Synthesis and thermal properties of side chain-type liquid crystalline polyurethanes

Abstract

The synthesis of side chain-type polyurethanes is described. Their thermal properties were investigated by differential scanning calorimetry and polarizing microscopy and are discussed in terms of the dependence of the polymer backbone on temperature as shown by FT-infrared spectroscopy. The hydrogen bonding which arises from the rather flexible polymer backbone plays a more important role in determining the thermal stability than does the rigid polymer backbone.     

Mecanisme d'ignifugation d'elastomeres organosiliciques par le platine

The role of platinum and of some mineral oxides in improving the thermal stability of a silicone rubber has been studied by temperature-programmed thermogravimetric analysis and by isothermal pyrolysis. Platinum has no significant influence on the scission of side chains. It limits the rupture of the polymer backbone by preventing the formation of a transition complex involved in silicone degradation. Mineral oxides combine with certain products of the thermal decomposition of the polymer.     

Siloxane/silarylene copolymers as stationary phases for capillary gas chromatography part I: Evaluation of silanol terminated dimethyl substituted polymers

The thermal stability of silicones can be improved on replacement of certain of the oxygen atoms in the polymer backbone by phenyl groups. Such a polymer has been synthesized and evaluated for use as stationary phase in fused silica capillary gas chromatography; the polymer was dimethyl substituted and silanol terminated. A selectivity was provided by the phenyl groups in the backbone. For comparative purposes, a silanol-terminated dimethylpolysiloxane has also been evaluated. Both stationary phases gave columns of highest separation efficiency and the supporting fused silica surface was deactivated by the stationary phases on thermal treatment. Further, low column bleeding was observed at the maximum temperature tested, 370°C. The phenyl-containing phase could be immobilized to 60% by heat treatment, but the pure dimethylpolysiloxane was 10% immobilized. The influence on immobilization of factors such as nature of the supporting surface, stationary phase silanol content, reaction temperature and atmosphere in the column during reaction has been studied.     

Diamond and diamond-like carbon from a preceramic polymer

The synthesis of poly(hydridocarbyne), one of a class of carbon-based random network polymers and a structural isomer of polyacetlyene, is reported. The network backbone of this polymer is primarily composed of tetrahedrally hybridized carbon atoms, each bearing one hydride substituent and linked via three carbon-carbon single bonds into a three-dimensional random network of fused rings. This atomic-level carbon network backbone confers unusual properties on the polymer, including facile thermal decomposition to form diamond or diamond-like carbon high-quality films at atmospheric pressure, by direct deposition or by chemical vapor deposition (CVD), without the use of hydrogen or any other reagent.     

Synthesis and characterization of liquid crystalline polymethacrylates,polyacrylates, and polysiloxanes containing 4-methoxy-4′-hydroxy-α-methylstilbene-based mesogenic groups

The synthesis and characterization of polymethacrylates and polyacrylates containing 4-methoxy-4′-hydroxy-α-methylstilbene side groups attached either directly or through flexible spacers containing eleven, eight, six, three, and respectively two methylenic units, and of the polysiloxanes containing the same mesogenic group connected through flexible spacers containing eleven, eight, six, and respectively three methylenic units are described. All polymers exhibit thermotropic liquid crystallinity. The nature of the mesophase is determined by the spacer length. However, the nature of the polymer backbone determines the thermal stability of the mesophase. That is, for the same spacer length and similar polymer molecular weight, the most flexible polymer backbone leads to the highest isotropization temperature.     

In situ monitoring the thermal degradation of PCPDTBT low band gap polymers with varying alkyl side‐chain patterns

The degradation pattern of a series of low band gap PCPDTBT polymers under thermal stress is investigated by in situ UV–vis and FT‐IR techniques combined with thermal degradation analysis. Thermogravimetric analysis is used to predetermine the decomposition intervals, revealing that thermolysis occurs in two stages. TG‐TD‐GC/MS shows that loss of the alkyl side chains predominantly happens within the first temperature regime and degradation of the polymer backbone occurs thereafter. UV–vis spectroscopy is used to monitor the evolution of the optical properties upon heating, reflecting the thermal stability of the conjugated backbone, whereas FT‐IR spectroscopy is applied to evaluate the chemical changes under thermal stress, with an emphasis on the polymer periphery. The influence of the side chains and possible defects, dependent on the synthesis protocol applied, on the thermal stability of the final polymers is discussed and is related to the application of said materials in organic photovoltaics. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 4912–4922     

Polyboramines for Hydrogen Release: Polymers Containing Lewis Pairs in their Backbone

The one‐step polycondensation of diamines and diboranes triggered by the in situ deprotonation of the diammonium salts and concomitant reduction of bisboronic acids leads to the assembly of polymer chains through multiple Lewis pairing in their backbone. These new polyboramines are dihydrogen reservoirs that can be used for the hydrogenation of imines and carbonyl compounds. They also display a unique dihydrogen thermal release profile that is a direct consequence of the insertion of the amine–borane linkages in the polymeric backbone.     

