Polyethylene-based polyurethane copolymers and block copolymers

Low molecular weight hydroxy terminated polyethylene (HTPE) containing on average an ethyl group every 16–18 carbon atoms, and a hydroxy functionality of 2.6, has been used to prepare polyurethane copolymers and block copolymers which have good solvent resistance. The polymers show somewhat complicated thermal behavior, including T_g's at around −40°C due to the HTPE and diffuse endotherms between 40 and 60°C. The simple copolymers, containing only the polyol and a diisocyanate, show infrared evidence for two phases in the case where CHDI (trans-1,4-diisocyanatocyclohexane) was used, and poorer phase separation where other diisocyanates were used. Dynamic mechanical spectra show very broad tan delta transitions for the copolymers in the range of -9 to −23°C. All the polymers exhibit another transition in the G” curve above room temperature. SAXS reveals a microphase separated structure at 30°C for the simple copolymers which increases in spacing, then disappears in the 60–70°C range. With cooling, the microphase separated structure reappears readily for the CHDI-based copolymer, while its reappearance shows a hysteresis resulting from rate effects for the other copolymers.     

Gradient copolymers

Gradient copolymers represent a relative new class of copolymers containing at least one section of the macromolecule where the chemical composition continuously changes along the polymer chain. Due to their structural relation to block copolymers, microphase-segregated structures can be formed in bulk, in solution, at surfaces, and interfaces exhibiting a blurred, less-defined border region between phases. The article reviews the preparation methods, the main physical peculiarities, and some proposed applications of gradient copolymers.     

Polyarylaminophosphazene copolymers

A series of polyarylaminophosphazene copolymers have been prepared and are described. In each preparation, two arylamines were allowed to competitively react with polydichlorophosphazene, and the substituent ratios of the resulting copolymers, determined by high-temperature ¹H-NMR spectroscopy, generally reflect expected steric and electronic effects on the relative reactivities of the arylamines studied. The copolymers have intrinsic viscosities of 0.64–1.25 dl/g, glass transition temperatures of 75–104°C, and decomposition temperatures of 220–260°C. These properties, which are comparable to those of polyarylaminophosphazene homopolymers, are discussed in regard to what they may reflect about the structure of the polymers.     

N-vinylpyrazole copolymers

Copolymers of N-vinylpyrazole with N-vinyl-4,5,6,7-tetrahydroindole and vinyl acetate were prepared by radical copolymerization. The composition, structure, and properties of the copolymers were studied. The reactivity constants of the monomers were calculated. Copolymer films were prepared from solutions by casting, and the proton conductivity of the films was determined.     

Organometallic ABC-triblock copolymers

The interaction of Fe and Pd complexes with double bonds of the polybutadiene (PB) block in polystyrene-polybutadiene-poly(methyl methacrylate) block copolymers has been studied. The incorporation of Fe(CO)₃ fragments into the PB bloc was found to result in an increase in its rigidity. The presence of iron or palladium complexes in the PB block affects strongly the morphology of the triblock copolymers.     

N-vinyl carbazole copolymers

The synthesis of N-vinyl carbazole (VCbz) copolymers, some of which contain electron-accepting groups, is described. The new copolymers are: copoly[N-vinyl carbazole-di(2-N-carbazylethyl)-fumarate](II); copoly(N-vinyl carbazole-vinyl-2,4-dinitrobenzene-sulfonate)(IV); copoly(N-vinyl carbazole-vinyl-2,4-dinitrobenzene-sulfenate)(V); copoly(n-butyl acrylate-t-butyl peracrylate)(VII); copoly(n-butyl acrylate-t-butyl acrylate-graft-N-vinyl carbazole)(VIII).     

Ferroelectric block copolymers

A block copolymer consisting of polystyrene and a side chain ferroelectric liquid crystalline polymer was synthesized using polymer analogous chemistry on a monodisperse poly(styrene-b-isoprene). Composition was adjusted to give lamellar microstructure after addition of the mesogenic side groups. If placed in an LC cell without orientation of domains, no ferroelectric response was observed. After shearing the thin film, presumably due to alignment of lamellae, a bistable ferroelectric switching could be detected.     

