Highly photosensitive polymethyl methacrylate microstructured polymer optical fiber with doped core

In this Letter, we report the fabrication of a highly photosensitive, microstructured polymer optical fiber using benzyl dimethyl ketal as a dopant, as well as the inscription of a fiber Bragg grating in the fiber. A refractive index change in the core of at least 3.2 × 10 has been achieved, providing a grating with a strong transmission rejection of -23 dB with an inscription time of only 13 min. The fabrication method has a big advantage compared to doping step index fiber since it enables doping of the fiber without using extra dopants to compensate for the index reduction in the core introduced by the photosensitive agent. © 2013 Optical Society of America.

Interactions between organic polymers and cement hydration products

Organic substances, particularly polymers, are finding increasing use in modifying the properties of cements and concrete. Although a significant amount of research has been conducted into the modification of the mechanical properties of cements by polymers, little is known about the nature of the interface and interactions taking place between the two phases. This thesis addresses the problem of elucidating such interactions. Relevant literature is reviewed, covering the general use of polymers with cements, the chemistry of cements and polymers, adhesion and known interactions between polymers and both cements and related minerals. Although several polymer systems were studied, two in particular were selected, as being well characterized. These were: - 1) polymethyl methacrylate (PMMA), the polymer derived from methyl methacrylate (MMA), and 2) an amine-cured epoxy resin system. By this approach, a methodology was developed for the examination of other polymer/cement interactions. Experiments were conducted in five main areas:- 1) polymer-cement adhesion and the feasibility of revealing interfacial regions mechanically, 2) chemical reactions between polymers and cements, 3) characterization of cement adhesion surfaces, 4) interactions affecting overall polymerisation rates, and 5) studies of polymer impregnated cements. The following conclusions were reached:- 1) The PMMA/cement interface contains calcium methacrylate as an interfacial reaction product, water being a reactant. Calcium methacrylate is detrimental to the properties of PMMA/cement composites, being highly water-soluble. 2) The pore surface of cement accelerates the polymerisation of MMA, leading to an increased molecular weight compared to polymerisation of pure MMA, minerals in hydrated cement powders having the opposite effect. 3) The investigation of reaction products presents a number of experimental problems, selection of appropriate techniques depending upon the system studied. For the two systems examined in detail, ion chromatography proved particularly useful; DTA, IRS and XPS indicated reactions, though the data was hard to interpret; XRD proving inconclusive. 4) It is impractical to reveal interfacial regions mechanically, but may be accomplished by chemical means.

Non-linear temperature response of Bragg gratings in doped and un-doped holey polymer optical fibre

We present measurements on the non-linear temperature response of fibre Bragg gratings recorded in pure and trans-4-stilbenemethanol-doped polymethyl methacrylate (PMMA) holey fibres.

