Lars-Olof Pietilä

On the molecular recognition and associations between electrically conducting polyaniline and solvents

The specific interactions between sulphonic acid protonated polyaniline (PANI) and solvents are here studied both by the semiempirical AM1 method and experimentally. Phenolic solvents are shown to have a relatively large interaction with the sulphonate anions of the counterions and with the amines in PANI. In addition, a properly functionalized counterion may form cyclic associations provided that there is a steric match between the molecules concerned. This concept is called molecular recognition and it is a novel concept in the context of PANI. For example, the carbonyl group in (±)‐10‐camphor sulphonic acid (CSA) can form a hydrogen bond to the hydroxyl group of m‐cresol, whereby the phenyl ring becomes coplanar with one of the PANI rings thus enabling enhanced van der Waals interaction. This additional specific interaction agrees with our observed increased solubility with CSA doped PANI in m‐cresol, compared to its solubility in dimethyl sulphoxide or chloroform, or to tosylene sulphonic acid doped P...

Processible polyaniline complexes due to molecular recognition: Supramolecular structures based on hydrogen bonding and phenyl stacking

Abstract We show that sulphonic acid doped polyaniline (PANI) can be plasticized using certain low-acidic organic compounds consisting of ring structures and hydrogen bonding moieties that are able to “recognize” the complementary moieties of the doped PANI. The achieved synergistic combination of interactions consists of phenyl stacking, hydrogen bonding and charge transfer due to protonation. Fusible electrically conducting supramolecular structures are rendered, as suggested also by quantum chemical calculations. For example, PANI doped by methanesulphonic acid, toluenesulpnonic acid, dodecylbenzenesulphonic acid, or camphorsulphonic acid can be plasticized by dihydroxybenzenes and bisphenols to obtain fusible particle-free films at the resolution of optical microscope. The generalization to other plasticizers and other aromatic polymers, such as polypyrrole, is obvious.

Cyclic oligomers in saturated polyesters

Abstract To get an in-depth understanding of the structure–property relationship in saturated polyester resins, the reactivity of various diols and diacids as well as reaction conditions were studied. Adipic acid (AA), phthalic anhydride (PA), isophthalic acid (IPA), terephthalic acid (TPA), 2-butyl-2-ethyl-1,3-propanediol (BEPD) and 2,2-dimethyl-1,3-propanediol (NPG) were addressed. It was found that in addition to linear oligomers with carboxyl and/or hydroxyl end groups cyclic oligomers were detected. Cyclic dimers of TPA and NPG are known to migrate to the coating surface causing “blooming”. The understanding of this phenomenon and the monomers capable of forming cyclic dimers are the subject of this study, where we combined molecular modeling and analytical characterization. The probability of the formation of macrocyclic structures was shown to decrease in the order: BEPD–PA>BEPD–AA≥BEPD–IPA>BEPD–TPA. The temperature dependence was found to be small.

Density functional studies of conformational properties of conjugated systems containing heteroatoms

Abstract The application of the Density Functional (DFT) method to conformational properties, which are pertinent to the parametrization of potential energy functions for molecular modelling of conjugated molecules, is investigated. Conformational structures and energy differences, vibrational spectra and electrostatic potential derived atomic charges have been determined for some nitrogen- and oxygen-substituted 1,3-butadienes. The molecules studied were 1,3-butadiene, 1,4-diaza-1,3-butadiene, 2,3-diaza-1,3-butadiene, glyoxal and acrolein. The calculations indicate that the DFT method performs well for most of the properties studied. Some of the torsional barriers are overestimated, and some minima are calculated too shallow by the DFT method.

Copolymerization of ethylene and non-conjugated dienes with Cp2ZrCl2/MAO catalyst system: effect of polymerization temperature on the copolymer structure

Abstract Ethylene was copolymerized with linear, non-conjugated dienes by the metallocene catalyst system Cp2ZrCl2/MAO at several temperatures from 20 to 80°C. The dienes were 1,5-hexadiene (HD), 1,7-octadiene (OD) and 7-methyl-1,6-octadiene (MOD). Incorporation of the dienes was studied by 1 H and 13 C NMR and FTIR. Polymerization conditions had a dramatic effect on the degree of crosslinking of the product. At polymerization temperatures from 20 to 65°C the copolymers of ethylene and HD or OD were nearly totally crosslinked, whereas at 80°C the degree of crosslinking was consistently under 10%. When MOD was used as comonomer the degree of crosslinking did not increase above 40% even for copolymer produced at 20°C.

