Poly(butylene terephthalate‐co‐5‐tert‐butyl isophthalate) copolyesters: Synthesis,characterization, and properties

A series of poly(butylene terephthalate) copolyesters containing 5‐tert‐butyl isophthalate units up to 50 mol %, as well as the homopolyester entirely made of these units, were prepared by polycondensation from a melt. The microstructure of the copolymers was determined by NMR to be random for the whole range of compositions. The effect exerted by the 5‐tert‐butyl isophthalate units on thermal, tensile, and gas transport properties was evaluated. Both the melting temperature (T_m) and crystallinity were found to decrease steadily with copolymerization, whereas the glass‐transition temperature (T_g) increased and the polyesters became more brittle. Permeability and solubility slightly increased with the content in substituted isophthalic units, whereas the diffusion coefficient remained practically constant. For the homopolyester poly(5‐tert‐butyl isophthalate), all these properties were found to deviate significantly from the general trend displayed by copolyesters, suggesting that a different structure in the solid state is likely adopted in this case. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 92–100, 2005     

Aromatic polyesters from naturally occurring monosaccharides: Poly(ethylene terephthalate) and poly(ethylene isophthalate) analogs derived from D‐mannitol and galactitol

The synthesis and characterization of a new series of aromatic polyesters based on D‐mannitol and galactitol are described. These polyesters were obtained by polycondensation reaction of the terephthaloyl chloride or isophthaloyl chloride and 2,3,4,5‐tetra‐O‐methyl‐D‐mannitol or 2,3,4,5‐tetra‐O‐methyl‐galactitol in o‐dichlorobenzene. All the new polyesters were characterized by elemental analyses, GPC, IR, and NMR. They were soluble in chloroform, but insoluble in water and other polar oxygenated solvents. They showed a notable hygroscopicity, lower for those containing isophthalic units. DSC and X‐ray diffraction studies showed that D‐mannitol‐based polyesters were stiffer and less crystalline than those derived from galactitol, which presented a noticeably lower thermal stability. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4570–4577, 2005     

Poly(ethylene terephthalate) terpolyesters containing isophthalic and 5‐tert‐butylisophthalic units

Poly(ethylene terephthalate‐co‐isophthalate‐co‐5‐tert‐butylisophthalate) (PETI^tBI) terpolymers were investigated with reference to poly(ethylene terephthalate) (PET) homopolymer and poly(ethylene terephthalate‐co‐isophthalate) (PETI) copolymers. Three series of PETI^tBI terpolyesters, characterized by terephthalate contents of 90, 80, and 60 mol %, respectively, with different isophthalate/5‐tert‐butylisophthalate molar ratios, were prepared from ethylene glycol and mixtures of dimethyl terephthalate, dimethyl isophthalate, and 5‐tert‐butylisophthalic acid. The composition of the terpolymers and the composition of the feed agreed. All terpolymers had a random microstructure and number‐average molecular weights ranging from 10,000 to 20,000. The PETI^tBI terpolyesters displayed a higher glass‐transition temperature and a lower melting temperature than the PETI copolymers having the same content of terephthalic units. Thermal stability appeared essentially unchanged upon the incorporation of the 5‐tert‐butylisophthalic units. The PETI^tBIs were crystalline for terephthalate contents higher than 80 mol %, and they crystallized at lower rates than PETI. The crystal structure of the crystalline terpolymers was the same as that of PET with the 1,3‐phenylene units being excluded from the crystalline phase. Incorporation of isophthalate comonomers barely affected the tensile modulus and strength of PET, but the brittleness of the terpolymers decreased for higher contents in 5‐tert‐butylisophthalic units. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 124–134, 2003     

Aromatic homo‐ and copolyesters from naturally occurring monosaccharides: PET and PEI analogs derived from L‐arabinitol and xylitol

The synthesis and characterization of new aromatic homo‐ and copolyesters based on l‐arabinitol and xylitol are described. These polymers were obtained by polycondensation reaction of the 2,3,4‐tri‐O‐methyl‐l‐arabinitol or 2,3,4‐tri‐O‐methyl‐xylitol, or their mixtures with ethylene glycol, with terephthaloyl chloride or isophthaloyl chloride in o‐dichlorobenzene or in the melt phase from the corresponding methyl phthalates. All the polymers were characterized by GPC, IR, and NMR. Their M_w values ranged between 11,500 and 46,500, with polydispersities from 1.5 to 2.3. They were found to be soluble in chloroform, but insoluble in water. In contrast with the homopolymers completely made with EG, they showed a significant hygroscopicity. DSC and TGA studies showed that the melting temperature of polyethylene terephthalate is depressed by the presence of pentitol units, whereas the thermal stability is kept above 350 °C. Only copolyesters containing 10% or less of pentitol units showed melting and produced X‐ray diffraction patterns characteristic of crystalline material. d‐Arabinitol‐based homopolyesters appeared to be more crystalline than those derived from xylitol and also presented a higher thermal stability. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 6394–6410, 2005     

Scalar quantum electrodynamics on lattice correlation inequalities and infinite volume limit

We consider Wilson's lattice approximation to scalar Quantum Electrodynamics. We establish correlation inequalities of Griffiths-Kelly-Sherman type and a rigorous transfer matrix formalism, from which existence and non triviality of the infinite volume limit follow.     

Intense shake-up satellites in the XPS spectra of planar and sterically hindered N-piperidyl-nitrobenzenes and -nitrothiophens

The shake-up satellites present in the O_1s and N_1s energy regions of the XPS spectra of the planar 4-N-piperidyl-nitrobenzene (1) and 2-N-piperidyl-5-nitrothiophen (3), and of the sterically hindered 2-N-piperidyl-nitrobenzene (2), 2-N-piperidyl-3-nitrothiophen (4) and 3-N-piperidyl-2-nitrothiophen (5) and, for comparison, of 2-bromo-3-nitrothiophen (6) have been analyzed with the help of CNDO/S CI calculations. The spectra of the planar derivatives closely resemble these of the related compounds previously analysed, the main satellites deriving from the transition between the highest occupied molecular orbital (HOMO, localized at the donor-ring moiety) towards the lowest unoccupied one (LUMO, localized at the nitro group). Calculations indicate that in the ortho derivatives new relaxation processes are allowed upon N_1s/NO₂ ionization. In 2, where the angle of rotation θ is closer to 90° than 60°, the NR ₂ lone-pair orbital relaxes through space towards the core-ionized N/NO₂ atom. In 4 and 5, where 45° ? θ ? 60°, both through-ring and through-space relaxations are present. The assignment of the main N_1s/NO₂ line in 1 is discussed.     

An mo study of the substituent effect in benzene radical ions

The effect of various types of substituents (X=OH, CH₃, CN, SiH₃) in benzene radical cations and anions have been investigated using INDO-SCF computations with and without π conjugation admitted between the substituent and the adjacent substrate. The inductive effect of the substituent has been found to play a minor role in determining the more stable configuration, the latter being determined in all cases investigated by the π conjugative interactions. A OEMO analysis of such interactions provides a better understanding of the key factors controlling the configuration preferentially stabilized in the various cases.     

Conformational studies by dynamic NMR. Part XV. The rotational barrier of N-methyl aniline

Low temperatures C-13 NMR spectra allowed the determination of the rotational barrier of N-methyl aniline in solution. The shifts of the anisochronous ortho and meta carbons were assigned by $\text{ab initio}$ calculations.