A model of non-Markovian random block copolymers is developed and used to study the effects of blockiness and compositional polydispersity on the phase behaviour of random block copolymers. The model approximates a random copolymer as a series of segments with equal lengths, while each segment is composed of sequences of different monomers drawn randomly from a distribution. The phase behaviour of the model random copolymers is first examined using the random phase approximation (RPA) to study the effects of blockiness and polydispersity on the order-disorder transition. It is observed that the critical point is inversely proportional to the blockiness. Compositional polydispersity is found to facilitate phase separation, and could induce macrophase separation. Next, the model is implemented into self-consistent field theory (SCFT) in order to elucidate the full phase behaviour of symmetric (A/B)-A random copolymers. Finally, the model is applied to the particular case of poly(styrenesulfonate-b-methylbutylene) (PSS-PMB) to study the effects of blockiness on the phase behaviour. In particular, the stability and structure of the `swollen gyroid' morphology predicted by previous Monte Carlo simulations is examined. / Thesis / Master of Science (MSc)

No description available.

Nitrile containing siloxane block copolymers were developed as stabilizers for siloxane magnetic fluids. The siloxane magnetic fluids have been recently proposed as internal tamponades for retinal detachment surgery. PDMS-b-PCPMS-b-PDMSs (PDMS = polydimethylsiloxane, PCPMS = poly(3-cyanopropylmethylsiloxane) were successfully prepared through kinetically controlled polymerization of hexamethylcyclotrisiloxane initiated by lithium silanolate endcapped PCPMS macroinitiators. The macroinitiators were prepared by equilibrating mixtures of 3- cyanopropylmethylcyclosiloxanes (DxCN) and dilithium diphenylsilanediolate (DLDPS). DxCNs were synthesized by hydrolysis of 3-cyanopropylmethyldichlorosilane, followed by cyclization and equilibration of the resultant hydrolysates. DLDPS was prepared by deprotonation of diphenylsilanediol with diphenylmethyllithium. It was found that mixtures of DxCN and DLDPS could be equilibrated at 100°C within 5-10 hours. By controlling the DxCN-to-DLDPS ratio, macroinitiators of different molecular weights could be obtained. The major cyclics in the macroinitiator equilibrate are tetramer (8.6 ± 0.7 wt%), pentamer (6.3 ± 0.8 wt%) and hexamer (2.1 ± 0.5 wt%). 2.5k-2.5k-2.5k, 4k-4k-4k, and 8k-8k-8k triblock copolymers were prepared and characterized. These triblock copolymers are transparent, microphase separated and highly viscous liquids. It was found that these triblock copolymers can stabilize nanometer gamma-Fe₂O₃ and cobalt particles in octamethylcyclotetrasiloxane or hexane. Hence PDMS-b-PCPMS -b-PDMSs represent a class of promising steric stabilizers for silicone magnetic fluids. / Master of Science

No description available.

Thesis (M.S.)--University of Missouri-Columbia, 2003. / Typescript. Includes bibliographical references (leaves 109-112). Also available on the Internet.

Thesis (M.S.)--University of Missouri-Columbia, 2003. / Typescript. Includes bibliographical references (leaves 109-112). Also available on the Internet.

No description available.

The morphology, crystallization and melting behaviors of a series of ethylene/alpha-olefin copolymers were investigated as a function of comonomer content, comonomer type and processing conditions, including crystallization temperature and time. This was achieved by using a combination of techniques such as Nuclear Magnetic Resonance Spectroscopy (NMR), Differential Scanning Calorimetry (DSC), Atomic Force Microscopy (AFM) and Fourier Transform Infrared Spectroscopy (FTIR). The results from the thermal analysis studies clearly indicated the existence of two distinct regions of crystallization, demarcated by a cross-over temperature, 𝑇*. The high temperature region (above 𝑇*) displayed cooling-rate dependence as well as significant hysteresis in crystallinity between cooling and heating processes, similar to that observed in linear polyethylene. This implied that the crystals associated with this region were formed via chain-folded lamellar growth. However, the lower temperature region (below 𝑇*) exhibited reversible changes in crystallinity between cooling and heating, and was found to be independent of the cooling rate. The temporal evolution of secondary crystallization in the copolymers was studied for times ranging from 100-106 min, at different crystallization temperatures (Tx). Two distinct melting endotherms were discerned at crystallization temperatures below 𝑇*. A higher melting endotherm that remained invariant with crystallization time (tx) was associated with lamellar crystals that were formed during primary crystallization. In contrast, both the positions as well as the magnitude of the lower temperature endotherm were found to vary systematically with log (tx). The peak positions of the low endotherm, i.e., the melting temperature of the secondary crystals, were found to consistently extrapolate to the crystallization temperature at very short times. Based on this and other considerations, the secondary crystals were associated with the melting of thin stacks of polymer chains aggregated in the form of "fringed-micelle"-like bundled crystals. The temperature dependence of the kinetic parameters (derived from Avrami and other analyses) above 𝑇* and their invariance below 𝑇*, suggested that the transformation in morphology from lamellar to bundled crystals was gradual and systematic, as the branch content was increased or as the crystallization temperature was lowered. Further verification of this result was obtained via AFM experiments. A systematic variation in morphology from lamellar to spot-like (lamellae were less clearly visible) was clearly discerned on increasing the comonomer content. Furthermore, a second morphological feature represented by bridge-like links between the lamellae, and approximately perpendicular to them, was also observed for some copolymers. This feature was correlated with the bundled crystals discussed above. The presence of an alternate crystal structure, in addition to the usual orthorhombic crystal form expected for linear polyethylene, was also established from the results of the FTIR studies. The relative proportions of the second crystal form in the copolymers as a function of branch content and temperature were modeled and estimated via mathematical deconvolution and curve-fitting processes. Comparing the results to those of the hexagonal rotator phase of n-paraffins, it was proposed that the second crystal structure in the copolymers could be assigned to a hexagonal type unit cell structure. Furthermore, the crystallization and melting behaviors of all three types of copolymers studied - ethylene/1-butene, ethylene/1-pentene and ethylene/1-hexene - were found to be identical to each other, suggesting that the crystallization process examined was independent of branch type for the ethyl, propyl and butyl branches examined. Since the lengthy butyl branch (in the ethylene-hexene copolymers) is not likely to be accommodated in the crystal, it was concluded that all three branch types were predominantly excluded from the crystal structure. Based on the results from these studies, a new model for the crystallization mechanism in these copolymers was proposed and could be further extended to other semicrystalline polymers such as PET, PEEK, PVC, PBT, i-PS and polycarbonate. In this model, the primary and secondary crystallization stages were redefined on the basis of the chain-folded lamellar growth process. According to the model, secondary crystallization involves the generation of the bundled crystals that may be viewed as physical cross-links in the amorphous phase. Therefore, it may provide a means of correlating the temporal evolution of secondary crystallization to the time and temperature dependence of the physical properties of semicrystalline polymers, above their glass transition temperatures. / Ph. D.