Amorphous cell studies of polyglycolic, poly(l-lactic), poly(l,d-lactic) and poly(glycolic/l-lactic) acids

Abstract In this paper static amorphous state properties (solubility parameter, free volume (using the Voorintholt method and the Voronoi tessellations) and pair correlation functions, the last ones also by including water molecules in the cells), which can be related to the probability for water uptake, have been studied for polyglycolic (PGA), poly( l -lactic) (PLLA), poly( l , d -lactic) (PLLA/PDLA) and poly(glycolic/ l -lactic) (PGA/PLLA) acids, known to be biodegradable polymers. The polymer consistent force field, as modified by the authors, has been used in the calculations. The main purpose of this paper is to investigate, which of the amorphous state properties would be relevant for water uptake. We also discuss the validity of th6e methods used for these kinds of studies, and the related reliability of the computed results. Chain flexibilities of the studied polyesters in the amorphous phase have been analyzed, and the intermolecular interactions are found to cause the most significant variations in the distributions of the adjacent chain dihedral angle pairs and in the related populations of the low-energy regions of the comonomers. The solubility parameters, as calculated from the cohesion energy densities of the constructed models, suggest PGA being most compatible with water, in agreement with experiments. On the other hand, the quantitative structure–property relationships method ‘Synthia’ suggests a very similar solubility in water for all particular polyesters. In the PLAs and PGA/PLLA, however, a larger number of hydrogen bonds is formed between the water molecules and the carbonyl oxygen atoms of the chains showing a better possibility of PLLA and its copolymers to break into shorter chains. As an explanation, the hydrophobic methyl groups of the lactide units are suggested to push the water molecules closer to the carbonyl groups than in homo-PGA.

Hydrogen bonding and protonation in acid–base complexes: Methanesulfonic acid-pyridine

In order to study proton transfer and hydrogen bonding interactions in acid/base complexes, the equilibrium structure of a stoichiometric pyridine–methanesulfonic acid complex has been investigated using density functional theory with different functionals and compared with second-order Moller–Plesset perturbation theory and restricted Hartree–Fock calculations. The basis sets range from 6-31G to 6-31++G(d,p). Additionally, interaction energies and equilibrium geometries were calculated with 6-311++G(d,p) basis set, while aug-cc-pVDZ was used only with BLYP method. In the gas phase, the optimized geometry shows hydrogen bonding without proton transfer between the molecules. The polarized continuum model suggests that embedding the complex in a dielectric medium enhances the proton transfer. The role of added water was studied explicitly by optimizing the geometry in the presence of 1 or 2 water molecules. In such cases the proton is observed to transfer. The crystalline structure of the pyridine–methanesu...

Studies on aliphatic polyesters. Part II. Ab initio, density functional and force field studies of model molecules with two carboxyl groups

Abstract This paper is a continuation of our study on the ester bond energetics. Here, model molecules for structural units of biodegradable polyglycolic and polylactic acids (HC( O)–O–CH 2 –C( O)–O–CH 3 and HC( O)–O–CH(CH 3 )–C( O)–O–CH 3 ), which contain two carboxyl groups in close vicinity to one another, have been considered. Rotations about the neighbouring C(sp 3 )–O(sp 3 ) and C(sp 3 )–C(sp 2 ) bonds adjacent to the CH 2 or CH(CH 3 ) group have been studied quantum chemically by ab initio and density functional methods (MP2, B3-LYP and B-LYP), using the standard Gaussian-type basis set 6-31G(d), as well as by the PCFF (Polymer CFF) force field. The quantum chemical results mostly are in good agreement with each other. However, for the C–O rotations, the Density Functional Theory (DFT) barriers are 0.5–3.1xa0kcal/mol lower than the corresponding MP2 ones. The conformational dependency of bond lengths, valence angles, and that of atomic charges also is similar in the MP2 and DFT methods. The changes in bond lengths with conformation are small, but the valence angles vary more and especially in high-energy states with low population they may open as much as 18°. The conformational dependence of the most significant atomic CHELPG charges also was found to be small, and the largest relative changes occurred in small charges that do not have a major impact on the electrostatic potential. The PCFF force field produced torsional energetics that was in serious disagreement with the quantum chemical results, especially in the case of the C–C rotations. By reoptimizing the pertinent torsion parameters of the PCFF force field, these disagreements could be removed.

Studies on aliphatic polyesters I: Ab initio, density functional and force field studies of esters with one carboxyl group

Abstract Rotations around the neighboring C–C(ue605O) and C(ue605O)–O bonds in two esters, H3C–CH2–C(ue605O)–O–CH3 (I) and H3C–CH(CH3)–C(ue605O)–O–CH3 (II) that represent model molecules for aliphatic main chain and side group polyesters were studied by ab initio and density functional methods (MP2, B3-LYP and B-LYP) using the standard Gaussian basis set 6-31G(d). The performance of the PCFF force field, developed for polymers, to reproduce the conformational behaviors of the C–C and C–O rotations in question was evaluated. Disagreements between the quantum chemical and force field results were removed by reoptimizing the PCFF force field torsion parameters of current interest. The conformational dependence of geometrical parameters and electrostatic potential derived (CHELPG) atomic charges was also studied.

Molecular modeling of metallocene catalyzed copolymerization of ethylene with functional comonomers

Abstract Metallocene catalyzed copolymerization of ethylene with comonomers having polar functional groups (alcohols, carboxylic acids and esters) has been studied experimentally and by molecular modeling. The polar functional groups strongly reduce the activity of the catalyst. The deactivation of the catalyst is investigated with DFT calculations on some model systems. The effect of the spacer length between the double bond and the functional group is analyzed using molecular dynamics and molecular mechanics methods, and compared with experiments.