Tin Coupled Polybutadiene for Low Hysteresis and Processability Applications Dr. Adel Halasa The Goodyear Tire & Rubber Company University Of Akron

Agenda n History and Background n Chemistry of coupling/uncoupling/interaction n Important Observations n Effects on Compound Properties n Acid Effects on Sn-polymers containing butadiene, isoprene and styrene

Background n Tin-coupled polymers are being produced to both improve processing and physical properties n Improvements in hysteresis are observed when tin-coupled polymers are used instead of non-functionalized polymers n Processing is improved by reduction in viscosity during processing n Further investigation into the exact nature of the “uncoupling” of the tin-coupled polymers during mixing needs to be addressed n The nature of the interaction with carbon black is also not well understood n A fundamental understanding of the chemistry involved would improve the ultimate utility of this technology

Anionic Polymerization n Advantages: Living –Molecular Weight (MW) & MW Distribution –Microstructure and Macrostructure –Architecture: Linear and Branched (Star) –Functionalization: Tin, amine, hydroxyl –Block Copolymers n Monomer Selections: –Butadiene, Isoprene, Styrene and  -Methylstyrene

Coupling Reaction n Anionic Polymerization is a unique method of making star and highly branched polymers. n Star polymers reduce cold flow. n Star and branched polymers behave differently than their linear counterparts in extrusion milling and processing.

Early History: 1970’s &1980’s n Phillips Petroleum and Firestone n Coupling Agents: Halides and di-functional –Silicon tetrachloride –Tin tetrachloride –Divinylbenzene (DVB) –Combination of DVB and silicon tetrachloride n Processible high MW, branched polymers for tire application

Tin-Containing Polymers (1) n JSR in the early 1980’s n Re-investigation of tin tetrachloride as coupling agents –Star polymers –Better filler-polymer interaction –Improving processibility

Tin-Containing Polymers (2) n Firestone in the 1990’S –Trialkyltin lithium initiators: Bu 3 Sn-Li and others n Other Rubber Producers n Applicable to BR, IBR, SBR, SIR,SIBR by lithium chemistry

Utilization of Alkyltin Compounds (Roderic P. Quirk & Jin-Ping Zhou) n No Halide Containing Organotin Compounds: –Tetraallyltin(TAT), Tetravinyltin, Tetraphenyltin, etc. n Lithium-tin exchange reaction –Allyl and vinyl >> Phenyl >>>> Butyl. n Mixture of star-branched and linear polymers for TAT added either with monomer or postpolymerization n Reversible chain transfer agent for TAT in situ n Tin polymer bonds can be cleaved by acids

Linking and Redistribution Reactions n High linking efficiency of P-Li with SnCl 4 n In the presence of excess of P-Li, linked polymer can grow after more monomer addition n Redistribution of arms after addition of different MW P-Li to fully linked P 4 Sn n Transmetallation via penta coordinated lithium-tin ate complex

Chemistry of coupling/uncoupling/interaction n The coupling of polymer chains using tin tetrachloride is reasonably well understood n The terminal position of the polymer chains attached to the tin atom can be described as either allyl or benzyl groups, depending on the active chain end at the point of coupling

Chemistry of coupling/uncoupling/interaction n The uncoupling of the polymer chains from the tin atom is less well understood n Several different chemistries can be operating involving the tin- carbon bond: –transmetallation (not likely) –reactions with electrophiles –reactions with radicals –ene reactions n Each chemistry can lead to different results in the “uncoupling” reaction, specifically affecting the subsequent interaction with carbon black

Chemistry of coupling/uncoupling/interaction n Reactions with electrophiles (like acids) can result in uncoupling that leaves an “unfunctional” chain end Sn(CH=CH 2 ) RCOOH  Sn(OCOR) CH 2 =CH 2 n Reactions with radicals can lead to transfer of the polymer chains from the tin (possibly to other polymer chains), although the source of the initial radicals and “RX” is unclear

