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. ...

This work is dedicated to Prof. Brigitte Voit on the occasion of her 60 th birthday. In a joint theoretical and experimental study, it is shown that the onset of the mechanically-induced spiropyran (SP) to merocyanine (MC) isomerization can be controlled by both the regiochemistry and the substitution pattern of SP. Four SP-based bifunctional initiators with consistently varied polymer chain anchor point and substituent are used to synthesize poly-𝝐-caprolactone (PCL). Theoretical calculations (1S and 3S COGEF methods) and in-situ visible light absorption measurements of films during uniaxial stress-strain experiments consistently show varying activation barriers of the force-induced ring-opening reaction of SP to give MC. SPs with PCL chains attached in ortho-position to the pyran oxygen isomerize at lower stress than their para-analogs. NO 2 -substituted SP mechanophores exhibit a lower activation barrier compared with H-substituted ones, but only if the -NO 2 substituent is located in para-position relative to the O at the pyran half. These results are consistent with theoretical loading rate-dependent rupture forces required to break the C-O bond of SP and may guide mechanophore design.

Liquid urethane (meth)acrylates represent attractive components of photocurable thermosets for applications ranging from coatings and adhesives to 3D printing. Herein we tailor liquid polyfunctional urethane methacrylates (UMA) derived from acrylic polyhydroxy urethanes. Cyclic carbonate methacrylates react with diamines to form dihydroxy-functional urethane dimethacrylates. In an "onepot" process the hydroxy groups are functionalized either by reaction with 2-isocyanatoethyl methacrylate (IEMA) or by esterification with methacrylic anhydride (MAA) and acetic anhydride (AA). The hydroxy group esterification substantially lowers the resin viscosity (26-156 Pa•s). Hydroxy functionalization with IEMA and MAA affords tetrafunctional methacrylates. The corresponding photo-cured thermosets exhibit higher crosslinking density and improved stiffness as reflected by increasing the Young's modulus from 2900 to 3700 MPa combined with increasing the glass temperature from 135 to 204 C. Hence, this facile molecular UMA design enables to control functionality and thermoset properties over a wide range and meets the demands of 3D printing applications.

Pine cones show functionally highly resilient, hygroscopically actuated opening and closing movements, which are repeatable and function even in millions of years old, coalified cones. Although the functional morphology and biomechanics behind the individual seed scale motions are well understood, the initial opening of the cone, which is often accompanied by an audible cracking noise, is not. We therefore investigated the initial opening events of mature fresh cones of Scots pine (Pinus sylvestris) and their subsequent motion patterns. Using high-speed and time lapse videography, 3D digital image correlation techniques, force measurements, thermographic and chemical-rheological resin analyses, we are able to draw a holistic picture of the initial opening process involving the rupture of resin seals and very fast seed scale motion in the millisecond regime. The rapid cone opening was not accompanied by immediate seed release in our experiments and, therefore, cannot be assigned to ballistochory. As the involved passive hydraulic-elastic processes in cracking are very fine-tuned, we hypothesize that they are under tight mechanical-structural control to ensure an ecologically optimized seed release upon environmental conditions suitable for wind dispersal. In this context, we propose an interplay of humidity and temperature to be the external “drivers” for the initial cone opening, in which resin works as a crucial chemical-mechanical latch system.