Mathematical Analysis of the Formation of Molecule Sizes on a Spinning Disc Reactor

A mathematical analysis of the behaviour of the molecular weights of addition polymers during a polymerisation process is described. Spinning disc reactor (SDR) technology has been shown to yield significant improvements in terms of polymerisation rates whilst retaining close control of the molecular weights and the molecular weight distributions^[1,2]. However, understanding of the kinetics of the polymerisation process on a SDR remains unresolved. One of the questions to be addressed concerns the sizes of the macromolecules preferably formed during the polymerisation process. To address this question, a mathematical analysis of the observed trends in number and weight average molecular weight, monomer concentration and polydispersity during the polymerisation process on a SDR has been undertaken. To validate the results, experimental data obtained from benzoyl peroxide initiated free radical polymerisation of styrene on a SDR^[2] was used. It was concluded that most of the monomers consumed are in the growth of smaller size chains.     

Effect of macro-RAFT agent on the morphology of polymer dispersed liquid crystals

In this study, macro-(RAFT) reversible additional fragmental chain transfer agent prepared by reversible additional fragmental chain transfer polymerisation has been incorporated into polymer dispersed liquid crystals (PDLCs). The effects of concentration, molecular weight and glass transition temperature of macro-RAFT agent were studied in terms of morphology, polymerisation kinetics, molecular weight of polymer matrix and electro-optical properties of the films. It was found that the key factor influencing morphology was the mobility of macro-RAFT agent chain rather than polymerisation rate and molecular weight of polymer matrix. Furthermore, the decrease in the mobility of macro-RAFT agent chain caused less liquid crystal nematic fraction, smaller liquid crystal domain size and greater driving voltage.     

Reactivation of a Poisoned Metallocene Catalyst by Irradiation with Visible Light

Both oxygen and carbon dioxide are efficient catalyst poisons, remarkably reducing the ethylene polymerisation rate, increasing the molecular weight of the resulting polyethylene, and broadening its molecular weight distribution (MWD). By introducing visible light into the contaminated polymerisation system, the catalyst activity was totally recovered. The molecular weight and MWD became similar to those of a non‐poisoned system, supporting the formation of new active sites during poisoning that are responsible for the lower activity and broader MWD.     

Molecular modelling of ring‐opening polymerisation of lactamimide‐containing macrocyclic esters

The molecular modelling of anionic (MeO^– initiated) and cationic (H⁺ initiated) polymerisation of lactamimide‐containing macrocyclic esters has been carried out at PM3 and HF/3‐21G levels of theory. It was found that it is strain release that drives the polymerisation of these macrocycles. Most likely that entropy gain on the ring‐opening can not compensate entropy loss on polymer formation due to the relative rigidity of cyclic molecules. Methanolate initiated anionic polymerisation will not lead to high molecular weight product due to the side reactions involving the attack of growing anionic species at carbonyls of lactamimide moiety, while the cationic polymerisation should proceed smoothly provided that polymerisation temperature is less than ceiling temperature.     

Development of Amino–Oxazoline and Amino–Thiazoline Organic Catalysts for the Ring‐Opening Polymerisation of Lactide

The ring‐opening polymerisation of lactide by a range of amino–oxazoline and amino–thiazoline catalysts is reported. The more electron‐rich derivatives are demonstrated to be the most highly active and polymerisation is well controlled, as evidenced by the linear relationship between the molecular weight and both the monomer conversion and the monomer‐to‐initiator ratio. Mechanistic studies reveal significant interactions between the monomer, initiator and catalyst and that the polymerisation is first order with respect to each of these components. These observations indicate that the polymerisation operates by a general base/pseudo‐anionic mechanism.     

Thiophosphoryl fluoride and phosphoryl fluoride as initiators for the polymerisation of tetrahydrofuran

Thiophosphoryl fluoride and phosphoryl fluoride have been found to initiate the polymerisation of tetrahydrofuran. The living polymer formed has a high molecular weight of the order of a million and the density is found to be between 0.98 - 1.02 g/cc. A cationic mechanism for the polymerisation has been proposed.     

