NEODYMIUM CATALYST FOR DIENE POLYMERIZATION Adel F. Halasa Bill W.L. HsuMichael J. Gintert The Goodyear Tire & Rubber Co. Presented at the Fall 172nd Technical Meeting of the Rubber Division, American Chemical Society Cleveland, OH October 16-18, 2007 Paper # 53

2 Background Natural vs. Synthetic Rubber Courtesy of P. Sandstrom, J. Verthe, R. Beers

3 Polymer T g near -70°C Narrow MW distribution Processes well in compounding Butadiene based to take advantage of monomer availability and cost Competitive to lower cost than NR Ideal Polymer to Replace NR Background Courtesy of P. Sandstrom, J. Verthe, R. Beers

4 Background The first report on the use of rare Earth metals as catalysts for polymerization was done at Goodyear by T. Morten using cerium metal carboxylate. More recently, much research has been done exploring the use of a Neodymium catalyst system for butadiene polymerization. The literature contains a large amount of work on the homo- polymerization of butadiene in bulk and in solution. Italian based Eni-Chem (Now Polymeri Europa) performed the pioneering research in this field

5 Background Most research published in this field focused on development of poly- butadiene (PBD) which will process easily in a production plant, as well as deliver improved tread-wear properties in tire tread compounds. Research at Goodyear in the early 1980’s made use of the Neodymium catalyst system for polymerization of polyisoprene homo-polymer (Homo-PI) as well as its block tapered and random co-polymers with butadiene rubber (IBR) Alkyl aluminum halide was used as a co-catalyst and gel preventative

6 Preformed catalyst Bell/Halasa developed the preformed catalyst system for making PI that possessed improved green strength over that made by the traditional titanium catalyst. The preformed catalyst was made by adding Neodymium versetate/Tibal/dibalCl/Alcohol and then heated to 70°C for 30 minutes. After this, it was ready to use. The alcohols used as the co-agent were triphenyl silanol or n-butanol.

7 Catalyst System: 1.Neodymium Versetate was alkylated with tri-isobutyl aluminum/di-isobutylalumium chloride and modified with di-isobutylaluminum hydride as molecular weight controls the presence of Butanol in a ratio of Nd(1) / R 3 Al(30) / R 2 AlCl(2) / BuOH(2) 2.This mixture was heated to 70°C for 30 min. 3.This preformed catalyst was used to homo-polymerize conjugated diene The preformed catalyst system was prepared in the following manner:

8 Neodymium Versetate alkylated with tri-isobutyl aluminum/di-isobutylalumium chloride and modified with di-isobutylaluminum hydride 1.PBD was difficult to process 2.Variation in molecular weight was easy to control 3.Observed an increase in the 3,4-and 1,2- contents This system was implemented in the Pilot Plant in a continuous process on a larger scale Results:

9 Preformed catalyst The PI made by this catalyst system resulted in a compound having much higher green strength over those made using the Titanium catalyst. However, properties were still not equal to those of Natural Rubber (NR). The research was continued at Goodyear to develop an improved Neodymium (Nd) catalyst system to polymerize PI worthy to be used as a total or partial replacement for NR. This is the subject of our talk today.

10 Examine the effect of preformed Neodymium-TriOctyl Aluminum (Nd-TNOA) catalyst system on the polymerization characteristics and resultant properties of Isoprene-butadiene Rubber and Polyisoprene, in both the virgin and compounded state. Objective:

11 1:10:2 Nd : TNOA : t-BuCl (alkylated Neodymium) (trioctyl aluminum) (tertiary-butylchloride) 1.5 mmol Nd catalyst for every 100g polymer. Catalyst System:

12  Temperature controlled, one-gallon glass bowl reactor  Reactor charged with appropriate amount of monomer premix to synthesize the desired polymers  Alkylated Nd added first, followed by t-BuCl  10mL of a 2% Isobutylene solution, an agent to prevent gel  Ingredients added at room temp., Reactor then heated to and maintained at 90  C  Samples taken periodically to check for % conversion  Reactions were short-stopped with denatured ethanol, and 2,6 - ditertbutylphenol  Polymer dried for several days in a hot oven to ensure evaporation of solvent Polymerization:

13 Series 1: 10/90 IBR; 1.5mmol/100g Polymer; Varying Temperature With Increasing Temperature:  Time to 90% Conversion is shorter  Molecular Weight is lower  Tg remains constant  Cis content increases, and 1,2-Bd decreases.

14 Series 2: (10/90) IBR 1.5mmol/100g Polymer; 90°C; Varying Monomer Ratio With Increasing Isoprene content:  Time to 90% Conversion is shorter  Molecular Weight is lower  Mooney Viscosity is lower  Tg is higher  As Ip/Bd ratio increases, 3,4-I content increases, which would be expected because more Isoprene is present. There is really no trend in Cis or 1,2-Bd content. MW TgTg Viscosity % Isoprene

15 Series 3: PI; 0.22mmol/100g Polymer; Varying Temperature With Decreasing Temperature:  Higher molecular weight polymers are produced  Time to full conversion is increased  3,4-I content increases, while there is no distinct trend in Cis content.

