The thermal reconstruction (80-110$\sp\circ$C) of surface-modified films of poly(chlorotrifluoroethylene) (PCTFE) was studied by contact angle and x-ray photoelectron spectroscopy. The modified surfaces studied, synthesized via the reaction of PCTFE with lithium reagents, were PCTFE-TMO (containing a 10 A thick modified layer of dimethyl-oxazoline functionality), PCTFE-COOH (produced by hydrolysis of PCTFE-TMO), PCTFE-OH (30 A and 1100 A thick modified layers), and PCTFE-OC(O)CH$\sb3$, PCTFE-OC(O)CF$\sb3$, PCTFE-OSiMe$\sb3$, and PCTFE-OC(O)(CF$\sb2$)$\sb3$CF$\sb3$ (produced by reaction of 30 A-modified PCTFE-OH). Two reorganization processes are evident--one occurs in PCTFE-TMO and PCTFE-OH (30 A) for which changes are observed both by contact angle and XPS; migration of PCTFE units into the outer 10 A is proposed. Another process is evident in the reconstruction of PCTFE-OC(O)CH$\sb3$ and PCTFE-OH (1150 A) for which only a contact angle change is observed; repeat units do not measureably migrate and rotation is proposed. The heterogeneous (gas-solid) reaction of polyethylene films with chlorine gas was studied with the goal of confining the chlorination to the surface (outer $\sim$100 A) of the film. The effect of chlorine concentration, light intensity, and reaction time on the depth of chlorination (thickness of the modified layer) and extent of chlorination (density of chlorine substitution on the PE chain) was studied by XPS, ATR-IR, TIR, and gravimetric analysis. Chlorination with 1 atm. Cl$\sb2$ in the dark gave a low extent of substitution ($\sim$1 Cl per 9 C after 22 h) although the reaction proceeded deeply into the film. Chlorination with 1 atm. Cl$\sb2$ under UV or visible light gave more highly chlorinated surfaces ($\sim$1 Cl per C in 2 min.) and the reaction occurred more surface-selectively. Chlorination with low chlorine pressures (2-50 mm) was used to prepare samples with very thin ($<$100 A thick) chlorinated layers. A variety of reactions of the chlorinated (and brominated) polyethylene surfaces were attempted in order to assess the feasibility of using the surface-confined alkyl halides as a reactive handle for the synthesis of other modified polyethylene surfaces. Although the halogenated surfaces could be partially dehydrohalogenated (and the resulting double bonds could be brominated or hydroborated and oxidized) substitution reactions were unsuccessful.

Biodegradable polymers, for biodegradable plastic utility and drug release biomedical applications, are the primary objectives of this thesis research. We have synthesized poly($\beta$-hydroxybutyrate) (PHB), poly($\beta$-malic acid) (PMA) and their copolymers by the ring-opening polymerization reactions of $\beta$-butyrolactone and $\beta$-benzyl malolactonate. A varity of catalysts were used, including the stereoregulating catalysts, ethyl aluminoxane (EAO) and the product of the in-situ preparation of Et$\sb3$Al/H$\sb2$O, as well as the non-stereoselective catalysts, Et$\sb2$Zn/H$\sb2$O and (5,10,15,20-tetraphenylporphinato)aluminum chloride (TPPAlCl). The degree of stereoregulation of the homopolymers was enhanced by the use of a stereoregulating catalyst, followed by product extraction. The resulting insoluble fractions of PHB and PBML are stereoregular crystalline polymers having high molecular weights, with the former compared with naturally occurring P( (R) -HB) in corresponding properties. The stereoregularity of the synthetic polymers was determined by $\sp{13}$C (75.4 MHz) NMR spectroscopy, differential scanning calorimetry (DSC) and FTIR spectroscopy. The yield of polymerization was optimized by using the Et$\sb2$Zn/H$\sb2$O and TPPAlCl catalysts, resulting the amorphous polymers with relatively low molecular weights. The analysis of copolymer tacticity and comonomer sequences by using $\sp{13}$C-NMR and DSC indicates a random distribution of the copolymer sequences. The stereochemical course of the ring-opening polymerization of BL with the Et$\sb3$Al/H$\sb2$O and Et$\sb2$Zn/H$\sb2$O catalysts was studied using (S) -BL as a stereochemical probe. The (S) -$\beta$-BL, which was prepared in five steps from naturally occurring P( (R) -HB), had an optical purity in excess of 97% as measured by $\sp1$H NMR spectroscopy in the presence of a chiral europium shift reagent, Eu(hfc)$\sb3$. The stereochemical configuration and isomeric purity of the repeating units in the polymers obtained were determined both from their specific optical rotation and by degradation of the polymers to their component methyl $\beta$-hydroxybutyrate units. From our investigations it was concluded that the ring-opening reaction can be carried out by different routes in the Al- and/or Zn-water catalysts, and the two enantiomers, P((R) -HB) and P((S) -HB) were obtained as the result of the configuration retention or inversion. These enantiomers of PHB are very useful for the study of the stereochemistry of synthetic poly($\beta$-lactone)s and their biodegradability.

