymerization of 4-vinyl pyridine in the presence of polyacids was one of the earliest cases of template polymerization studied. Vinyl pyridine polymerizes without an additional initiator in the presence of both low molecular weight acids and polyacids such as poly(acrylic acid), poly(methacrylic acid), polyCvinyl phosphonic acid), or poly(styrene sulfonic acid). The polyacids, in comparison with low molecular weight acids, support much higher initial rates of polymerization and lead to different kinetic equations. The authors suggested that the reaction was initiated by zwitterions. The chain reaction mechanism includes anion addition to activated double bonds of quaternary salt molecules of 4-vinylpyridine, then propagation in the activated center, and termination of the growing center by protonization. The proposed structure of the product, obtained in the case of poly(acrylic acid), used as a template is ... 

The autoaccelerated character of acrylic acid polymerization is strictly correlated with such a form of monomer organization. The fast zip-up propagation takes place along oriented double bonds. Template mechanism of polymerization in these systems was also confirmed by examination of the tacticity of the polymer obtained. 

The most examined monomers for template polymerization have been either acrylic or methacrylic acids. This is probably because many polymers, such as poly(ethylene oxide), PEG, and poly(vinyl pyrrolidone), PVP, form complexes with poly(acrylic acid). 

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. 

Figure 4.3. Variation of degree of polymerization of poly(acrylic acid) with degree of polymerization of template PVP. Reprinted from J. Ferguson, S. Al-Alawi, andR. Granmayeh, Eur.Polym. J.,...

Application of classical type of kinetic equations to the template polymerization was demonstrated by Kabanov at al It was shown that 4-vinylpyridine, in the presence of poly(methacrylic acid), poly(acrylic acid), poly(l-glutamic acid), and polyphosphate, polymerizes according to the classical equation and the order of reaction with respect to the monomer is 2 as demonstrated in the Figure 8.1. In log-log coordinates, for the all sets of polymerizations, experimental points fit straight lines. In the same paper dependence of the initial rate on the molar ratio of acid to monomer was examined. This relationship is shown on the Figure 8.2. The rate of polymerization in the presence of the poly(acrylic acid) is much higher than that for the low molecular analogue (acetic acid). The polymerization rate riches its maximum for the molar ratio [acid]/[monomer] 2. The authors found kinetic equation for template polymerization of 4-vinylpyridine in the presence of different polyacids in the form ... 

The solvent used can change interaction between template and monomer. For instance polymerization of methacrylic or acrylic acid in water and in water-methanol mixtures proceeds with different rates which depend on the composition of the solvents mixture as pertaining from the results in Figure 8.14. 

Rates of polymerization of methacrylic acid or acrylic acid in water in the absence of template, PEG, was much higher than that for template polymerization. However, the rate decreases with methanol concentration increasing, while the rate of template... 

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