2,3-Epoxy-l -propano1 has been introduced into isocyanate-terminated polyurethane to form glycidyl-terminated polyurethane resins. A series of glycidyl-terminated polyurethanes based on hydroxyterminated poly(oxypropy1ene) (poly(oxypropylene)glycol, PPG), toluene diisocyanate (TDI), and 1 ,4-butanediol (BD) was synthesized with various PPG soft segment lengths (MW 700, 1000 and 2000) and soft segment concentrations (30, 50 and 70 wt.-Vo). The effect of glycidyl-terminated polyurethane on the adhesion properties and the phase separation were investigated. The adhesion properties at liquid nitrogen temperature coincide with the phenomenon observed in the phase separation behavior of polyurethane. Differential scanning calorimetry (DSC) and infrared technique (IR) were used to assess the phase separation content. The enthalpy jump at the glass transition temperature (AC,) and the unique spectroscopic features in the N-H and C=O stretching regions were applied to characterize the phase separation behavior. It was found that the modified resins do not only show superior adhesion at liquid nitrogen temperature but also exhibit some unique properties, e. g., room temperature curing and good storage stability. ZUSAMMENFASSUNG:Die Klebeeigenschaften und das Phasentrennungsverhalten von Polyurethanen aus ,,weichen" Poly(oxypropy1en)-Einheiten (PPG) und ,,harten" Segmenten aus Toluoldiisocyanat (TDI) und 1,4-Butandiol (BD) wurden untersucht. Die Lange der PPG-Weichsegmente (PPG mit MW 700, 1 OOO bzw. 2000) sowie deren Konzentration (30, 50 and 70 Gew.-Vo) wurden variiert. Die Isocyanat-Endgruppen dieser PU-Harze wurden mit 2,3-Epoxy-l-propanol zu Glycidyl-Endgruppen umgesetzt. Die Klebeeigenschaften bei der Temperatur flussigen Stickstoffs folgen dem Phasentrennungsverhalten der Polyurethane. Die Phasentrennung wurde mit DSC-(Enthalpiesprung bei der Glasternperatur) und IR-Messungen (Veranderungen im Bereich der N-H-und C=O-Streckschwingungen) untersucht. Die rnodifizierten PU-Harze weisen neben verbesserter Haftung bei tiefen Temperaturen auch gute Lagerungseigenschaften sowie die Fahigkeit der Hartung bei Raumtemperatur auf.
A method for grafting oligo‐(p‐hydroxybenzoic acid) to carboxyl‐functional oligomers or polymers to give copolymers having mesogenic side chains was developed. The method employs dicyclohexylcarbodiimide (DCC) to promote esterification of PHB at mild temperatures and to remove water. Pyridine is used as solvent, and catalytic amounts of p‐TSA are added to suppress side reactions. Grafting efficiencies are estimated to range from 74 to 90%. Ungrafted oligo‐PHB and other by‐products are readily removed. Structure assignments were supported by IR,1H‐NMR, GPC, DSC and model compound studies. The method appears capable of grafting oligo‐PHB side chains to any pyridine soluble oligomer or polymer having carboxyl groups and no other reactive groups that could interfere.
SynopsisA previously reported synthetic procedure was used to graft oligo-p-hydroxybenzoic acid (oligo-PHBA) to COOH-functional acrylic copolymers. Most of the products were side-chain LC copolymers. Length of the mesogenic oligo-PHBA groups averaged up to five aromatic rings per group. Because these long mesogenic groups have a strong tendency to form LC domains, it was possible to prepare LC side-chain copolymers having as little as 5 mol ' % of mesogenic monomer. Thus this synthetic procedure provides a versatile route for exploration of the properties of LC copolymers having relatively few but especially effective mesogenic groups. The potential utility of such LC copolymers as binders for nonbake coatings was assessed. Variables studied were molecular weight and TK of the acrylic copolymer backbone, number and average length of oligo-PHBA segments, and the presence or absence of a flexible spacer between the acrylic backbone and the PHBA segments. Optimum LC copolymers have moderate (15,OOO-30,OOO) M n , low ( -10°C) backbone TK, and low (5-7.5 mol '%) population of long (5 PHBA units) oligo-PHBA units. Such copolymers have two major advantages as coatings binders: They form concentrated, stable, low-viscosity dispersions in common solvents, a very desirable characteristic for application. Coating films have excellent adhesion to metal, and they have an extraordinary combination of hardness (H-2H) and impact resistance (> 80 in. lb). These properties are key indicators of coating performance and indicate that LC copolymers have excellent potential for use as binders for nonbake coatings. Other properties remain to be investigated.
SynopsisCarboxyl functional liquid crystalline (LC) acrylic copolymers were synthesized and were compared with carboxyl functional control copolymers of an about 5000-15,000. Both types were crosslinked with a hexakismethoxymethyl melamine (HMMM) resin at 150"C, a temperature below the clearing points of the LC copolymers. Birefringent phases were visible in the crosslinked films made from LC polymers. BY'-IR indicated the presence of unreacted COOH in all crosslinked materials. Unreacted COOH groups in crosslinked LC copolymers appeared only slightly higher than those in crosslinked amorphous copolymers. The potential utility of these LC copolymers as binders for thermosetting coatings was assessed. Variables studied were HMMM content, the length of PHBA grafts, Tg and an of the acrylic copolymer backbone, and functionality.Optimum LC copolymers have low backbone TB (< OT) and low functionality (< 7.5 mol %). Cured films of such copolymers have both high hardness (> 35 KHN), high impact resistance (> 80 in. lb), excellent adhesion, and good solvent resistance. INTRODUCTIONMelamine resin crosslinked acrylic high solids coatings are widely used when hard, weatherable films are required.' However, hard films of such coatings tend to be brittle. A combination of high hardness and good toughness cannot be achieved by adjusting the usual structural parameters such as Sn, functionality, Tg, and content of melamine resin.2 This article concerns a new approach toward this desirable combination of properties.In a previous article3 we reported a convenient method for grafting phydroxybenzoic acid (PHBA) segments to COOH-functional oligomers or polymers (Scheme I). Oligomers or polymers grafted with oligo-PHBA segments usually have thermotropic, liquid crystalline phases, although a few are crystalline.In another article4 we reported that liquid crystallinity in alkyd resins provides at least three important practical benefits: solution viscosity is reduced by formation of nonaqueous dispersions, dry times are sharply reduced, and films are both hardened and toughened. We also reported5 that liquid crystalline acrylic lacquers have two major advantages as binders for higher-solids nonbake coatings: (1) They form concentrated, stable, low viscosity dispersions in common solvents, a very desirable characteristic for application. (2) Coating films have an extraordinary combination of high hardness and high impact resistance. In recent articles Wang and Jones' and Dimian and Jones7 showed that LC oligoesters can be crosslinked with hexakismethoxymethyl melamine (HMMM) to give hard, impact-resistance coatings.Journal of Applied Polymer Science, Vol. 37, 1063-1078 (1989 Here we report the use of melamine resins to crosslink LC acrylic copolymers to give coating f i l m s that are both hard and tough. In this study COOH-functional low molecular weight LC acrylic copolymers were synthesized as des~ribed.~ These copolymers were crosslinked with HMMM at 150"C, a temperature below the clearing points of their LC phases. It will be sh...
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