Editorial

This time of year we look back at the year that has passed and make plans for the next year. I like to reflect on things that I have learnt and people that I have met, especially those who facilitated that learning. In 2009 I went to various conferences, The BCLA conference in Manchester, The Romanian Optical Society meeting in Brasov, Transylvania (where the university is actually on Vlad Tepes Street), The European Council for Optometry and Optics (ECOO) in Brno, Czech Republic, The American Academy of Optometry (AAO) in Orlando USA, The International Association of Contact Lens Educators (IACLE) meeting in Tianjin China and finally The Vereinigung Deutscher Contactlinsen-Spezialisten (VDCO) meeting in Jena. All were interesting places and thoroughly all were enjoyable conferences with their own highlights but I wanted to focus on Jena and one person I met there and his inspirational search for knowledge and the contributions he made in the field of contact lenses. Jena itself is a fascinating place and should be on the ‘must visit’ list of anyone involved in eye care. It is the birth place of Carl Zeiss of course and where he started his company. It is also the birth place of Ernst Abbe (physicist and optometrist and expert lens maker), and Otto Schott (chemist and technologist who made high quality glass. There are many road signs bearing witness to these famous pioneers. The optical museum is worth spending a few hours looking around too. I was invited to speak at the VDCO at the kind invitation from colleagues at the Jena School of Optometry, Professor Wolfgang Sickenberger and Professor Sebastian Marx. At this meeting I met 87-year-old Willi KAUE who was being awarded the Adolf Wilhelm Müller-Welt prize by the VDCO for contribution to contact lenses over his 60-year career. At the age of 15 Willi Kaue took up an apprenticeship to become an Optician in Germany in 1937. At this time he first heard about the scleral glass lenses made by the Carl Zeiss Company in Jena. This started his lifelong fascination which was to become his passion but not yet his career. During the war he was enlisted into military service but immediately after was back to his former career. In 1950 Willi corrected his own 3.5 dioptres of myopia with a plastic scleral lens. His fascination strengthened as for the first time he himself could experience a wider field of view than his spectacles gave him, less aberrations and less retinal minification. He also appreciated the fact that contact lenses did not cause pressure on the nose or ears and did not slide down his nose plus remained optically centred with his eye movements. He decided that form now on he would make fitting contact lenses his career. He travelled to London to learn more about contact lenses and how to fit them but initially did not find many willing teachers and to start with became largely self-taught. He wanted to know how to make scleral lenses. So far he only knew that pulverized polymethyl methacrylate (PMMA) was pressed and moulded. In 1951 he met Berlin optician Otto Marzock. He made his only scleral lenses from using military PMMA windshields. His process involved lathe cutting the lenses and resulted in lenses that were thinner than moulded ones. Willi developed a manufacturing method, using a rotary diamond drill, starting form the outer edge and towards the centre at a constant cut speed. This enabled him to make more reproducible lenses and in less time. His enthusiasm in the field was clear from the travels he made in the pursuit of advancement - travelling around Europe, South America, North America and Asia. In 1963 he visited George Nissel in Hemel Hempstead, England. Constantly thriving towards innovations Willi came across the new Naturalens from the USA made from HEMA at a congress in Marseille in 1969. Amongst his contributions to the field, was his own technique of fitting ocular prosthetics, using an alginate impression of the orbit. I was fortunate enough to have dinner with Willi Kaue and learnt more about his fascinating career through the patient interpreting skills of Hilmar Bussacker (the 2008 winner of the same award and the 2007 winner of the European Federation of the Contact Lens and IOL Industries Award). I look forward to 2010 with eager anticipation as to what I may learn and who I might meet!!! Copyright © 2009 British Contact Lens Association. Published by Elsevier Ltd. All rights reserved.

Synthesis and evaluation of nanoparticle-polymer composites

This thesis describes the synthesis of functionalised polymeric material by variety of free-radical mediated polymerisation techniques including dispersion emulsion, seeded emulsion, suspension and bulk polymerisation reactions. Organic fluorophores and nanoparticles such as quantum dots were incorporated within polymeric materials, in particular, thiol-functionalised polymer microspheres, which were fluorescently labelled either during synthesis or by covalent attachment post synthesis. The resultant fluorescent polymeric conjugates were then assessed for their utility in biological systems as an analytical tool for cells or biological structures. Quantum dot labelled, thiol-functionalised microspheres were assessed for their utility in the visualisation and tracking of red blood cells. Determination of the possible internalisation of fluorescent microspheres into red blood cells was required before successful tracking of red blood cells could take place. Initial work appeared to indicate the presence of fluorescent microspheres inside red blood cells by the process of beadfection. A range of parameters were also investigated in order to optimise beadfection. Thiol-functionalised microspheres labelled successfully with organic fluorophores were used to image the tear film of the eye. A description of problems encountered with the covalent attachment of hydrophilic, thiol-reactive fluorescent dyes to a variety of modified polymer microspheres is also included in this section. Results indicated large microspheres were particularly useful when tracking the movement of fluid along the tear meniscus. Functional bulk polymers were synthesised for assessment of their interaction with titanium dioxide nanoparticles. Thiol-functionalised polymethyl methacrylate and spincoated thiouronium-functionalised polystyrene appeared to facilitate the attachment of titanium dioxide nanoparticles. Interaction assays included the use of XPS analysis and processes such as centrifugation. Attempts to synthesise 4-vinyl catechol, a compound containing hydroxyl moieties with potential for coordination with titanium dioxide nanoparticles, were also carried out using 3,4-dihydroxybenzaldehyde as the starting material.

