Patrick B. Smith

Acrylic acid polymerization kinetics

The kinetics of the isothermal polymerization of acrylic acid were determined utilizing 1H-NMR spectroscopy. The polymerization rate was observed to depend approximately on the power of monomer and the power of sodium persulfate concentration. This is consistent with a model in which the rate of initiation is itself dependent on the monomer concentration. The polymerization rate was also observed to have a strong dependence on percent neutralization, decreasing with increasing level of neutralization up to 75 to 100% neutralization, and then increasing again. The activation energy for the rate of polymerization was between 9 and 13 kcal/mol except for 100% neutralized acrylic acid, which had an activation energy of 18 kcal/mol. These data suggest that a transition in mechanism occurred at 100% neutralization. Increasing the ionic strength by the addition of sodium chloride also increased the rate. The dependence of the molecular weight on the above variables was also quantified for use in the model. It decreased with increasing conversion, decreasing ionic strength and increasing initiator.

Crosslinker reactivity and the structure of superabsorbent gels

A 13C-labeled crosslinker (trimethylolpropane triacrylate, TMPTA) was synthesized and copolymerized with acrylic acid while monitoring the relative rates of reaction of the crosslinker and acrylic acid by 13C-NMR. This allowed easy quantification of the concentration of the minor component (crosslinker) in the polymer and monomer mixture to levels as low as 0.02%. Polymerizations were conducted in 5 mm NMR tubes under varied temperature, percent neutralization (pH), and percent solids. Reactivity ratios were determined from the rates of incorporation of the components into the gel by use of the integrated form of the copolymerization equation, and their sensitivity to the above variables was quantified. The relative rate of incorporation of the crosslinker into the gel was exceedingly fast. The reactivity ratio, r1 for acrylic acid, varied from 0.31 (65% neutralization) to 0.77 (unneutralized). The reactivity ratio was affected by the percent solids (solvent effect), but was insensitive to temperature over the range of 55–80°C. It was observed that all of the double bonds of TMPTA were incorporated into gel network as opposed to prior models predicting only two bonds reacting. The reported inefficiency of TMPTA is postulated to be caused by a solubility problem in the monomer mixture. Very low levels of extractables were found in the products even though the crosslinker was consumed by 70% conversion. Based on these data, we propose that a major component of the gel network is graft polymer that forms late in the polymerization onto the crosslinked gel formed earlier.

Quantitative analysis and structure determination of styrene/methyl methacrylate copolymers by pyrolysis gas chromatography.

A pyrolysis gas chromatography (Py-GC) method has been developed to study the composition and microstructure of styrene/methyl methacrylate (STY/MMA) copolymers. The composition was quantified by Py-GC using monomer peak intensity. Because of the poor stability of methyl methacrylate oligomers, neither MMA dimer nor MMA trimers were detected under normal pyrolysis conditions. The number-average sequence length for STY was determined by pure and hybrid trimer peak intensities. The number-average sequence length for MMA was determined by using formulas that incorporate composition and the number-average sequence length of STY. This method is a new approach for the investigation of the microstructure of those copolymers that do not produce dimer and trimer peaks upon pyrolysis.

Raman characterization of orientation in poly(lactic acid) films

Poly(lactic acid) is a new biopolymer material which is marketed by Cargill Dow Polymers under the tradename Nature Works*. One major application for this material is biaxially oriented films for food packaging because it possesses excellent barrier for flavor constituents, deadfold and heat sealability. Shrinkage must be minimized when the film is heat sealed for these applications and, therefore, characterization of the orientation of the amorphous phase of PLA films is necessary. Raman spectroscopy methodology has been developed to quantify orientation in PLA films. Bands were assigned to crystalline and amorphous phases of PLA such that orientation in both phases could be monitored. Raman depolarization ratios were used to characterize uniaxial systems but were insufficient for most biaxial draws. A new phenomenon for oriented films involving Raman band shifts was observed in these systems, and was shown to be capable of determining orientation, even for symmetrical biaxially drawn films. The origin of these shifts, as well as their use for the quantification of orientation will be discussed. Further, since the line widths of the bands could be used to quantify crystallinity, both crystallinity and orientation could be determined with one measurement.

