Liquid polythioethers

A non-crystallizing water, solvent, fuel and temperature resistant linear, liquid polythioether containing no carbonyl groups and having the formula <CHEM> wherein each of R1, R2, R3 and R4 is hydrogen or lower alkyl with the provision that a sufficient number of R1, R2, R3 and/or R4 are lower alkyl in said polymeric backbone to render said backbone non-crystallizing; X is a divalent organic radical selected from -CH2-CH2-, -CH2-CH2-CH2-CH2-, CH2-CH2-S-CH2-CH2-, or CH2-CH2-O-CH2-CH2-: n is 15 to 200, p is 0 or 1 and B is a terminating radical which does not substantially reduce the water, solvent and fuel resistance, said terminating radical being either a chemically non-reactive radical or a vulcanizable radical curable to an elastomeric sealant.