FIELD

[001] The disclosure relates to selectively hydrogenated block copolymers and articles made thereof.

BACKGROUND

[002] Conventional styrenic block copolymers in the prior art exhibit desirable mechanical properties as required for certain applications, but difficult for processes such as molding, extrusion, 3D printing, and fiber spinning applications, and the like, due to their high viscosity. Therefore, it is a common practice to add substantial amounts of polyolefins, extending oils, tackifying resins and waxes and/or other processing aids to make these block copolymers low viscosity thereby improving their processability. However, additives often lead to inferior elastic properties and cause undesirable processing problems such as smoking and die build-up.

[003] On the other hand, even if some conventional styrenic block copolymers have low viscosity and improved processability, they neither exhibit required mechanical properties nor aid in the preparation of molded and extruded articles.

[004] Therefore, there is a need to produce styrenic block copolymers having a balance of low viscosity, improved elastic properties, and/or isotropic mechanical properties.

SUMMARY

[005] In one aspect, a selectively hydrogenated styrenic block copolymer is disclosed. The block copolymer has an S block and an Ei block, and a general formula: (S-Ei) _n X, wherein “n" has a value of 2 to 6, X is a coupling agent residue, molecular weight of the S block is 3,500 to 5,600 g/mol, a solution viscosity of the block copolymer is less than 80 centipoise (cP), and a polystyrene content in the block copolymer is 20 to 40 wt. %. The block copolymer has up to 70 wt. % of diblock units of formula S-Ei _. wherein prior to hydrogenation, the S block is a polystyrene block, the Ei block is a polydiene block selected from the group consisting of polybutadiene, polyisoprene and mixtures thereof, and having a molecular weight of from greater than 13,000 to 18,000 g/mol, and a total vinyl content of the polydiene block is 60 to 85 mol%. Subsequent to hydrogenation, 0-10 percent of styrene double bonds in the block copolymer are reduced, and at least 80 percent of conjugated diene double bonds in the block copolymer are reduced.

[006] In another aspect, the present disclosure relates to an article made from the composition as described above. The article is selected from toys, medical devices, films, tubing, profiles, 3D printed article, sheet, coating, band, strip, molding, tube, foam, tape, fabric, thread, filament, ribbon, fibers, fibrous web, overmolded automotive parts, dipped goods, sheet molded articles, hot melt adhesives, tie-layers, roofing sheets, membranes, tire treads, and tire inner layers, and tires.

[007] In yet another aspect, the article is made by direct extrusion, capable of being used alone, or in a laminate structure with a plurality of other layers. In yet another aspect, the article is a flexible part prepared by any of injection molding, slush molding, rotational molding, compression molding, and dipping.

BRIEF DESCRIPTION OF FIGURES

[008] FIG l is a plot showing the dependence of complex viscosity across the Order- Disorder Transition Temperature (ODT) range for the block copolymer of Example 3 measured at 0.005 hertz and 0.2 hertz.

DESCRIPTION

[009] The following terms will have the following meanings unless otherwise indicated.

[010] “Vinyl content” refers to the content of a conjugated diene that is polymerized via 1,2-addition in the case of butadiene, or via both 1,2-addition and 3,4-addition in case of isoprene.

[011] “Polystyrene content” or PSC of a block copolymer refers to the % weight of polymerized styrene in the block copolymer, calculated by dividing the sum of molecular weight of all polystyrene blocks by the total molecular weight of the block copolymer. PSC can be determined using any suitable methodology such as proton nuclear magnetic resonance (NMR).

[012] Polymer molecular weights can be measured with gel permeation chromatography (GPC) using polystyrene calibration standards, such as is done according to ASTM 5296-19. The chromatograph is calibrated using commercially available polystyrene molecular weight standards. The molecular weight of polymers measured using GPC so calibrated are styrene equivalent molecular weights. The styrene equivalent molecular weight may be converted to true molecular weight when the styrene content of the polymer and the vinyl content of the diene segments are known. The detector can be a combination ultraviolet and refractive index detector. The molecular weights expressed herein are measured at the peak of the GPC trace, converted to true molecular weights, and are commonly referred to as “peak molecular weights”, designated as Mp. Unless converted to true molecular weights, as described above, the molecular weights refer to the styrene equivalent peak molecular weights. Unless specified otherwise, all of the reported molecular weights are true molecular weights.

