| 摘要 |
<p>A two-step process for the post-chlorination of PVC homopolymer and other predominantly vinyl chloride-containing polymers is disclosed, which process produces chlorinated PVC ("CPVC") containing at least 70% by weight Cl, in a fast, but controllable, aqueous, two-step process catalyzed using an organic peroxide catalyst instead of actinic radiation. Less than 10% excess Cl remains after the second stage, even when 75 wt% Cl CPVC is made. In the first step, an aqueous slurry of PVC is chlorinated in the absence of liquid chlorine and free oxygen, preferably at a starting temperature in the range from about 30 DEG C to 75 DEG C, in the presence of at least an essentially stoichiometric amount of chlorine required to make the desired Cl content in the end product, and, a catalytic amount of the peroxy catalyst, at least sufficient to produce 'first step CPVC' having an intermediate Cl level of chemically bound Cl in the range from 67% to 72% by weight. The temperature is maintained below the Tg of the first step CPVC formed. In a second step, the first step CPVC formed is further chlorinated in the presence of less than a 10 wt% excess of chlorine, at a temperature in the range from 90 DEG to 130 DEG C until the Cl content in the CPVC is in the range from 69% to 75% by weight. At least a 3% increase in Cl content of the first step CPVC is obtained within about 30 min irrespective of the volume of the slurry. Preferably, a substantial excess of chlorine is not used, and no remaining chlorine needs to be recovered. CPVC with a 75% Cl content is made in about 3 hr. The CPVC end product so obtained is unexpectedly more easily thermoformed than another CPVC end product having the same Cl content, but made by a prior art aqueous process.</p> |
