Josée Brisson

Hydrogen bonds in poly(methyl methacrylate)-poly(4-vinyl phenol) blends: 1. Quantitative analysis using FTi.r. spectroscopy

Abstract FTi.r. was used to investigate quantitatively hydrogen bonds in poly(methyl methacrylate) (PMMA) and poly(4-vinyl phenol) (PVPh) blends. An absorption coefficient of free (or non-hydrogen bonded) carbonyl vibration of 750 ± 40 cm−1 m2 mol−1 was determined from pure PMMA using the Beer-Lambert law, along with precise measurements of film thickness and density. By making the approximation that this value is the same for pure PMMA and for PMMA in blends, the absorption coefficient of the hydrogen bonded carbonyl vibration was calculated as 910 ± 50 cm−1m2 mol−1. Using these values, it was deduced that less than 45% of carbonyl groups are involved simultaneously in hydrogen bonding for a blend where the PVPh to PMMA mole ratio was 1 to 1. In pure PVPh, OH groups exist as n-mers, with a predominance of shorter mers such as trimers or tetramers. Upon addition of PMMA to PVPh, the fraction of intra-associated OH bonds remains, within experimental error, constant whereas inter hydrogen bonds between PVPh and PMMA chains increase, resulting in a decrease in free OH groups. Above 45.5 wt% PMMA, almost all ‘free’ OH groups have disappeared, and intra- and inter-associated hydrogen bonds are distributed among the available OH groups. Finally, at high PMMA content (90 wt% PMMA, or 10 wt% PVPh), the probability of two PVPh chains to be close enough to allow intra-hydrogen bond formation is small, and only inter-hydrogen bonds between PVPh and PMMA are observed.

Hydrogen bonds in poly(methyl methacrylate)-poly(4-vinyl phenol) blends: 2. Quantification near the glass transition temperature

Abstract Changes in the proportion of hydrogen bonds of poly(4-vinyl phenol) (PVPh) and poly(methyl methacrylate) (PMMA) blends have been investigated by FT i.r. spectroscopy both above and below the glass transition temperature T g . Changes in three spectral regions, namely the carbonyl, hydroxyl and aromatic ring vibration regions, are attributed to variations in hydrogen bonding with increasing temperature. Both hydrogen bonded OH and CO stretching vibrations shift to higher frequencies, indicating a weakening of interassociated hydrogen bonds at higher temperatures. A clear transition is observed in the absorbance behaviour of these vibrations at T g . The reduction in total area of OH and CO vibration regions is attributed not only to the breaking of hydrogen bonds at T g , but also to the decrease of absorption coefficients of hydrogen bonded OH and CO stretching vibrations. Quantification of the decrease in concentration ratio of hydrogen bonds between carbonyl groups vs. total carbonyl groups showed a decrease of 0.5% in the number of hydrogen bonds was occuring at T g + 30, when T g is taken as the midpoint of the transition as determined by DSC, for the 30 wt% PVPh composition. For higher compositions, this percentage increased, reaching 3.5% for the 80 wt% PVPh composition, which is related to the increase in T g of the blend.

Preparation of aromatic copolyamides containing regularly placed 1,6-hexamethylenediamine units

Copolyamides based on poly(m-phenylene isophthalamide) and poly-(p-phenylene terephthalamide), to which 1,6-diaminohexane units were regularly inserted every 3 or 5 phenylene monomer units, were synthesized. The copolymers were obtained by condensation of individually prepared diamino- and dicarboxylic-building blocks via the Yamazaki–;Higashi reaction. Solubility of the copolyamides are discussed in relation with the structure.

Towards the simulation of poly(vinyl phenol)/poly(vinyl methyl ether) blends by atomistic molecular modelling

Molecular simulations of poly(vinyl phenol)/poly(vinyl methyl ether) (PVPh/PVME) blends were performed and their degree of miscibility evaluated as a preliminary step before orientation simulations. A minimum of three periodic boundary condition amorphous models was constructed and analysed in terms of solubility parameter, X-ray pattern, pair correlation function, hydrogen bond fraction and backbone conformation. The values obtained are consistent with miscibility of the systems, although it is suggested that the degree of mixing is not uniform for the different models.

Orientation and relaxation of orientation of amorphous poly(ethylene terephthalate)

Abstract Poly(ethylene terephthalate) (PET) has been uniaxially stretched at different draw ratios and draw rates above its glass transition temperature, in the 80–105°C temperature range. Molecular orientation and relaxation have been followed by birefringence. A decrease in temperature reduces the mobility of the oriented chains resulting in a slow relaxation while an increase in stretching rate results in higher orientation values and rapid relaxation after the extension. The same relaxation behavior has been observed from birefringence and polarization modulation infrared spectroscopy. Rouse relaxation times have been estimated from rheological master curves and birefringence relaxation data, while retraction and the reptation times have been deduced from the scaling laws proposed by Doi and Edwards.

