Multi-modal polyisoolefin compositions and processes therefor

#The present invention relates to polyisoolefin compositions, especially butyl rubber compositions, and processes for production thereof.

#Butyl rubbers are understood to be copolymers of an isoolefin and one or more, preferably conjugated, multiolefins as co-monomers. Specifically, poly(isobutylene-co-isoprene) (IIR) is a high molecular weight copolymer produced via cationic polymerization with isobutylene (IB) and isoprene (IP). Since the 1940's, IIR has been prepared through the random cationic copolymerization of isobutylene with small amounts of isoprene (usually not more than 2.5 mol %). Butyl rubber or butyl polymer is generally prepared in a slurry process using methyl chloride as a diluent and a Friedel-Crafts catalyst as part of the polymerization initiator. This process is further described in U.S. Pat. No. 2,356,128 and Ullmanns Encyclopedia of Industrial Chemistry, volume A 23, 1993, pages 288-295, the contents of which are herein incorporated by reference.

#An improvement on the catalyst system for the production of butyl rubber containing <2.5 mol % isoprene was presented by Gronowski (U.S. Pat. No. 6,403,747) wherein a dialkylaluminum is reacted with a minor component of diethylaluminum and small quantities of water or other additives. The improvements presented in Gronowski allow for the production of a more uniform catalyst with improved activity for the production of butyl rubber. Such advancements can be applied to the present invention.

#In order that the invention may be more clearly understood, embodiments thereof will now be described in detail by way of example, with reference to the accompanying drawings, in which:

#FIG. 1 depicts a gel permeation chromatogram (GPC) illustrating the effect of reaction time of diisobutylene (DIB) chain transfer agent on the production of a low molecular weight fraction in the solution co-polymerization of isobutylene and isoprene, where the chain transfer agent was added 30 minutes after initiation of the co-polymerization;

#FIG. 2 depicts a graph showing the effect of DIB reaction time on the amount of low molecular weight fraction produced in the solution co-polymerization of isobutylene and isoprene, where the DIB was added 30 minutes after initiation of the co-polymerization;

#In this specification including the claims, the use of the article “a”, “an”, or “the” in reference to an item is not intended to exclude the possibility of including a plurality of the item in some embodiments. It will be apparent to one skilled in the art in at least some instances in this specification including the attached claims that it would be possible to include a plurality of the item in at least some embodiments.

#The polyisoolefin-based polymer composition has a multimodal molecular weight distribution. There is a low molecular weight fraction having a peak molecular weight (Mp) of less than about 100,000 g/mol and a high molecular weight fraction having a peak molecular weight (Mp) of greater than about 250,000 g/mol. The low molecular weight fraction is present in the composition in an amount less than the high molecular weight fraction, thus the high molecular weight fraction is present in greater amount than the low molecular weight fraction. While the polymer composition comprises at least two distinct molecular weight peaks (Mp), there may be three, four, five or more distinct molecular weight peaks. In one embodiment, the polymer composition has a bimodal molecular weight distribution exhibiting two molecular weight peaks.

#The amount of the low molecular weight fraction in the polymer composition may be less than about 50 wt % based on total weight of polymer, for example, no more than about 45 wt %, no more than about 40 wt %, no more than about 35 wt %, no more than about 30 wt %, no more than about 25 wt % or no more than about 20 wt %. The amount of the low molecular weight fraction in the polymer composition may be at least about 5 wt % based on total weight of polymer, for example, at least about 10 wt %, at least about 15 wt %, at least about 20 wt %, at least about 25 wt %, at least about 30 wt %, at least about 35 wt %, at least about 40 wt % or at least about 45 wt %, provided the amount of the low molecular weight fraction is less than the amount of the high molecular weight fraction. In various embodiments, the amount of the low molecular weight fraction may be within any combination of the limits expressed above. A particularly preferred range is 15-25 wt %. The Mp of the low molecular weight fraction is less than about 100,000 g/mol. In some embodiments, the Mp may be within a range of about 10,000 g/mol to about 100,000 g/mol, or about 25,000 g/mol to about 100,000 g/mol, or about 50,000 g/mol to about 100,000 g/mol.