[013] The order-disorder-transition temperature (ODT) refers to the temperature at which the microdomain structure of the block copolymer begins to disappear. ODT is defined as the temperature above which a zero shear viscosity can be measured by dynamic rheology. ODT temperatures can be measured using dynamic mechanical analysis (DMA), with temperature sweeps performed over various frequencies, wherein the ODT is identified as the temperature where complex viscosity begins to collapse to a single value independent of frequency at low frequencies

[014] “Melt index” is a measure of the melt flow of the polymer, measured according to ASTM D1238 at 190°C and 2.16 kg weight, expressed in units of grams of polymer passing through a melt rheometer orifice in 10 minutes.

[015] ASTM D412 refers to the test method to determine the tensile properties of thermoplastic elastomers and vulcanized thermoset rubbers. A dumbbell and straight section specimens or cut ring specimens can be used. For the tests, a Mini D die with a dumbbell central width of 0.1 inch and the length of the narrow parallel sided central portion of 0.5 inch is used to cut the specimens and a 50 mm/min. tensile rate is used.

[016] Block copolymer composition: In one embodiment, the composition comprises a selectively hydrogenated coupled block copolymer having an S block and Ei block and having the general formula: (S-Ei) _n X, where “n” can be from 2 to 6, or from 2 to 4, or 2. In one embodiment, the coupled block copolymer of formula (S-Ei) _n X has between 5 and 50 wt. %, or between 5 and 40 wt. % of diblock copolymer units of formula (S-Ei).

[017] Prior to hydrogenation, the S block of the block copolymers can be a polystyrene block having a molecular weight from 4,400 to 5,600 g/mol, alternately from 4,000 to 5,000 g/mol. [018] Prior to hydrogenation, the Ei block is a polydiene block selected from the group consisting of polybutadiene, polyisoprene and mixtures thereof. In one embodiment, the Ei block is a polydiene block having a molecular weight range of from greater than 13,000 g/mol to 18,000 g/mol, alternately from 15,000 to 17,000. The coupled block copolymer can have a general formula, e.g., S-Ei - X - Ei-S or (S-E _I ) ₃ X, wherein the Ei block is a polydiene block, selected from the group consisting of polybutadiene, polyisoprene and mixtures thereof, having a molecular weight of from greater than 13,000 to 18,000 g/mol; and X is a coupling residue of an alkoxy silane coupling agent.

[019] The block copolymer can be prepared by reacting an anionically charged diblock polymer chain of formula (S-Ei) with a coupling agent that is at least difunctional. A linear coupled block copolymer is made by forming the first S block and E block and then contacting the diblock (S-Ei) with a difunctional coupling agent. Methyl benzoate is an example of a difunctional coupling agent. A radial block copolymer can be prepared by using a coupling agent that is at least trifunctional. Useful coupling agents for forming radial block copolymers include, for example, silicon tetrachloride, alkoxy silanes, polyepoxides, polyisocyanates, polyimines, polyaldehydes, polyketones, polyanhydrides, polyesters, polyhalides, diesters, methoxy silanes, divinyl benzene, 1,3,5-benzenetricarboxylic acid trichloride, glycidoxytrimethoxy silanes, and oxydipropylbis(trimethoxy silane).

