The photolysis of poly(p-hydroxystyrene)

The photochemistry of poly(p-hydroxystyrene) (PPHS) has been investigated, thin films being exposed to 254 nm radiation under high vacuum at 298K. H₂ is the principal volatile product, but small amounts of H₂O are also formed. The polymer becomes rapidly coloured, but unlike other styrene polymers, which remain yellow, PPHS undergoes a progressive colour change from yellow through orange to brown. Infrared spectral data indicate the depletion of OH group concentration, and a concomitant formation of carbonyl, possibly quinonoid species. Crosslinking is rapid and no chain scission was detected. It is likely that the polymeric phenoxy radicals formed by photolysis or by subsequent H-abstraction contribute to the formation of both quinonoid species and crosslinks. The mechanism of the photolysis is discussed.     

Crystal structures of syndiotactic poly(p-methylstyrene) clathrates with two guest molecules having very similar shape and volume

In the present paper we report on the clathrate structures of syndiotactic poly(p-methylstyrene) (s-PPMS) containing chlorobenzene (cell constants: a = 23.5 Å, b = 12.0 Å, c = 7.9 Å and γ = 112.4°; space group: P2₁/a) and toluene (cell constants: a = 19.5 Å, b = 13.5 Å, c = 7.9 Å and γ = 90°; space group: P2₁). Despite the extreme similarity between the shape and volume of these two molecules, they give rise to completely different clathrate structures, the first belonging to α class, the second belonging to β class. Moreover the clathrate form containing chlorobenzene represent the first case in which a α class clathrate form of s-PPMS contains two guest molecules in each cavity while the crystal structure here proposed for the s-PPMS/toluene clathrate represents a new example of chiral crystalline phase in which the polymer helices assume all the same chirality in the lattice. These results underline the fact that the choice of a particular structural organization in the process of clathrates’ formation of s-PPMS is not easily referable only to steric effects but seems to be dependant even on the chemical structure of the guest molecules. A comparison with syndiotactic polystyrene is also done.     

Photodegradation kinetics of poly(para-substituted styrene) in solution

The UV irradiation effects on stability of polystyrene, poly(4-methoxystyrene), poly(4-methylstyrene), poly(α-methylstyrene), poly(4-tert-butylstyrene), poly(4-chlorostyrene), and poly(4-bromostyrene) in dichloromethane, dichloromethane, tetrahydrofuran, and N,N-dimethylformamide solutions were studied in the presence of oxygen at different intervals of irradiation time. The photodegradation was studied at 293 K using fluorescence spectroscopy. Solutions of these polymers were accompanied by quenching of monomer and excimer emissions during the exposure of their solutions to UV light, and by a change in the structure of the fluorescence spectrum. Irradiation of poly(4-methylstyrene) and poly(α-methylstyrene) at excitation wavelength of 265 nm showed an increase of fluorescence intensity of a broad band, at longer wavelength without clear maxima. This may indicate that photodestruction of these polymers by irradiation with light of frequency absorbed by the polymer, may start from a random chain scission, with the possibility of formation of polyene and carbonyl compounds.     

Photolysis of poly(p-isopropyl styrene)

The photodegradation of films of poly(p-isopropyl styrene) with 254 nm radiation at 10^?6mbar and 25±1° has been studied. The principal product is hydrogen but smaller quantities of methane and ethane and a trace of propane are also formed, indicating that the p-substituent also undergoes decomposition. Ultraviolet spectra show rapid changes, particularly in the 230–240 nm region, and a long wave absorption system extending into the visible region also appears. Solubility data indicate the simultaneous occurrence of cross-linking and chain scission, rates of both processes being significantly greater than those for poly(styrene); these results are explicable in terms of the inductive (+I) stabilization (due to the p-C₃H₇ group) of radicals formed on chain scission and of the participation of the p-C₃H₇ group in addition reactions. Quantum yields for the evolution of the gaseous products have been estimated.     

Study of amphiphilic poly(1-dodecene-co-para-methylstyrene)-graft-poly (ethylene glycol): Part I. Preparation of poly(1-dodecene-co-para-methylstyrene) copolymer and its molecular weight regulation

Poly(1-dodecene-co-para-methylstyrene) copolymers with a broad composition range were prepared by an MgCl₂ supported TiCl₄ catalyst. The effects of temperature and hydrogen on catalyst activity were investigated. It was found that catalyst activity reached a maximum at around 60 °C, and then decreased with the rising temperature. Hydrogen showed an activation effect on the Ziegler-Natta catalyst. ¹H NMR and ¹³C NMR spectra showed that para-methylstyrene (pMS) could be effectively and randomly incorporated into the copolymer chains. The single glass transition indicated there was no block sequence in the copolymer. The copolymerization reaction was examined by the reactivity ratios of comonomers and the relatively low reactivity ratios of 1-dodecene and pMS indicated that both of them had little tendency of consecutive insertion and should be homogeneously distributed in the copolymer chains. Furthermore, the molecular weights of copolymers were regulated by chain transfer agents (diethyl zinc and hydrogen) and temperature. The molecular weights reduced greatly with the addition of diethyl zinc and hydrogen and with the increasing temperature.     

