The reaction between cyclic carbonates and amines to produce hydroxyurethanes is an important alternative to current urethane chemistry. In order to address the issue of slow reaction rates, an efficient ring opening of cyclic carbonates with amines has been achieved utilizing cooperative catalysis. A new Lewis acid/Lewis base combination substantially decreases the reaction times for small molecule systems to reach complete conversion. Although triazabicyclodecene (TBD) has a substantial impact on the reaction rate, the addition of lithium triflate (LiOTf) as a co-catalyst allows for the fastest ring opening reported in the current literature. Cooperative catalysis is also applied to the synthesis of polymers containing hydroxyurethane linkages and is able to achieve rapid conversion of the bis-cyclic carbonate and diamine precursors when compared with the uncatalyzed reaction.

Rice husk ash (RHA) is an agrowaste byproduct resulting from the incineration of rice husks for power production; white RHA is ∼90 wt% or more silica, which makes it a potentially sustainable and inexpensive substitute for commercial (less “green”) silica filler. Past research on polypropylene (PP)-RHA hybrids made by melt processing has yielded modest increments in Young's modulus, reduced yield strength, and drastic reductions in elongation at break relative to neat PP. Using the industrially scalable solid-state shear pulverization (SSSP) process, PP-RHA hybrids are made with 4–38 wt% RHA. As determined by microscopy and other methods, composites made by SSSP have much better RHA dispersion than composites reported in the literature made by twin-screw extrusion. The superior dispersion leads to major enhancements in tensile modulus (up to 100% increases relative to neat PP) while maintaining the yield strength of neat PP and remarkably high values of elongation at break (e.g., 520% at 19 wt% RHA), far higher than composites made by melt processing. The properties of hybrids made by SSSP are competitive with and in some cases superior to those of PP hybrids made with commercial silica. The PP-RHA hybrids also exhibit major increases in hardness, approaching that of polycarbonate in the case of a 38 wt% RHA hybrid. The 38 wt% RHA hybrid exhibits solid-like rheology at low frequency. Nevertheless, all PP-RHA hybrids made by SSSP exhibit viscosities at moderate to high shear rates that are little changed from that of neat PP. POLYM. COMPOS., 34:1211–1221, 2013. © 2013 Society of Plastics Engineers

Application of traditional block copolymer microscopy techniques to gradient copolymers yields limited results, due to the low compositional contrast provided from the sinusoidal composition profiles of their phase segregated nanostructures. In contrast, optical microscopy and profilometry allow for the first direct visualization of their phase segregation properties through surface features formed in annealed thin films. Three comonomer systems are studied; one block and one gradient copolymer are compared for each system. Island/hole topography is observed in all block cases. Of the three gradient copolymers, one showed no pattern development and two showed emergence of island/hole patterns, which coarsen over initial annealing and then appear to anneal away. These results are related to the lower driving force for phase segregation from gradient sequencing, which lowers the potential of gradient copolymers to form island/hole patterns and also to pin any patterns formed. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012

Gradient copolymers with gradients in composition along the chain lengths are synthesized by controlled radical polymerization, and their damping behaviors are compared to those of random and block copolymers. The effect of comonomer incompatibility is studied by comparing behaviors of strongly segregating styrene/4-hydroxystyrene (S/HS) and moderately segregating styrene/n-butyl acrylate (S/nBA) copolymers. The effect of composition gradient steepness is studied by designing “constant” or “increasing” gradients via the comonomer addition rate during semibatch polymerization. Dynamic mechanical analysis (DMA) is used to compare the temperature dependences of the storage modulus (E′), loss modulus (E″), and tan δ of the materials. A glass transition breadth (ΔT_g) is defined by a temperature range over which E′ decreases from 10⁹ Pa to 10⁸ Pa. The gradient copolymer ΔT_gs are at least four times larger than the random copolymer ΔT_gs. The S/nBA gradient copolymers show strong effects of gradient steepness on ΔT_g, with ΔT_g being much larger for the increasing gradient than for the constant gradient. DMA data are compared to predictions by Hashimoto et al. for tapered block copolymers in the limit where the taper extends across the entire chain. The shapes of their calculated temperature dependences of E′ and E″ correspond well to the gradient copolymers with large ΔT_g values, providing strong support for symmetric gradient copolymers forming nanoscale, ordered domains with sinusoidal composition profiles. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 48–58, 2008

The effect of nanoscale confinement on the glass transition temperature, T_g, of freely standing polystyrene (PS) films was determined using the temperature dependence of a fluorescence intensity ratio associated with pyrene dye labeled to the polymer. The ratio of the intensity of the third fluorescence peak to that of the first fluorescence peak in 1-pyrenylmethyl methacrylate-labeled PS (MApyrene-labeled PS) decreased with decreasing temperature, and the intersection of the linear temperature dependences in the rubbery and glassy states yielded the measurement of T_g. The sensitivity of this method to T_g was also shown in bulk, supported PS and poly(isobutyl methacrylate) films. With free-standing PS films, a strong effect of confinement on T_g was evident at thicknesses less than 80–90 nm. For MApyrene-labeled PS with M_n = 701 kg mol⁻¹, a 41-nm-thick film exhibited a 47 K reduction in T_g relative to bulk PS. A strong molecular weight dependence of the T_g-confinement effect was also observed, with a 65-nm-thick free-standing film exhibiting a reduction in T_g relative to bulk PS of 19 K with M_n = 701 kg mol⁻¹ and 31 K with M_n = 1460 kg mol⁻¹. The data are in reasonable agreement with results of Forrest, Dalnoki-Veress, and Dutcher who performed the seminal studies on T_g-confinement effects in free-standing PS films. The utility of self-referencing fluorescence for novel studies of confinement effects in free-standing films is discussed. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 2754–2764, 2008

The critical micelle concentrations (CMCs) of styrene–methyl methacrylate (S-MMA) block and gradient copolymers present in a homopolymer poly(methyl methacrylate) (PMMA) matrix were determined using an intrinsic fluorescence technique based on the ratio of excimer to monomer fluorescence from styrene repeat units. The homopolymer molecular weight (MW) and copolymer MW, composition, and sequence distribution were varied to determine their effects on the CMC, and comparisons were made to theory. Although the effects of these parameters on micelle formation have been the focus of significant theoretical study, few experimental studies have addressed these issues. The MW of the S block (forming the micelle core) has a strong effect on the CMC. For example, an order of magnitude reduction in the CMC (from ∼ 1 to ∼ 0.1 wt %) is observed when the S block MW is increased from 51 to 147 kg/mol while maintaining the MMA block and PMMA MWs at 48–55 kg/mol. Increasing the PMMA matrix MW also has a strong an effect on the CMC, with the CMC for a nearly symmetric S-MMA block copolymer with each block MW equal to 48–51 kg/mol decreasing by a factor of 5 and by several orders of magnitude when the matrix MW is increased from 55 to 106 kg/mol and 255 kg/mol, respectively. In contrast, similar changes in the MMA block MW have little effect on the CMC. Finally, when present in a 55 kg/mol PMMA matrix, a 55 kg/mol S-MMA gradient copolymer with a styrene mole fraction of 0.51 exhibits a factor of 6 larger CMC than a block copolymer of similar MW and composition. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 2672–2682, 2008