Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Patent
1998-12-15
2000-12-05
Wu, David W.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
526 89, 526347, 5263471, 526296, 5262922, 5262924, 5262927, 5263071, 5263072, 5263182, 52631845, C08F 238, C08F21208
Patent
active
061568554
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a process for preparing a branched polymer from a vinyl aromatic monomer in the presence of a molecular weight regulator.
The use of molecular weight regulators or chain transfer agents in polymerization reactions are known in the art. Alkanethiols have been used traditionally, but have an objectionable odor, can lead to wide weight average molecular weight (Mw) distribution and don't allow for the production of telechelic or living polymers.
U.S. Pat. No. 3,271,375 by Delacretaz et al. discloses a free radical polymerization process wherein a polar monomer is polymerized in the presence of a molecular weight regulator, such as 2-methyl-indole. However, this process produces a substantially linear, low molecular weight polymer.
Additionally, U.S. Pat. No. 5,385,996 by Rizzardo et al. discloses the use of molecular weight regulators of the formula CH.sub.2 .dbd.C(Y)R, such as .alpha.-(t-butanethiomethyl)styrene, to produce a lightly branched polymer via an addition-fragmentation mechanism. However, the molecular weight regulators used in the process of Rizzardo have low activity, therefore low levels of branching occur and high levels of the unreacted molecular weight regulator contaminate the final polymer product.
Branched polymers have also been previously produced by polymerizing a vinyl aromatic monomer in the presence of a vinyl functional initiator, such as n-butyl-t-butylperoxyfumarate, as described in U.S. Pat. No. 4,376,847. However, in this method, branching occurs in the early stages of the polymerization, causing gels to form. Gels tend to build up after extended periods of continuous operation and lead to reactor fouling as discussed in US-A-5,455,321 issued to Cummings, et al.
Accordingly, it remains highly desirable to provide an efficient method of producing a high molecular weight branched polymer from a vinyl aromatic monomer which allows for high levels of branching and the production of telechelic or living polymers, without the production of gels.
SUMMARY OF THE INVENTION
The present invention is a free radical polymerization process for producing a branched polymer which comprises polymerizing a vinyl aromatic monomer in the presence of a molecular weight regulator of the formula R.sup.1 CH.sub.2 (R")C.dbd.CHR'", wherein R.sup.1 is a leaving group and R" and R'" are each activating groups.
This process produces high molecular weight branched polymers, which have improved properties over linear polymers in extensional rheology, melt strength, and viscosity.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Vinyl aromatic monomers suitable for use according to the present invention include, but are not limited to, those vinyl aromatic monomers known for use in polymerization processes, such as those described in U.S. Pat. No. 4,666,987, U.S. Pat. No. 4,572,819 and U.S. Pat. No. 4,585,825, which are herein incorporated by reference. Preferably, the monomer is of the formula: ##STR1## wherein R' is hydrogen or methyl, Ar is an aromatic ring structure having from 1 to 3 aromatic rings with or without alkyl, halo, or haloalkyl substitution, wherein any alkyl group contains 1 to 6 carbon atoms and haloalkyl refers to a halo substituted alkyl group. Preferably, Ar is phenyl or alkylphenyl, wherein alkylphenyl refers to an alkyl substituted phenyl group, with phenyl being most preferred. Typical vinyl aromatic monomers which can be used include: styrene, alpha-methylstyrene, all isomers of vinyl toluene, especially paravinyltoluene, all isomers of ethyl styrene, propyl styrene, vinyl biphenyl, vinyl naphthalene, vinyl anthracene, and mixtures thereof. The vinyl aromatic monomers may also be combined with other copolymerizable monomers. Examples of such monomers include, but are not limited to acrylic monomers such as acrylonitrile, methacrylonitrile, methacrylic acid, methyl methacrylate, acrylic acid, and methyl acrylate; maleimide, phenylmaleimide, and maleic anhydride. In addition, the polymerization may be conducted in the presence of predissolved elastomer to prepar
REFERENCES:
patent: 5408023 (1995-04-01), Priddy et al.
Harlan R.
The Dow Chemical Company
Wu David W.
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