16 Series 4: PI; Varying Amount of Preformed Catalyst at 90°C Series 5: PI; Varying Amount of Preformed Catalyst at 75°C Series 4 and 5 behaved similarly, such that: With Decreasing Catalyst Level:  Time to 90% Conversion is longer  Molecular Weight is higher  Mooney Viscosity is only slightly higher  Tg remains constant Contrasting Series 4 and 5: At Lower Temperature:  Time to 90% Conversion is Longer  Molecular Weight is slightly higher  Mooney Viscosity is only slightly Higher  Tg remains constant Changing the catalyst concentration has no significant effect on Cis or 3,4-I content, regardless of the reaction temperature. Time to 90% Conversion (min) Molecular Weight Viscosity Catalyst Level (mmol)

17 Series 6: PI; Nd-based Catalyst System – Replacing Chloride with Iodide and Bromide – Varying catalyst level; Reaction Temp. 90°C When Bromide is used:  The reaction took approx. 20% longer to reach full (90%) conversion than did the Chloride system  Molecular Weight is relatively low, resulting in high polydispersity  Tg is still normal for PI  Reduces Cis content, while at the same time increasing 3,4-I content significantly. When Iodide is used:  The reaction never reached full (90%) conversion  Molecular Weight is significantly lower than those of the Chloride or Bromide systems, resulting in high polydispersity  Tg is still normal for PI  Reduces Cis content even further, and increases 3,4-I substantially as well.

18 Compounding: Five of the polyisoprene polymers selected - different catalyst levels and polymerization temperatures Compared to NATSYN Basic carbon-black tread rubber recipe The polymers chosen to be compounded, in correlation with their batch numbers, are shown as follows: Neodymium Polyisoprene vs. Titanium Polyisoprene

19 Tensile testing was conducted to compare stress / strain properties of the compounds: Compound Testing:

20 RPA testing was done to characterize the storage modulus and tangent delta properties of the compounds: Compound Testing: Examining RPA data, it is seen that increasing the catalyst level increases the uncured G’, and decreases Tangent Delta. All of the Nd PI’s had higher G’ values than NATSYN, and most had lower Tangent Deltas than NATSYN.

21 Discussion: The results of these experiments fell in line with what was expected. Reducing catalyst level produces higher molecular weight. Fewer reaction sites at the end of catalyst molecules, means fewer molecules are able to be formed. Available monomer continues to attach to active sites Results in higher molecular weight polymer molecules.

22 Discussion: Polyisoprene polymerizations: Reaction temperature had a similar effect on conversion time and molecular weight. Reducing temperature has the same effect as reducing catalyst level: longer conversion times and higher molecular weights. Which produces higher Mooney viscosity values as well.

23 Discussion: Polyisoprene Tg was relatively constant at approx. -64°C With many polymers, varying the reaction temperature often results in variations of the Tg. Similarly, no change with conditions was detected in Cis content, which held constant at approximately 95%. Only when the halogen component of the catalyst system was altered was a change in Cis content observed. Interesting to note:

24 Discussion : Isoprene/Butadiene polymers: Cis content is directly related to reaction temperature, but does not seem to be a function of Isoprene to Butadiene ratio. This catalyst is very stereo-specific for conjugated diene polymerization.

25 Discussion : Higher catalyst level increases ultimate stress and tan delta in the cured compound, while reducing uncured G’. Polyisoprene made by Nd catalyst polymerized gives practically identical stress/strain properties as Ti-PI, with higher G’ and much lower Tan Delta at both 75° and 90° polymerization temperature. Compound testing:

26 Conclusions : The Neodymium Catalyst system allows for: Easy control of molecular weight – due to homogeneous nature Can be stored indefinitely at any temperature without any changes in catalyst activities and behavior Alkylated Neodymium Versetate system can be activated with elemental halogens as well as a variety of halogen-containing compounds without the formation of gel and molecular weight control Change in polymer microstructure - Observed an increase in the 3,4- and 1,2 contents – with bromine and iodine Elemental chlorine and chlorine-containing compounds produce a higher molecular weight, higher cis-content, and more narrow molecular weight distribution than bromine and iodine-containing compounds.

27 Conclusions : Neodymium-catalyzed polyisoprene performed equally as well as Ti-PI in carbon-black-filled tread rubber compounds with respect to: The Neodymium Catalyst system allows for: Excellent polyisoprene compound properties Stress / Strain properties Higher Modulus / Lower Tan Delta Excellent Processabiliity

28 Conclusions : Overall: Neodymium catalyst system produced PI and IBR with good physical properties High green strength Desirable molecular weight Desirable Mooney Viscosity values Excellent compound properties

29 This catalyst system is very unique! Unlike any other Neodymium catalyst system in publication, this particular system can be alkylated (preformed) well before its use and stable on storage. It possesses a significant shelf life. When needed, the catalyst is simply added to the monomer, along with the appropriate chloride, and the desired polymer is easily attained. Conclusions : Most Importantly….

30 Thank you – The authors would like to thank: The Goodyear Tire and Rubber Co., and specifically Ken Bates, Kuo-Chih Hua, Laurie Austin, Chad Jasiunas, and Corey Yon for their contributions to this work.