[020] In one embodiment, the coupling agent is an alkoxy silane of the general formula Rx — Si — (OR') _y , where x=0, 1 or 2, and x+y=4, R and R' are the same or different, R is selected from the group consisting of aryl hydrocarbon radicals, linear alkyl hydrocarbon radicals and branched alkyl hydrocarbon radicals, and R' is selected from linear and branched alkyl hydrocarbon radicals. The aryl radicals preferably have from 6 to 12 carbon atoms. The alkyl radicals preferably have 1 to 12 carbon atoms, more preferably from 1 to 4 carbon atoms. Under melt conditions, these alkoxy silane coupling agents can couple further to yield functionalities greater than 3. Examples of trialkoxy silanes include methyl trimethoxy silane (“MTMS”), methyl triethoxy silane (“MTES”), isobutyl trimethoxy silane (“IBTMO”) and phenyl trimethoxy silane (“PhTMO”). Preferred dialkoxy silanes are dimethyl dimethoxy silane (“DMDMS”), dimethyl diethoxy silane (“DMDES”) and methyl diethoxy silane (“MDES”).

[021] Block copolymer preparation: The block copolymers can be prepared by anionic polymerization of styrene and a diene selected butadiene, isoprene and mixtures thereof. The polymerization is accomplished by contacting the styrene and diene monomers with an organoalkali metal compound in a suitable solvent at a temperature from -150°C to 300°C, preferably from 0°C to 100°C. Examples of anionic polymerization initiators include organolithium compounds having the general formula RLi _n where R is an aliphatic, cycloaliphatic, aromatic, or alkyl -substituted aromatic hydrocarbon radical having from 1 to 20 carbon atoms; and n has a value from 1 to 4. Preferred initiators include n-butyl lithium and sec- butyl lithium. Methods for anionic polymerization known in the art can be used to obtain the block copolymers.

[022] In an embodiment, a coupled block copolymer is made by forming the first S block and Ei block and then contacting the diblock with a difunctional or trifunctional coupling agent. The process comprises a coupling reaction between a living polymer having the formula S-Ei — Li and the coupling agent as defined above, wherein Li is lithium.

[023] The quantity of coupling agent employed with respect to the quantity of living polymers S-Ei — Li present depends largely upon the degree of coupling and the properties of the coupled polymers desired. Preferably, the coupling agent is used in an amount from 0.35 to 0.7 moles of coupling agent per mole of lithium, S-Ei-Li; or from 0.4 to 0.55 moles of coupling agent based upon the moles of lithium; or most preferably 0.45 moles of coupling agent per mole of lithium.

[024] The temperature at which the coupling reaction is carried out can vary over a broad range and often is the same as the polymerization temperature, e.g., from 0° to 150°C., from 30°C. to 100°C., or from 55°C. to 80°C.

[025] The coupling reaction is normally carried out by simply mixing the coupling agent, neat, or as a solution in a suitable solvent, with the living polymer solution. The reaction period can be quite short, and affected by the mixing rate in the reactor, e.g., from 1 minute to 1 hour. Longer coupling periods may be required at lower temperatures.

[026] After the coupling reaction, the coupled polymers may be recovered, or subjected to a selective hydrogenation of the polymerized diene units of the polymer. Hydrogenation generally improves thermal stability, ultraviolet light stability, oxidative stability, and weatherability of the final polymer.

[027] Hydrogenation of block copolymer: In one embodiment, the block copolymer is a hydrogenated block copolymer. The block copolymers can be selectively hydrogenated using processes known in the art. Any hydrogenation method that is selective for the double bonds in the conjugated polydiene blocks, leaving the aromatic unsaturation in the polystyrene blocks substantially intact, such as for example, reduction of up to 10 mol % of the aromatic unsaturation, can be used to prepare the hydrogenated block copolymers.

[028] In one embodiment, the method employs a catalyst or catalyst precursor comprising a metal, e.g., nickel or cobalt, and a suitable reducing agent such as an aluminum alkyl. Also useful are titanium based systems. The hydrogenation can be accomplished in a solvent at a temperature from 20°C to 100°C, and at a hydrogen partial pressure from 100 psig (689 kPa) to 5,000 psig (34,473 kPa). Catalyst concentrations within the range from 10 ppm to 500 ppm by wt. of iron group metal based on total solution are generally used. The reaction time can vary from 60 to 240 minutes. After the hydrogenation is completed, the catalyst and catalyst residue can be separated from the polymer.

