Radiation induced polymerization of isoprene: A spectroscopic study

Isoprene polymerizes under the action of γ-radiation from a ⁶⁰Co source yielding a low molecular weight polyisoprene which remains soluble in the unreacted monomer. The electronic absorption spectrum of polyisoprene oligomer in isoprene monomer has been explained using squalene, a polyisoprene hexamer, as model compound. The radiation chemical yield for polyisoprene formation has been estimated from both gravimetric and spectrophotometric data pertaining the amount of polymer formed. An average G value of 35 molecules/100 eV has been determined suggesting that the polymerization mechanism involves free radicals. The chemical structure of the resulting polyisoprene radio-oligomer has been determined by FT-IR spectroscopy and found identical to that of a reference polyisoprene sample prepared by a chemically-initiated free radical polymerization process. The structure determination by FT-IR spectroscopy has been reported in detail.     

In situ control of surface molecular order in liquid crystals using a localised polymer network and its application to electro-optical devices

A liquid crystal (LC) alignment technique has been developed that allows local control of the polar pretilt angle over the range of 0–90°. This was achieved through the formation of a polymer network localised in the vicinity of the LC cell substrates. The network was formed as a result of in situ UV-induced polymerisation of a photo-reactive monomer added at concentrations of 0.5–1%. Localisation of the polymer network at the LC–substrate boundary was achieved by the application of a high voltage before polymerisation. The resultant pretilt angle was determined by the voltage applied during the polymerisation and/or the duration of the voltage application before the polymerisation step. The desired pretilt angle could be set over a small area of the sample, which allows the fabrication of LC devices with spatially variable optical retardation. Using this method we fabricated a converging lens, a bi-prism, and a phase diffraction grating with resolution greater than 50 lines mm^?1.     

Synthesis and Controlled Polymerisation of a Novel Gramicidin S Analogue

Summary: The controlled polymerisation of a bulky, peptide‐based monomer was investigated. The cyclic β‐sheet forming decapeptide gramicidin S was modified with a methacrylate handle and subsequently polymerised via atom transfer radical polymerisation (ATRP), to yield a well‐defined gramicidin‐S‐containing polymer. The secondary structure of the peptide moiety was retained within the resulting polymer, as indicated by IR spectroscopy. This is the first example of the use of ATRP to create a synthetic polymer with a cyclic peptide as a side chain.

The gramicidin S based monomers synthesised here were then polymerised by ATRP.     

Melting of solvents nanoconfined by polymers and networks

Thermoporosimetry is becoming increasingly used to study nanoscale heterogeneity and structure in polymer networks. The starting point for thermoporosimetry is the Gibbs-Thomson (GT) relation between melting point and inverse crystal size. In the case of polymers, the Flory-Huggins (FH) model also predicts that there is a depression of the melting point because of the mixing of the polymer and the solvent molecules, and this needs to be taken into account. The first step in analysis of size heterogeneity using thermoporosimetry and the GT equation requires that there be quantitative agreement between the FH theory and the melting points of the diluent in the uncrosslinked rubber. We find that both benzene and hexadecane exhibit excessive melting point depressions in uncrosslinked polyisoprene. This may imply that the uncrosslinked polymer is divided into ‘nanoheterogeneities’. We further find that the heat of fusion decreases as polymer concentration increases for the benzene, but not for the hexadecane. Finally, we compare pore size distributions obtained for a crosslinked polyisoprene as determined from the melting behavior of n-hexadecane as a diluent, using different references for how the uncrosslinked polymer behaves. While number average distribution is not very different between the different analyses, the weight average distribution is. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 3475–3486, 2006     

Lithiation of diene polymers

It was found that the metallation of diene polymers with n-butyllithium in n-heptane takes place in the presence of a tert amine, i.e. N,N,N′,N′-tetramethylethylenediamine. Butyllithium was added to the diene polymer in n-heptane in the presence of an equimolar amount of the amine, and the mixture was allowed to react at 80°C. for 60 min. under nitrogen. As a result, 27% and 9% per monomer unit for polybutadiene and polyisoprene, respectively, were metallated. The effects of the concentrations of the diene polymer, butyllithium, and the amine on the reaction were studied at 80°C., and the reaction mechanism was discussed. The overall rate of metalation was proportional to the diene polymer concentration and to the square root of the butyllithium concentration. The overall activation energies of metalation were 6.6 and 8.4 kcal./mole for polybutadiene and polyisoprene, respectively. Many kinds of polymer derivative were obtained by treating the metalated polymers with various reagents, such as carbon dioxide, Michler's ketone, trimethylchlorosilane, triphenylchlorosilane, benzaldehyde, and pyridine.     