Dynamic light scattering (DLS) and forced Rayleigh scattering (FRS) were used to study polymer diffusion in solution in two kinds of porous materials: porous glasses and suspensions and gels formed from fumed silica particles. The diffusants were: dendritic polyamidoamines, linear polystyrenes, and dye-labeled polystyrenes. Polymer diffusion in porous glasses was investigated, by using DLS, as a function of time scale (t), polymer hydrodynamic radius (R$\sb{\rm H}$), and pore radius (R$\sb{\rm P}$). As t increases, the apparent diffusion crosses over from single pore diffusion (in which steric obstruction is weak) to macroscopic diffusion (in which the tortuosity of the pore networks is fully effective). Computer simulated diffusion agreed qualitatively with the crossover observed by DLS. The dependence of hindered diffusion on the size ratio $\lambda\sb{\rm H}$ = R$\sb{\rm H}$/R$\sb{\rm P}$ was studied for dendritic polyamidoamines and linear polystyrenes in porous glasses. For $\lambda\sb{\rm H}$ $\ll$ 1, when hydrodynamic interactions dominate, dendritic polymers diffuse more slowly than linear polymers of comparable $\lambda\sb{\rm H}$. The diffusion results of the dendritic polymer and of the linear flexible polymer agreed quantitatively with the hydrodynamic theories for a hard sphere in a cylindrical pore, and for a random-coil macromolecule in a cylindrical pore, respectively. At large $\lambda\sb{\rm H}$, irregularities in local pore size lead to conformational entropy changes as the macromolecule moves. The experimental data agree qualitatively with the entropy barrier theory. Diffusion of dye-labeled polystyrenes within gels and suspensions formed from fumed silica was studied using FRS. Untreated silica was found to adsorb the labeled polymer, leading to strong hindrance even at very low silica concentration. Thorough quenching of the silica surface by silanization prevented polymer adsorption. The dependence on silica volume fraction of the resulting weakly hindered diffusion in treated silica was found to be consistent with simple theories of steric obstruction.

This thesis describes the synthesis and characterization of segmented and triblock copoplymers with mesogenic hard blocks and flexible spacer soft blocks. Three series of segmented block copolymers, one series of twin liquid crystal (LC) polymers and a variety of model compounds have been prepared. The first series of segmented block copolymers consist of potentially mesogenic dyad hard block and oligomeric flexible spacers. These materials are not liquid crystalline, although chain extended analogs do show elasticity and strength. The second and third series of segmented polymers consists of well defined tetrad and pentad mesogenic blocks. These polymers and their analogous model compounds exhibit liquid crystallinity. The preparation of these materials involved the condensation of a bisphenolic prepolymer of, either poly(tetramethylene ether)glycol, polyTHF, or polypropylene glycol, PPG, of varying molecular weight, with a variety of aromatic diacid chlorides: 4,4$\sp\prime$-azobiphenylene, 4,4$\sp\prime$-azoxybiphenylene, 4,4$\sp\prime$-biphenylene, 2,6-naphthalene and 4,4$\sp\prime$-terephthaloyloxybiphenylene. The resulting polymers are liquid crystalline and exhibit reproducible melt transitions by differential scanning calorimetry, DSC and polarized optical microscopy, POM. The polymer melts are birefringent, and textures for some of the polymers are consistent with either smectic or nematic mesophases. The LC polymers show a convergence of Ti with Tm as the spacer length increases from 40 to $\sim$200 atoms. It is also shown that the type of polymeric soft segment used to prepare tetrad LC polymers has a remarkable effect on the liquid crystallinity and physical properties of the resulting polymer. Finally, variations in the hard block can dramatically effect both the stability and structure of a liquid crystalline phase. In the final section, "twin" or triblock LC polymers are described. These polymers were prepared to compare thermal properties of segmented vs. triblock copolymers with chemically identical blocks. The preparation involved the synthesis of a novel mono functional mesogen. The twins exhibit thermal trends similar to those of the corresponding segmented polymers.