[029] The microstructure in the Ei blocks can be controlled to achieve a desired degree of pendant vinyl groups in the polymerized diene units. This can be achieved during the polymerization of the diene by using a control agent, such as those known in the art, e.g., diethyl ether or diethoxypropane.

[030] Hydrogenation can be carried out under such conditions that at least 80 % of the conjugated diene double bonds are reduced, and up to 10 % of the arene double bonds are reduced.

[031] Using the above methods, block copolymers can be prepared having from 60 to 85 mol % of pendant vinyl groups in the Ei blocks, prior to hydrogenation.

[032] The styrene content of the block copolymer can be from 25 wt. % to 40 wt. %.

The coupling efficiency can be in the range of 50-95% in one embodiment, and at least 80% in another embodiment. In embodiments, subsequent to hydrogenation, from 0 to 10 percent of the styrene double bonds in the S blocks can be hydrogenated.

[033] Functionalization of block copolymer: In some embodiments, the hydrogenated block copolymer is functionalized to include an additional functional group or moiety.

Exemplary monomers to be grafted onto the block copolymers include fumaric acid, itaconic acid, citraconic acid, acrylic acid, maleic anhydride, itaconic anhydride, citraconic anhydride, and their derivatives. Maleic anhydride is a preferred grafting monomer. [034] Grafting with maleic anhydride provides a hydrogenated block copolymer having maleic anhydride groups grafted thereto. Maleation of the block copolymer may be done in the melt, in solution, or in the solid state. The process can be carried out batchwise or continuously. Various free radical initiators, including peroxides and azo compounds can be used to facilitate the maleation. In some embodiments, the block copolymer contains from 0.1 to 10, preferably 0.2 to 5 percent by weight of a grafted monomer.

[035] In one embodiment, the hydrogenated styrenic block copolymer is functionalized via reaction with maleic anhydride. Such functionalized polymers have additional polarity that makes them useful where adhesion to metals or other polar polymers is desired, such as in overmolding, tie layer, adhesive, and coating applications, or in compatibilization with certain engineering thermoplastics, such as for example, polyamides or epoxy resins.

[036] Optional Components: In applications, the block copolymer compositions can also be admixed with other optional components, such as block copolymers, olefin polymers, styrene polymers, tackifying resins, end block resins, engineering thermoplastic resins, or mixtures thereof.

[037] Styrene polymers include, for example, crystalline polystyrene, high impact polystyrene, medium impact polystyrene, styrene/acrylonitrile copolymers, styrene/acrylonitrile/butadiene (ABS) polymers, syndiotactic polystyrene and styrene/olefm copolymers. Other polymer examples include polyisobutylene polymers, substantially random ethyl ene/styrene or propyl ene/styrene copolymers, preferably containing at least 20 weight percent copolymerized styrene monomer; styrene-grafted polypropylene polymers; and other block copolymers such as styrene-diene-styrene triblock, radial or star block polymers, styrene- diene diblock polymers, and the hydrogenated versions of these polymers.

[038] Examples of engineering thermoplastic resins include thermoplastic polyester, thermoplastic polyurethane, poly(aryl ether), poly(aryl sulfone), acetal resin, polyamide, nitrile barrier resins, poly(methyl methacrylate), cyclic olefin copolymers, coumarone-indene resin, polyindene resin, poly(m ethyl indene) resin, polystyrene resin, vinyl toluene-alphamethylstyrene resin, alphamethylstyrene resin and polyphenylene ether, in particular poly(2, 6-dimethyl- 1,4- phenylene ether), and mixtures thereof.

[039] Suitable midblock compatible resins are C5 resins (based on cyclopentadiene, cyclopentene, DCPD, piperylene, etc), hydrogenated C5 resins, hydrogenated C5/C9 resins, hydrogenated C9 resins, terpene resins, rosin ester resins, hydrogenated rosin ester resins, or combinations thereof.