Preparation and characterization of three-dimensionally ordered macroporous styrene/p-methylstyrene syndiotactic copolymer

Three-dimensionally ordered macroporous (3DOM) styrene/p-methylstyrene syndiotactic copolymer (sPMS) with pore size 170 nm were fabricated by means of silica templates using (dbm)₂ Ti(OPh)₂/MAO catalytic system. The resulting materials were characterized by NMR, SEM, GPC and DSC. The results indicated that the 3DOM sPMS were highly syndiotacic, and the pore contraction was approximately 20.6%. Compared with bulk sPMS, 3DOM sPMS possessed the lower number-average molecular weight and broader molecular weight distribution. In terms of DSC results, the bulk sPMS exhibited the lower glass transition temperature than that of 3DOM one.     

Morphology and structure of poly(p-dioxanone)

The morphology of solution grown single crystals of poly(p-dioxanone) was investigated. Different crystallization conditions (solvent, precipitant agent and temperature) were tested. Dendritic growth, screw dislocations and striations were observed. Crystals usually exhibited a lozenge morphology, whose apex angle changed with the crystallization conditions. In all cases, however, a single crystal electron diffraction pattern was recorded. Spherulitic morphologies were obtained by evaporation of formic acid solutions. Lamellae gave rise to well resolved electron diffraction patterns that allowed determination of the main packing characteristics. Patterns of tilted specimens helped establish an orthorhombic unit cell, whose parameters indicate a deviation from the all trans molecular conformation. Quantum mechanical calculations were performed on small model compounds to study the conformational preferences. Simulated diffraction patterns were consistent with a unit cell containing four repeat units and a P2₁2₁2₁ space group. Molecular packing suggests the existence of different kinds of folds for an assumed adjacent reentry. Polyethylene decoration hardly highlighted a crystal sectorization. Also enzymatic degradation of lamellar crystals was evaluated by using a Pseudomonas cepacia lipase.     

Miscibility and hydrolytic degradation in alkaline solution of poly(l-lactide) and poly(p-vinyl phenol) blends

Poly(l-lactide) (PLLA) was melt-blended with poly(p-vinyl phenol) (PVPh) using a two-roll mill, and the miscibility between PLLA and PVPh and degradation of the blend films were investigated. It was found that PLLA/PVPh blend has miscibility in the amorphous state because only single T_g was observed in the DSC and DMA measurements. The T_g of the PLLA/PVPh blend could be controlled in the temperature range from 55 °C to 117 °C by changing the PVPh weight fraction. In alkaline solution, degradation rate of PLLA/PVPh blends was faster than that of neat PLLA because PVPh could dissolve in alkaline solution. The surface morphology of degraded PLLA and PLLA/PVPh blend were observed by SEM. The surface morphology of degraded PLLA/PVPh blend was finer than that of PLLA. Young's modulus of PLLA/PVPh blend increased with increasing PVPh content. Yield stress of PLLA/PVPh blends whose PVPh content was less than 30 wt% kept the level of about 55 MPa and that of PLLA/PVPh blend whose PVPh content was 40 wt% is much lower than that of neat PLLA.     

Photoelectrochemical effect with poly(p-phenylene sulfide) films

Poly(p-phenylene sulfide) films coated on conducting SnO₂ and Pt surfaces were found to attain p-type semiconducting properties on electrochemical cycling. Upon illumination of these films with visible light (λ < 500 nm) a photoelectrochemical effect was observed. The performance of a photoelectrochemical cell employing this polymer film coated electrode is discussed.     

Synthesis and solution properties of poly[2-methoxy-4,6-di(p,p′-isopropylidene diphenyloxy)-s-triazine] I

Poly[2-methoxy-4,6-di(p,p′-isopropylidene diphenyloxy)-s-triazine] has been synthesized by interfacial polycondensation of 2-methoxy-4,6-dichloro-s-triazine with bisphenol A. The conditions have been optimized to prepare a sample of both high solubility and molecular weight. The polymer has been fractionated by fractional precipitation and the fractions characterized by viscometry, osmometry and gel permeation chromatography. Mark-Houwink-Kuhn-Sakurada (MHKS) expressions have been developed for three solvents. The values of unperturbed dimensions $\text{(<R}{}^2\text{>}{}_0\text{/M)}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$, solvent-polymer interaction parameter (B and χ₁) and conformational parameter (σ) have been computed by applying the two-parameter theories of excluded volume developed by Fixman, Kurata, Stockmayer and Roig and by Flory, Fox and Schaefgen.     

