The effect of specifically interacting functional groups (sticky foot) located at the chain ends of polystyrene on the adsorption rate, adsorbance, graft density and surface excess are discussed from cyclohexane, a theta solvent and toluene. Polystyrenes with hydroxyl and carboxylic acid end-groups (PS-OH, PS-COOH, HO-PS-OH and HOOC-PS-COOH) in narrow molecular weight distribution are synthesized by anionic polymerization of styrene followed by suitable termination reactions. Thin layer chromatography (TLC) is developed as an analytical technique to predict trends in the adsorption of the polymers in a range of solvents. In particular the information about the location of the end-group and therefore different chain architectures at the interface are inferred from this simple technique. Adsorption isotherms are obtained for each of the functionalized polymers of four different molecular weights, the selection of which was based on the TLC results. Kinetics of adsorption and the adsorbance data are determined by liquid scintillation counting of tritium labelled polymers. Graft density and surface excess data are calculated from the adsorbance data and other known parameters. It is shown, from these data, that polystyrenes with a carboxylic acid end-group form weakly stretched brushes at the glass-cyclohexane interface and mushrooms at the glass-toluene interface a result consistent with the higher osmotic repulsions towards packing in good solvents. Polystyrenes with functional groups at both the chain ends are hypothesized to form a range of structures from those dominated by tails at higher concentrations to those dominated by loops (in a good solvent) and trains (in a theta solvent) at lower solution concentrations. At higher molecular weights it is shown that functionalized polystyrenes behave as though they are not functionalized a result consistent with the TLC predictions. Hydroxyl end-group is shown to be an ineffective sticky foot from its adsorbance vis-a-vis polystyrene. The segment density distribution away from a polished silicon surface for a carboxylic acid end-functionalized polystyrene adsorbed from cyclohexane is determined by neutron reflection technique. The dry film thicknesses of polymer modified glass surfaces are determined by x-ray photoelectron spectroscopy. It is shown from the water contact angle data that a highly hrdrophilic surface of glass is converted to a completely hydrophobic surface by the adsorption of the functionalized polystyrenes. (Abstract shortened by UMI.)

In the first part of this thesis, we consider the physical phenomena accompanying the growth of highly branched polymers through computer simulation. The resultant dendritic molecules have unique properties arising from their "modified" Cayley tree branching pattern. We first consider growth of starburst molecules with flexible spacers separating tri-functional branch points. A self-avoiding walk algorithm is employed to kinetically grow the molecules. From the intramolecular density profiles of these structures, we find that the branch ends traverse the molecule throughout growth and are not confined to its surface. Further we observe that the branches are highly folded at all stages of growth. We observe power law relationships correlating the radius of gyration of the molecule to its molecular weight, M, and spacer length, P, finding in general: $R\sb{g}\sim M\sp\rho P\sp\nu$ with $\rho=0.22\pm 0.05$ and $\nu=0.50\pm 0.05$ at high molecular weights. From this we predict the hydrodynamic characteristics of the molecule. We then explore generalizations of the starburst structure by considering first the effect of branch stiffening, and second, the effect of changes in dendrimer connectivity by considering a related structure, the comb-burst. We repeat our study described above for these structures. In general we observe similar behavior to that described above, however slightly modified due to the structural modifications employed. The second part of this thesis addresses polymeric systems exhibiting the phenomenon of self-assembly. The specific problem under consideration is the characterization of phase transitions in diblock copolymer systems using density functional theory. We present a comprehensive, general scheme which allows the characterization of microphase separation of A-B diblock copolymer systems in terms of observed physical phenomena at all degrees of segregation. Our method is based on the density functional theory of Melenkevitz and Muthukumar and uses the technique of density profile parameterization to greatly reduce the technical complexity of the solution. We find that the microphase separated systems pass through three stages of ordering as the system is quenched. These are the weak, intermediate, and strong segregation regimes. We have calculated the phase diagram for three ordered morphologies: lamellae, hexagonally-packed cylinders, and body-centered-cubic spheres. We also characterize these microphases by the dependence of the lattice constant, D, and the interfacial width, $\sigma\sb{o},$ on the quench parameter $\chi N.$ We correctly reproduce the behavior predicted by previous theories describing the weak and strong segregation regimes. Through investigation of $D\sim N\sp\alpha,$ we find that $\alpha$ depends on both block length and morphology in the intermediate segregation regime. We attribute this behavior to chain stretching arising from the phenomenon of localization.

