polyaziridine may also act as a cross linking agent in the polymerisable composition e g by reaction with an acid monomer or polymeric acid which may suitably be present in the composition as described above the polyaziridine should be generally soluble in monomers included in the polymerisable composition such that the parts of the two part composition can be readily mixed by u201c soluble u201d is meant that no evidence of gross phase separation at room temperature i e about 20 u00b0 c to about 25 u00b0 c is visible to the unaided eye similarly the organoborane should also desirably be soluble in thepolyaziridine although slightly warming a mixture of the organoborane and the polyaziridine may be helpful in forming a solution of the two at room temperature i e about 22 u00b0 c to about 25 u00b0 c preferably the polyaziridine is a liquid at or near room temperature i e within about 10 u00b0 c of room temperature or forms a liquid solution with the organoborane at or near room temperature suitable carriers for the initiator system may be present including liquid polyethers liquid polyethers capped with non reactive groups being groups which are not susceptible to free radical polymerisation such as epoxies liquid polyesters polyisoprene or polybutadiene a thickened solvent could also be used as a carrier polytetrahydrofuran could be used as both solvent and carrier the quantity of carrier may suitably be in the range from about 5 to about 50 by weight for example 5 to 25 by weight particularly 5 to.