As imple and high-yielding route to tough polyarylenes of the type poly(meta,meta,para-phenylene) (PmmpP) is developed. PmmpP is tough even in its as-synthesized state which has an intermediate molar mass of M w % 60 kg mol À1 and exhibits outstanding mechanical properties at further optimized molecular weight of M w = 96 kg mol À1 ,E= 0.9 GPa, e = 300 %. Statistical copolymers with para,para-spiropyran (SP) are mechanochromic, and the toughness allows mechanochromism to be investigated. Strained samples instantaneously lose color upon force release.D FT calculations showt his phenomenon to be caused by the PmmpP matrix that allows build-up of sufficiently large forces to be transduced to SP,and the relatively unstable corresponding merocyanine (MC) form arising from the aromatic co-monomer.M Cu nits covalently incorporated into PmmpP show adrastically reduced half life time of 3.1 scompared to 4.5 hobtained for SP derivatives with common 6-nitro substitution.Polyarylenes have intrigued material scientists since the invention of transition-metal-catalyzed cross-coupling reactions. [1,2] In 2007, Schlüter et al. introduced ah igh molecular weight (MW) poly(meta,para-phenylene) (PmpP) by careful selection of catalyst, solvent mixture,c oncentration, and temperature. [3] In their pioneering work ac rude polymer of M w = 83 kg mol À1 was synthesized and the molecular weight further increased to M w = 255 kg mol À1 by fractionation. After fractionation, this material showed at oughness close to that of aromatic polycarbonates (E = 1GPa, e = 122 %). This was aremarkable feat both from asynthetic as well as amaterials science point of view,b ecause polyarylenes are inherently chemically more stable than polycarbonates as aresult of the exclusive presence of aryl-aryl bonds in the backbone. Subsequently,S chlüter et al. investigated various kinked polyarylenes,w ith some of them exhibiting toughness at high molecular weight after fractionation. [3][4][5][6][7] Our interest in tough polyarylenes stems from their potentially ideal use as stable,tough yet amorphous matrices for covalent incorporation of mechanochromic dyes,s uch as spiropyrans (SPs). [8][9][10] SPs isomerize to their colored merocyanine (MC) form under an umber of external stimuli, including force,and can therefore be used as mechanical force sensors. [11][12][13][14][15] Compared to matrix polymers used so far in combination with covalently linked SPs,t ough polyarylenes have several distinct advantages.T heir toughness allows drawing samples and thus to transduce mechanical force to SP.A lso,t hey are typically amorphous,h ence mechanochromism can be investigated within an isotropic matrix which is not possible with semi-crystalline polymers.H erein we show that the nature and high strength of polyarylenes is of striking additional advantage in that high forces can be transduced to SP co-monomers.We found existing methods for kinked polyarylene synthesis to be cumbersome,expensive,and inefficient owing to significant loss of polymer during fractionation. ...

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Suzuki-Miyaura polycondensation (SPC) is widely used to prepare a variety of copolymers for a broad range of applications. Although SPC protocols are often used in many instances, the limits of this method and issues of molecular weight reproducibility are not often looked at in detail. By using a spiropyran-based (SP) mechanochromic copolymer, we present an optimized protocol for the microwave-assisted synthesis of a mechanochromic, alternating copolymer P(SP-alt-C-10) via SPC that allows the reproduction of molecular weight distributions. Several parameters such as microwave power, temperature, stoichiometry, and ligand are screened, leading to molecular weights up to M-w similar to 174 kg mol(-1). The process of optimization is guided by NMR end group analysis which shows that dehalogenation, oxidative deborylation and SP cleavage are the limiting factors that impede further increase of molar mass, while other classical side reactions such as protiodeborylation are not observed. Embossing films of P(SP-alt-C-10) yields the colored merocyanine (MC) copolymer P(MC-alt-C-10) that undergoes a thermally facilitated back reaction to P(SP-alt-C-10). DFT suggests that the barrier of the SP -> MC transition has two contributions, with the first one being related to the color change and the second one to internal bond reorganizations. The barrier height is 1.5 eV, which suggests that the ease of the thermally facilitated back reaction is either due to residual energy stored in the deformed polymer matrix, or arises from an MC isomer that is not in the thermodynamically most stable state

The modification of molecular properties by the use of substituents is a versatile route for molecular design. Here we show for the example of multiresponsive spiropyrans that substituent effects and their correlations can be accurately described by Hammett constants, which in turn can be obtained directly from density functional theory calculations. The internal energetic difference ΔU between the noncolored and the colored form is determined for 63 spiropyran derivatives with substituents at the spiropyran N- and C-positions, and can be described by only five parameters with an accuracy better than 0.1 eV (9.75 kJ/mol) using Hammett constants. This enables the prediction of ΔU values for other substituents without the need for further calculations nor experiments.

This work reports on the isomerisation behaviour of alkylated spiropyrans and aliphatic main chain spiropyran copolymers.