An investigation of acid-base interactions and zinc transition-metal complexations in ionomeric blends of sulfonated poly(ethylene terephthalate) (PET) with pyridine containing polymers will be discussed in relation to the level of specific intermolecular interactions, as measured with FTIR, and the degree of compatibilization, as observed from DSC and DMTA. Two pyridine containing polymer systems were evaluated: (1) a novel main-chain thermotropic liquid crystalline polyester containing pyridine dicarboxylate units, and (2) poly(ethyl acrylate-co-4-vinyl pyridine). Model thermotropic liquid crystalline polyester systems were developed and screened based on a set of macromolecular structure requirements directed toward future blends studies with PET and PBT. The first investigation discussed the preparation and characterization of TLCPs based on the biphenyl mesogen, 4,4$\sp\prime$-bis(6-hydroxyhexoxy)- biphenyl, BHHBP. Two series of TLCPs were prepared and characterized by CPOM, DSC, and WAXD. Both series of polymers exhibited smetic A phase types. The second investigation discussed the preparation and characterization of thermotropic liquid crystalline polyester based on the triad mesogen monomer, 4,4$\sp\prime$- (terephthaloyldioxy)dibenzoyl dichloride, (ClHTHCl). Various dihydroxy flexible spacers having chemical substituents similar in structure to the repeat units of PET and/or PBT were copolymerized with ClHTHCl and evaluated by CPOM, DSC, and WAXD. From this investigation, a series of polymers were characterized as an enantiotropic nematics. From this series, a candidate was selected as a model system, where the composition of flexible spacers was: 75% bis(4-hydroxybutyl) terephthalate and 25% 1,6-hexanediol. The flexible spacers of the model system was then modified to contain pyridine dicarboxylate units. This modified model system (TLCP$\sb{\rm N}$) was characterized as having a similar phase and phase-temperature relationship when compared to the model system. Upon development and characterization of TLCP$\sb{\rm N}$, ion exchange procedures were developed to exchange the sodium ions of PET-SO$\sb3$Na for hydrogen and subsequently hydrogen ions for zinc. Stoichiometric blends of both the free acid and zinc neutralized form of sulfonated PET were prepared and characterized by FTIR, DSC, and DMTA. For both these blends there was no evidence for specific intermolecular interactions or compatibilization. In the final investigation, both the free acid and zinc neutralized forms of sulfonated PET were blended with poly(ethyl acrylate-co-4-vinyl pyridine). The stoichiometric blends were prepared and characterized similar to the previous study. A zinc blend containing 77% sulfonated PET (7% SO$\sb3$Zn) and 23% poly(ethyl acrylate-co-4-vinyl pyridine) (10.6% VP) appeared to be predominately single phase by DSC and partially phase separated by DMTA. Where similar blends containing 58% poly(ethyl acrylate-co-4-vinyl pyridine) (5.2% VP) appear partially phase separated by both DSC and DMTA.

Several carbonyl-selective reactions were carried out with semicrystalline poly(ether ether ketone) (PEEK) film to assess the reactivity of the diaryl ketones at the film-solution interface. Surface analyses with X-ray photoelectron spectroscopy (XPS), attenuated total reflectance infrared spectroscopy (ATR IR) and contact angle measurement indicate that a thin layer of reagent-induced functionality results from these derivatizations in roughly 50% reaction yield. Data obtained indicate that derivatized surfaces can be functionalized further. Several PEEK-alcohol surfaces were prepared containing primary, secondary and tertiary alcohols, and the secondary and tertiary species were chain extended by reaction with lithium diisopropylamide and ethylene oxide. Primary alcohol groups were introduced by reacting PEEK with acetaldehyde lithiopropyl ethyl acetal and subsequent deprotection. Secondary alcohols were produced by reducing PEEK with Red-Al$\circler$ reagent, and tertiary hydroxyls result from reaction with methyllithium. In general, the alcohol surfaces were reactive toward electrophiles. XPS and contact angle measurement were used to follow surface reconstruction in heat-treated samples containing specific concentrations of surface active polystyrenes (SAP) in a polystyrene matrix (Mn = 10 K). The objective was to determine how certain molecular and environmental parameters influence surface reconstruction. The SAPs were prepared with three different architectures: the first (SAP:E-1) (Mn = 1, 5, 10, 40 and 100 K) contained a single perfluoroalkyl endgroup, the second (SAP:E-2) (Mn = 10 K) contained two fluorinated endgroups and the third contained a single perfluoroalkyl group in the middle of the chain (SAP:M-1) (Mn = 10 K). SAP:E-1 samples were annealed at different temperatures (180, 150, 110$\sp\circ$C and room temperature) for varied lengths of time (24, 48, 72, 96, 120 h and two weeks) to determine optimum annealing conditions to maximize surface fluorine enrichment (as detected by XPS). Comparison of these data indicate the effect of increasing polystyrene tail length on surface-activity of perfluoroalkyl groups. Optimum annealing conditions were used for heat treatment of SAP:E-2 and SAP:M-1 samples and comparisons were made on the basis of differences in architecture.

