Molecular weight enhancement of vinyl chloride–propylene copolymers

Abstract

SynopsisThe chain transfer activity of propylene leads to the formation of vinyl chloride-propylene copolymers with molecular weights lower than those of PVC homopolymers produced under similar conditions. I t has been found that the addition of specified quantities of monomers with two or more active double bonds can increase the molecular weight of these copolymers without causing crosslinking. INTRODUCTIONVinyl chloride-propylene copolymers have lower melt viscosities than the homopolymer.'P2 This gives rise to improved processibility and increased thermal stability.2 But, as propylene is a chain transfer agent, the molecular weight of the copolymer is lower than that of the homopolymer prepared under the same conditions, thus limiting the field of application of these copolymers. The work reported here deals with a technique for obtaining practicably higher molecular weight copolymers without detracting from the processibility advantage they have over the homopolymer. This technique is based on the addition of small quantities of molecular weight enhancers which are monomers with two or more active double bonds. EXPERIMENTAL PolymerizationThe polymerizations were performed in a 1.5 liter glass reactor (Inginieurbuero SFS, Zurich, Switzerland) using a rectangular blade impeller at 500 rpm and the following recipe: monomers, 330 g; diethyl peroxydicarbonate (laboratory preparation), 0.24 g; Tensaktol A (BASF), 0.1 g; Methocel90 HG 100 cps (Dow), 0.44 g; (NH4)2C03,0.03 g; water, 560 g. Polymerizations were run at 50°C for 12 hours unless otherwise indicated. Processibility MeasurementsA Brabender Plastograph OHG, Duisberg, Germany, with a Type 30 head was used at 63/42 rpm and a bath temperature of 190°C. The following formulation was used: resin, 34 g; stearic acid, 0.18 g; stabilizer, Mark 292,l g. Infrared SpectroscopyTo establish the incorporation of the molecular weight enhancer, the resin was doubly precipitated from a 1% tetrahydrofuran solution using a fivefold voldme of hexane and dried in a vacuum oven at 50°C. A 0.25-mm-thick pellet of this material was pressed in a KBr pellet press heated to 120OC. Additive incorporation was confirmed by the appearance of bands characteristic of the material. For example, triallyl cyanurate has bands characteristic of the s -triazine ring a t 1560 cm-l and 820 cm-l. For esters, confirmation of incorporation was obtained for materials initiated with lauryl peroxide, The latter in the absence of other carbonyl-containing material gives rise to a barely detectable carbonyl band in the resin, which did not interfere with the detection of ester carbonyl. RESULTS AND DISCUSSIONValyi et al.3 have shown that small incremental additions of diisopropenyldiphenyl to styrene increases the molecular weight of the resulting polymer until a concentration is reached where crosslinking begins and the polymer becomes insoluble. Similar results were reported by Breitenbach4 for styrene-m,m'-

Application of a compositional rotatable plan in modeling the propylene content in a vinyl chloride/propylene copolymer

“…Adding small quantities of monomers with two or more active double bonds can increase the molecular weight of the copolymer without causing crosslinking. When increasing the molecular weight, diallyl and triallyl esters are the most effective [8].…”