Comparative analysis of the clathrate forms of syndiotactic polystyrene,poly (p-methylstyrene) and poly (m-methylstyrene)

The crystal structures of the clathrate forms of syndiotactic polystyrene (s-PS), poly (p-methylstyrene) (s-PPMS) and poly (m-methylstyrene) (s-PMMS) containing guest molecules having widely different steric hindrance are compared in detail. Common features and differences concerning the packing of the chains, the shape and the dimensions of the cavities and the stability of the forms deprived of the guest molecules are pointed out. A new clathrate form of s-PPMS containing CS₂ is also described.     

On the clathrate structures of syndiotactic poly(m-methylstyrene)

The crystal structures of clathrate forms of syndiotactic poly(m-methylstyrene) containing guest molecules having different steric hindrance (CS₂, benzene and orto-dichlorobenzene) are presented. The structures are all characterized by polymer chains in s (2/1)2 helical conformation and guest molecules packed in an orthorhombic unit cell according to the space group Pcaa. All the presented clathrates belongs to β class indipendently from the dimensions of the guest molecule. In this aspect they differ both from clathrate forms of syndiotactic polystyrene, all belonging to α class, and from clathrate forms of syndiotactic poly(p-methylstyrene) that belong to α or β class according to the steric hindrance of the guest molecule.     

Thermal degradation of poly(p-methylstyrene)

The thermal degradation behaviour, in the absence of oxygen, of poly(p-methylstyrene) has been investigated. Monomer is the main product formed in the degradation process, together with different oligomers which have been identified and whose amounts have been determined. A reaction mechanism accounting for the formation of the degradation products, and similar to the mechanism established for polystyrene, is proposed. The main differences of the process comparing with polystyrene are the higher amount of monomer which is produced and the crosslinking structures which are formed at T < 400° C.     

Preparing a functionalized thermoplastic elastomer: Chlorination and synthesis of poly(p-methylstyrene)-block-polyisoprene-block-poly(p-methylstyrene)

A poly(p-methylstyrene)-block-polyisoprene-block-poly(p-methyl styrene) thermoplastic elastomer was synthesized via anionic polymerization using n-butyllithium as an initiator. The sequential method used for the synthesis has resulted in a nearly monodispersed polymer with a polydispersity of 1.02. Chlorination of such formed copolymer using aqueous sodium hypochlorite was then conducted in a variety of solvents. At a 6.9 mol ratio of sodium hypochlorite to monomer unit, chlorination occurred via a substitution reaction instead of an addition reaction, regardless of the type of solvent used. Nevertheless, the location at which the chlorine was incorporated into the polymer varied with the type of solvent used. The chlorination occurred primarily in the two poly(p-methylstyrene) end blocks when conducted in n-hexane solvent. However, only the polyisoprene middle block was chlorinated in chloroform. All three blocks could be chlorinated when the reaction was carried out in methylene chloride. The microstructure of the chlorinated molecules were analyzed using ¹H-NMR and ¹³C-NMR, and the degree of chlorination varied from 7 to 50% of constituting monomer units. A significantly higher degree of chlorination occurred when the reaction was conducted in methylene chloride due to its high dielectric constant. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 2969–2980, 1997     

Conformation of syndiotactic poly(styrenesulfonic acid)

A conformational energy map for syndiotactic PSSA indicates that a planar trans sequence of chemical repeat units with a side-chain orientation of χ ? 10° is favored over helix or glide-plane sequences. As the electrostatic potential of this planar sequence is greater than for the (0°,?120°) or (0°, ?80°) sequences it is especially favored under conditions of high ionic strength. Only a very small energy is needed to cause rotational transitions from a planar trans sequence, so that many different sequences exist at any one time in solution. Sequences such as (0°,?20°) are calculated to be hypochromic with respect to the other probable sequences, and this seems consistent with some experimental evidence on the apparent hypochromicity of the band near 261.5 nm under conditions of high ionic strength.     