Positron annihilation investigations on poly(methyl methacrylate)

Positron lifetime and Doppler broadened annihilation radiation were measured for seven different samples of poly(methyl methacrylate) at room temperature in vacuum. The polymerisation of methyl methacrylate was carried out as a bulk polymerisation in the presence of benzoyl peroxide as an initiator. The effect of the amount of the initiator on the viscosity-average molecular weight was studied. It was found that the viscosity-average molecular weight decreased with increasing amount of the initiator. The average lifetime and intensity of ortho-positronium (o-Ps) increased with increasing viscosity-average molecular weight up to 6.85 × 10⁴ and remained constant after that. The S-parameter showed a similar behaviour as that of the o-Ps intensity.     

Poly(vinyl alcohol) star polymers prepared via MADIX/RAFT polymerisation

Poly(vinyl acetate) stars were prepared using MADIX/RAFT polymerisation mediated by xanthates. The polymerisation shows living characteristics with molecular weight increasing with conversion. The subsequent hydrolysis of these three and four arm stars led to the formation of poly(vinyl alcohol) stars.     

Intramolecular Polycomplexes Formed by Dextran-Grafted Polyacrylamide: Effect of the Components Molecular Weight

Graft copolymers of Polyacrylamide-g-Dextran were synthesized using ceric-ion-initiated solution polymerisation technique. It is shown that the macromolecular parameters of these copolymers and their molecular structure strongly depend on the molecular weight of the Dextran part.     

Effect of the nature of the alkyl group on initiation and termination in R3Al/RLi initiation of methyl methacrylate

The polymerisation of methyl methacrylate has been investigated with mixed aluminium and lithium alkyls. The use of sterically hindered aluminium alkyls such as triisobutyl aluminium in conjunction with tert-butyl lithium leads to living polymerisation at 0°C with little complications from secondary initiation or premature termination. The use of less bulky alkyl groups on either aluminium or lithium leads to both secondary initiation, as observed by the formation of high molecular weight polymer by GPC-LALLS and termination via cyclisation as observed by MALDI-TOF-MS. The initiator efficiencies, even when living polymerisation ensues, are considerably less than 100%.     

Kinetics of the surfactant-free emulsion polymerization of styrene:-The post nucleation stage

The kinetics of the surfactant-free emulsion polymerisation of styrene have been studied. Reactions were sampled at several stages throughout their course, and the samples characterized by electron microscopy, gravimetric weights analysis and gel permeation chromatography, After an initial period of particle nucleation and coagulation, the reaction proceeds at a constant number density. The theories developed for emulsion polymerisation in the presence of surfactant above its critical micelle concentration might be expected, in Interval II, to apply to the surfactant-free system if due regard is taken of the lower number densities and larger particle sizes developed. The results are in best accord with theories invoking a surface phase polymerisation mechanism. None of these theories predict a bimodel molecular weight distribution as found here and which is ascribed to polymerisation in two loci. The activation energy was found to be the same as for surfactant containing emulsion polymerisations.     

The effect of 4-vinylcyclohexene on the degradation of polystyrene and on the polymerisation of styrene

It has previously been postulated that the inhibition of polystyrene degradation observed in the initial stages of the isothermal degradation of polystyrene-polybutadiene blends is partly due to reaction of polystyryl radicals with 4-vinylcyclohexene (4VCH) evolved from the polybutadiene. This hypothesis has been tested by examining the effect of small amounts of 4VCH on polystyrene degradation and on the free radical polymerisation of styrene. The results provide support for the hypothesis: there is an induction period in the degradation and the polymerisation is retarded. From molecular weight measurements on polymers made in the presence of various amounts of 4VCH, a chain transfer constant in styrene polymerisation at 60°C of 117 × 10^?5 has been calculated.     

The effect of the chemical structure of chain ends on the thermal degradation of polystyrene

A set of polystyrenes of comparable molecular weight around 4000, prepared by anionic polymerisation, were end-capped with various structures. Their thermal degradation behaviour (weight loss kinetics, nature and amount of volatile by-products) is governed by the nature of the chain ends. Some features of the degradation mechanisms are discussed.     

