An overall mechanistic scheme for the suspension polymerization of vinyl chloride is presented. The process can be resolved into five discrete stages, each of which presents a unique environment for the interaction of the systems parameters. It is shown that the surface area of the polymer formed during the reaction is not a major factor in autoacceleration and that the increase of kinetic chain length with conversion is due to a radical dilution effect. The latter is a direct result of the difference in rates between polymerization and radical formation, the former being greater. The increase of the initial polymerization rate and the reduction of autoacceleration brought about by chain transfer agents can be explained by the lower diffusion rate and greater bulkiness of the chain transfer agent radical relative to that of the monomer radical. The chaintransfer agent CBr4 is preferentially absorbed by PVC from solution in vinyl chloride. With lauryl peroxide as initiator it is shown that the “hot spot” is the result of a build‐up of initiator in the monomer caused by its exclusion from the polymer phase. Vinyl chloride was found to dissolve 0.03% PVC at ambient temperature and to have no effect on the decomposition rate of lauryl peroxide.
Methyl methacrylate has been grafted on artificial isoprene rubber (IR) latex, with use of redox initiation. The properties of latices containing up to 40 phr methyl methacrylate (MMA) as well as solid products containing up to 80 phr of this compound were studied. Compared with ungrafted IR latex with the same solids content, the grafted IR latices had a lower viscosity, owing to their particle size being larger. Vulcanised films obtained from the grafted latices showed a considerably higher modulus, particularly at large deformations, than those based on IR or blends of IR with polymethyl methacrylate. by incorporation of certain reinforcing white fillers in the MMA‐grafted IR latices, a further increase in the modulus of the latex films was effected.
Because of the allylic nature of propylene, the vinyl chloride–propylene system exhibits polymerization behavior markedly different from that of vinyl chloride, even at relatively low propylene concentrations. Propylene acts as a degradative chain‐transfer agent, and as a result, both the polymerization rate and the molecular weight of the resultant copolymers are lower than those of the homopolymer, decreasing with increasing propylene content. Even at propylene concentrations as low as 10% the rate of polymerization is proportional to the initiation rate, indicating kinetic control by the propylene. The reactivity ratios of these monomers given by Cain were verified. The reciprocal intrinsic viscosity of the copolymer was found to be linearly related to the monomer feed composition.
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'-
SynopsisThe bulk and tap densities of a series of PVC resins were found to be related linearly t o each other and hyperbolically to the resin specific surface.
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