Daniel M. Knauss

Hydrate plug prevention by anti-agglomeration

Dispersing hydrates into a condensate phase by anti-agglomerants is an alternative to kinetic or thermodynamic inhibitors to prevent hydrate plug formation in a gas production pipeline. In this work, both commercially available surfactants and synthesized anti-agglomerants were tested in high-pressure apparatuses at typical pipeline conditions. Candidates from families of commercially available surfactants, chosen based on their hydrophilic–lipophilic balance (HLB), were tested in an H2O-hydrocarbon mixture of 30% water and 70% octane (volume). It was found that, at of the water mass with a synthetic natural gas, some commercial surfactants (Span 20, Span 40, Span 60, Span 80) could keep hydrate particles suspended in a range of condensate types and shear numbers at 4°C and . However, a synthesized chemical dodecyl-2-(2-caprolactamyl) ethanamide was a more efficient dispersant at of the water mass. Both synthesized and commercial chemicals passed 5-day shut-in tests based upon torque measurements and visual hydrate observations. Flow-loop testing is needed to extend this work to field applications.

Melt rheology of variable L-content poly(lactic acid)

Polylactides (PLAs) have been known for several decades and have recently gained considerable commercial significance. This development makes it highly desirable to have the rheological properties of these materials well characterized and reduced to useable mathematical models. However, comprehensive rheological characterization of PLAs is not yet available from the literature. In this study, rheological and thermal measurements were made on a comprehensive and well-characterized set of homopolymers and copolymers spanning wide ranges of molecular mass and stereoisomer proportions (L content). For all compositions within the weight average molecular weight range of 105–106(g∕mol) and a reference temperature of 180 °C, the zero shear viscosity is described by the relationship log(η0)=−14.26+3.4log(Mw), the plateau modulus is 1.0±0.2MPa, and average WLF parameters are c1=3.241∕K and c2=164.9K; the later correspond to a Vogel temperature of 288.25 K. The values of the glass transition temperatures at infinit...

Phosphite stabilization effects on two-step melt-spun fibers of polylactide

The effects of molecular weight stabilization on mechanical properties of polylactide (PLA) fibers are investigated. The textilegrade PLA contains a 98:02 ratio of L:D stereocenters and fibers are produced by the two step method, involving a primary quench and cold drawing. Molecular weight loss, which is approximately 30% for unstabilized PLA, can be eliminated by the addition of small amounts of tris(nonylphenyl) phosphite prior to processing. The thermal and mechanical properties of fibers produced with two different concentrations of TNPP are compared to those of unstabilized PLA. Faster crystallization rates are obtainable with addition of the stabilizer, but final crystallinities are unaffected. Mechanical properties of the TNPP-enriched fibers are greatly improved over their unstabilized counterparts. Tensile strengths can be improved by 10–30% at a given draw ratio, while modulus may be improved by 10–25%. Excessive amounts of TNPP or insufficient mixingresult in inhomog eneities that are deleterious to mechanical properties. Based on the available information, chain extension is believed to be the most likely mechanism for the molecular weight stabilization. # 2002 Elsevier Science Ltd. All rights reserved.

Polystyrene with dendritic branching by convergent living anionic polymerization. II. Approach using vinylbenzyl chloride

Vinylbenzyl chloride (VBC) has been used as a coupling agent in Convergent Living Anionic Polymerization to produce polymers with dendritic branching. The slow addition of a stoichiometric amount of VBC to living polystyrene chains allows the coupling to proceed through macromonomer formation followed by vinyl addition. Changing the reaction conditions produced two types of structures. Star-shaped polymers with a hyperbranched core were made by the continuous slow addition of VBC alone, and chain-extended hyperbranched structures with varied molecular weight between branch points were produced by the slow addition of VBC mixed with different amounts of styrene monomer. The extent of growth of the two different types of structures ranged from 2.4 to 2.6 generations for the case of VBC added alone, corresponding to an average of 5.3 to 6.1 arms attached to the hyperbranched core, and from 3.2 to 4.2 generations for polymers produced from the addition of VBC mixed with styrene. Relatively low polydispersities were obtained for all samples. The highly branched nature of the polymers was reflected in the low intrinsic viscosity relative to linear polystyrene and in the dependence of glass-transition temperature on the molecular weight relative to the number of end groups.