[040] In embodiments, the hydrogenated block copolymer is blended with a thermoplastic elastomer or a thermoplastic for use in tire tread formulation as a plasticizer.

[041] In embodiments, the optional polymer is an olefin polymer, e.g., ethylene homopolymers, ethylene/alpha-olefm copolymers, propylene homopolymers, propylene/alpha- olefin copolymers, high impact polypropylene, butylene homopolymers, butylene/alpha olefin copolymers, and other alpha olefin copolymers or interpolymers. In other embodiments, the polymer is selected from ethylene/acrylic acid (EAA) copolymers, ethylene/methacrylic acid (EMAA) ionomers, ethylene/vinyl acetate (EVA) copolymers, ethylene/vinyl alcohol (EVOH) copolymers, ethylene/cyclic olefin copolymers, polypropylene homopolymers and copolymers, propyl ene/styrene copolymers, ethylene/propylene copolymers, polybutylene, ethylene carbon monoxide interpolymers (for example, ethyl ene/carb on monoxide (ECO) copolymer, ethylene/acrylic acid/carbon monoxide terpolymer and the like.

[042] Additives: The block copolymer compositions are characterized as having low viscosities and high melt flows that allow them to be easily molded or continuously extruded into shapes or films, or spun into fibers. This property allows end users to avoid, or at least limit, the use of additives that degrade properties, cause area contamination, smoking, or even build-up on molds and dies. The hydrogenated block copolymers have such low ODTs and high melt indexes that they can be used to prepare articles without using processing aids. However, a processing aid can also be used, if desired. Other additives that can be used include polymer extending oils, waxes, fillers, reinforcements, lubricants, stabilizers, and mixtures thereof. In embodiments, the additives are selected from fillers and pigments. The filler can be one or more members selected from T1O2, CaC0 ₃ , and carbon black.

[043] In one embodiment, the hydrogenated block copolymer is blended with 0.001 to 10 wt. % of a mineral oil (paraffinic, naphthenic, or aromatic); or from 0.001 to 9 wt. %; 0.001 to 7.5 wt. %; and 0.001 to 5 wt. % of a mineral oil.

[044] Properties of block copolymer: One characteristic of the hydrogenated block copolymers is that they have a low order-disorder temperature (ODT), with the ODT being typically less than 180°C. For ODT above 180°C., the polymer may be more difficult to process in certain applications, although in certain instances, ODTs greater than 180°C. can be utilized for those applications., e.g., when the block copolymer is combined with other components to improve processing. Such other components may be thermoplastic polymers, oils, resins, waxes or the like. In embodiments, the ODT is from 140°C. to 180°C; or from 150°C. to 160°C; or less than 180°C. [045] In one embodiment, the hydrogenated block copolymers have a high melt index allowing for easier processing, with a melt index from 80 g/10 min. to 1,000 g/10 min at 190°C. and 2.16 kg weight. In other embodiments, the melt index can be from 200 g/10 min to 800 g/10 min, alternately from 400 g/10 min to 600 g/10 min.

[046] In embodiments, the hydrogenated block copolymer has a toluene solution viscosity (at 25 wt. % and 25°C) of greater than 10 cP, or less than 80 CP; or from 15 to 80 cP, or from 20 to 50 cP.

[047] In embodiments, the hydrogenated block copolymer has an elongation at break of at least 300%, or at least 450 %, or from 300% to 1000%, or from 400% to 800%.

[048] In embodiments, the hydrogenated block copolymer has a tensile strength of at least 1.5 MPa; or at least 2 MPa, or at least 3.5 MPa; or 5 MPa or less, or 1.5 - 5 MPa, or 2 - 4

MPa, as measured on compression molded films according to ASTM D412.

