Head to head polymers

Pure head to head (H–H) addition polymers, such as H–H polyolefins, H–H acrylates and H–H poly(vinyl halides), have been of interest for the understanding of the structure/properties relationship of addition polymers. These polymer structures have provided challenges of synthesis, characterization and of the measurements of their mechanical and rheological properties. H–H polymers have never been prepared by direct synthesis and indirect polymerization techniques have to be used. Some of the H–H polymers, the polyolefins, were made by polymerization of properly substituted dienes followed by hydrogenation. The H–H polyacrylates were synthesized by copolymerization followed by polymer reactions and the poly(vinyl halides), by halogenation of poly(1,4-butadiene). Improved halogenation techniques for poly(1,4-butadiene) have made H–H poly(vinyl chloride) and H–H poly(vinyl bromide) accessible in larger quantities and have allowed an extensive characterization of these polymers.

Blends of H–H with H–T polymers as well as H–H polymers with other polymers were studied. H–H Poly(vinyl chloride) or poly(vinyl bromide) blends with polycaprolactone and poly(methyl methacrylate) were also investigated. The thermal behavior and the thermal degradation behavior of these blends were investigated. The most striking result of these investigations was that H–H and H–T poly(vinyl chloride) are immiscible as is H–H and H–T polyisobutylene over almost the entire range of compositions.     

Head to head polymers

Blends of poly(-caprolactone) with either head-to-head or head-to-tail poly (vinyl chloride) were prepared by solvent casting in the form of films and their glass transition temperatures were determined by DSC analysis. The DSC scans of the blends of both poly(vinyl chloride) isomers were very similar. For blends containing 25% and 50% of poly(-caprolactone), a single transition step, a T_g, was observed, whereas for a blend containing 75% of poly (-caprolactone) three transition steps were observed, one glass transition and also a crystallization and a melting transition.Part 19: H. Kawaguchi, J. Muggee, Y. Sumida and O. Vogl, Polymer (London), in press     

Head to head polymers. XXV: Properties of head to head polyisobutylene

Head-to-head polyisobutylene, prepared by the Grignard coupling reaction of 2,2,3,3-tetramethyl-1,4-dibromobutane had molecular weight of 3,000 to 10,000 and was characterized by wide angle x-ray diffraction, optical microscopy and thermal behavior. Head-to-head polyisobutylene is crystalline, with a crystalline melting point of 187°C and a glass transition temperature of 87°C (measured by DSC at a scan rate of 20°/min.); these values compare to a glass transition temperature of head-to-tail polyisobutylene of similar molecular weight of ?61°C and a crystalline melting point of 5°C, which can only be observed when the sample was stretched. The maximum rate of degradation of head-to-head polyisobutylene (20°/min. programmed temperature increase) is at 315°C, 70°C lower than that of head-to-tail polyisobutylene.     

Head to head polymers IX: The rheological behavior of H-H and H-T atactic polystyrenes

The rheological behavior of a sample of H-H polystyrene of M_n of 41,000 and a M_w/M_n of 2 was compared at 160 and 190°C with a sample of H-T atactic polystyrene of similar molecular weight. The melt viscosity of H-H polymer (unlike the H-T polymer) was non-Newtonian at low stresses and decreased more rapidly with stress. This observation seems to indicate a stiffer polymer chain for the H-H polystyrene. The flow activation energy (E*) of H-H polystyrene was found to be dependent on the dynamic shear stress and decreased with increasing dynamic shear stress. The dynamic shear storage modulus of the H-H polymer has a smaller increase of G′ with ω than that of the H-T polystyrene.     

Synthesis of biomembrane-mimic polymers with various phospholipid head groups

Lipid bilayers in biomembranes consist of diverse phospholipids, including phosphatidic acid (PA), phosphatidylcholine (PC), phosphatidylethanolamine (PE), and phosphatidylserine (PS) with various compositions according to the cell and tissue types. We synthesized biomembrane-mimic polymers, poly(2-methacryloyloxyethyl phosphoric acid) (PMPA), poly(2-methacryloyloxyethyl phosphorylethanolamine) (PMPE), and poly(2-methacryloyloxyethyl phosphorylserine) (PMPS), with PA, PE, and PS head groups, respectively. PA monomer was synthesized from 2-hydroxyethyl methacrylate (HEMA) and dimethyl chlorophosphate (DCP). PE and PS monomers were synthesized from N-tert-butoxycarbonyl (tBoc) protected ethanolamine and serine through the reaction with 2-chloro-2-oxo-1,3,2-dioxaphospholane (COP). Each biomembrane-mimic polymer was successfully synthesized by atom transfer radical polymerization (ATRP) from the monomer. The molecular weight distributions of PMPA, PMPE, and PMPS were analyzed by gel permeation chromatography (GPC) and in vitro cytotoxicity was also examined by 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT) and lactate dehydrogenase (LDH) assay. The new biomembrane-mimic polymers could be used to prepare a polymeric platform that mimic a cell- or tissue-specific membrane for future applications in biomedical fields such as tissue engineering or bioimplants.     

