J. P. Pascault

Influence of epoxy hardener on miscibility of blends of poly(methyl methacrylate) and epoxy networks

Abstract In this paper, we investigate poly(methyl methacrylate) (PMMA)-modified epoxy thermoset based on DGEBA before and after curing of the epoxy with various aromatic amines by means of different techniques: Differential Scanning Calorimetry (DSC), Size Exclusion Chromatography (SEC), Infra-Red Spectroscopy (FT-IR), Dynamic Mechanical Analysis (DMA) and Transmission Electron Microscopy (TEM). The DSC analyses demonstrate the complete miscibility between PMMA and DGEBA. Neither specific interaction nor trans-esterification reaction is revealed by SEC and FT-IR between these components. With respect to reactive blends, the nature of the curing agent affects the polymerization kinetics and the structure of the PMMA-modified epoxy network. The usual polymerization induced phase separation occurs using DDS or MDA leading to a material with a two-phase structure revealed by TEM and DMA. On the other hand, the use of MCDEA as curing agent does not entail any noticeable phase separation during curing even if cured samples appear slightly turbid. No acceleration of the epoxy–amine reaction can be observed contrary to DDS and MDA based blends presenting the usual acceleration of the reaction just after the phase separation. In the case of blends using MCDEA as the hardener, we really have what some call a semi-IPN.

Morphological analysis of photocured polyurethane acrylate networks. Correlation with viscoelastic properties

In this paper, we investigate the final morphology of photocured polyurethane acrylates based on polypropylene oxide by means of Transmission Electron Microscopy (TEM), Small Angle X-ray Scattering (SAXS), and dynamic mechanical measurements. Two interrelated structural features on two different size scales can occur in these systems. TEM analysis demonstrates the presence of inhomogeneities on the length scale of 10–200 manometers, mostly constituted by clusters of small hard units (diacrylated diisocyanate) connected by polyacrylate chains. The bimodal shape of the dynamic mechanical relaxation spectra corroborates this two-phase structure. Besides, a suborganization of the reacted diisocyanate hard segments inside the polyurethane acrylate matrix is revealed by SAXS measurements, depending on the nature of the hydroxylacrylate used for the synthesis of the precursor. Finally, UV-exposure time is found to induce modifications on the viscoelastic properties of the final network, even at high double-bond conversion: this effect can be due to a postreaction and to an increase of the crosslinking density inside the hard segments domains.

Relationships between glass transition temperature and conversion

SummaryThe Couchman approach to the expression of the compositional variation of glass transition temperature (or the Di-Benedetto equation) can be used to evaluate the effect of molecular weight on Tg for a stepwise linear polymer. An expression for the KL constant in the Fox-Flory equation is proposed. It is also possible to estimate the TgL corresponding to the hypothetical linear structure defined in a three-dimensional network. For different epoxy-diamine systems, we have found a good concordance with the results obtained previously using an additive law.

Unsaturated polyester prepolymer from rosin

Abstract Unsaturated polyester prepolymer was synthesized from maleopimaric acid (MPA), diethylene glycol (DEG) and maleic anhydride (MA) in the molar proportions 1:4:3 respectively. MPA was prepared from natural rosin and MA. Kinetic studies of the reaction were performed, and the reactivities of MPA, MA and phthalic anhydride (PA) with respect to diethylene glycol were compared. Copolymerized with styrene, this prepolymer gave samples with higher Vicat distortion temperatures than usual commercial samples prepared from PA, MA and propylene glycol, while mechanical properties such as modulus and strength were similar.

Polymerisation anionique de lactones amorcees par les composes d'insertion K C24: Caracterisation des polymeres obtenus

Resume Le compose lamellaire du graphite K C 24 amorce la polymerisation de la caprolactone, la propiolactone et la pivalolactone. Les polycaprolactones obtenus presentent une double distribution des masses moleculaires avec une proportion importante de grandes masses. Les polymeres sont semicristallins et les valeurs et les distributions des masses moleculaires influencent leur comportement a la cristallisation et a la fusion.

Synthesis of butadiene-acroleine block polymers

SummaryFrom GPC and 1H NMR results, we have shown that block polymers built with acroleine and butadiene units can be synthesized. Moreover, the cross-linkage ability of the acroleine blocks in these products under UV irradiation has been checked. This is very interesting for an industrial application. Indeed, homopolyacroleines can be used as a photopolymer layer to prepare negative or positive printing plates.