[049] In embodiments, the hydrogenated block copolymers have a hysteresis recovery of greater than 35 percent and a permanent set of less than 35 percent on the first retraction cycle after elongation to 300 percent. [050] The block copolymers also exhibit a marked decrease in viscosity, such as complex viscosity, over the order - disorder transition temperature range. This can be studied by measuring the complex viscosity of the polymer as a function of temperature. In embodiments, the block copolymer has a rate of decrease in complex viscosity as a function of order - disorder transition temperature of from 500 Pa-s/°C to 1400 Pa-s/°C at 0.005 hz, alternately from 600 - 1200 Pa-s/°C at 0.005 hz, alternately from 700 - 1100 Pa-s/°C at 0.005 hz, alternately from 800 -

1000 Pa-s/°C at 0.005 hz. For example, the complex viscosity of Example 3 block copolymer drops at least two orders of magnitude (~ 1100 Pa-s/°C at 0.005 hz) over the ODT range, as can be seen in Figure 1.

[051] Industrial applicability: The hydrogenated block copolymers are useful in a wide variety of applications either as a neat polymer or in a compound. Examples include, for example, toys, medical devices, films, tubing, profiles, 3D printed article, sheet, coating, band, strip, molding, tube, foam, tape, fabric, thread, filament, ribbon, fiber, plurality of fibers and fibrous web, overmolding applications for automotive parts, dipped goods such as gloves, thermoset applications such as in sheet molding compounds or bulk molding compounds for trays, hot melt adhesives, tie-layer for functionalized polymers, asphalt formulations, roofing sheets, geomembrane applications. The article can be formed by processes known in the art, such as injection molding, overmolding, dipping, extrusion, roto-molding, slush molding, fiber spinning, film making, 3D printing and foaming. In embodiments, the hydrogenated block copolymers are added to rubber compositions for making tire treads or inner layers.

[052] In embodiments, the hydrogenated block copolymers are for use in making web layers for the construction of an adsorbent personal hygiene product such as a baby diaper article, adult incontinence article, or feminine napkin article. In applications such as melt blown articles, the composition may contain an additional component of a high flow polyolefin having a melt flow rate of >40 g/10 min., polyisobutylene, polybutene, thermoplastic polyurethane, thermoplastic copolyester, oil, styrenic block copolymer with melt flow rate <100 g/10 min., and/or mid-block or end block resin.

[053] In embodiments, the hydrogenated block copolymers are used as an additive, e.g., as a plasticizer, to thermoplastic compositions or thermoplastic elastomers in amount ranging from 0.1 to 90 wt.%; or from 0.5 to 70 wt% , or 1 to 50 wt. %, or 5-35 wt. % based on the total weight of the thermoplastic or thermoplastic elastomer composition.

[054] In embodiments, the hydrogenated block copolymers are for use in adhesive formulations, e.g., a personal hygiene construction adhesive, elastic attachment adhesive, and hot-melt adhesive. The formulations could comprise a blend such as 0 to 80 wt. % poly-alpha- olefin, 10 to 60 wt. of a tackifying resin, and 10 to 50 wt. % of the hydrogenated block copolymer. Examples of tackifying resins include C5 resin (cyclopentadiene, cyclopentene, DCPD, piperylene, etc based resin .), hydrogenated C5 resin, hydrogenated C5/C9 resins, hydrogenated C9 resins, terpene resin, rosin ester resin, hydrogenated rosin ester resins, or combinations thereof

[055] EXAMPLES: The following examples are provided to illustrate the disclosure.

[056] Example 1: A selectively hydrogenated block copolymer is prepared by anionic polymerization of styrene and then butadiene in the presence of a microstructure control agent followed by coupling and then hydrogenation: a diblock polymer anion, S-Ei-Li, is prepared by charging 6 L of cyclohexane and 321 g, of styrene to a reactor. The reactor temperature was increased to 50 °C. 198 ml of a solution of an approximately 12 % wt solution of s-butyllithium in cyclohexane was added, and the styrene was allowed to complete polymerization at 60 °C.