Chemistry of coupling/uncoupling/interaction n Ene reactions involving the tin-carbon bond are known, especially with active carbonyl groups

Chemistry of coupling/uncoupling/interaction n Investigations by Tsutsumi, Oshima and Sakikibara helped provide evidence for the reaction with the tin-functionalized polymer with some functional groups believed to be on the surface of carbon black

Chemistry of coupling/uncoupling/interaction n These chemistries demonstrate that different compounding routines should result in different products; – that is, “uncoupling” with acid should not provide end groups that interact differently than the main chain –reaction with carbon black without acid might result in direct coupling between the polymer chain and carbon black –control of competing chemistries may be a key component n The reactivity of the tin-carbon species depends on the carbon group attached; the following general order is based on a variety of chemistries involving organotin species: phenyl > vinyl > aryl > allyl ~ benzyl > alkyl

Important Observations (Tsutsumi, Oshima, Sakikibara) n Effectiveness of hysteresis drop depends on chain end functionality - butadienyl is more effective than styryl n Less hindered tin-carbon bonds are more effective in lowering hysteresis - presumed to be from more effective interaction with carbon black n End-functional tin is more effective than main chain tin for hysteresis drop n Molecular weight of the polymer functionalized with tin needs to be greater than 10 5 to be effective in hysteresis drop n The decrease in hysteresis observed is attributed to good carbon black dispersion (“Payne Effect”) and not “bound rubber” n Cleavage of tin-carbon bonds with acid prior to mixing with carbon black results in no hysteresis improvement

Important Observations n Breakdown in polymer structure with stearic acid was noted by GPC n Noted Payne Effect and carbon black dispersion results; also examined effect of styrene chain ends n Mixing effect studied; observed improved processing and importance of correct staging n Evaluated molecular weights and coupling levels for processability and properties n Examined tin-coupling and end-capping; observed improved processing and physical properties n Compared Sn-IBR versus linear IBR; noted improved processing and some improved physical properties

Chemistry Conclusions n There appears to be a competition between acids (stearic, etc.) and the carbon black for reaction with the tin-coupled polymers; the stearic acid uncouples to produce a relatively non-interactive species while the carbon black produces a specific interaction (chemical bond?) n Higher levels of tin (end-capped versus tin-coupled) produce more interaction with the carbon black; steric hindrance may limit the effectiveness of coupled polymers interacting with carbon black n Addition of acid (stearic) may begin uncoupling (reducing steric hindrance) allowing more effective interaction with carbon black n All proof of chemical bonding to carbon black is indirect n The kinetics of the “uncoupling” process is not delineated in the literature

Compound Properties n US Patent 6,271,317: Asymmetrical Tin- Coupled Rubbery Polymers and Methods of Making n Illustrates compound data and how coupling affects overall properties. n Uses both batch and continuous data

Compound Properties

Acid Effects n Investigate butadiene, isoprene and styrene containing polymers n Viscosity of Sn polymers and filled compounds vs. acid level n Strain sweep: Tan Delta vs. Strain

Viscosity of Tin-Coupled Polymers vs. Acid Amount

Viscosity of Tin-Coupled Polymers w/C-B vs. Acid Amount (at 50 phr C-B)

PBd and Sn-PBd Compound Mooney (at 50 phr C-B)

Strain Sweep at 100  C and 11Hz (at 50 phr C-B)

IR and Sn-IR Compound Mooney (at 50 phr C-B)

Strain Sweep at 100  C and 11Hz (at 50 phr C-B)

Compound Properties at 50% Strain, 1 Hz and 100°C (at 50 phr C-B)

Summary Conditions needed to break tin-carbon bonds by mixing: In the cases with no carbon black, up to one phr acid is needed. In the cases with carbon black:  no acid is needed for tin-butadiene  half phr acid is needed for tin-styrene or tin- isoprene

Acknowledgements n Don Burlett n Yi Feng n Chuck Pearson n Bill Hsu n Jin - Ping Zhou n Chad Jasiunas