The effects of MEHQ on the polymerization of acrylic acid in the preparation of superabsorbent gels

The effect of the monomethyl ether of hydroquinone (MEHQ) on the polymerization of acrylic acid was studied. The rate of polymerization was quantified at various levels of MEHQ by use of an in situ NMR technique. While oxygen functions as an inhibitor in acrylic acid polymerizations, MEHQ was shown to function as a retarder. The decrease in the rate of polymerization allowed the calculation of an inhibition constant for this system. MEHQ was found to remain in the polymerizing mixture throughout the course of the reaction, significantly reducing the rate of polymerization, but not reducing the molecular weight of the polymer. The data are consistent with direct reaction of MEHQ with initiator fragments, but not termination of growing chains. Superabsorbent polyacrylic acid gels were prepared and the properties measured.

Thermal degradation of epoxidized soybean oil in the presence of chlorine-containing polymers

Abstract The thermal degradation of epoxidized soybean oil has been examined using thermal and spectroscopic methods. In both the presence and absence of chlorine-containing polymers, epoxidized soybean oil undergoes thermal degradation to form ring-opened products. In the absence of other reactants, the primary degradation reaction is apparently intermolecular ether formation. The degradation in a highly-chlorinated polymer matrix appears to be facilitated by reaction with hydrogen chloride generated by polymer degradation. Fully epoxidized soybean oil (7.0 wt.% oxirane oxygen) appears to contain two types of oxirane groups: type I which begins to undergo thermal ring-opening at about 175 °C and type II which opens at ⪢ 325 °C. Both ring openings are exothermic and irreversible. Type I oxirane groups account for approximately one-third of the total oxirane content of fully epoxidized soybean oil. Partially epoxidized soybean oil (3.28 wt.% oxirane oxygen) contains only type II oxirane functionality.

Compositional and structural studies of vinylidene chloride/vinyl chloride copolymers by pyrolysis gas chromatography

A pyrolysis gas chromatography approach has been developed to study the composition and structure of vinylidene chloride/vinyl chloride copolymers. The composition and number average sequence length, which reflects the monomer arrangement in the polymer, were calculated using formulas that incorporate the pure trimer peak intensities and hybrid trimer peak intensities. Because of the reactivity difference between vinyl chloride and vinylidene chloride monomers, the structure of the polymer has been further investigated on the basis of the percentage of grouped monomers (i.e., the number average sequence length for vinyl chloride and vinylidene chloride repeat units). For the vinylidene chloride/vinyl chloride copolymer examined in this study, the composition and number average sequence length elucidated from the pyrolysis gas chromatography study are compared to the product composition specification and/or the composition measured by (1)H-NMR.

Synthesis and properties of 2,2,6,6-tetramethyl-1-(1-phenethyloxy)piperidine, an initiator for living free radical styrene polymerization

SummaryAn initiator for living free radical polymerization may be prepared by trapping the benzylic ethylbenzene radical with the stable 2,2,6,6-tetramethylpiperidinyl-1-oxy (TEMPO) radical. The adduct, 2,2,6,6-tetramethyl-1-(1-phenethyloxy)piperidine (TMPEP), smoothly undergoes thermal fragmentation at temperatures approaching 140° C to afford an active carbon radical capable of initiating polymerization and a passive mediating nitroxyl radical to reversibly cap and preserve the propagating polymer chain.

Thermal degradation of trimethylolpropane/adipic acid hyperbranched poly(ester)s

Hyperbranched poly(ester)s offer attractive features for applications in a number of areas, particularly as platforms for the support of controlled release actives in the agricultural and biomedical fields. Such materials have been generated from trimethylolpropane and adipic acid, and fully characterized using chromatographic, spectroscopic, and thermal methods. The thermal stability of these polymers has been assessed using thermogravimetry and infrared spectroscopy. The degradation characteristics of these materials have been compared to those of two linear adipic acid polymers. The prominent feature of the thermal degradation of the hyperbranched poly(ester)s is ether formation while that for the comparable linear poly(ester)s is ester pyrolysis resulting in chain scission.

Thermal degradation of glycerol/adipic acid hyperbranched poly(ester)s containing either hydroxyl or carboxyl end-groups

Glycerol-derived hyperbranched poly(ester)s offer superior properties for utilization in agriculture, personal care and biomedical areas. These materials are compatible with bio-environments, are generally nontoxic and are biodegradable. When either hydroxyl or carboxyl end-groups are present, they may be conjugated with a wide variety of active agents to provide controlled-release compositions. Glycerol/adipic acid hyperbranched poly(ester)s have been prepared and characterized using chromatographic, spectroscopic and thermal analysis methods. The thermal degradation characteristics of these polymers have been established using thermogravimetry and infrared spectroscopy. The prominent feature for the degradation for polymers with hydroxyl end-groups is cross-linking ether formation while that for polymers with carboxyl end-groups is decarboxylation.