The glass transition temperature (T g) is a key property that dictates the applicability of conjugated polymers. The T g demarks the transition into a brittle glassy state, making its accurate prediction for conjugated polymers crucial for the design of soft, stretchable, or flexible electronics. Here we show that a single adjustable parameter can be used to build a relationship between the T g and the molecular structure of 32 semiflexible (mostly conjugated) polymers that differ drastically in aromatic backbone and alkyl side chain chemistry. An effective mobility value, ζ, is calculated using an assigned atomic mobility value within each repeat unit. The only adjustable parameter in the calculation of ζ is the ratio of mobility between conjugated and non-conjugated atoms. We show that ζ correlates strongly to the T g , and that this simple method predicts the T g with a root-mean-square error of 13°C for conjugated polymers with alkyl side chains.

Novel families of ultrahigh-molecular-weight polyethylene (UHMWPE) nanocomposites, containing uniformly dispersed, functionalized graphene (FG) nanosheets, were prepared by means of the polymerization filling technique (PFT). Unparalleled by any other carbon and boehmite nanocomposites, FG/UHMWPE exhibited an unusual simultaneous improvement in stiffness, elongation at break, and effective nucleation of polyethylene crystallization at only 1 wt % FG content. FG nanosheets are ultrathinwith a thickness of only one carbon atom and lateral dimensions of several micrometers. Owing to the presence of surface hydroxyl groups on the FG, single FG/methylaluminoxane (MAO) nanosheets can be effectively dispersed in n-heptane, thus enabling immobilization of an MAO-activated chromium (Cr1) single-site catalyst on FG. In contrast to nanometer-scale carbon black (CB), multiwall carbon nanotubes (CNT), graphite, and nanoboehmite, which failed to form stable dispersions, FG/MAO/Cr1 afforded the highest catalyst activities and excellent morphological control. In polymerization filling, the integration of a nanoparticle dispersion into the polymerization process eliminated the need for special safety and handling precautions typically required by conventional compounding of nanoparticles with ultralow bulk densities.

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