Investigation of the molecular mass characteristics of ni- trogen-containing monoalkyl (C8-C12) phenol- formaldehyde oligomers by gel-chromatography

Abstract

Modification of phenol-formaldehyde oligomers with nitrogen-containing compounds improves their adhesion to the metal surface, enhances the protective properties when used in various applications. Concerning, studies on the synthesis of monoalkyl (C₈-C₁₂) phenol-formaldehyde oligomers modified with amidoamines based on natural petroleum acids and polyamines-diethylenetriamine, triethylenetetraamine, polyethylenepolyamines were carried out.

Analyzes were carried out on a high-performance liquid chromatograph with a refractometric detector from Kowo (Czech Republic) using exclusive chromatography. The fixed Separan-SGX phase was 3.3x150 mm in size, with a particle size of 7 µm and pores of 100 Å, and dimethylformamide was taken as the eluent at a flow rate of 0.3 cm³/min. The tests were carried out at a temperature of 20-25°C. When deter- mining the MWD parameters, the calibration dependence of lgM on V_R in the range M₁ = (1.5-100)10² was obtained using polyethyleneglycol as a standard, which is permissible for relatively low molecular weight. This dependence is expressed by lgM=(С₁-V_R)/C₂ from V_R=С₁-С₂lgM, where С₁=24.4; С₂=4.0.As a result lgM=6.1-0.25 V_R. Calculations are carried out according to the equations:

М_w = ∑М_iω_i; M_n=

where М_i - is the molecular weight corresponding to the i area of the chromatogram; ω_i - is the fraction of the area of part i.

It was found that irrespective of the composition of the amidoamines used, all the samples consist of different fractions of high (I) and low (II) molecular fractions: when a content of I fraction 2.50-4.54%, М_w=5100-8500, М_n=4560-7300, while for II fraction of 95.5-97.5%, М_w=650-960, М_n=470-610. The content of I fraction for monoalkyl(C₈-C₁₂) phenol-formaldehyde oligomers modified with amidoamines based on distilled natural petroleum acids and polyethylenepolyamines is slightly higher in comparison with analogues modified with amidoamines based on distilled natural petroleum acids with diethylenetriamines and triethy- lenetetramine. Typically, the weight-average and number-average molecular weight indices of their individu- al fractions are much higher than those modified with amidoamines based on lower polyamines. This is prob- ably due to the high functionality of amidoamines based on polyethylene polyamines in comparison with other polyamines and the possibility of growth of the oligomeric chain in several directions. In a series of samples using amidoamines prepared on the basis of the same polyamine as a modifier, a decrease in the weight-average and number-average molecular weight is observed with an increase in the molar amount of acid in the composition of the modifier. This is probably due to a decrease in the functionality of amidoamine with increasing mole amount of acid. A similar pattern is observed for oligomers obtained using amidoa- mines based on triethylenetetramine.

As a rule, the high fraction of all oligomers is characterized by a narrower polydispersity, very close to that of a monomolecular system. Obviously, high-molecular fractions are part of oligomers, consisting of macromolecules, which contain fragments of amidoamines and the latter are part of a very small number of macromolecules. On the other hand, the functionality of amidoamines being equal to 2 or more can promote chain growth in several directions. The sharp difference in the parameters of the weight-average and the number-average molecular weights of individual fractions at a finite value of the average molecular weight, as well as the general polydispersity, compared with individual fractions, takes higher values.