Adhesion of glow discharge polymers to metals and polymers

Adhesion of glow discharge polymers to metals and polymers in an adhesive joint was measured by lap-shear test and immersion in hot water of 70°C °C for an extended time. A glow discharge polymer was deposited onto polymers [polyethylene and poly(tetrafluoroethylene)] and metals (aluminum and stainless steel) prior to when the polymer and metal were joined. It is found that the lap-shear strength is enhanced by coating the surfaces of these substrates with plasma film produced from methane, ethylene, and acetylene, and that deterioration of the adhesive bonding part, when immersed in hot water of 70°C, is strongly dependent on the gas used as well as operational conditions where a polymer film is formed. The adhesion of a polymer produced from methane on the polymer and metal is strong enough to apply for durable, adhesive joints.     

Heat transfer to molten polymers

The processing of polymers and other solids, such as waxes and acids, often requires the melting of a bulk or granular charge before its introduction into a process stream. Two approximate techniques for relating heat transfer and melting rates are presented here and the shielding effect of the melt formation is considered. The heat available for melting is sometimes remarkably decreased by the heat carried away by the flowing melt. Means are presented for quantitatively determining the shielding or sensible heat effect of the film. The thermal efficiency of the phase transformation process is discussed, and the effects of heat loss to both increased bulk temperature of the flowing melt and conduction in the solid are demonstrated. A comparison with experiment is made using temperature and melt flow data for polyethylene and polyoxymethylene. Heat transfer coefficients and melting correlations useful in practice are presented.     

Bile acids bound to polymers

Summary Bile acids are steroids containing one — lithocholic acid, two — desoxycholic acid, and three — cholic acid hydroxyl groups, respectively. The hydroxyl group in position 3 of the steroid skeleton after esterification of the carboxyl group at C-24 under suitable conditions selectively reacts with methacryloyl chloride to give the corresponding methacrylic ester derivatives which undergo radically initiated uni- and copolymerizations to yield high molecular weight polymers.This paper is dedicated to Professor Georg Manecke on the occasion of his 70th birthday     

The connection number of polymers with particular reference to carbon polymers

The use of a connection number is proposed for the simple topological analysis of random networks. This is illustrated with some carbon polymers.     

Adhesion of polymers to reinforcing fibres

A single fibre pull out technique is presented which makes it possible to measure the strength in the interface between fibre and polymer with high precision even if the embedded length of the fibre is short. The method allows measurements for all kinds of fibres in thermoplastic or thermosetting polymers. The effect of fibre surface treatment can be investigated as well as the effect of morphology or internal stresses in the polymer. Examples are given. The shear strength results are compared with results of tensile shear tests performed on symmetrically notched unidirectional reinforced composite samples. The correlation is good and it is shown that the new single fibre pull out method is able to give a better discrimination between the composites than other methods. An analysis of mechanical stress induced during the pull out demonstrates the use and limitation of this method.     

Permeability of silicone polymers to hydrogen

Permeability coefficients, P?, for H₂ in 10 different types of silicone polymer membranes were measured in the temperature range of 10.0–55.0°C and at pressures up to 100 psig (～6.8 atm). The values of P? decrease slightly with increasing Δp, the pressure difference across the membranes. The permeability of silicone polymers to H₂ increases with an increase in temperature; the values of the energy of activation for permeation are in the range of 1.4–4.3 kcal/mol. The substitution of different functional groups in the backbone and side chains of silicone polymers has similar effects on the permeability of the polymers to H₂ as observed in earlier studies with other light gases. P? for H₂ decreases with an increase in the bulkiness of the substituted functional groups. The substitution of Si? O bonds with stiffer Si? C bonds in the backbone chains also results in a considerable decrease in permeability.     

一种新型快开式封头介绍

介绍了种新型快开式封头的结构，分析了该封头的密封机理、特点及使用场合，并对其安全联锁装置作了简明阐述。