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Pressure-sensitive adhesives represent one of the most important commercial applications of block copolymers. The large-strain tensile properties of these soft adhesive materials play a dominant role in determining their adhesive properties. In many cases changes in the polymer architecture significantly affect the large-strain properties and the resultant adhesive performance, with little or no effect on the linear viscoelastic properties. In this Perspective we provide several examples, using model systems based on diblock, triblock, tetrablock, and star-block copolymers of polystyrene and polyisoprene.

General methods. All manipulations of air-and/or water-sensitive compounds were carried out under dry nitrogen using a Braun UniLab drybox or standard Schlenk techniques.1 H NMR spectra were recorded using either a Varian Mercury (300 MHz) or Varian Inova (500 MHz) spectrometer. 13 C NMR spectra were recorded on a Varian Inova (500 MHz) spectrometer equipped with a 1H/BB switchable with Z-pulse field gradient probe and referenced versus residual non-deuterated solvent shifts. Mass spectrometry analyses were performed by the School of Chemical Sciences Mass Spectrometry Laboratory at the University of Illinois at Urbana-Champaign. Elemental analyses were performed by Robertson Microlit Laboratories, Inc. Madison, New Jersey. The LDI mass spectrum was recorded using a Waters MALDI Micro MX system. The sample was prepared by using the dried droplet method with no matrix present. Ionization was by a 257 nm UV nitrogen laser and the accelerating potential was 17.2 keV. The spectrum was recorded using the reflectron in positive ion mode.Materials. Toluene and hexanes were purified over columns of alumina and copper (Q5). Methylene chloride and THF were purified over an alumina column and degassed by three freeze-pump-thaw cycles before use. Methylmagnesium bromide (3.0 M in Et 2 O) (Aldrich), 3,5-dimethylbenzoate (Alfa Aesar), 1-naphthoicacid methyl ester (TCI), zinc dust (Aldrich), diiodomethane (Aldrich), titanium(IV) chloride (Aldrich, 1.0 M in CH 2 Cl 2 ), 3',4'dimethylacetophenone (Avocado), 6-acetyl-1,2,3,4-tetrahydronaphthalene (Alfa Aesar), 2,6di-tert-butyl-4-methylphenol (BHT) (Aldrich), P 2 O 5 (Aldrich), α-methylstyrene (Aldrich), 2iso-propenylnaphthalene (TCI), acenaphthenequinone (Alfa Aesar), formic acid, acetic acid, p-toluenesulfonic acid, p-toluidine (Acros), CF 3 SO 3 H (Aldrich) and (dimethoxyethane)NiBr 2 ((DME)NiBr 2 , Aldrich) were used without further purification. . MeMgBr (3.0 M in Et 2 O, 19.7 mL, 59.2 mmol) was slowly added to a 0 °C solution of methyl 3,5-dimethylbenzoate (3.89 g, 23.7 mmol) in S3 40 mL THF, under N 2 . The resulting solution was allowed to warm to room temperature. After 4.5 hours, the reaction mixture was cooled to 0 °C and saturated NH 4 Cl(aq) was added. To dissolve the inorganic byproduct, 2 M HCl(aq) was carefully added to the resulting suspension. The mixture was extracted three times with diethyl ether and the organic layer was washed successively with water, saturated NaHCO 3 (aq) and brine and then dried over MgSO 4 . Volatiles were removed in vacuo to yield a yellow liquid. (2.82 g, 72.4% yield). 2-(3,5-Dimethylphenyl)propan-2-ol