Amidation of syndiotactic poly(2-methylallyl hydrogen carboxylate)

The amidation of syndiotactic polyacids and the ¹H- and ¹³C-NMR spectroscopic characterization of the resulting polyamides are described. The polyacids have been derived from syndiotactic poly(2-methylallyl alcohol) by esterification with cyclic dicarboxylic acid anhydrides, including N^α-protected aspartic acid anhydrides and glutamic acid anhydrides. The poly(hydrogen carboxylate) were in turn condensed with a series of amines, some of which possessed additional functional groups, e.g. (L)-1-phenylethylamine, histamine, and glycine methylester.     

Raman spectra of extended-chain syndiotactic poly(vinyl chloride)

Raman spectra have been obtained for a typical poly(vinyl chloride) (PVC) of low crystallinity and for a highly crystalline sample of syndiotactic PVC obtained by irradiation of a urea-canal complex. Raman measurements have been made on the three different ordered chain structures possible for ordinary PVC. Extended and folded conformations for the syndiotactic structure and a helical structure for the isotactic molecule obey different selection rules and have different dichroic properties in the infrared and Raman spectra. The observed Raman spectrum is consistent with the model of the extended syndiotactic conformation for crystalline PVC. With the new Raman data some additional assignments can be made in the vibrational spectra of PVC.     

Vapor sorption in emptied clathrate samples of syndiotactic polystyrene

The analysis of chloroform vapor sorption at 35°C in semicrystalline syndiotactic polystyrene samples shows remarkably different sorption isotherms, depending on the crystalline form of the samples. In particular, “emptied” clathrate (“emptied” δ form) samples are characterized by higher equilibrium sorption levels and the differences are particularly relevant for low vapor activities. Moreover, sorption kinetics detected at a vapor activity equal to 0.5 show that in the case of “emptied” δ form samples the sorption rate is much higher than for the other semicrystalline samples. The larger sorption equilibrium uptakes and sorption rates of the “emptied” δ form samples are essentially due to their ability to absorb chloroform, already for low activities, by clathration in the crystalline phase. The measured equilibrium uptakes and sorption kinetics suggest that “emptied” δ form samples of syndiotactic polystyrene could be suitable for removing polluting chlorinated compounds from vapor and liquid streams. © 1997 John Wiley & Sons, Inc.     

Crystal growth in syndiotactic poly(vinyl alcohol) hydrogels

Aqueous solutions of syndiotacticity-rich poly(vinyl alcohol) (s-PVA) form gels easily. The optimum condition of growth of the calcium tartrate crystal formed by diffusing calcium chloride into hydrogels containing tartaric acid was studied with use ofs- PVA of a syndiotacticity of 56 % and a degree of polymerization of 1460. The crystal grew in the gel of the concentrations of 2 % s-PVA and of 0.5 N tartaric acid at pH=4. The relation between the formation of Liesegang rings and shear modulus of a gel was studied by diffusing silver nitrate into gels containing potassium chromate. The distance between rings decreased with increasing shear modulus of a gel in the range from 670 to 7500 dyne/cm². The Liesegang rings were not formed for the shear modulus gel for 280 and 16200 dyne/cm₂.     

Stereoregularity of radically polymerized poly(alkyl acrylates) and poly(trimethylsilyl acrylates) and the preparation of syndiotactic poly(methyl acrylate)

Nuclear magnetic resonance (NMR) spectroscopy was used to determine the stereoregularity of radically polymerized poly(ethyl acrylates), poly(trimethylsilyl acrylates), and poly(isopropyl acrylate-α,β-d₂). The ethyl acrylate polymers consisted of a random configuration having about 50% of isotactic diads, and their stereoregularities were independent of the polymerization temperature (40 to ?78°C). Poly(trimethylsilyl acrylates) and poly(isopropyl acrylate-α,β-d₂) prepared at low temperatures had a syndiotactic configuration. Syndiotactic poly(methyl acrylate) was derived from syndiotactic poly(trimethylsilyl acrylate). For poly(methyl acrylate), an approximate estimation of the stereoregularity by infrared spectroscopy was proposed.     

