OLIGOMERIC STABILIZERS OF HALS TYPE - INFLUENCE OF POLARITY AND MOLECULAR MASS ON EFFICIENCY

The optimal performance of the polymer additives is usually a compromise of several often contradictory requirements. The high efficiency of a given additive whose activity is determined by its chemical structure must be supported by good compatibility and high mobility of additive in the polymer substrate and low volatility and washability during processing and service. The improvement of physico-chemical parameters can be achieved by increasing the molecular mass (at least above 103) of the low molecular mass additive. In this case the compatibility of the system polymer—oligomeric additives begins to play a pivotal role. The compatibility of this system is good when the polarity of its component is similar. To estimate the polarity of oligomeric stabilizers, the ratio of the intensity of two vibrational bands I3/It of monomer fluorescence of pyrene was used. Chimasorb 944 was found to be the least polar oligomeric HALS stabilizer under study. It was found that copolymers 2,2,6,6-tetramethyl-4-piperidyl acrylate with n-octadecyl acrylate in the range of molecular mass between 103 and 105exhibit the same polarity. The efficiency of these polymeric stabilizers in the inhibition of unoriented polypropylene films photooxidation decreases according to the relationship Er = aMn -b where Er is the relative efficiency, Mn is the number average molecular mass of the oligomeric stabilizer, a and b are constants. The value of b is 0.25 which is within the range of the dependence of any rate constant on the molecular mass. © 1990, Taylor & Francis Group, LLC. All rights reserved.