Anomalous freezing point depression of solvents in a swollen homogeneous rubber network

The freezing point depression of a solvent, imbibed by crosslinked polyisoprene networks, was studied. It is argued that in a swollen vulcanizate, polymer chains subdivide the solvent, creating zones too small for nucleation on cooling to occur at the normal freezing point of the solvent. The freezing point of the solvent is identified with the temperature at which nuclei can form in the swollen network. A linear relationship between freezing point and the volume fraction of rubber in the swollen gel is predicted for a uniformly crosslinked network. Such a relationship is shown to hold for gamma-irradiated polyisoprene, but not for peroxide-cured samples, where deviations from linearity are interpreted as indicative of nonuniformity in the network. © 1993 John Wiley & Sons, Inc.     

Pd‐Catalysed Direct Arylation Polymerisation for Synthesis of Low‐Bandgap Conjugated Polymers and Photovoltaic Performance

Low‐bandgap conjugated copolymers based on a donor–acceptor structure have been synthesised via palladium‐complex catalysed direct arylation polymerisation. Initially, we report the optimisation of the synthesis of poly(cyclopentadithiophene‐alt‐benzothiadiazole) (PCPDTBT) formed between cyclopentadithiophene and dibromobenzothiadiazole units. The polymerisation condition has been optimised, which affords high‐molecular‐weight polymers of up to M _n = 70 k using N‐methylpyrrolidone as a solvent. The polymers are used to fabricate organic photovoltaic devices and the best performing PCPDTBT device exhibits a moderate improvement over devices fabricated using the related polymer via Suzuki coupling. Similar polymerisation conditions have also been applied for other monomer units.     

Effects of monomer structure on the morphology of polymer networks and the electro-optical properties of polymer-dispersed liquid crystal films

Polymer-dispersed liquid crystal (PDLC) films were prepared by photochemical polymerisation with a series of (meth)acrylate monomers. The effects of monomer structure on the morphology of polymer networks in the PDLC films were studied. The acrylate monomers without sidegroup chain formed uniform polymer networks. The methacrylate monomers with methyl as their sidegroup chains formed lace-like networks. The size of the LC droplets increased with increasing the length of the flexible chain of both methacrylate and acrylate monomers. Meanwhile, the effects of the morphology of the polymer network on the electro-optical properties of PDLC films were also investigated.     

Effect of the remaining lanthanide catalysts on the hydrolytic and enzymatic degradation of poly-(ϵ-caprolactone)

Poly-(ϵ-caprolactone) is a biodegradable polymer, which can be used for both medical and environmental applications. Due to its multiple applications the synthesis of such a polymer has been attracting an increasing attention in the past few decades. In our work, the polymers were synthesised by bulk polymerisation, using different lanthanide halides as initiators. The lanthanide derivatives are known as very active catalysts in the ring-opening polymerisation of cyclic esters. Moreover, they are not toxic in comparison of catalysts, which are usually used for this synthesis. In this paper, the influence of the lanthanides on both the hydrolytic and enzymatic degradation of the PCL obtained by ring-opening polymerization of ϵ-caprolactone with different lanthanide-based catalysts such as: lanthane chloride (LaCl₃), ytterbium chloride (YbCl₃) and samarium chloride (SmCl₃) was assessed. Samarium seems to slightly accelerate the hydrolytic degradation of the polymer and to slow down or inhibit its enzymatic degradation, mainly when the molecular weight of the polymer is high. The behaviour of PCL containing another lanthanide like lanthane is dependent on the nature of the metallic ion. Complete degradation, by the Lipase PS from Pseudomonas cepacia, is achieved only with Ytterbium.     

Organolanthanides as single component homogeneous catalysts for isoprenehex—1-ene co-polymerisation

Bisallylansalanthanide complexes act as single component catalysts of diene polymerisation; from an equimolar mixture of isoprene and hex-1-ene, a co-polymer hex-1-ene/isoprene = 1:10 is obtained, this copolymer is essentially formed of 1,4-transpolyisoprene blocks separated by only one inserted hexyl group.     

Re-examination of the Reactivity of N-Carboxy Amino Acid Anhydrides 1. Polymerisation of Amino Acid NCAs in Acetonitrile and in the Solid State in Hexane

Ring-opening polymerisation of N-carboxy anhydrides of γ-benzyl-L- glutamate, L-alanine and L-leucine by a primary amine initiator in acetonitrile and in hexane was examined, with care taken to avoid contamination by moisture. The polymerisation of amino acid NCAs initiated by butylamine in hexane proceeded in the crystalline state (solid state) because the NCA crystals did not dissolve in hexane. Although amino acid NCAs were believed to polymerise completely in acetonitrile, polymerisation of the amino acid NCAs in acetonitrile was found to stop at around 20% conversion. As resulting polypeptides did not dissolve in acetonitrile, the polymer terminals were considered to be occluded in the polymer precipitate. On the other hand, each amino acid NCA was much more reactive in the solid state in hexane than in acetonitrile. Especially, L-leucine NCA showed remarkable reactivity in the solid state. The reactivity in the solid state was explained with reference to the crystal structure.     

