Prestabilization of halogen-containing polymers

A process for preparing a stabilized suspension/emulsion PVC polymer comprising

• (1) adding a polymer thermal stabilizer mixture compatible with the polymerization medium prior to, during or directly after the polymerization, prior to the isolation of the polymer from the polymerization medium, wherein the polymer thermal stabilizer mixture comprises:
• a) a perchlorate compound or salt thereof, and
• b) an alkanolamine of the formula (I)
• where
• x=1, 2 or 3;
• y=1, 2, 3, 4, 5 or 6;
• n=from 1 to 10;
• R1, R2=independently of one another, H, C1-C22-alkyl, —[—(CHR3a)y—CHR3b—O—]n—H, —[—(CHR3a)y—CHR3b—O—]n—CO—R4, C2-C20-alkenyl, C2-C18-acyl, C4-C8-cycloalkyl, which may be OH-substituted in the β position, C6-C10-aryl, C7-C10-alkaryl or C7-C10-aralkyl, or when x=1, R1 and R2 may additionally combine with the N to form a closed 4-10-membered ring of carbon atoms and optionally up to 2 heteroatoms, or when x=2, R1 may additionally be C2-C18-alkylene which may be OH-substituted at both β-carbon atoms and/or may be interrupted by one or more O-atoms and/or one or more NR2 groups, or dihydroxy-substituted tetrahydrodicyclopentadienylene, dihydroxy-substituted ethylcyclo-hexanylene, dihydroxy-substituted 4,4′-(bisphenol A dipropyl ether)ylene, isophoronylene, dimethylcyclohexanylene, dicyclohexylmethanylene, or 3,3′-dimethyldicyclohexylmethanylene, and if x=3, R1 may also be trihydroxy-substituted (tri-N-propyl isocyanurate)triyl;
• R3a, R3b=independently of one another, C1-C22-alkyl, C2-C6-alkenyl, C6-C10-aryl, H or CH2—X—R5, where X=O, S, —O—CO— or —CO—O—;
• R4=C1-C18-alkyl/alkenyl or phenyl, and
• R5=H, C1-C22-alkyl, C2-C22-alkenyl or C6-C10-aryl;
• or salt thereof:
• and
• (2) adding to the pre-stabilized PVC polymer, after isolation of the polymer from the polymerization medium, one or more additives selected from the group consisting of heat-stabilizers, UV stabilizers, lubricants, plasticizers, pigments, fillers, metal soaps, antioxidants, wetting agents, optical brighteners, and antisettling agents.