Novel perfectly alternating segmented copolymers containing imide junction points were synthesized via terminal amine-anhydride coupling from poly(dimethylsiloxane)s and either poly(arylene ether)s or polyimides. The copolymers were characterized in solution and the solid state. The -(-A-B-)-n architecture and molecular design of these linear systems afforded thermodynamically microphase separated systems which gave rise to interesting copolymer properties. Each controlled molecular weight oligomeric segment, or homopolymer, was initally synthesized with reactive endgroups and fully characterized prior to copolymerization. Thus, anhydride-terminated poly(dimethylsiloxane)s were prepared via cationic ring-opening polymerization in the presence of a "monofunctional" bis-norbornane anhydride disiloxane endcapping species. Aromatic amine-terminated engineering thermoplastics were synthesized through either nucleophilic aromatic substitution in the presence of a “monofunctional” aminophenol endcapper (as for poly(arylene ether ketone)s and poly(arylene ether sulfone)) or by solution imidization using a controlled excess of the diamine monomer. A solution imidization method was developed for the segmented copolymerization that simplified the typically two-step, two-solvent method into a one-step approach with a single solvent. Thus, a previously described condensation catalyst, 2-hydroxypyridine, was utilized which was demonstrated to be essential in obtaining high molecular weight copolymers. These segmented copolymers generally were fibrous and highly soluble in many common organic solvents. Creasable, transparent, solution-cast films were readily prepared. Thermal and morphological analyses demonstrated that the copolymers exhibited phase separation, and displayed lower and upper Tg's as a result of the two components employed. At short hard block lengths, uper Tg's were somewhat depressed, implying partial miscibility. / Master of Science

Over the years there have been many studies on the theoretical and phenomenalogical aspects of starblock, di- and tri-block copolymer systems with very narrow molecular weight distributions. However, in many real multiblock systems the effect of such variables as; chemical composition distribution, molecular weight distribution and block architecture, among others, are not very well understood. The key to gaining a better understanding of these systems lies in the use of synthetic and process controlled variables. Seven different systems were used to study the effect of various synthetic and process controlled variables. The poly(butene sulfone) (PBS)-polydimethylsiloxane (PDMS) graft copolymers were synthesized by a free radical technique which involves the terpolymerization of butene, SO, and hexenyl functionalized polydimethylsiloxane macromonomers. The surface and bulk morphologies of a series of PBS-g-PDMS compolymers with 1, 5, 10, and 20K PDMS graft molecular weights at 5 and 20Wt.% PDMS incorporation. Additionally, for each graft molecular weight and at each composition, copolymers with a low and a high degree of polymerization of the PBS backbone were analyzed. A two phase morphology was found to exist with PDMS domain size increasing with increasing PDMS graft length. The type of morphology observed was dependent on PDMS composition, and in some cases the degree of polymerization and average number of grafts/backbone. These factors were also found alter the nature of the surface morphology and the related surface properties. The effect of PDMS segment molecular weight, the chemical nature of the polyimide segment, the procedure used to imidized the polyimide and processing conditions on the structure-property relationships in a series of polyimide-PDMS containing approximately 15Wt.% PDMS was studied. It was determined that as the polarity of the polyimide segment increased the morphology shifted to texture with lower surface/volume ratios. Casting the copolymers from an NMP solution favored a more discrete morphology than the thermally treated compression molded samples. The modulus was found to increase as the degree of phase separation increased with increasing PDMS segment size at constant composition. In addition, the solution cast films were found to have a higher modulus than the compression molded analogs. The morphology of a series of methacrylate based block ionomer was investigated. The effect of ionic block length, the architecture of the segments, and variations in the nature of ionic group were studied. SAXS revealed the presence of multiple scattering maxima in the dilbock materials. Both highly ordered and disordered region were observed from TEM analysis. The observed spacing from TEM measurements and SAXS were in good agreement. The interdomain spacings between the ionic domains were found to be a strong function of ionic block length. / Ph. D.