Infra-red dichroic study of orientation in poly(vinyl phenol)

Abstract Fourier transform infra-red ( FT i.r.) spectroscopy was used to investigate the orientation of uniaxially stretched films of poly(vinyl phenol) (PVPh). The α angles of the various vibrations were determined with respect to the CH 2 …CH 2 axis. No evidence was found for any influence of the hydrogen bonds on the orientation of PVPh when compared to polystyrene (PS). On the other hand, it was noted that, upon formation of hydrogen bonds, the α angle of the hydroxyl groups changes from 26 to 65°.

Atomistic studies of RDX and FOX-7 -Based Plastic-Bonded explosives: molecular dynamics simulation

Abstract Molecular dynamics simulations were carried out to study the effects of interface interactions between a crystalline structure and a plastic bonded explosive (PBX) system. In this work, the hydroxyl-terminated polybutadiene (HTPB) represents the polymer, isophorone diisocyanate (IPDI) is the diisocyanate and dioctyl adipate (DOA) is the plasticizer. Two different crystal high explosives components were used, hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), which is characterized by a high chemical stability, and 1,1-diamino-2,2-dinitroethylene (FOX-7) which is known for its low sensitivity. The molecular model is composed of RDX or FOX-7 which represent the main body and PBXs which contain a small amount of polymer/plasticizer. The polymer and crystal were modeled using the atomistic classical force-field COMPASS. Interface structures of RDX and FOX-7 (hkl) crystal surface together with the HTPB-IPDI/DOA blend were predicted as well as interfacial binding energies. Bonding energy calculations have been performed in order to investigate the adhesion of the polymer to diverse atomic (hkl) planes of crystals. The (020) surface plane of RDX and (010) surface plane of FOX-7 have the largest binding energies and therefore a strongest ability to interact with the polymer was observed. NPT ensemble molecular dynamics simulation was applied to study specific mechanical properties: Poissons ratio ν and various moduli such as Youngs E, bulk K and shear G, for RDX and FOX-7 -based PBXs. The investigation of mechanical properties shows that the (020) plane providing HTPB-IPDI-DOA/RDX blends is more flexible and ductile. However, for FOX-7-based blends, the three crystallographic planes that were explored present surprisingly comparable ductility.

Quantitative analysis of hydrogen bonding in poly(4-vinylphenol) blends using near infrared spectroscopy

Quantitative evaluation of hydrogen bonding of poly(4-vinyl phenol)/poly(ethylene oxide) PVPh/PEO blends was conducted using Fourier transform near infrared (FT-NIR) spectroscopy. Absorption coefficients of the free (aF), intra- (PVPh–PVPh) (aA) and inter-associated (PVPh–PEO) hydroxyl groups (aI) were estimated. Two sets of approximations were tested, including adopting a least-squares refinement method to calculate absorption coefficients from all NIR spectra or using a literature value for aF. Each set of absorption coefficients thus estimated were used to determine hydroxyl concentration for the free and hydrogen-bonded hydroxyl overtone bands in the blends. A comparison is made among the resultant concentrations of the free, intra- and inter-associated hydroxyl groups. The concentration of free hydroxyl groups markedly decreases with PEO percentage, and that of intra-associated hydroxyl remains almost constant. Concentration for the inter-associated hydroxyl groups in the blends increases very slowly above 0.2 PEO weight fraction. When concentration of OH groups is reported per PVPh chain, FT-NIR measurements show a broad maximum in the number of interchain hydrogen bonds. This result can be used to explain partially previous orientation behaviour observed for PVPh/PEO blends.

Morphological and orientation studies of injection moulded nylon-6,6/Kevlar composites

Abstract In this work, nylon-6,6/Kevlar short fibre composites have been processed by injection moulding. Their microstructure, and fibre and matrix orientation, measured by wide-angle X-ray diffraction (WAXD), have been studied as a function of two major processing variables, i.e. the injection speed and the mould temperature. At low mould temperatures, skin, underskin and core structures have been observed, while at high mould temperatures only skin and core structures were found. Fibre orientation patterns exhibit both a processing and a geometrical dependence. Matrix orientation patterns are different from those of the pure polymer moulded material and are mainly influenced by the fibre orientations, which are themselves affected by the processing conditions.

Effects of Interface Interactions on Mechanical Properties in RDX-Based PBXs HTPB-DOA: Molecular Dynamics Simulations

Atomistic molecular dynamics simulation was carried out to study interface interactions between a crystal structure and a plastic bonded explosive (PBX) system. In this work, the polymer is hydroxyl-terminated polybutadiene (HTPB), the plasticizer is dioctyl adipate (DOA) and the crystal phase is hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX). Experimental RDX crystallo-graphic data show that (020 ), (200 ) and (210 ) crystal faces usually dominate, and these were therefore only these were studied. Interface models were built and interfacial bonding energies calculated to investigate HTPB/RDX adhesion properties in the (DOA+HTPB)/RDX system. Mechanical properties such as Poissons ratio, Young, bulk and shear moduli were also predicted. The most favourable interactions occur between HTPB-DOA and the RDX (020) crystal face: obtaining crystals with prominent (020) faces may provide a more flexible mixture, with a lower Youngs modulus and an increased ductility.