Direct pyrolysis in the mass spectrometer of aromatic polysulfonates and polythiosulfonates

The thermal degradation mechanism of three aromatic polysulfonates and polythiosulfonates was investigated by direct pyrolysis in the ion source of a mass spectrometer. Thermal degradation reactions were followed directly by this method by detecting the thermal and electron impact induced fragments. The results obtained have provided evidence that sulfur dioxide extrusion from the polymer backbone takes place in these polymers above 300°C. The synthesis and molecular characterization of the polymers studied are reported in the text.     

Negative thermal expansion of polymer crystals: Lattice model

The lateral thermal motion of atoms in an inextensible polymer chain would cause a shortening along the chain direction. This effect could explain the observed negative thermal expansivity α along the chain direction of a polymer crystal. Using this idea, the expansivity α is calculated for a lattice of parallel linear chains. A value of ?1.3 × 10^?5 K is obtained for chains with a carbon backbone, in good agreement with data for polyethylene.     

New indole-based chromophore-containing main-chain polyurethanes: architectural modification of isolation group, enhanced nonlinear optical property, and improved optical transparency

Three indole-based nonlinear optical (NLO) chromophores with changeable isolation groups were successfully introduced into the polymer backbone to yield a series of main-chain polyurethanes. Thanks to the main-chain structure and the advantages of the indole-based chromophores, all of the polymers show excellent transparency, good processability, thermal stability, and relatively good NLO effects. The obtained experimental results indicated that the polymer backbone, in addition to the linked isolation moieties, could act as isolation spacers in some special cases. The tested NLO results demonstrated that the isolation groups with apparent site-isolation effect might not benefit the macroscopic NLO effect of the resultant polymers.     

Photocrosslinking and thermal behavior of the polyesters containing conjugated diacetylenes

A series of polyesters containing conjugated diacetylenic groups in the polymer backbone were synthesized by interfacial condensation of 3,5-hexadiyne-1,6-diol and diacid chlorides of succinic, glutaric, adipic, azealic, sebacic, terephthalic, and isophthalic acids. The polyesters were characterized by their infrared and ultraviolet absorption spectra, elemental analysis, and viscosity measurements. Powder x-ray patterns indicated high degress of crystallinity. The polyesters were found to be highly photoreactive. The relative photoreactivities of the polyester films were determined by the adhesion method. Only small differences in the reactivity have been observed despite structural changes in the R group in the polymer backbone. Differential thermal analysis behavior of all polymers in the temperature range ambient to 300°C and isothermal behavior of HGI at two different temperatures have been studied.     

Cast Polyurethanes: Effect of Chain Extenders on Thermal Mechanical and Dynamic Mechanical Properties

Effects of various diol chain extenders on thermal, mechanical, and viscoelastic properties of polyurethanes are discussed. Elastomers were prepared by using polyester (polyethylene-co-propylene adipate), toluene-2,4-diisocyanate, and α,ω-aliphatic diols. The properties imparted by the extenders are explained on the basis of the number of methylene carbons in the extenders. Butanediol-extended polymer showed superior properties, which are ascribed to regularity in the backbone chain of the polymer and ease of formation of hydrogen bonds.     

Thermomechanical enhancement of DPP-4T through purposeful π-conjugation disruption

The design of polymer-based organic semiconductors that offer mechanical deformability while maintaining efficient semiconducting characteristics remains a significant challenge. Recent synthetic efforts have incorporated small alkyl segments directly into otherwise π-conjugated polymer backbones to enhance processability, mechanical deformability, and other properties. The resulting polymers can be used as stand-alone materials or as matrix polymers in complementary semiconducting polymer blends offering reasonable charge-carrier transport properties, thermal healing, and deformability. Here, a family of diketopyrrolopyrrole-tetrathiophene variants is explored via large-scale atomistic molecular dynamics simulations to examine the effect of alkyl segments incorporated into the polymer backbone on the polymer structure, dynamics, and thermal properties. Longer alkyl segments lead to polymer chains that are more flexible, compact, and mobile, with lower glass transition temperatures for the condensed phase.     

IN AQUA SYNTHESIS OF A HIGH MOLECULAR WEIGHT ARYLETHYNYLENE POLYMER EXHIBITING REVERSIBLE HYDROGEL PROPERTIES

ABSTRACT

A high molecular weight poly(aryleneethynylene) (M_w ～ 60,000) is prepared by the palladium catalyzed copolymerization of 3,5-diiodobenzoic acid and acetylene gas in a basic aqueous medium. The polymer has a “zig-zag”, fully conjugated backbone. The polymer has been characterized by a variety of methods and exhibits high thermal stability. Furthermore, the polymer is readily soluble in aqueous base and is reversibly switchable from the solution state to a hydrogel state, in water, by changing the pH of the solvent.     