Diffusion of linear polyisoprene molecules into polyisoprene networks

Diffusion and equilibrium absorption of polyisoprene liquids into crosslinked samples of cis-polyisoprene (natural rubber) have been studied by direct observation of volume swelling. Natural rubber was crosslinked in the form of fine threads, about 40 ± 20 μm in diameter, using a gaseous reaction with SO₂ and H₂S (the Peachey process). An optical microscope was used to observe the relatively rapid absorption of linear high-molecular-weight polyisoprene liquids by these fine threads. From the kinetics of absorption, values of the self-diffusion coefficient D_s of polyisoprene were estimated. They ranged from 10^?16 m²/s to 10^?12 m²/s, depending upon molecular weight, and varied with molecular weight approximately as M^?2 over the entire range employed, from 1,000 to 60,000 g/mol, i.e., both above and below the entanglement molecular weight. Amounts of polymer absorbed at equilibrium varied widely, depending upon the degree of crosslinking of the host material and the molecular weight of the absorbing liquid. They were in reasonable agreement in all cases with simple swelling theory, with the heat of mixing equated to zero.     

Nanodroplets of polyisoprene fluid contained within poly(acrylic acid‐co‐acrylamide) shells

The preparation and characterization of macromolecular nanostructures possessing an amphiphilic core–shell morphology with a hydrophobic, fluidlike core domain with a low glass‐transition temperature are described. The nanostructures were prepared by the self‐assembly of polyisoprene‐b‐poly(acrylic acid) diblock copolymers into polymer micelles, followed by crosslinking of the hydrophilic shell layer via condensation between the acrylic acid functionalities and 2,2′‐(ethylenedioxy)bis(ethylamine), in the presence of 1‐(3′‐dimethylaminopropyl)‐3‐ethylcarbodiimide methiodide. The properties of the resulting shell‐crosslinked knedel‐like (SCK) nanoparticles were dependent on the microstructure and properties of the polyisoprene core domain. SCKs containing polyisoprene with a mixture of 3,4‐ and 1,2‐microstructures underwent little shape distortion upon adsorption from aqueous solutions onto mica or graphite. In contrast, when SCKs were composed of polyisoprene of predominantly cis‐1,4‐repeat units, the glass‐transition temperature was ?65 °C, and the nanospheres deformed to a large extent upon adsorption onto a hydrophilic substrate (mica). Adsorption onto graphite gave a less pronounced deformation, as determined by a combination of transmission electron microscopy and atomic force microscopy. Subsequent crosslinking of the core domain (in addition to the initial shell crosslinking) dramatically reduced the fluid nature and, therefore, reduced the SCK shape change. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1659–1668, 2003     

Synthesis and characterisation of star-shaped liquid crystalline polymer with a POSS core

The star-shaped POSS-graft-LCP with POSS as the core and liquid crystal polymer, poly{6-(4?-octyloxyphenyl-4″-benzoyl)hexyl acrylate}, as arms was prepared by atom transfer radical polymerisation technique using octa(3-chloropropyl) polyhedral oligomeric silsesquioxane [POSS-(CH₂CH₂CH₂Cl)₈] as initiator. For comparison, the linear liquid crystal polymer, poly{6-(4?-octyloxyphenyl-4″-benzoyl)hexyl acrylate} (LLCP), was obtained by conventional radical polymerisation. Both liquid crystal polymers were characterised by FT-IR, ¹H NMR, ¹³C NMR, gel permeation chromatography, thermogravimetric analysis, differential scanning calorimetry, polarised optical microscopy and X-ray diffraction analysis. The liquid crystal phase behaviour research demonstrated that both liquid crystal polymers were reversible thermotropic nematic liquid crystal materials. The number of polymerisation degree of every arm attached on POSS in POSS-graft-LCP impacted greatly on the liquid crystal properties and only a small one was necessary for it to exhibit a broad liquid crystal range. Results further demonstrated that the special star-shaped topology of POSS and the eight arms attached helped POSS-graft-LCP form and stabilise liquid crystal phase easily. This research may further expand the way to star-shaped LCPs by employing a variety of (meth)acrylate and other vinyl liquid crystalline monomers.     