X-ray diffraction study of poly(p-phenylene terephthalamide) fibres

On the basis of an X-ray diffraction study, a model is proposed for the crystal and molecular structure of poly(p-phenylene terephthalamide). The monoclinic (pseudo-orthorhombic) unit cell [$\text{a = 7·87}\text{A}\text{?}\text{, b = 5·18}\text{A}\text{?}\text{, c (}\text{fibre axis}\text{) = 12·9}\text{A}\text{?}\text{and}\text{γ = 90°}$] possesses Pn or P2₁/n space-group symmetry. Two molecular chains pass through the cell, one through the centre and the other through a corner. Approximate values for the orientation angles between the phenylene planes and the amide planes are 38° for the p-phenylene diamine segment and -30° for the terephthalic segment. Hydrogen bonds are formed between adjacent chains lying in the (100) plane. The conformation of the chain is primarily governed by competitive intramolecular interactions between the conjugated groups.     

Solution properties and unperturbed dimensions of poly(p-tert-butylstyrene)

The conformational and thermodynamic properties of poly(p-tert-butylstyrene) were investigated by osmometry, intrinsic viscosity, light scattering, gel permeation chromatography and phase equilibria measurements. Polymeric samples were anionically synthesized. 1-Nitropropane was found to be a θ-solvent for this polymer and the θ-temperature was determined as 31°C. Intrinsic viscosity-molecular weight relationships were obtained in a few solvents. Unperturbed dimensions, estimated from both viscosity and light scattering results, led to the characteristic ratio, C_α, of 13.4 ± 0.7 at 31°C. Comparison of this value with those for other polystyrene derivatives shows that the characteristic ratio increases with the bulkiness of the side-group due to the steric effect.     

Thermal degradation of poly(p-phenylene-graft-?-caprolactone) copolymer

The thermal degradation of poly(p-phenylene-graft-?-caprolactone) (PPP), synthesized by Suzuki polycondensation of poly(?-caprolactone) (PCL) with a central 2,5-dibromo-1,4-benzene on the chain with 1,4-phenylene-diboronic acid, has been studied via direct pyrolysis mass spectrometry. The thermal degradation occurred mainly in two steps. In the first step, decomposition of PCL chains occurred. A slight increase in thermal stability of PCL chains was noted. In the second stage of pyrolysis, the decomposition of the polyphenylene backbone takes place. The evolution of CL monomer or small CL segments left on the phenyl ring continued also in the temperature region where degradation of PPP backbone started.     

Aqueous solution properties of amphiphilic triblock copolymer poly(p-dioxanone-co-l-lactide)-block-poly(ethylene glycol)

A poly(ethylene glycol) (PEG)-based new amphiphilic block copolymer bearing the poly(p-dioxanone-co-l-lactide) (PPDO/PLLA) hydrophobic moieties was prepared. Depending on the copolymer composition and molecular weights, solubility of the polymeric samples in water was varied. Its diluted aqueous solution properties were studied by viscometry, dye solubilization, ¹H-NMR and dynamic light scattering. 1,6-Diphenyl-1,3,5-hexatriene solubilization and ¹H-NMR spectra carried out in CDCl₃ and D₂O were used to prove the existence of hydrophobic domains as the core of micelle. Average particle size of 60-165 nm with low polydispersity and lower negative zeta (ξ) potential of −3 to −14 mV were observed on the aqueous copolymer dispersion.     

Photo- and thermo-oxidation of poly(p-phenylene-vinylene) and phenylene-vinylene oligomer

This paper reports a study of the photo- and thermo-degradation of poly(p-phenylene-vinylene)-type (PPVs) materials, including a five-ring n-octyloxy substituted phenylene-vinylene oligomer (Ooct-OPV5) and poly(p-phenylene-vinylene) (PPV). The modifications in the chemical structure of the thin films submitted to UV-visible light irradiation and thermal oxidation were analysed with infrared spectroscopy, and the oxidation products were identified by derivatisation reactions. Results showed that the photochemical and thermal behaviour of the Ooct-OPV5 oligomer was similar to that of MDMO-PPV (poly[2-methoxy-5-(3′,7′-dimethyloctyloxy)-1,4-phenylenevinylene), which is a polymer used in organic solar cells. Additionally, the identification of the products resulting from the oxidation of the vinylene bonds was simpler in Ooct-OPV5 and PPV compared to MDMO-PPV In contrast, the oxidation mechanisms of PPV, which has no ether substituent, and MDMO-PPV are not identical; the disappearance of the double bonds in PPV does not involve the formation of aromatic ketones. It was also shown that the absence of ether substituents does not decrease the rate of photo-oxidation of PPV compared to MDMO-PPV. Finally, as the same mechanisms proposed for Ooct-OPV5 and PPV occur under both photo- and thermo-oxidative conditions of ageing, this confirms that singlet oxygen does not play a decisive role in the photo-oxidation of PPVs.     

