Semicrystalline ionomers are an important class of polymers that are utilized in a wide range of applications. The particular end-use applications of these materials are determined by their chemical, physical, and thermomechanical properties which are directly related to their crystallization behavior. It is therefore critical to identify structure-property relationships for these materials. Sulfonated syndiotactic polystyrene (SsPS) is used as a model semicrystalline ionomer and two approaches are utilized to control the rate of crystallization of the SsPS ionomer in the presence of ionic aggregates. The first approach investigates the effect of the incorporation of nanoscale particles, montmorillonite clay, on the crystallization behavior of SsPS. The morphology of the ionomer clay hybrids were studies via TEM and WAXD while the crystallization behavior of SsPS in the presence of the clay was evaluated using DSC. It was found that the SsPS matrix containing 5 wt.% organically-modified clay crystallized more rapidly than the sPS homopolymer containing the same clay content. This behavior is attributed to the presence of homogenously dispersed nanoscale clay platelets that act as nucleation sites distributed throughout the ionomer matrix. The second approach that employed involved the manipulation of SsPS ionomer architecture via a controlled placement of the ionic sulfonate groups along the polymer backbone. A post-polymerization sulfonation technique was developed to place the sulfonate groups along the homopolymer backbone in a non-random fashion leading to a pseudo-block ionomer architecture. The crystallization behavior of the non-randomly sulfonated SsPS ionomer is compared to randomly sulfonated SsPS using differential scanning calorimetry. The morphologies of the two ionomers were studied using SALLS and SAXS. We have found that the non-randomly sulfonated SsPS ionomer crystallizes much more rapidly than the randomly sulfonated ionomer. The more rapid crystallization behavior of the non-random ionomer to the presence of longer sequences of unsulfonated homopolymer that are able to readily organize into crystalline structures than the random SsPS ionomer containing the same ionic content. / Ph. D.

Simultaneous differential scanning calorimetry (DSC), small-angle (SAXS) and wide-angle X-ray scattering (WAXS) measurements were adopted for more precise determination of the equilibrium melting temperatures (Tm*) of a and b phases in bulk-crystallized syndiotactic polystyrene. On the basis of Kratky-Porod approximation, a new method for determining crystalline lamellar thickness from SAXS profiles obtained at high temperatures where there are only limited number of discrete crystalline lamellae dispersed in the melt matrix was developed. This method is shown to be reliable as it gave comparable results obtained from the conventional 1D correlation function method for SAXS profiles obtained at lower temperatures where lamellae are closely stacked. Results of the subsequent Gibbs-Thomson analysis indicated that the trigonal a phase is the entropically favored high temperature phase with Tm* = 355 oC whereas the b phase is enthalpically favored at lower temperatures, with Tm* = 314 oC. Compared to previous held contention in the temperature-dependent phase stability of these two phases, the current phase stability assignment is more consistent with both the density and the symmetry of the corresponding crystal structures. It also explains various observations reported previously on the competition between the two polymorphs during crystallization and during melting.

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The main object of this study is to explore the possibility of using metallocene catalyst and reagent toe preparation syndiotactic polystyrene (sPS) framework connected with different polymer segments. Despite its enhanced thermal stability, the stereo-regular sPS generally has poor miscibility with other conventional polymers, which substantially limits its use in commerce. Therefore, chemical modifications on sPS were attempted in this study to hopefully introduce polar chain segments into the olefinic sPS chains and to possibly vary its properties and so, its miscibility with other polymers. Here, a novel metallocene catalyst prepared from (

The sterically expanded octamethyloctahydrodibenzofluorene moiety, C29H38 (Oct), has been incorporated into ansa-metallocenes and constrained geometry catalysts (CGC's). Utilization of this sterically expanded version of fluorene has resulted in solidstate anomalies for both systems. The ansa-metallocenes Me2C(n5-C5H4) (n5-C29H36)MCl2, M = Zr, Hf and Me2C(n5-C5H4)(n5-C29H36)ZrBn2 demonstrate crystal motifs expected for ansametallocenes while Me2C(n5-C5H4)(n5-C29H36)MMe2, M=Zr, Hf exhibit diffuse diffraction, a phenomenon that is extremely unusual for organometallic complexes. This crystalline anomaly is the result of a disorder restricted to two dimensions caused by the rare pillared motif of the system. The best solution for this system consists of parallel and anti-parallel pillars present in a 60:40 ratio. The solid state anomaly observed for the Oct-CGC's occurs on a molecular level. The parent Oct-CGC, Me2Si(1-C29H36)(1-N-tBu)ZrCl2·OEt2, demonstrates an unprecedented n1 ligation to the fluorenyl-based ring. Systematic derivatization of this system via halide substitution, alkylation, and exchange of Zr for Hf has revealed that the n1 ligation persists for systems with small substituents on the metal center capable of retaining a coordinated ether. It is hypothesized that the unusual structure of this new Oct-CGC results in Me2Si(1-C29H36)(1-N-tBu)ZrCl2·OEt2/MAO (MAO = methylaluminoxane) being six times more active in the homopolymerization of 1-octene than ethylene. When compared to the prototypical Ti-CGC Me2Si(n5-C5Me4)(n1-N-tBu)TiCl2/MAO, the Oct-CGC is 85 times more reactive in the homopolymerization of 1-octene and 52 times more active in the copolymerization of 1-octene and 4-methyl-1-pentene. The high reactivity of the Oct-CGC towards alpha-olefins results in the observation of an unyielding comonomer effect in the copolymerization of these olefins with ethylene. In addition, the Oct-CGC is perhaps the most syndioselective catalyst known. With an enantiofacial selectivity of 99.7% and a remarkably high activity towards alpha-olefins, the Oct-CGC is capable of producing the highest melting syndiotactic polypropylene (Tm = 165oC, annealed = 174oC) reported thus far. The high activity and syndioselectivity of the Oct-CGC can be extended to the production of syndiotactic poly(4-methyl-1-pentene) with the highest melting point thus far reported (Tm = 215oC).