Two closely related series of hydrocarbon polymers that contain mesogenic units interconnected by flexible methylene spacers along the main chain were prepared. The liquid crystalline properties of these two series of polymers were studied by differential scanning calorimetry (DSC), polarized light optical microscopy (POM) and X-ray diffraction. The first series of hydrocarbon polymers having biphenyl mesogenic units and polymethylene spacers in the main chain were prepared by a nickel catalyzed carbon-carbon coupling reaction. Polymers with number average molecular weights in the range of 4000 to 6000 have been obtained. Homopolymers with spacer units varying from 6 to 10 methylene units and equimolar copolymers with 6/8, 6/10, and 8/10 methylene spacers were found to exhibit smectic mesophases. The effect of the variation of the lengths of the methylene spacers on liquid crystalline properties is discussed. In general, increasing the length of the methylene spacers is accompanied by a decrease in the isotropization temperature. An alternating odd-even effect in transition temperatures is also observed with the even members having higher isotropization temperatures than the odd members. Two different X-ray diffraction patterns for odd and for even membered homopolymers were observed for unoriented samples. The second series of hydrocarbon polymers having tolan mesogenic units and polymethylene spacers in the main chain were prepared by a palladium catalyzed carbon-carbon coupling reaction. Polymers with number average molecular weights in the range of 3000 to 4000 have been obtained. Four polymers with 6, 8, 10 and 12 methylene spacers were prepared and they were found to exhibit smectic mesophases. Lengthening the polymethylene spacer between the tolan mesogenic groups decreased both the melting points (T$\sb1$) and the isotropization temperatures (T$\sb{\rm i}$) and also narrowed the mesomorphic ranges.

The thermodynamics of narrow molecular weight distribution binary blends of polystyrene/poly(alpha-methylstyrene) (PS-P$\alpha$MS) have been studied. The range of miscibility of these blends as a function of molecular weight has been determined by differential scanning calorimetry and optical techniques. Neutron scattering in the miscible region using the random phase approximation was used to determine the interaction parameter and correlation length. The temperature and composition dependence of these parameters were also obtained. Flory-Huggins-Staverman theory and Koningsveld's empirical "g" parameter were used to fit the temperature and composition dependence of the interaction parameter determined from neutron scattering data. The interaction parameter shows a composition dependence, in contrast to some previous studies. The temperature dependence of the neutron scattering has been measured for the first time for this system, and suggests LCST behavior should be observed for this system in the molecular weight range studied. Previous researchers' work shows this system to have a UCST, but our phase behavior data are in agreement with equation of state LCST predictions of Cowie and McEwen. An explanation as to why the LCST behavior has not been observed by light scattering techniques is presented.

Polyurethanes containing the biphenyl mesogen were synthesized and characterized by differential scanning calorimetry, wide-angle X-ray scattering and polarizing optical microscopy. One polyurethane (D6T24), which has an asymmetric structure, displays a monotropic smectic mesophase. The crystallization and mesophase-forming behavior of D6T24 is highly dependent on molecular weight. Another polyurethane (D6T26), which has a symmetrical structure, also displays a monotropic smectic mesophase. Because the crystalline unit cells of D6T24 and D6T26 are significantly different, combining the two polyurethanes in copolymers and blends suppresses crystallization, and in some cases produces enantiotropic systems. Blends of D6T24 and D6T26 containing more than 30% D6T24 by weight, and a random copolymer containing 47% D6T24 repeat units and 53% D6T26 repeat units, form enantiotropic smectic mesophases which do not crystallize. Annealing at high temperatures appears to transform the blends into copolymers, probably by means of transurethanification reactions.

This research was motivated by theoretical and experimental objectives regarding blends of thermotropic liquid crystalline polymers and flexible coil polymers with specific application to in situ fiber-reinforced composites. The primary aim has been the prediction of the phase behavior of blends and diblock copolymers containing rigid (liquid crystalline) species. The objective was to first derive a free energy expression that went beyond the mean field theories by taking composition fluctuations into account. Computational procedures were then developed for the evaluation of the free energy. The analytical derivation and the computational procedures provide the means for predicting the phase behavior of blends and diblocks as a function of molecular weight. The connectivity of the diblock molecule is shown to be responsible for a shifting of the isotropic-nematic transition in composition and a lowering of the critical $\chi$ value. A critical examination of the theory is difficult due to the lack of experimental data required for comparison. A secondary aim was to resolve some specific questions about a novel blend system that shows good prospects as an in situ composite. Investigation concerned the effect of blend composition on crystallization, the nucleating properties of the liquid crystalline component relative to those of more common nucleating agents, and the degree of miscibility between the blend components. The liquid crystalline component was shown to decrease crystallinity with increasing concentration. Its nucleation properties were similar to those of more common nucleating agents. No evidence of immiscibility was found in the blend system.