Electroactive block copolymers

Synthesis, characterization and properties of microphase separated mixed (ionic and electronic) conducting or MIEC block copolymers are reported. Poly{[ω-methoxyocta(oxyethylene) methacrylate]-block-(4-vinylpyridine)}, abbreviated as P[MG8–4VP], and poly{(3-methylthiophene)-block-[(ω-methoxyocta(oxyethylene) methacrylate]}, abbreviated as P[3MT-MG8], have been synthesized. Differential scanning calorimetry (DSC) studies indicate that the polymers form a microphase separated structure. P[3MT-MG8] can be doped with I₂ and LiClO₄ to generate electronic and ionic conducting microdomains, respectively. For the P[3MT-MG8] series, bulk electronic conductivity as high as 1×10⁻³ S cm⁻¹ and bulk ionic conductivity as high as 6.6×10⁻⁷ S cm⁻¹ is observed at 30°C. This work represents a new concept in the area of electroactive polymers and should impact the microelectrochemical device industry.     

Alternating divinylarene-silylene copolymers

A summary of recent advances on the chemistry and photophysics of silylene-spaced divinylarene copolymers is presented. The silicon moieties have been shown to serve as an insulating spacer in these copolymers. The photophysical studies have provided useful insights into how chromophores in polymers interact intramolecularly. Because different chromophores can be regioregularly introduced into the polymeric chain, these copolymers have been extensively used as models for studying energy transfer, light harvesting as well as chiroptical transfer.     

DNA multiblock copolymers

Single stranded (ss) DNA block copolymers were applied to synthesize DNA multiblock architectures by hybridization; these polymeric bioorganic hybrids were characterized by gel electrophoresis and MALDI-TOF mass spectrometry.     

Block copolymers and liquid crystalline block copolymers: A bird's-eye view

Block copolymers and liquid crystals are separately known to order at different length scales. Various types of molecular interactions in liquid crystalline block copolymers determine complex phase behaviors and states of order, and thereby can provide a way of tailoring the material properties. Examples of liquid crystalline block copolymers will be discussed as they may offer unique opportunities for both theoretical and experimental research.     

Organoboronium amphiphilic block copolymers

A new class of amphiphilic organometallic block copolymers with cationic organoboron pendant groups was developed. Selective replacement of one of the bromine substitutents on each boryl group of the block copolymer PSBBr₂‐b‐PS with an organometallic reagent ArM (ArM = 2,4,6‐trimethylphenyl copper, 4‐t‐butylphenyltrimethyl tin) followed by treatment with 2,2′‐bipyridine gave the novel block copolymers [ 3Ar ](Br)_n as light yellow solid materials that show good stability in air and moisture and high solubility in most organic solvents. Their structure and composition were confirmed by multinuclear NMR, GPC, and elemental analysis. Highly regular micellar aggregates form in block‐selective solvents (e.g., MeOH, toluene) as demonstrated by ¹H NMR, dynamic light scattering, and transmission electron microscopy. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6612–6618, 2009     

Photoconductive copolymers containing N-vinylcarbazole

The synthesis of N-vinylcarbazole (VCbz) copolymers in which electron-accepting groups are incorporated into the polymer chain is reported. The acceptors were introduced by appropriate reactions of VCbz–vinyl acetate or VCbz–acryloyl chloride copolymers and consisted of 3,5-dinitrobenzoyl, 2,4-dinitrophenyl acrylate, β-2,4-dinitrophenoxy propionate, and trichlorobenzoquinone units. The copolymer containing the 3,5-dinitrobenzoyl units required no chloranil as a dopant to be photoconductive, and in fact showed a slightly improved photoresponse relative to conventional poly VCbz doped with external chloranil.     

Carbon-chain polymers and copolymers

Summary 2,4-Dichlorostyrene and its polymer were prepared and the rate constant of polymerization of the monomer at 100° and the vitrification point of the polymer determined.