Non-linear temperature response of Bragg gratings in doped and un-doped holey polymer optical fibre

We present measurements on the non-linear temperature response of fibre Bragg gratings recorded in pure and trans-4-stilbenemethanol-doped polymethyl methacrylate (PMMA) holey fibres.

Studies in the anionic polymerization of methyl methacrylate

A study has been made of the anionic polymerization of methyl methacrylate using butyllithium and polystyryl lithium as initiators and using aluminium triisobutyl as a cocatalyst. The aspects of the polymerization that were examined were the effect of changing the order of addition of reagents, the temperature at which polymerization takes place and the polarity of the solvent. Trends were assessed in terms of molecular weight, molecular weight distribution and tacticity. In addition, a second monomer addition test was carried out to verify that the polymerization was truly a living one, and a kinetic study was attempted. Studies to investigate the effect of changing the order of addition of reagents showed that polymer with similar polydispersities and tacticities are produced whether the pre-mixing (mixing initiator and cocatalyst before addition of monomer) or the post-mixing (mixing monomer and cocatalyst before addition of initiator) method were used. However, polymerizations using the post-mixing mixing method demonstrated lower initiator efficiencies, possibly indicating a different initiating species. Investigations into the effect of changing the polymerization temperature show the molecular weight distribution to narrow as the temperature decreases, although a small amount of low molecular weight tailing was also observed at low temperature. A clear relationship between tacticity and temperature was observed with syndiotacticity increasing with decreasing temperature. Changes in solvent polarity were achieved by using mixtures of the standard solvent, toluene, with varying amounts of cyclohexane, tetrahydrofuran or dichloromethane. Experiments at low solvent polarity (using toluene/cyclohexane mixtures) showed problems with initiator solubility but produced polymer with lower polydispersity and higher syndiotacticity than in toluene alone. Experiments using toluene/THF mixtures yielded no polymer, thought to be owing to a side reaction between THF and aluminium triisobutyl. Increased solvent polarity, achieved using toluene/dichloromethane mixtures produced polymer with higher polydispersity and at lower yields than the conventional system, but also with higher syndiotacticity. Second monomer addition reactions demonstrated that the polymerization was 'living' since an increase in molecular weight was observed with no increase in polydispersity. Kinetic studies demonstrated the high speed of the polymerization but yielded no useful data.

Polymer PCF Bragg grating sensors based on poly(methyl methacrylate) and TOPAS cyclic olefin copolymer

Fibre Bragg grating (FBG) sensors have been fabricated in polymer photonic crystal fibre (PCF). Results are presented using two different types of polymer optical fibre (POF); first multimode PCF with a core diameter of 50µm based on poly(methyl methacrylate) (PMMA) and second, endlessly single mode PCF with a core diameter of 6µm based on TOPAS cyclic olefin copolymer. Bragg grating inscription was achieved using a 30mW continuous wave 325nm helium cadmium laser. Both TOPAS and PMMA fibre have a large attenuation of around 1dB/cm in the 1550nm spectral region, limiting fibre lengths to no longer than 10cm. However, both have improved attenuation of under 10dB/m in the 800nm spectral region, thus allowing for fibre lengths to be much longer. The focus of current research is to utilise the increased fibre length, widening the range of sensor applications. The Bragg wavelength shift of a grating fabricated in PMMA fibre at 827nm has been monitored whilst the POF is thermally annealed at 80°C for 7 hours. The large length of POF enables real time monitoring of the grating, which demonstrates a permanent negative Bragg wavelength shift of 24nm during the 7 hours. This creates the possibility to manufacture multiplexed Bragg sensors in POF using a single phase mask in the UV inscription manufacturing. TOPAS holds certain advantages over PMMA including a much lower affinity for water, this should allow for the elimination of cross-sensitivity to humidity when monitoring temperature changes or axial strain, which is a significant concern when using PMMA fibre.

