Polymeric polyacid

Poly(vinyl chloride) or a chlorinated pol5rvinyl chloride is stabilized with composition comprising either methyl, butyl or octyl tin mercaptide stabilizer and salt of a polymeric polyacid material in the solid form. The last improves performance of tin stabilizer, especially if the moisture level in composition is higher than 0.52 wt%. 

Poly(acrylic acid) and its salts have been known to have useful binding properties for some thirty years they have been used for soil consolidation (Lambe Michaels, 1954 Hopkins, 1955 Wilson Crisp, 1977) and as a flocculant (Woodberry, 1961). The most interesting of these applications is the in situ polymerization of calcium acrylate added to soil (de Mello, Hauser Lambe, 1953). But here we are concerned with cements formed from these polyacids. 

The most common poly(alkenoic acid) used in polyalkenoate, ionomer or polycarboxylate cements is poly(acrylic acid), PAA. In addition, copolymers of acrylic acid with other alkenoic acids - maleic and itaconic and 3-butene 1,2,3-tricarboxylic acid - may be employed (Crisp Wilson, 1974c, 1977 Crisp et al, 1980). These polyacids are prepared by free-radical polymerization in aqueous solution using ammonium persulphate as the initiator and propan-2-ol (isopropyl alcohol) as the chain transfer agent (Smith, 1969). The concentration of poly(alkenoic add) is kept below 25 % to avoid the danger of explosion. After polymerization the solution is concentrated to 40-50 % for use. 

The molecular mass of the polyacid obtained lies between 10000 and 55000. Increasing the temperature of polymerization and the concentration of ammonium persulphate serves to decrease the molecular mass of the poly(alkenoic acid). 

A fundamental criticism of the resin-modified glass polyalkenoate cements is that, to some extent, they go against the philosophy of the glass polyalkenoate cement namely, that the freshly mixed material should contain no monomer. Monomers are toxic, and HEMA is no exception. This disadvantage of composite resins is avoided in the glass polyalkenoate cement as the polyacid is pre-polymerized during manufacture, but the same cannot be said of these new materials. For this reason they may lack the biocompatibility of conventional glass polyalkenoate cements. These materials also absorb excessive amounts of water because of the hydrophilic nature of polyHEMA (Nicholson, Anstice McLean, 1992). 

It was reported that such systems exhibit cooperative stabilization of the complex, which means that the state and behaviour of every unit mainly depends on its interactions with neighboring units. Moreover, a minimal chain length is required for stable complex formation a polybase, which forms a complex with a long chain of polyacid, must have a degree of polymerization larger than a critical number corresponding on the minimum chain length (5-7. ... 

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 authors thus concluded that the polymerization studied was affected by the template. The rules observed for polymerization of 4-vinylpyridine in the presence of low molecular weight acids and polyacids can be summarized as in the Table 4.1. ... 

Figure 4.6. Dependence of polymerization rate of MA (1) and specific viscosity of solutions of equimolar mixtures of polyacid and PEG (2) on molecular weight of PEG. 1 -[MA]=[PEG]=3.BxlO [K2S2O8l=3.7xl0- mol/L, 50 C. 2 - PMAM=120,000 cpma=0.1 g/dL, 45"C. Reprinted from I. M. Papisov, V. A. Kabanov, E. Osada, M. Leskano Brito, J. Reimont, and A. N. Gvozdeckii, Vysokomol. Soed., 14, 2462 (1972) with kind permission from Iz. Nauka.

Figure 8.3. Dependence of calculated from vopKn/KakplM] initial polymerization rate in presence of various polyacids at 20°C with pH (1) - pH adjusted by the ratio [PAA]/[4-VP] [4-VP] = 0.1 mol/L (2) - pH adjusted by addition HCl or NaOH at [PAA]=[4-VP] =0.1 mol/L (3) - pH adjusted by addition o polyphosphate - poly(ethylenephosphoric acid) at [4VP] =0.1 mol/L. Reprinted from V.

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 ... 

Aleksina et al. investigating polymerization of methacrylic acid in the presence of poly-L-lysine found that the complex obtained by template polymerization has a 1 1 stoichiometry, while the same components obtained by separation of the complex and repeated mixing gave a complex in which the ratio of polylysine units to polyacid units is 2 3. The stable conformation of polylysine macromolecule in the complex obtained by template polymerization is the conformation of a-helix. 

If a product of template polymerization is composed of a daughter polymer and a template involved in polymer complex, the first step of analysis is separation of these two parts. Separation of two polymers forming a complex is sometimes difficult and depends on interactions between the components. Very often polymeric complexes are insoluble in water and also in organic solvents. In order to dissolve such compounds, aqueous or non-aqueous solutions of inorganic salts such as LiBr, LiCl, NH4CNS are used. Dimethylformamide or dimethylacetamide are commonly used as non-aqueous solvents. If one of the components is a polyacid, alkali solutions are used as solvent. Ferguson and Shah reported that the complex obtained by polymerization of acrylic acid in... 

Water-soluble biodegradable polycarboxylates with an acetal or ketal weak link were inventions of Monsanto scientists in the course of their search for biodegradable deteigent polymers. However, the polymers were prevented by economics from reaching commercial status. The polymers are based on the anionic or cationic polymerization of glyoxylic esters at low temperature (molecular weight is inversely proportional to the polymerization temperature) and subsequent hydrolysis to the salt form of the polyacid, which is a hemiacetal (R = H) or ketal (R = CH3) if methylglyoxylic acid is used, and stable under basic conditions. 

T0 prepare models of TA, the corresponding cyclic alkylene phosphoric acids cannot be directly polymerized because the presence of acidic protons of the phosphate group makes the ionic polymerization impossible. Thus, cyclic phosphorus compounds with blocked third functions have to be used. These are phosphates., phosphoramidates and phosphites. After polymerization the obtained polymer is converted by deblocking into the polyalkylene phosphate, e.g. polysalt or polyacid form. 

Similar results were obtained more recently by Yasuda et al.55). Monomers 60 and 61 were polymerized in benzene using (C2H5)2Mg as an initiator. The resulting 62 and 63 were insoluble in benzene. Both polymers heated in an Ar atmosphere at above 80 °C easily lost isobutylene and produced the required polyalkylenephos-phates. The deblocking was almost quantitative (95 % removal). M of polyacids 59 and 64, measured by GPC, were 2.8 x 104 and 1.8 x 104, respectively. 

The influence exerted by the matrix on the direction of the elementary growth steps of the daughter chains was observed for the matrix polymerization of 4PV on polyacids when the daughter P4VP had ionene structure 81), and for the matrix polycondensation of urea and formaldehyde in water, with PAA being present 88,89). In the latter case, the daughter chains of PFU contained the structures... 

At this point it is convenient to mention a special effect of polyelectrolytes. Kabanov et al. were the first to mention the possibility of monomer polymerization on a polyelectrolyte matrix [35], particularly of vinylpyridine on polyacids. Blumstein et al. described the radical polymerization of vinylsul-phonic acid on a polydiazabicyclo-[2,2,2-octyl-1-butane matrix [36]... 

In one example polymer segment density profiles of weak polyacid brushes consisting of polymethacrylic acid (PMAA) chains were investigated as a function of the pH of the environment by means of multiple-angle ellipsom-etry [68]. The polymer brushes were prepared by surface-initiated polymerization of methylacrylic acid as described above. 

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