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Utilization of methylaluminoxane (MAO) activated metallocene and constrained geometry (CGC) olefin polymerization catalysts containing fluorenyl or octamethyloctahydrodibenzofluorenyl (Oct) moieties has yielded three series of syndiotactic copolymers of propylene with higher a-olefins. The melting temperatures of these polymers were analyzed, and found to correspond directly with the mole percent incorporation of comonomer, as well as with the frequency of stereoerrors in the polymers. Further analysis indicated that rmrr stereoerrors, a result of site epimerization, occur in close proximity to the incorporated comonomers. The MAO-activated fluorenyl/Oct-containing metallocene and CGC catalysts were further utilized to produce syndiotactic samples of poly(1-butene) (s-PB) and poly(1- pentene) (s-PPe). The syndiotacticity of the samples was quantified by 13C NMR and the melting temperatures determined by DSC. The samples of s-PB and s-PPe produced by Me2Si( h1-C29H36)( h1-N-tBu)ZrCl2·OEt2 (Oct-CGC) were found to melt at higher temperatures (55.9 and 43.1 °C, respectively) than any previously reported samples. The MAO-activated Oct-CGC was also used to produce polyethylene samples at a variety of polymerization temperatures and pressures. All of the samples were found to contain an unprecedented degree of branching (13-65 total branches per 1000 carbon atoms) for an early transition metal single-site catalyst. The branches were found to be almost exclusively of two or greater than five carbon atoms in length, and the levels of the longer branches could be controlled by varying the polymerization conditions. The number of ethyl branches was roughly 5 per 1000 carbon atoms for all samples. Finally, a binary catalyst system comprising the Oct-CGC and a chromium-based ethylene trimerization catalyst, ((tBuSCH2CH2)2NH)CrCl3, was developed. This MAOactivated catalyst system could be tuned to produce polyethylene samples with 17-49 total branches per 1000 carbon atoms. Between 4 and 16 of these branches were found to arise from incorporation of 1-hexene produced by the chromium oligomerization catalyst. Adjusting the ratios of oligomerization catalyst, polymerization catalyst, and activator was found to allow rational control over the branch content of the polymers. The branching levels could also be varied by altering the time between injection of the oligomerization and polymerization catalysts into the system.

Reported is a study of the crystallization behavior of syndiotactic polystyrene (sPS) and its copolymers (with 4-bromostyrene as the comonomer or with atactic polystyrene arms grafted on the comonomer sites) via three sets of experiments. The first involves the study of structural identification of negatively birefringent spherulites by means of polarized light microscopy (PLM) and scanning electron microscopy (SEM). Results indicated that the optically positive and optically negative spherulites have same morphological features. Differences in the optical texture are due entirely to differences in orientation of the (anisotropic) sheaf-like precursors: the rigid nature of crystalline lamellae renders incomplete development of spherical symmetry even at the axialitic size of tens of microns. In the second part, we propose a modified approach for more precise determination of the Tm* value by taking advantage of the dual-mode distribution of crystalline lamellae in analyzing small-angle X-ray scattering (SAXS) profiles. This method should be generally applicable to other semi-crystalline polymers with dual-mode distribution in lamellar thickness. Results from wide-angle X-ray diffraction (XRD) suggest the presence of ?'-to-?" phase transformation at ca. 264 oC; no indications for the previously proposed ?-to-? transformation are identified. We therefore conclude that the ?' form is truly metastable; the ?"-form is the entropically favored high temperature phase (with Tm* = 300 oC) whereas the more ordered ?' phase (with Tm* = 288 oC) is enthalpically favored at lower temperatures. In the third set of experiments, identification of effects of copolymerization has been studied via a combination of PLM, differential scanning calorimetry (DSC), XRD, SAXS, and transmission electron microscopy (TEM). Results show that the equilibrium melting temperatures (determined via either Hoffman¡VWeeks or Gibbs¡VThomson plots) of the copolymers are significantly lower than that of the corresponding sPS homopolymer. The PLM observations indicate that the axialitic growth rates in copolymers are drastically lower than that of the corresponding homopolymer at comparable backbone length and supercooling. Both XRD and TEM results indicate preferred formation of the ?" phase upon melt crystallization in the bulk state; however, the ?" phase (instead of ?' phase that is the more commonly observed for sPS homopolymers in the bulk state) is dominant in thin films.

A series of four novel halosilylsubstitued monocyclopentadienyl titanium complexes; [Si(CH3)2FCp]TiCl3 – FSiTTC, [Si(CH3)F2Cp]TiCl3 F2SiTTC, [Si(CH3)Cl2Cp]TiCl3 - Cl2SiTTC, [Si(CH3)2ClCp]TiCl3 - ClSiTTC was tested as catalytic precursors for polymerization of styrene in toluene. The maximum polymerization activity was achieved after polymerization period of 20 minutes. Activity decreased in order FSiTTC/MAO > F2SiTTC/MAO > Cl2SiTTC/MAO > ClSiTTC /MAO. Prepared polystyrenes were characterized using 13C NMR spectroscopy and DSC analysis. Syndiotacticity index of obtained PSs was determined by means of Soxhlet extraction with butan-2-one as solvent. Syndiotacticity indexes of PSs obtained by investigated catalysts possessed higher values then those obtained by standard catalysts (CpTiCl3 a Cp*TiCl3) at comparable polymerization conditions.