Molecular design of free volume as a route to low-kappa dielectric materials

Polymers incorporating the triptycene subunit were prepared for the molecular-level design of low dielectric constant (low-kappa) materials that can be used to manufacture faster integrated circuits. Triptycenes having restricted rotation by multiple point attachment to the polymer backbone are shown to introduce free volume into the films, thereby lowering their dielectric constants. The triptycene containing polymers exhibit a number of desirable properties including low-water absorption and high thermal stability. Systematic studies wherein comparisons are made between two separate classes of triptycene polymers and their non-triptycene containing analogues demonstrate that proper insertion of triptycenes into a polymer backbone can give rise to a reduction in the material's dielectric constant while also improving its mechanical properties. These characteristics are desired by the semiconductor industry for the next generation of microprocessors and memory to provide insulation of the increasingly shrinking features.     

New block-copolymer thermoassociating matrices for DNA sequencing: effect of molecular structure on rheology and resolution

A new family of matrices for DNA sequencing by capillary electrophoresis is presented. These matrices combine easy injection with high sieving performances, due to thermal switching between a low and a high viscosity state through a modest increase in temperature (approximately 20 degrees C). They are constructed from a hydrophilic polymer backbone with grafted lower critical solution temperature (LCST) side chains. The comb-like LCST copolymers are characterized in terms of size of the polymer backbone, the size of LCST side chains and the grafting densities. The dependance of rheological behavior and electrophoretic performance of these copolymers is correlated with their microstructure. Without complete optimization, a resolution of order 0.5, corresponding to a very reasonable limit for read length with current base calling softwares, could be achieved for segments around 800 bases differing by 1 base in less than one hour in a commercial ABI 310 apparatus.     

Synthese de sequences polychlorure de vinyle α-ω difonctionnelles et extension en copolymeres multisequences

It is possible to synthesize α-ω diacid PVC sequences by direct ozonization of the polymer, but their thermal stability is low because peroxides are introduced simultaneously in the polymer backbone. Also they cannot be used to prepare block copolymers by polycondensation at temperature above 100°. They are reactive enough to be transformed to α-ω acid chlorides which can be condensed with diols, diamines and bisphenol A to give block copolymers. Triethylamine acts as catalyst but also as HCl acceptor and favours high molecular weight formation. The α-ω acid chlorides can be hydroxylated and polycondensed with diphenylmethane diisocyanate. The thermal stability of these block copolymers is satisfactory if the peroxides are previously reduced.     

The effect of 3,5-ditert.butyl-4-hydroxybenzylthioglycollate and tinuvin P on the thermal,photo and natural degradation of ABS

A newly synthesized antioxidant 3,5-ditert.butyl-4-hydroxybenzyl thioglycollate (DBHBT) and Tinuvin P have been used as additives for normal ABS. The thermal and photo-oxidative stabilities of the polymer containing these additives have been compared with those for unstabilized ABS. It is concluded that the new additive gives very good thermal stability to ABS and acts as a peroxide decomposer. It was found that it could be grafted on to the polymer backbone during processing. Synergism was obtained with a combination of Tinuvin P and DBHBT. It was found that considerable protection was offered to the base polymer when ABS containing these additives was exposed to weathering.     

Stochastic Bullvalene Architecture Modulates Structural Rigidity in π-Rich Macromolecules

The synthesis and processing of π-rich polymers found in novel electronics and textiles is difficult because chain stiffness leads to low solubility and high thermal transitions. The incorporation of “shape-shifting” molecular cages into π-rich backbone provides an ensemble of structural kinks to modulate chain architecture via a self-contained library of valence isomers. In this work, we report the synthesis and characterization of (bullvalene-co-phenylene)s that feature smaller persistence lengths than a prototypical rigid rod polymer, poly(p-phenylene). By varying the amount of bullvalene incorporation within a poly(p-phenylene) chain (0–50 %), we can tune thermal properties and solution-state conformation. These features are caused by stochastic bullvalene isomers within the polymer backbone that result in kinked architectures. Synthetically, bullvalene incorporation offers a facile method to decrease structural rigidity within π-rich materials without concomitant crystallization. VT NMR experiments confirm that these materials remain dynamic in solution, offering the opportunity for future stimuli-responsive applications.     

Synthesis of thermally degradable epoxy adhesives

We have developed a new strategy for the synthesis of epoxide‐containing polymers where the pendant reactive groups are connected to the main backbone via thermally labile oxonorbornene groups. The polymers were synthesized by radical 1,4‐polymerization of the appropriate bicyclic diene monomer. The produced polymers can be crosslinked in the presence of a diamine and de‐crosslinked by thermal treatment at 160 °C, which induces retro‐Diels–Alder reaction and cleaves pendant groups from the polymer backbone, as confirmed by differential scanning calorimetry. The potential for the utilization of this polymer as a thermally removable adhesive was demonstrated by a simple adhesion test. This method provides access to thermally cleavable epoxy networks that can be quickly and irreversibly disintegrated into nonvolatile components upon heating to a specified temperature. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 4992–4997