Stress‐Induced Melting of Crystals in Natural Rubber: a New Way to Tailor the Transition Temperature of Shape Memory Polymers

Lightly cross‐linked natural rubber (NR, cis‐1,4‐polyisoprene) was found to be an exceptional cold programmable shape memory polymer (SMP) with strain storage of up to 1000%. These networks are stabilized by strain‐induced crystals. Here, we explore the influence of mechanical stress applied perpendicular to the elongation direction of the network on the stability of these crystals. We found that the material recovers its original shape at a critical transverse stress. It could be shown that this is due to a disruption of the strain‐stabilizing crystals, which represents a completely new trigger for SMPs. The variation of transverse stress allows tuning of the trigger temperature T_trig(σ) in a range of 45 to 0 °C, which is the first example of manipulating the transition of a crystal‐stabilized SMP after programming.     

Isoprene polymerization with cerium(III) acetylacetonate–diethylaluminum chloride in toluene: Effects of water concentration

Isoprene has been polymerized in toluene using a cerium(III) acetylacetonate–diethylaluminum chloride catalyst. The microstructure of obtained polyisoprene is predominantly trans-1,4 structure. For this system the effects of water concentration on the conversion of isoprene to polymer, the microstructure and the molecular weight of polyisoprene have been examined. The conversion at a given polymerization time has a maximum at [H₂O]/[DEAC] ratio of 1:0–1.1. The amounts of trans-1,4 structure and the viscosity average molecular weights of polyisoprene are nearly independent of the water concentration. Although the conversion increases with the concentration of catalyst, the trans-1,4 content is not affected by the catalyst concentration and the molecular weight of polyisoprene decreases slightly with increasing catalyst concentration.     

Recent advances in the neodymium catalysed polymerisation of 1,3-dienes

The benefits of using a homogeneous neodymium-based catalyst for the industrial “high cis” polymerisation of 1,3-butadiene are underlined. Preformed homogeneous catalysts for the “high cis” polymerisation of 1,3-butadiene based on Nd(carboxylate)₃/diisobutylaluminium hydride/^tbutyl chloride have been examined. The effects of changing (a) the order of catalyst component addition, (b) the carboxylate component and (c) the halogen component, on catalyst homogeneity, activity and polymer characteristics have been examined.     

Polymerisation of dithiocarbamates by oxidative coupling using iodine as oxidant—I. Synthesis and characterisation

A novel polymer has been synthesised by reacting hexamethylene diamine with carbon disulphide by the oxidative coupling method using iodine as oxidant. The first step of the polymerisation involves the formation of dithiocarbamate by reacting a diamine with carbon disulphide in alkaline medium at low temperature (5–10°) in a protic solvent such as alcohol or water. Next, the dithiocarbamate is coupled with a diamine using iodine as the oxidant at ambient temperature. The polymerisation proceeds by a radical mechanism. The molecular weight of the polymer is not very high (∼ 12,000); it is soluble in polar solvents. It was characterised by elemental analysis (N, S) and i.r. and NMR spectroscopy. The physical characteristics have been studied.     

Polyamide-6 nanocomposites with electron-beam-treated clay

The “in situ” polymerisation principle has been applied in our work to modify the efficiency of montmorillonite (MMT) as a reinforcement in polymer composites. The dry silica powder of MMT has been dispersed in (2-hydroxyethyl)-methacrylate (HEMA) monomer, and it has been treated by electron-beam (EB) and by heat. The treated silica powder has been mixed in polyamide (PA) melt by a Brabender kneader. The solid polymer samples have been tested for mechanical features as well as for dynamic-mechanical properties (DMA), X-ray diffraction (XRD), differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). Surprisingly the thermally initiated “in situ” polymerisation was more efficient than 150 kGy EB dose in improving the composite properties.     

新型高分子多孔小球的研究

本文研究出一种用双甲基丙烯酸乙二醇酯作交联剂, 通过二次聚合反应得出新型高分子多孔小球(NKG), 可作为气相色谱法的固定相. 它比通用的商品高分子多孔小球具有较高的分离效能和较广的应用范围, 并且克服了后者由于使用难以纯化的二乙烯苯作交联剂所导致的缺点. 提出以五种有机化合物的保留指数表征高分子多孔小球的极性. NKG有较高的柱效, 表明二次聚合反应大大地增加了它的溶剂效应, 从而使色谱过程中气液色谱占主导地位。通过测定NKG的吸附焓,证明二次聚合加强了组份固定相之间的相互作用. 此外, 本文还对双甲基丙烯酸乙二醇酯的合成方法进行研究, 用一种新的催化剂使酯交换反应时间从一般方法需要8h缩短到2h, 并且收率和纯度分别可达95和98%以上。