Functionalisation of ethylene-propylene rubber with glycidyl methacrylate in the presence of comonomer and in situ compatibilisation of PET/f-EPR blends

The main aim of this work was two fold, firstly to investigate the effect of a highly reactive comonomer, divinylbenzene (DVB), on the extent of melt grafting of glycidyl methacrylate (GMA) on ethylene-propylene rubber (EPR) using 2,5-dimethyl-2,5-bis-(tert-butyl peroxy) hexane (Trigon ox 101, Tl 01) as a free radical initiator, and to compare the results with a conventional grafting of the same monomer on EPR. To achieve this, the effect of processing conditions and chemical composition including the concentration of peroxide, GMA and DVB on the extent of grafting was investigated. The presence of the comonomer (DVB) in the grafting process resulted in a significant increase in the extent of the grafting using only a small concentration of peroxide. It was also found that the extent of grafting increased drastically with increasing the DVB concentration. Interestingly, in the comonomer system, the extent of the undesired side reaction, normally the homopolymerisation of GMA (polyGMA) was shown to have reduced tremendously and in most cases the level of polyGMA was immeasurable in the samples. Compared to a conventional EPR-g-GMACONV (in the absence of a comonomer), the presence of the comonomer DVB in the grafting system was shown to result in more branching and crosslinking (shown from an increase in melt flow index (MFI) and torque values) and this was paralleled by an increase in DVB concentration. In contrast, the extent of grafting in conventional system increased with increasing the peroxide concentration but the level of grafting was much lower than in the case of DVB. Homopolymerisation of GMA and excessive crosslinking of EPR became dominant at high peroxide concentration and this. reflects that the side reactions were favorable in the conventional grafting system. The second aim was to examine the effect of the in-situ functionalised EPR when used as a compatibiliser for binary blends. It was found that blending PET with functionalised EPR (ƒ-EPR) gave a significant improvement in terms of blend morphology as well as mechanical properties. The results showed clearly that, blending PET with ƒ-EPRDVB (prepared with DVB) was much more effective compared to the corresponding PET/ƒ-EPRCONV (without DVB) blends in which ƒ-EPRDVB having optimum grafting level of 2.1 wt% gave the most pronounced effect on the morphology and mechanical properties. On the other hand, blends of PET/ƒ-EPRDVB containing high GMA/DVB ratio was found to be unfavorable hence exhibited lower tensile properties and showed unfavorable morphology. The presence of high polyGMA concentration in ƒ-EPRCONV was found to create damaging effect on its morphology, hence resulting in reduced tensile properties (e.g. low elongation at break). However, the use of commercial terpolymers based on ethylene-methacrylate-glycidyl methacrylate (EM-GMA)or a copolymer of ethylene-glycidyl methacrylate (E-GMA) containing various GMA levels as compatibilisers in PET/EPR blends was found to be more efficient compared to PET/EPR/ƒ-EPR blends with the former blends showing finer morphology and high elongation at break. The high efficiency of the terpolymers or copolymers in compatibilising the PET/EPR blends is suggested to be partly, higher GMA content compared to the amount in ƒ-EPR and due to its low viscosity.

Reactive processing of polymers: structural characterization of products by 1H and 13C NMR spectroscopy for glycidyl methacrylate grafting onto EPR in the absence and presence of a reactive comonomer

Grafted GMA on EPR samples were prepared in a Thermo-Haake internal mixer by free radical melt grafting reactions in the absence (conventional system; EPR-g-GMA(CONV)) and presence of the reactive comonomer divinyl benzene, DVB (EPR-g-GMA(DVB)). The GMA-homopolymer (poly-GMA), a major side reaction product in the conventional system, was almost completely absent in the DVB-containing system, the latter also resulted in a much higher level of GMA grafting. A comprehensive microstructure analysis of the formed poly-GMA was performed based on one-dimensional H-1 and C-13 NMR spectroscopy and the complete spectral assignments were supported by two-dimensional NMR techniques based on long range two and three bond order carbon-proton couplings from HMBC (Heteronuclear Multiple Bond Coherence) and that of one bond carbon-proton couplings from HSQC (Heteronuclear Single Quantum Coherence), as well as the use of Distortionless Enhancement by Polarization Transfer (DEPT) NMR spectroscopy. The unambiguous analysis of the stereochemical configuration of poly-GMA was further used to help understand the microstructures of the GMA-grafts obtained in the two different free radical melt grafting reactions, the conventional and comonomer-containing systems. In the grafted GMA, in the conventional system (EPR-g-GMA(CONV)), the methylene protons of the GMA were found to be sensitive to tetrad configurational sequences and the results showed that 56% of the GMA sequence in the graft is in atactic configuration and 42% is in syndiotactic configuration whereas the poly-GMA was predominantly syndiotactic. The differences in the microstructures of the graft in the conventional EPR-g-GMA(CONV) and the DVB-containing (EPR-g-GMA(DVB)) systems is also reported (C) 2009 Elsevier Ltd. All rights reserved.