Local and global dynamics of polylactides. A dielectric spectroscopy study

Abstract Polylactides (PLAs) are a family of degradable plastics having a component of the dipole moment both perpendicular and parallel to the polymer backbone (i.e. is a type-A polymer). We have studied the sub-glass, segmental and global chain dynamics in a series of fully amorphous samples having an L : D ratio of 80:20, with molecular weights in the range: 3.8×10 3 M n 4 . Finite size effects have been observed for both the segmental and the sub-glass process. The segmental mode was found to have a steeper temperature and pressure dependence compared to the longest normal mode in accord with findings from other type-A polymers. The molecular weight dependence of the longest normal mode relaxation times ( τ ∼ M n 3.1 ) reflects on the intermediate molecular weight regime ( M e ∼6×10 3 ) from Rouse to entangled chains. These findings are compared with the viscoelastic results on the same system. Agreement in the c 2 value of the WLF equation is found but the scaling of the normalized longest relaxation time derived from the rheological measurements shows a stronger than expected dependence on the molecular weight.

Synthesis of hybrid dendritic-linear block copolymers with dendritic initiators prepared by convergent living anionic polymerization

Hybrid dendritic-linear block copolymers were made in one-pot by convergent living anionic polymerization. Dendritic polystyrene macroinitiators were synthesized by slowly adding a mixture of either vinylbenzyl chloride (VBC) or 4-(chlorodimethylsilyl)styrene (CDMSS) and styrene (1 : 10 molar ratio of coupling agent to styrene) to a solution of living polystyryllithium. The addition was ceased prior to the addition of a stoichiometric amount of coupling agent to retain a living chain end. To the living dendritically branched polystyrene was then added either styrene or isoprene to polymerize a linear block from the dendritic polystyrene. The resulting copolymers were characterized by gel permeation chromatography coupled with multiangle laser light scattering (GPC-MALLS), which clearly demonstrated the formation of diblock copolymers. The diblock copolymers were further characterized by 1H NMR, which showed the presence of the two blocks in the case of dendritic polystyrene-block-linear polyisoprene. The measurement of intrinsic viscosity showed that the dilute solution properties of the block copolymers are greatly influenced by the dendritic portion.

Base stable poly(diallylpiperidinium hydroxide) multiblock copolymers for anion exchange membranes

The development of base-stable cationic groups for anion exchange membranes is important for application in alkaline fuel cells. Spirocyclic ammonium groups have been shown to be particularly base stable, although few examples exist that incorporate them into polymer structures. A telechelic polymer with spirocyclic ammonium repeat units was designed by the cyclopolymerization of diallylpiperidinium chloride with a photoiniferter. A series of hydrophobic–hydrophilic multiblock copolymers with varying ion exchange capacities were produced by copolymerizing the end-functionalized polydiallylpiperidinium oligomers with polysulfone monomers. The multiblock copolymers were solution cast in the hexafluorophosphate form from DMAc resulting in mechanically robust, colorless, transparent membranes. Tapping mode atomic force microscopy and differential scanning calorimetry demonstrated microphase separation of the blocks. The multiblock copolymers were determined to be highly conductive with hydroxide conductivities as high as 102 mS cm−1 at 80 °C with 45% water uptake. Thermogravimetric analysis of the polydiallylpiperidinium oligomers and the multiblock copolymers demonstrated the materials to be highly thermally stable with the multiblock copolymers in the hydroxide form showing 5% weight loss at 360 °C. No degradation of the polydiallylpiperidinium was observed by proton NMR after 1000 hours at 80 °C in a 1 M KOH/methanol-d4 solution. Membranes were found to maintain at least 92% of their hydroxide conductivity after being treated in 1 M KOH at 80 °C for 5 days.

Polycarbonate networks. Part 2. Cure study and determination of mechanical, adhesive, and crystallization properties

Abstract Vinylphenylcarbonate terminated oligocarbonates were thermally cured into insoluble three-dimensional networks. The cure reaction of the functional oligomers with varied molecular weights was studied under different reaction temperatures and cure times. The K 1c fracture toughness was determined for the cured samples and the values obtained show that the polycarbonate networks retain some of the toughness of linear thermoplastic polycarbonate. Dynamic mechanical analysis was performed on the uncured, partially cured, and fully cured samples and a shift in glass transition temperature ( T g ) to higher values was observed with extent of cure. The low temperature secondary relaxation peaks were observed to broaden toward higher values with extent of cure. Tensile measurements of cured samples demonstrated an increase in tensile strengths for the cured materials relative to low molecular weight oligomers, but with no change in modulus, while the tensile elongations of the cured samples showed an improvement over oligomers. The crystallizability of the cured materials was examined and it was determined that a significant improvement in solvent resistance to crystallization was obtained over that of linear polycarbonate. The materials also show potential as structural adhesives.