Unexpected photo-initiated oxidation of antimony in (tetra-tert-butyl)phthalocyaninatoantimony(III) complex in the presence of singlet oxygen acceptors

The title complex cation, [Sb(tbpc)]⁺ (where tbpc denotes tetra(tert-butyl)phthalocyaninate, C₄₈H₄₈N₈²⁻), was gradually bleached under irradiation with visible light (900 > λ/nm > 600) in aerated nonaqueous solvents, such as CH₂Cl₂, CHCl₃, benzene, chlorobenzene. On the other hand, irradiation under the same conditions but in the presence of 1,3-diphenylisobenzofuran (DPBF) caused slow oxidation of [Sb(tbpc)]⁺ to the corresponding antimony(V) derivatives, [Sb(tbpc)LL′]⁺, (L and L′ denote monoanionic axial ligands containing oxygen as the donor atom), which was monitored by optical absorption and ESI-MS spectra of the photolyzed solutions. Both the photobleaching and oxidation have efficiently been inhibited by preliminary addition of β-carotene in photolyzed solutions, indicating that photosensitization of singlet oxygen (¹O₂) by [Sb(tbpc)]⁺ itself is involved. The use of furans (except dibenzofuran) or oxazoles instead of DPBF gave rise to similar oxidation but not in the case of the other type ¹O₂-acceptors, such as 9,10-diphenylanthracene, tetraphenylcyclopentadienone, or 2,3-dimethyl-2-butene, indicating that formation of ozonide-type endo-peroxide through 1,4-cycloaddition with ¹O₂ is essential. Peroxides, such as EtOOH and H₂O₂, generated through nucleophilic attack to the ozonide by EtOH and H₂O (present in the solvent) respectively, are considered to oxidize [Sb(tbpc)]⁺ to the antimony(V) species. Photochemistry of antimony–phthalocyanine complex has been studied for the first time of pnicogen derivatives of phthalocyanine.     

A facile approach to preparation of long-chain-branched poly(p-dioxanone)

Long-chain-branched poly(p-dioxanone)s (LCB-PPDOs) with different branch densities were prepared via the chain-extending reaction of hydroxyl group terminated linear bi-functional PPDO (2a-PPDO) and star-like tri-functional PPDO (3a-PPDO) prepolymers, which were synthesized by the ring-opening polymerization of p-dioxanone (PDO) using 1,4-butanediol (BD) and trimethylolpropane (TMP) as multi-functional initiators, respectively. The undesirable gelation was successfully depressed by adjusting the chain length and feed ratio of prepolymers. The average molecular weight between branch points (M_b) and the average number of branch per 100,000 g/mol (B_n) of LCB-PPDOs were calculated from the ¹H NMR spectra. The average number of branch ranged from 0 to 6.72 branch points per 100,000 g/mol, and the number-average molecular weights between branch points ranged from 6900 to 20,500 g/mol. The results of differential scanning calorimetry (DSC) showed that the crystallization behavior of LCB-PPDOs was changed evidently with the branch density. Small-amplitude dynamic oscillatory rheometer was used to investigate the rheological properties of the melts of LCB-PPDO including zero-shear viscosity, storage modulus, relaxation times and loss angle, which largely depended on the branch density and length of LCB-PPDOs. Therefore, the rheological behaviors of PPDO can be well-controlled via synthesizing LCB-PPDOs with the desired architectures.     

Synthesis and characterization of p-toluenesulfonate incorporated poly(3,4-ethylenedioxythiophene)

Poly(3,4-ethylenedioxythiophene) (PEDOT), a conducting polymer, was electrochemically synthesized with p-toluenesulfonate (TSNa) as a dopant on gold surface. The electrochemical properties of the polymer were studied by impedance spectroscopy and cyclic voltammetry (CV). It was found that the impedance magnitude of the electrode significantly decreased over a wide range of frequency from 10⁰ to 10⁴ Hz after the polymer deposition. The CV demonstrated enhanced reversibility of the PEDOT film. The surface morphology was investigated by scanning electronic microscope (SEM) and atomic force microscope (AFM). Due to the effect of TSNa structure, nano-fungus was observed. Polymerization time was optimized and 30 min deposition resulted in the highest charge capacity, showing the highest electroactive surface area, possibly due to its porous structured polymer. Moreover, the high specific surface area could be favorable for cell attachment. The stability of PEDOT in glutathione (GSH), a common biologically relevant reducing agent, was studied with polypyrrole (PPy) as a baseline. It showed that the former had much better stability than the latter and it could be an excellent candidate for potential applications of in vivo neural devices.