In the first half of this dissertation, density functional theory of first order transitions was used to describe the ordering phenomena of amorphous diblock copolymers. The resulting formalism was then applied to the ordering of symmetric diblock copolymers to the lamellar morphology for values of $\chi$N above the microphase separation transition. $\chi$ refers to the Flory interaction parameter and N is the number of statistical segments comprising the copolymer. Three distinct regimes for the N dependence of the domain space, D, were identified. For 10.495 $<$ $\chi$N $<$ 12.5, the weak segregation limit is realized where D is proportional to N$\sp{0.5}$. For $\chi$N $>$ 105, the strong segregation limit is achieved where D is proportional to N$\sp{0.67}$. Between these limits, for 15 $<$ $\chi$N $<$ 95, a new regime with characteristics distinctly different from those of the weak and strong segregation regimes was found. Within this "intermediate" regime, D is proportional to N$\sp{0.72}$ and the domain boundaries support substantial fluctuations. The distinct features of the microscopic density profiles in the various regimes are discussed. In addition, density functional theory was employed to investigated the phase behavior of non-symmetric diblock copolymers. In the second half of this dissertation, Monte Carlo simulations were performed in order to study the dynamics of a polyelectrolyte chain in three-dimensional random porous media with an applied electric field. It was found that the dependence of the chain mobility, $\mu$, on the number of segments comprising the polymer, N, is in qualitative agreement with actual gel electrophoresis experiments. Further, three regions for the N dependence of the mobility were identified and determined to be a function of the average size of the polyelectrolyte in relation to the average pore size in the random medium. In the region of small N, the mobility is influenced primarily by collisions with the random media. As the average size of the polymer becomes comparable to the average pore size, the existence of entropic barriers has the effect of introducing a strong dependence of the mobility on N. In the high N regime, the polymer chains become significantly entangled with the random medium, further impeding the motion of the chains. However, in this high N regime, the chain dynamics cannot be explained by reptation. Lastly, it was demonstrated that the chain dynamics of a polyelectrolyte in the presence of a regular array of obstacles with an applied electric field defers from the dynamics of a chain in a random medium. Indeed, it was demonstrated that the presence of random medium gave rise to a much more efficient separation of polyelectrolytes of different N.

Entanglement is one of the most important--but poorly understood--effects that occur in polymeric materials of high molecular weight. This work studies aspects of three long-standing problems--self-entanglement in a ring polymer, mutual entanglement between a ring and a rod, and network self-entanglement--and their solutions, by means of computer simulation. In self-entanglement, ring polymers are represented with the off-lattice rod-bead model. Perfect unbiased model instances are produced that have between N = 32 and 2048 beads, produced at several different values of bead radius, to represent polymers in solvents of varying quality. The topological state of each ring is represented with the Alexander polynomial. It is observed that the probability of observing a trivial knot $(P\sb{U})$ has a decreasing exponential dependence on the contour length (N) of the polymer, or that $P\sb{U}(N)=\exp(-N/N\sb0).$ The characteristic length $(N\sb0)$ varies by many orders of magnitude depending on solvent quality. In mutual-entanglement, a ring polymer is represented with the off-lattice rod-bead model, as in the study of self-entanglement. An infinitely long spike of zero radius is inserted at a (minimum) distance r from the center of mass of the ring, and the resulting system is deemed to be entangled if the resulting Gauss winding number (GWN) between the ring and the spike is zero. For a Gaussian chain with no excluded volume, the probability of a non-zero GWN is given by ${\cal P}(r,N)\approx A\exp(-(r/R\sb{g})\sp2/2B),$ where A = 0.7, B = 0.8, and $R\sb{g}$ is the radius of gyration of the ring. Cases where the ring has excluded volume and the spike has non-zero radius are also studied. Finally, a reasonable mathematical definition is provided of what might constitute "entanglement" in terms of a polymeric network. Model instances of networks are created given various initial compositions, and physical and virtual cross-links are both counted. The ratio of virtual to physical cross-links, $R\sb{e},$ depends strongly on the parameters which are used in the formation of the network. We suspect that entanglement effects are significant in rubber elasticity, but they are by no means of paramount importance.