Search

Due to their outstanding mechanical properties and high aspect ratios, carbon nanotubes (CNTs) are envisioned as attractive nanofillers in polymer composites. However, due to strong van der Waals interactions, deleterious aggregation of CNTs is typically observed in polymer nanocomposites. Moreover, due to low stress transfer between the matrix polymer and the nanotube filler, only limited reinforcement is obtained. We report here a novel functionalization strategy to obtain CNTs with pendant self-complementary hydrogen bonding groups in order to address these limitations. Multi-walled CNTs were functionalized with ureidopyrimidinone (UPy) groups, which display multiple hydrogen bonding. The functionalized CNTs were blended with acrylic copolymers containing pendant UPy moieties and significant enhancement in tensile performance of the nanocomposites was observed.

Novel polydimethylsiloxane (PDMS) based polyionenes were synthesized by a modified Menschutkin reaction involving reaction between bromo-terminated PDMS oligomers and various ditertiary amino compounds. In this study, the nature of the hard segment was varied by using various ditertiary amino compounds and in some cases by incorporating chain extenders, while the soft segment content was varied by changing the molecular weight of the PDMS oligomers. The mechanical properties of these materials were found to be dependent on both the nature and amount of the hard segments. These materials also showed distinct evidence of a microphase-separated morphology where under normal conditions, the hard segments formed in what are believed to be cylindrical ion-rich microdomains dispersed randomly in the soft PDMS matrix. When subjected to uniaxial deformation, the ionic cylinders were found to orient along their long axes in the stretch direction.

Novel hybrid inorganic-organic network materials have been synthesized and applied as transparent abrasion-resistant coatings for metal substrates. A specially functionalized low molecular weight organic material (diethylenetriamine) served as a precursor for all coating formulations. Combination of this functionalized organic material with metal alkoxide(s) and other alkoxysilane functional materials in the sol–gel reaction led to hybrid inorganic–organic chemical networks. While still a liquid, the initiated coating formulations were applied to the desired metal substrates by a spin coating process followed by thermal curing. The substrates used in this study included aluminum, plain steel, conversion coated steel, stainless steel, copper, and brass. A fluorinated monomer has also been utilized in selected cases to tailor the surface-free energy of the coatings. Such coatings displayed a linear increase in the water contact angle with increasing mass fraction of fluorinated monomer in the formulation. O...

Triethoxysilylated diethylenetriamine (f-DETA) and its mixtures with tetramethoxysilane (TMOS) have been hydrolyzed and condensed to form abrasion resistant coatings for optical plastics such as bisphenol-A polycarbonate and CR39. In this paper, the influences of the pH and water concentration on the morphology of gels derived from f-DETA alone (f-DETA100) or equal weights of f-DETA and TMOS (f-DETA50TMOS50) were studied. For the f-DETA50TMOS50 system, with an equivalent ratio (r) of water to alkoxysilane (OH/SiOR) of 4.4, sol-gel reactions at pH 0–2 often led to a particulate gel structure. However, if the reaction was carried out pH 4–5, the resulting gel often had a uniform compact structure although some particulate features were found on the surface. For the f-DETA100 system at pH 0–2, as r increased from zero, the resulting f-DETA gels exhibited a morphological transition from a monolithic uniform structure, to a porous particulate structure, and then to a compact fine particulate structure. A simil...

Novel hybrid organic–inorganic network materials have been generated based on poly(propylene oxide) (PPO) and tetramethoxysilane (TMOS). The PPO source chosen for this study was the family of JEFFAMINE®s often employed as epoxy curing agents. These materials were end–functionalized with trialkoxysilane groups which later were exploited in the sol–gel reaction. The sol–gel variables of water and acid catalyst concentration had little influence on the final structure and properties of the resulting network materials for the ranges probed. Increasing the TMOS content, however, generated a structure that angle X-ray scattering revealed a correlation length associated with a silicate phase separated by PPO chains, which increased with PPO molecular weight, as expected.

Novel hybrid inorganic-organic network materials were generated through a modified sol-gel process based on poly(propylene oxide) (PPO) and tetramethoxysilane. The PPO sources chosen for study were (a) JEFFAMINE® D2000, an amine terminated PPO oligomer available commercially from the Huntsman Corporation, and (b) ACCLAIM™ 2220N, a polyether polyol avail-able from Lyondell which is a copolymer of ethylene oxide (≈ 25%) and propylene oxide (≈ 75%). Overall, the structure- property relationships of ceramers made from these two oligomers are similar. Among the few differences is the tensile stress-strain behavior. The ACCLAIM™ based ceramers can be drawn to higher extents before failure. Also among the discrepancies is the dynamic mechanical behavior in the rubbery region. The ACCLAIMT™ based ceramers appear to more closely mimic ideal rubber elasticity behavior, whereas the JEFFA-MINE® based materials show less than direct proportionality of the storage modulus to temperature. These differences in behav-ior ...

The solid-state ordered structures formed by low M a ionic diblock copolymers of less than 10,000 g/mol, made by group-transfer polymerization of methacrylates, were studied. The unquaternized diblocks exhibit no structure via small-angle x-ray scattering (SAXS) and are apparently below their critical value of XN in a disordered melt state at room temperature. However, the amine salt ionomers exhibit morphologies ranging from dispersed spheres to lamellae which were investigated by SAXS and transmission electron microscopy (TEM). The morphology depends strongly on the size and proportion of the blocks, the extent of quaternization, and the concentration of the blocks in the casting solution.

The first structure-property relationships are reported for segmented polyrotaxane ionenes which possess the rotaxane moiety at the hard segment. These ionenes are based on PTMO/MDI (PTMO M n of 650, 1000, or 2000 daltons) as the elastomeric segment and paraquat hard segments with either PF6 − or Br− as the counterion. GPC indicates that these ionenes have a highly variable architecture with respect to the placement of the ionene hard segment. SAXS also supports the notion of a randomly placed hard segment because the interionic domain d spacings are not predictable or consistent. SAXS also shows there are few “lone multiplets” in the PF6 − derivative whereas there are considerable numbers of isolated ion pairs in the Br− ion-exchanged ionenes. Tensile testing shows that the PTMO-1000 and PTMO-2000 materials are elastomeric with good properties, but the PTMO-650 ionene is not elastomeric with the ionic hard segment as a continuous phase. Dynamic mechanical tests also indicate that these segmented...

Novel abrasion-resistant coatings prepared by a sol-gel process have been developed and applied on the polymeric substrate Bisphenol A polycarbonate. In general, coatings utilize either 4,4′-diaminodiphenyl sulfone (DDS) or diethylenetriamine (DETA) that are then functionalized at their amine groups with 3-isocyanatopropyltriethoxysilane. Following functionalization, these coating materials are then spin coated onto bisphenol A polycarbonate sheet and cured. These reactants undergo a comparable sol-gel reaction similar to typical metal alkoxide chemistry, thereby producing an insoluble network material containing a good dispersion of the functionalized organic along with the hydrolyzed and condensed silicon alkoxide groups. The final coating is transparent and of a few microns in thickness. Following curing, an index of the abrasion resistance is assessed by an optical method, and the adhesion behavior of the coatings is investigated and quantified. It is demonstrated that these thin transparent ...