Michael Matthew Satkowski

Synthesis of high-molecular-weight poly([r]-(-)-3-hydroxybutyrate) in transgenic Arabidopsis thaliana plant cells

High-molecular-weight poly([R]-(-)-3-hydroxybutyrate) (PHB), a biodegradable thermoplastic, was produced from a suspension culture of transgenic Arabidopsis thaliana plant cells expressing two genes from the bacterium Alcaligenes eutrophus involved in the synthesis of PHB. The molecular structure of the plant-produced polymer was analysed by gas chromatography, mass spectrometry, proton nuclear magnetic resonance spectroscopy, infra-red spectroscopy, spectropolarimetry, differential scanning calorimetry, X-ray diffraction and size exclusion chromatography. The results indicate that the polymer from transgenic plants appears to have a chemical structure identical to that of PHB produced by bacteria. However, the molecular weight distribution of the plant-produced PHB was much broader than that of typical bacterial PHB.

Structural evolution in microbial polyesters.

The crystallization behavior of microbially synthesized poly(3-hydroxybutyrate) (PHB) and its copolymers [P(HB-co-HHx)] containing 2.5, 3.4, and 12 mol % 3-hydroxyhexanoate (HHx) comonomer and the melting of the resultant crystals were studied in detail using time-resolved small-angle X-ray scattering and differential scanning calorimetry. The polyesters were found to undergo primary crystallization as well as secondary crystallization. In the primary crystallization, the thicknesses of the lamellar crystals were sensitive to the crystallization temperature, but no thickening was observed throughout the entire crystallization at a given temperature. The thickness of the lamellar crystals in the PHB homopolymer was always larger than that of the amorphous layers. In the copolymers, by contrast, the randomly distributed HHx comonomer units were found to be excluded from the lamellar crystals into the amorphous regions during the isothermal crystallization process. This interrupted the crystallization of the copolymer chains, resulting in the formation of lamellar crystals with thicknesses smaller than those of the amorphous layers. The lamellar crystals in the copolymers had lower electron densities compared to those formed in the PHB homopolymer. On the other hand, secondary crystallization favorably occurred during the later stage of isothermal crystallization in competition with the continuous primary crystallization, forming secondary crystals in amorphous regions, in particular in the amorphous layers between the primarily formed lamellar crystal stacks. Compared to the primarily formed lamellar crystals, the secondary crystals had short-range-ordered structures of smaller size, a broader size distribution, and a lower electron density.

Microphase-separated poly(styrene-b-isoprene)n multiblock copolymers with constant block lengths

Abstract Linear multiblock copolymers, like their diblock analogues, are capable of ordering into periodic microstructures when the blocks are sufficiently incompatible. In this work, a series of four linear poly(styrene-b-isoprene)n (SI)n (1 ≤ n ≤ 4) multiblock copolymers with nearly equal block lengths has been synthesized via living sequential anionic polymerization. All of the copolymers are microphase-separated, as discerned by transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS), and exhibit lamellar morphologies in which the microdomain periodicity decreases with n. This behaviour suggests that the middle blocks contract the microdomains along the lamellar normal. Microstructural characteristics are compared with predictions from formalisms proposed for linear multiblock copolymers and, along with conformational considerations, are used to interpret the thermal and tensile properties of the copolymers.

Synchrotron X-ray scattering studies on the structural evolution of microbial poly(3-hydroxybutyrate)

The crystallization behavior of microbially synthesized poly(3-hydroxybutyrate) was studied in detail using time-resolved small-angle X-ray scattering. This polyester was found to undergo primary crystallization as well as secondary crystallization. In the primary crystallization, the thicknesses of the lamellar crystals were sensitive to the crystallization temperature, but no thickening was observed throughout the entire crystallization at a given temperature. The thickness of the lamellar crystals in the polyester was always larger than that of the amorphous layers. Secondary crystallization favorably occurred during the later stage of isothermal crystallization in competition with the continuous primary crystallization, forming secondary crystals in amorphous regions, in particular in the amorphous layers between the primarily formed lamellar crystal stacks. Compared to the primarily formed lamellar crystals, the secondary crystals had short-range-ordered structures of smaller size, a broader size distribution, and a lower electron density.

Study of blends with narrow molecular weight distribution: hydrogen and deuterium labeled polystyrene and poly(vinyl methyl ether)

Abstract Polyvinyl methyl ether) PVME with polydispersity of less than 1.1 has been synthesized. This material has been used to study the effects of molecular weight on the phase diagram of blends of PVME with polystyrene (PS). The role of specific interactions in the phase behavior of the PS/PVME system also was studied using specifically deuterated PVME. Dynamic infrared linear dichroism (DIRLD), has indicated that two different chemical environments for the methoxyl groups of PVME may exist. One type of methoxyl interacts with the PS phenyl group such that their reorientational motions under oscillatory strain are synchronized, while another substantial population of methoxyl groups shows no such synchronization.

