Лако-красочные материалы — производство

Preparation of liquid polysulfide polymers has been discussed extensively [1-4]. The polymer is synthesized by reacting aqueous sodium polysulfide with bis(2-chloroethyl) formal. Cross-linking is introduced by including a small amount of 1,2,3-tri-chloropro — pane. The reactions of polymerization done at 100°C produce a mixture of chain lengths in which sulfur is present as — C-S2-C- or — C-S3-C-. Dihalide monomer is added to aqueous polysulfide solution containing bischlorobutyl formal and bis-4-chlorobutyl ether is used in small amounts where improvement in low-temperature performance is required. Specific emulsifying and nucleating agents (alkyl naphthalene sulfonate and magnesium hydroxide sol) are used in the polymerization. The polymerization reaction is as follows:

nClCH2CH2OCH2OCH2CH2Cl + nNa2S2:25 -! IcH2CH2OCH2OCH2CH2S2 25| + 2nNaCl

L _ln

The high-molecular-weight solid polysulfide polymer is reduced by sodium sulfite, result­ing in splitting of the polymer into segments that are simultaneously terminated by mer­captan groups as follows:

RSSH + NaSH + NaHSO3—> 2RSH + Na2S2O3

The concentration of the splitting salts regulates the molecular weight from 1000 to 8000. The extent of cross-linking depends on the mole percent of trichloropropane, a cross­linking agent used in the initial reactions, usually in the range 0.05 to 2.0mol%. The amount of cross-linking agent regulates modulus and elongation: a decrease gives the lower modulus and higher elongation desirable in applications involving greater movement.

The typical structure of a liquid polysuifide (e. g., Morton’s LP-32) is

HS|CH2CH2OCH2OCH2CH2SS ]|CH2CH2OCH2OCH2SH

Use of a mixed dihalide monomer feed will produce random copolymers. During copolymerization, interchange takes place, resulting in randomization. Therefore, block copolymers cannot be prepared by stepwise addition of dihalide monomers. To prepare block copolymers, homopolymers should be made, blended in the desired proportion, and then the blend co-cured by a conventional technique. When cured by mixing an oxidizing agent, water is split off, with the hydrogen coming from the mercaptan groups of two polymer molecules and the oxygen being supplied by the oxidizing curative. The molecules are joined at the sulfurs.