Reactive processing of polymers:effect of bifunctional and tri-functional comonomers on melt grafting of glycidyl methacrylate onto polypropylene

Two reactive comonomers, divinyl benzene (DVB) and trimethylolpropane triacrylate (TRIS), were evaluated for their role in effecting the melt free radical grafting reaction of the monomer glycidyl methacrylate (GMA) onto polypropylene (PP). The characteristics of the GMA-grafting systems in the presence and absence of DVB or TRIS were examined and compared in terms of the yield of the grafting reaction and the extent of the main side reactions, namely homopolymerisation of GMA (poly-GMA) and polymer degradation, using different chemical compositions of the reactive systems and processing conditions. In the absence of the comonomers, i.e. in a conventional system, high initiator concentrations of peroxides were typically required to achieve the highest possible GMA grafting levels which were found to be generally low. Concomitantly, both poly-GMA and degradation of the polymer by chain scission takes place with increasing initiator amounts. On the other hand, the presence of a small amount of the comonomers, DVB or Tris, in the GMA-grafting system, was shown to bring about a significant increase in the grafting level paralleled by a large reduction in poly-GMA and PP degradation. In the presence of these highly reactive comonomers, the optimum grafting system requires a much lower concentration of the peroxide initiator and, consequently, would lead to the much lower degree of polymer degradation observed in these systems. The differences in the effects of the presence of DVB and that of TRIS in the grafting systems on the rate of the GMA-grafting and homopolymerisation reactions, and the extent of PP degradation (through melt flow changes), were compared and contrasted with a conventional GMA-grafting system.

Photosensitivity mechanism of undoped poly(methyl methacrylate) under UV radiation at 325 nm and its spatial resolution limit

In this Letter, we provide evidence suggesting that the main photosensitive mechanism of an undoped poly(methyl methacrylate)-based microstructured optical fiber under UV radiation at 325 nm is a competitive process of both photodegradation and polymerization. We found experimentally that increasing strain during photo-inscription leads to an increased photosensitivity, which is evidence of photodegradation. Likewise, refractive index change in the fiber was measured to be positive, which provides evidence for further polymerization of the material. Finally, we relate the data obtained to the spatial recording resolution of the samples. © 2014 Optical Society of America.

Humidity responsivity of poly(methyl methacrylate)-based optical fiber Bragg grating sensors

The humidity response of poly(methyl methacrylate) (PMMA)-based optical fiber Bragg gratings (POFBGs) has been studied. The characteristic wavelength of the grating is modulated by water absorption-induced swelling and refractive index change in the fiber. This work indicates that anisotropic expansion may exist in PMMA optical fiber, reducing the humidity responsivity of the grating and introducing uncertainty in the responsivity from fiber to fiber. By pre-straining a grating, one can get rid of this uncertainty and simultaneously improve the POFBG response time. © 2014 Optical Society of America.

Controlled growth of poly(2-(diethylamino)ethyl methacrylate) brushes via atom transfer radical polymerisation on planar silicon surfaces

Progress in making pH-responsive polyelectrolyte brushes with a range of different grafting densities is reported. Polymer brushes of poly(2-(diethylamino)ethyl methacrylate) were synthesised via atom transfer radical polymerisation on silicon wafers using a 'grafted from' approach. The [11-(2-bromo-2-methyl) propionyloxy]undecyl trichlorosilane initiator was covalently attached to the silicon via silylation, from which the brushes were grown using a catalytic system of copper(I) chloride and pentamethyldiethylenetriamine in tetrahydrofuran at 80°C. X-ray reflectivity was used to assess the initiator surfaces and an upper limit on the grafting density of the polymer was determined. The quality of the brushes produced was analysed using ellipsometry and atomic force microscopy, which is also discussed.