The nature of the crystal/amorphous interface in polyethylene and its blends

ABSTRACT The crystalline/amorphous interface is a region where there is a transition from the ordered to disordered state. It must accommodate chain folds and defects which cannot lie within the crystal. This transition must occur over a finite distance, estimated to be of the order of 20A and represents a zone of intermediate mobility and order. Consequences are (1) an intermediate Tg, (2) loss peaks associated with limited mobility, (3) lower miscibility in this region arising from the lower entropy of mixing, and (4) concentration of excluded species in this region. Evidence for this comes from (1) Kratky analysis of small-angle x-ray scattering data, (2) observation of an enhanced concentration of excluded species by small-angle neutron scattering, and (3) rheo-optical studies of mobility. Previous NMR studies can also be interpreted in terms of this model. The model suggests how this “interphase” may be controlled via the nature and amount of the excluded species.

Bicomponent Block Copolymers Derived from One or More Random Copolymers as an Alternative Route to Controllable Phase Behavior

Block copolymers have been extensively studied due to their ability to spontaneously self-organize into a wide variety of morphologies that are valuable in energy-, medical-, and conservation-related (nano)technologies. While the phase behavior of bicomponent diblock and triblock copolymers is conventionally governed by temperature and individual block masses, it is demonstrated here that their phase behavior can alternatively be controlled through the use of blocks with random monomer sequencing. Block random copolymers (BRCs), i.e., diblock copolymers wherein one or both blocks are a random copolymer comprised of A and B repeat units, have been synthesized, and their phase behavior, expressed in terms of the order-disorder transition (ODT), has been investigated. The results establish that, depending on the block composition contrast and molecular weight, BRCs can microphase-separate. We also report that large variation in incompatibility can be generated at relatively constant molecular weight and temperature with these new soft materials. This sequence-controlled synthetic strategy is extended to thermoplastic elastomeric triblock copolymers differing in chemistry and possessing a random-copolymer midblock.

Synthesis and Morphological Studies of (AB)n Multiblock Copolymers

Abstract While numerous efforts have been put forth to correlate the morphology of microphase-separated diblock and triblock copolymers with molecular characteristics such as composition and chain length, far fewer studies have been devoted to elucidating the role of molecular architecture on microstructure in more complex linear copolymers. This is particularly surprising since many segmented copolymers, for example, have found their way into commercial applications. In this work, we present some of our recent work to bridge the gap between well-defined di/triblock copolymers and segmented copolymers. Here, a novel set of well-defined linear (AB) n multiblock copolymers possessing equal compositions and chain lengths, but different numbers of AB block pairs (n= 1,2,3,4), have been synthesized. Their microphase-separated morphologies have been characterized using both transmission electron microscopy (TEM) and small-angle x-ray scattering (SAXS). A recently-developed thermodynamic model based on confined-chain statistics is presented, and predictions are found to compare well with experimental data.

Compositionally symmetric diblock copolymer blends of moderate polydispersity

Recent experimental evidence and theoretical predictions indicate that binary blends of relatively monodisperse diblock copolymers remain miscible if the molecular weight disparity of the constituent copolymers is not too great. In this work, we examine the effect of moderate copolymer polydispersity on both the microstructural characteristics and phase behavior of blends prepared from four compositionally symmetric poly(styrene-b-isoprene) (SI) diblock copolymers ranging in polydispersity (Mw/Mn) from 1.02 to 1.30. Blend periodicities, measured by small-angle X-ray scattering, compare favorably with predictions from a strong segregation theory proposed for lamellar diblock copolymer blends composed of monomolecular copolymers. Transmission electron microscopy, employed to ascertain the real-space morphological characteristics of these blends, reveals that a lamellar → cylindrical transition occurs in macrophase-separated blends.

Effect of Systematic Hydrogenation on the Phase Behavior and Nanostructural Dimensions of Block Copolymers

Unsaturated polydienes are frequently hydrogenated to yield polyolefins that are more chemically stable. Here, the effects of partial hydrogenation on the phase behavior and nanostructure of polyisoprene-containing block copolymers are investigated. To ensure access to the order-disorder transition temperature (TODT) over a wide temperature range, we examine copolymers with at least one random block. Dynamic rheological and scattering measurements indicate that TODT increases linearly with increasing hydrogenation. Small-angle scattering reveals that the temperature-dependence of the Flory-Huggins parameter changes and the microdomain period increases, while the interfacial thickness decreases. The influence of hydrogenation becomes less pronounced in more constrained multiblock copolymers.