J. Scott Parent

Composition distribution in poly(ethylene-graft-vinyltrimethoxysilane)

Abstract Insight into the composition distribution created by free-radical mediated addition of vinyltrimethoxysilane (VTMS) to high-density polyethylene (HDPE) has been gained using physical methods of polymer characterization as well as detailed structural studies of a model hydrocarbon system. Analysis of poly(ethylene- graft -vinyltrimethoxysilane), or HDPE- g -VTMS, by moisture curing and by differential scanning calorimetry–successive self-nucleation and annealing (DSC–SSA) indicated that the distribution of pendant alkoxysilane grafts amongst polymer chains was non-uniform. Fractionation and characterization of a graft-modified model compound, tetradecane- g -VTMS, showed that composition distributions were influenced strongly by intramolecular hydrogen atom abstraction, yielding multiple grafts per chain in the form of single pendant units as opposed to oligomeric grafts. Chain transfer to the methoxy substituent of bound VTMS was found to contribute significantly to the product distribution.

EPDM Synthesis by the Ziegler Catalyst Cp*TiMe3/B(C6F5)3

The utilization of the Ziegler catalyst Cp*TiMe3/B(C6F5)3 for the terpolymerization of ethylene, propylene and 5-ethylidene-2-norbornene to give EPDM is investigated, and the major factors affecting yields, molecular weights, molecular weight distributions and compositional distributions of the EPDM polymers are assessed. High molecular weight polymers with narrow molecular weight distributions are obtained at ˜18°C.

Foaming of reactively modified polypropylene: Effects of rheology and coagent type

A series of linear controlled rheology polypropylenes were produced through reaction with dicumyl peroxide in the melt state, to investigate the effect of molecular weight and viscosity on foaming. Foaming experiments by compression molding, using a chemical blowing agent (azodicarbonamide), and by batch foaming using nitrogen-blowing agent, revealed that lower viscosity promoted higher expansion ratios and larger cells, due to reduced resistance to cell growth. Linear polypropylene was further modified using trimethylolpropane trimethacrylate and triallyl trimesate coagents. Coagent modification resulted in pronounced changes in the shear thinning and elasticity of the modified polypropylenes. However, evidence of long-chain branching was only present in polypropylene modified by triallyl trimesate. Foams based on coagent-modified polypropylenes had higher expansion ratios than their degraded counterparts. This was ascribed in part to the lower viscosities, and to a nucleating effect, arising from the presence of a finely dispersed phase of coagent-rich nanoparticles. Strain hardening in polypropylenes modified by triallyl trimesate further resulted in a finer cell structure, due to suppressed coalescence.

Auto-catalytic chemistry for the solvent-free synthesis of isobutylene-rich ionomers

Ionomer derivatives of brominated poly(isobutylene-co-isoprene) rubber (BIIR) are prepared by alkylation of PPh3,imidazole and 2-[2-(dimethylamino)ethoxy]ethanol under solvent-free conditions. Halide displacement is shown to be accompanied by allylic bromide rearrangement to kinetically more reactive endo-allylic bromide isomers. Alkylation to give quaternary onium-halide salts produces an isomerisation catalyst in situ, owing to a rapid SN2′ isomerisation by free bromide. As a result, a continuous process for PPh3 alkylation can be catalyzed by the recycling of a small amount of IIR-PPh3Br product to the feed, thereby supporting an irreversible ionomer synthesis that proceeds to full conversion without the generation of reaction byproducts.

Selecting polymers for two-phase partitioning bioreactors (TPPBs): Consideration of thermodynamic affinity, crystallinity, and glass transition temperature.

Two‐phase partitioning bioreactor technology involves the use of a secondary immiscible phase to lower the concentration of cytotoxic solutes in the fermentation broth to subinhibitory levels. Although polymeric absorbents have attracted recent interest due to their low cost and biocompatibility, material selection requires the consideration of properties beyond those of small molecule absorbents (i.e., immiscible organic solvents). These include a polymers (1) thermodynamic affinity for the target compound, (2) degree of crystallinity (wc), and (3) glass transition temperature (Tg). We have examined the capability of three thermodynamic models to predict the partition coefficient (PC) for n‐butyric acid, a fermentation product, in 15 polymers. Whereas PC predictions for amorphous materials had an average absolute deviation (AAD) of ≥16%, predictions for semicrystalline polymers were less accurate (AAD ≥ 30%). Prediction errors were associated with uncertainties in determining the degree of crystallinity within a polymer and the effect of absorbed water on n‐butyric acid partitioning. Further complications were found to arise for semicrystalline polymers, wherein strongly interacting solutes increased the polymers absorptive capacity by actually dissolving the crystalline fraction. Finally, we determined that diffusion limitations may occur for polymers operating near their Tg, and that the Tg can be reduced by plasticization by water and/or solute. This study has demonstrated the impact of basic material properties that affects the performance of polymers as sequestering phases in TPPBs, and reflects the additional complexity of polymers that must be taken into account in material selection.

Imidazolium-based polyionic liquid absorbents for bioproduct recovery

Solid imidazolium-based polyionic liquids (PILs; a class of polyelectrolyte) were synthesized for the absorption of n-butanol and other inhibitory biosynthesis products from dilute aqueous solutions. Conventional hydrogels prepared by cross-linking water-soluble PILs demonstrated biocompatibility with Saccharomyces cerevisiae, successfully eliminating cytotoxicity concerns associated with the IL monomers. However, the cross-linked PILs’ solute absorption capacity and selectivity for butanol relative to water were below the levels likely needed for a viable extractive fermentation process. Uncross-linked PILs bearing long-chain aliphatic substituents also proved to be biocompatible by virtue of their insolubility in water, and delivered significantly improved absorptive performance. Among biocompatible absorbents, these PILs demonstrated some of the highest absorptions of n-butanol and other hydrophilic fermentation products reported to date, with n-butanol partition coefficient (PC) values up to 7.6 and butanol/water selectivity (αb/w) values up to 78. The influence of linear N-alkyl side chain length (C8 to C16) and counter anions (Cl−, Br−, I−, BF4−, co-SS−) on solute partition coefficient, selectivity and physical properties are detailed and discussed. In all, this work demonstrates that polymerization of cytotoxic ILs can successfully yield biocompatible absorbents with excellent absorptive performance for the recovery of hydrophilic bioproducts.

Isobutylene-rich imidazolium ionomers for use in two-phase partitioning bioreactors

Imidazolium ionomer derivatives of an isobutylene-rich elastomer demonstrated superior absorption characteristics for target molecules of biological interest compared to their non-ionic parent material, while retaining biocompatibility with a range of suspended cell cultures. Halide displacement from brominated poly(isobutylene-co-paramethyl styrene) was used to introduce 0.23 mmol per g-polymer of imidazolium bromide functionality to the polymer, resulting in up to 10-fold improvements in n-octanol and n-butanol partition coefficients (PCs) and up to 4-fold improvements in selectivity (α). In contrast to analogous imidazolium ionic liquids (ILs) that were cytotoxic toward Saccharomyces cerevisiae, Clostridium acetobutylicum and Pseudomonas putida, the ionomers had no effect on suspended cell growth. In addition, these ionomers demonstrated surface antimicrobial activity towards select microorganisms under static conditions with direct surface/microbe contact. Thus, these materials do not affect suspended cell growth while simultaneously reducing cell proliferation at the ionomer interface.