Rayleigh-brillouin spectroscopy of syndiotactic poly(n-butyl methacrylate) near the glass transition

We present Rayleigh-Brillouin light scattering data of highly syndiotactic poly(n-butyl methacrylate) [PBMA] whose glass transition temperature as measured by DSC is 55°C. The Brillouin peak shifts, Brillouin peak widths, and Landau-Placzek ratios from ?15 to 130°C are reported. The Brillouin peak widths decrease continuously through the glass transition region. This indicates a continual decrease in the strength of processes whose relaxation times are about 10^?10 s with decreasing temperature even as the system becomes glassy. The Landau-Placzek ratio above the glass transition is about 3, indicating the high optical purity of our sample. This low Landau-Placzek ratio arises from the sample's homogeneous stereochemistry. Some of the anomalous behavior observed around 40–50°C in previous PBMA studies is explained in terms of syndiotactic regions within a largely atactic sample.     

Polymerization of vinyloxyaluminum and formation of syndiotactic poly(vinyl alcohol)

The polymerization of diisobutylvinyloxyaluminum, CH₂?CHOAl(i-Bu)₂, and diethylvinyloxyaluminum, CH₂?CHOAlEt₂, did not take place in the presence of typical radical or cationic initiators. The polymerization was realized at 60°C by the addition of tetrahydrofuran (THF) or tetrahydropyran, no conventional initiator being required. Diethyl ether, glyme, and dioxane were not effective on the polymerization. At Dry Ice–acetone temperature, polymerization did not take place, even in the presence of tetrahydrofuran, but did take place in the presence of both THF and SnCl₄. The role of cyclic ethers in the polymerization was studied. Polymers were converted into poly(vinyl alcohol) (PVA) by solvolysis. All the resulting PVA was syndiotactic; particularly polymers obtained at ?78°C showed syndiotactivity of 89%, which is the highest value ever reported.     

Synthesis of isotactic,syndiotactic, and heterotactic poly(tributyltin methacrylate) and poly(tributyltin methacrylate-co-styrene)

Pure isotactic and enriched syndiotactic poly(tributyltin methacrylate) were synthesized by the reaction of the respective poly(methacrylic acid) with tributyltin oxide. The heterotactic polymer was prepared in a similar manner and from free radical initiated (AIBN or BPO) polymerization of tributyltin methacrylate. In each case, polymer configuration was confirmed by ¹H-NMR of the hydrolyzed/esterfied product. The relatively large ¹¹⁹Sn-NMR linewidth of the isotactic tributyltin containing polymer suggests an intra-molecular exchange of the pendant tin groups. T_g, T_d, and M _v data are also reported. Poly(tributyltinmethacrylate-co-styrene) was prepared by free radical polymerization and reactivity ratios [r(styrene) = 0.51, r(TBTM) = 0.49] and Q-e values for TBTM (0.78, 0.38) were determined.     

Photon correlation spectroscopy of syndiotactic poly (n-butyl methacrylate) near the glass transition

Slow relaxing longitudinal density fluctuations in bulk syndiotactic poly (n-butyl methacrylate) [PBMA] were studied by photon correlation spectroscopy as a function of temperature from 70 to 90°C. The shape of the light-scattering relaxation function broadened as the temperature approached the glass transition (T_g = 55°C). The average relaxation time shifted with temperature, consistent with previous studies of PBMA. The relaxation functions were analyzed in terms of a distribution of relaxation rates. The calculated distribution was clearly bimodal and the shape altered with temperature. The higher frequency peak in the distribution corresponds well with previous mechanical and dielectric relaxation studies of the intramolecular relaxation of the acrylate ester side chain. The resolution of the distribution into two modes is due to a well-defined side-chain motion with relaxation strength comparable to the primary glass-rubber relaxation. © 1994 John Wiley & Sons, Inc.