This work describes the phase behavior and morphology of otherwise immiscible polymer blends that contain small numbers of specific interactions. The experimental results are explained in terms of a new model for phase separation, termed the "ionic crosslink model". Sulfonated polystyrene in both the acid and zinc-neutralized forms was blended with either ethyl acrylate/4-vinylpyridine copolymers or styrene/4-vinylpyridine copolymers. The blends were investigated using differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA), and optical microscopy. At substitution levels of 2%, 5%, and 8% the blends are macrophase separated, microphase separated, and phase mixed, respectively. Microscopy shows that the macrophase separated blends exhibit smaller, more uniform sized domains compared to the unfunctionalized blend. The experimental results are qualitatively consistent with the proposed "ionic crosslink model" for phase separation, in which the chains between ionic groups phase-separate due to an unfavorable free energy of mixing, but the presence of ionic interactions restricts the size of the domains. Aggregation of the ionic groups within the blends was examined using DMTA and small angle x-ray scattering (SAXS). Viscoelastic measurements show the existence of a high temperature loss peak, similar to the peak observed in ionomers. However, the temperature of the transition is depressed relative to the parent ionomers due to internal plasticization. The presence of ionic aggregates was confirmed by calculating the average network functionalities. Activation energies for the high temperature transition are related to the relative strengths of the interactions, which is consistent with the transition being due to motion of the ionic groups. SAXS measurements show that the "ionic peak" present in ionomers is destroyed upon blending. The combined DMTA and SAXS results are consistent with intraparticle scattering models for ionomer morphology and are inconsistent with interparticle scattering models. Tensile properties show enhanced toughness and strength due to the presence of specific interactions. The improved properties are attributed to two factors: the presence of interactions which enhance the interfacial adhesion between phase separated domains and the presence of ionic aggregates which act as filler particles. Examination of freeze-fractured surfaces shows evidence for improved interfacial adhesion and enhanced formation of crazes.

The synthesis and adsorption characteristics of specifically functionalized block copolymers have been investigated. Specifically functionalized polymers are block copolymers of controlled MW, MWD, block size and block placement, and meet the requirement that one of the blocks interact strongly with a given surface whereas the other one does not. Synthetic procedures involved living anionic polymerization of various monomers, allowing preparation of narrow-dispersity block copolymers of specific molecular weight, overall composition, block lengths and (in one system used) block placement. The location (along the chain) of the surface attachment could be controlled through appropriate block sequences. The grafting of polystyrene chains to the surface of poly(chlorotrifluoroethylene) film was accomplished by reaction of the surface with three living polymer anions: polystyryl lithium, butadiene endcapped polystyryl lithium and ethylenesulfide endcapped polystyryl lithium. The effects of solvent, reaction temperature, reaction time and anion concentration of the grafted layer were studied by XPS, ATR-IR, gravimetrics and contact angle. The synthesis of styrene/propylenesulfide block copolymers was studied in some detail and was found to result in polymeric dimers caused by disulfide formation. These disulfide linkages were cleaved by reaction with dithiothreitol (DTT). Endcapping with ethyl bromide stabilized the polymers against disulfide formation and degradation of the polypropylenesulfide block. These polymers were adsorbed onto gold surfaces (from THF and cyclohexane) and analyzed by XPS, contact angle, and photomodulated external reflectance IR spectroscopy. The amount adsorbed was found to decrease with increasing size of the polypropylenesulfide (sticky) block. The largest body of work presented discusses the synthesis of SF polymers with controlled placement of SF blocks at desired locations along the chain. This work focussed on the specific functionalization of the styrene blocks in styrene/tert-butyl styrene block copolymers. The various sulfonation reactions investigated gave poor results. Reaction with DEOM/SnCl$\sb4$ was found to be very selective, controllable and allowed introduction of hydroxydiethyl malonate SF at various positions along the chain. The adsorption of these (diblock and triblock) polymers to various silica surfaces was investigated. The data are qualitatively compared with theoretical predictions by both Marques and Evers.