The molecular weight of the polystyrene produced in this reaction was determined to be 4,900 by GPC. 10 ml. of 1,2 - diethoxypropane was added, followed by 638 g of butadiene at rates to allow the temperature to remain at 60 °C. A sample collected at the end of the butadiene polymerization had a styrene content of 35 wt. % and a vinyl content of 76 % basis 'H NMR, and an overall molecular weight of 34,000 g/mol. After polymerization of the butadiene, 3.6 ml of DMDMS was added, and the coupling reaction was allowed to proceed for 60 minutes at 60°C. 2 ml of an alcohol was added to terminate the reaction. The final product had a coupling efficiency of 76 % and 100 % of the coupled species were linear.

[057] The polymer was hydrogenated to a residual olefin concentration of less than 0.15 meq/g and the catalyst was removed using techniques known in the art. The polymer was recovered via steam stripping. The selectively hydrogenated block copolymer was tested for polymer composition, solution viscosity, and ODT. The results are in Table 1. The selectively hydrogenated block copolymer was also tested for mechanical properties and melt index. The results are shown in Table 2.

[058] Example 2: . The polymer in Example 2 was made in a similar manner to Example 1, but with small differences in styrene, butadiene and DMDMS charges to allow for different styrene and butadiene block molecular weights and polymer coupling efficiency. Details are shown in Table 1.

[059] The selectively hydrogenated block copolymer was tested for composition, solution viscosity, and ODT. The results are shown in Table 1. The solution viscosity is slightly higher than Example 1 because the midblock molecular weight is higher than Example E However, the solution viscosity would be even higher if the coupling efficiency were not low compared to Example 1 (51 % versus 76 % in Example 1). The Example 2 copolymer was also tested for mechanical properties and melt index. The results are shown in Table 2. Example 2 block copolymer has a lower styrene block molecular weight and styrene concentration than Example 1. Consequently, the ODT, modulus and tensile strengths are lower than that for Example 1 block copolymer. [060] Example 3 and Example 4: . The polymers in Example 3 and 4 were made in a similar manner to Example 2, but with small differences in the DMDMS charges to increase the coupling efficiency relative to Example 2. Table 1 shows details regarding the composition, solution viscosity and ODT, and Table 2 shows the values for the mechanical properties and melt indexes.

[061] Examples 3 and 4, in comparison to Example 2, demonstrate the effect of higher coupling efficiency on viscosity (higher solution viscosity and lower melt flow); see Table 1 and 2. Likewise, higher coupling efficiency typically results in higher tensile strength; as seen from Table 2. [062] Examples 2-4 represent styrenic block copolymers with exceptionally low solution and melt viscosity, and ODTs, but surprisingly, still possessing reasonable modulus, tensile strength and elongation at break. When compared to two low molecular weight commercially available polymers (Examples 5 and 6) that were previously considered two of the lowest molecular weight and lowest viscosity styrenic block copolymers available, Examples 1 - 4 are considerably lower viscosity (see Tables 1 and 2; solution viscosity and melt index). Also, in Tables 1 and 2, one can see the effect of vinyl content on solution and melt index by comparing Example 2-4 to Example 6. A vinyl group effectively reduces the chain length, and consequently, the polymer viscosity; see the solution viscosity and melt index for Examples 2 - 4 (high vinyl) compared to Example 6 (38 % vinyl). In addition, high vinyl also reduces the number of chain entanglements usually resulting in lower tensile strength compared to an equivalent lower vinyl polymer; refer to the tensile strength for Examples 2-4 compared to Example 6. However, considering their low molecular weight and high vinyl, Examples 2-4 still demonstrate relatively high modulus, tensile strength and elongation to break. This is partly due to how strongly phase separated the hard polystyrene domains are from the rubbery mid-block domains after selective hydrogenation of the mid-block. Referring to the ODT for Example 3 in Figure 1, it can be seen there is at least a two order of magnitude drop in viscosity across the ODT at 0.005 hertz, indicating strong phase separation of the respective polymer blocks. Table 1. Polymer Composition, Solution Viscosity and ODT. PSC = polystyrene content.

Table 2. Mechanical Properties and Melt Index (MI).