The stress relaxation behavior of critical gels originating from six highly entangled polybutadienes of low polydispersity with molecular weights from 18,100 to 97,000 g/mole were investigated. The polymers were vulcanized by a hydrosilation reaction which takes place nearly exclusively at the pendant 1,2-vinyl sites which are distributed randomly along the polybutadiene chain. The empirical BSW-spectrum was found to describe the relaxation behavior of the uncrosslinked precursor state. A characteristic parameter of the BSW-spectrum is the longest relaxation time of the precursor. Crosslinking increases this longest relaxation time even further but had little effect on the relaxation behavior in the entanglement and transition zones. The relaxation time spectrum of the material at the gel point (critical gel) was found to be well represented by the superposition of the BSW-spectrum and CW-spectrum with minor modifications to the intermediate time regime. The long time behavior follows a power law as described by the Chambon-Winter equation, G(t) = St$\sp{\rm -n}.$ n was found to be constant with a value close to 0.5 over a stoichiometric ratio range of 0.25 $<$ r $<$ 3.0. The gel strength (S) was found to scale with the precursor molecular weight as $\rm S \sim M\sbsp{w}{zn}$ where z is the exponent from the zero shear viscosity molecular weight relationship $\rm\eta\sb0\sim M\sbsp{w}{z},$ is commonly found to be z = 3.3-3.6. A simple empirical model combining first order kinetic analysis with the Flory-Stockmayer branching theory was developed to predict the gel time as a function of stoichiometric ratio and precursor functionality. In-situ rheological measuring techniques of gelation allow for accurate determination of the gel point. The kinetic model was found to agree well with experimental data.

Model networks of polytetrahydrofuran (PTHF) were prepared by end-linking reaction with the known functionality of cross-links, and the specific number of network chains of known molecular weight distribution. Bimodal networks are composed of stoichiometric amounts of short and long chain prepolymers. By selectively labeling either short or long chains with deuterium, one can simultaneously evaluate the local structure of each species by such methods as infrared (IR) and small-angle neutron scattering (SANS). The micro-structure of the bimodal networks were studied by these methods with an emphasis on the effect of spatial distribution of chain lengths between cross-links. IR results have revealed that the segmental orientation function for the long chains is almost equal to the one for the short species during the uniaxial deformation. There are two possible interpretations for the deformation mechanism from this equality according to the rubber elasticity theory of Kuhn and Grun. One is that the extension ratios of the two species are not equal as expected, therefore individual chain segments deform non-affinely. Another is that the bimodal network follows an affine deformation if it is treated as an "averaged unimodal" system consisting of the chain segments with the weight-averaged length between the long and short chains. SANS results have indicated spatial inhomogeneity in the bimodal network with a high mole fraction of short chains. The inhomogeneity is attributed to the formation of clusters of highly cross-linked domain of short chains in the media of sparsely cross-linked long chains. Size of a cluster increases in proportion to the increasing amount of short chains, while the average distance between clusters seems to be less dependent upon. The deformation ratios of the distance between clusters and that of the gyration radius of long chains were quantified. In all cases, it has observed that the bimodal network deforms locally in a non-affine manner, however, at the larger scale the effective functionality from the short chain clusters dominates and deforms close to affinely. These results suggest that theoretical developments incorporating the structural information are necessary to have a better understanding of the local behavior and to relate to macroscopic properties in real polymer networks.

No description available.

No description available.