The synthesis and X-ray structure of a phenoxyimine catalyst tailored for living olefin polymerisation and the synthesis of ultra-high molecular weight polyethylene and atactic polypropylene

A phenoxyimine catalyst (bis-(N-(3′,5′-diiodo-salicylidene)-2,6-difluoroaniline)-titanium(IV)-dichloride has been synthesised. The ligand as well as the complex have been fully characterised. An X-ray structure of the titanium complex was obtained. After activation with MAO, it was used as highly active catalyst in living olefin polymerisation of ethylene and propylene. Ultra-high molecular weight polyethylene and atactic polypropylene of low polydispersity were obtained. The living character of the polymerisation was shown by online polymerisation kinetics and linear growth of number-average molar mass with polymerisation time. In addition, the influence of hydrogen as a chain transfer agent was studied in living olefin polymerisation.     

The mechanism of polymerisation of butyl cyanoacrylate in aqueous dispersions

Butyl cyanoacrylate has been polymerised by dispersion in acidified water to yield nanoparticles. Reactions have been carried out at various temperatures and the molecular weight of the growing polymer measured. In all cases polymerisation proceeds by generation of discrete populations of oligomers, which are then re‐initiated and undergo further growth. The peak molecular weight is around 1300 g/mol and it is considered that a stepwise initiation, termination and re‐initiation process continues until diffusionally limited by the internal viscosity within the nanoparticle.     

The preparation of monodisperse polyacrylonitrile particles in the presence of AB block co-polymers of poly-2-vinylpyridine/poly tertbutylstyrene

Radical dispersion polymerisation of acrylonitrile in cyclohexane was performed in the presence of the diblock copolymer poly-2-vinylpyridine/poly tertbutylstyrene, giving polymer latex particles stabilised by surface layers of chains of poly tertbutylstyrene. A seeded polymerisation route was employed and the addition of up to a further seven feeds of reactants resulted in the particle growth and the total volume fraction of particles increased to 0.2. The effect of varying the molecular weight of the stabiliser and stabiliser concentration was also investigated. Particle diameter in the range 40–150 nm were obtained depending on the condition of the polymerisation.     

Influence of structure and solubility of chain transfer agents on the RAFT control of dispersion polymerisation in scCO2

Reversible addition–fragmentation chain transfer (RAFT) dispersion polymerisation of methyl methacrylate (MMA) is performed in supercritical carbon dioxide (scCO₂) with 2-(dodecylthiocarbonothioylthio)-2-methylpropionic acid (DDMAT) present as chain transfer agent (CTA) and surprisingly shows good control over PMMA molecular weight. Kinetic studies of the polymerisation in scCO₂ also confirm these data. By contrast, only poor control of MMA polymerisation is obtained in toluene solution, as would be expected for this CTA which is better suited for acrylates. In this regard, we select a range of CTAs and use them to determine the parameters that must be considered for good control in dispersion polymerisation in scCO₂. A thorough investigation of the nucleation stage during the dispersion polymerisation reveals an unexpected “in situ two-stage” mechanism that strongly determines how the CTA works. Finally, using a novel computational solvation model, we identify a correlation between polymerisation control and degree of solubility of the CTAs. All of this ultimately gives rise to a simple, elegant and counterintuitive guideline to select the best CTA for RAFT dispersion polymerisation in scCO₂.

RAFT dispersion polymerisation of methyl methacrylate is performed in scCO₂ with 2-(dodecylthiocarbonothioylthio)-2-methylpropionic acid (DDMAT) present as chain transfer agent (CTA) and surprisingly shows good control over PMMA molecular weight.     

Synthesis of light harvesting polymers by RAFT methods

Polymers prepared by RAFT polymerisation containing acenaphthyl energy donors and a terminal anthryl energy acceptor have a narrow molecular weight distribution and exhibit excitation energy transfer efficiencies up to 70%.     

Cyclopentadienyl titanium hydroxylaminato complexes as highly active catalysts for the polymerization of propylene

Half sandwich complexes of titanium bearing eta1 or eta2 bound nitroxide ligands are highly active catalysts for the polymerisation of propylene to high molecular weight atactic poly(propylene).     

Vinyl chloride suspension polymerisation and the control of polymer properties

A number of poly(vinyl alcohols), used in the suspension polymerisation of vinyl chloride, have been fractionated and characterised. The most effective had the highest molecular weight and contained the most unsaturation. The more insoluble fractions gave the best balance of product properties. Reactor sampling experiments have been used to determine the mechanism of polymerisation. In most polymerisations, the final grain size is determined by factors that control the coalescence and break-up of the monomer droplets during the first 15% conversion. It is suggested that the structure within the grains is controlled by the formation of a continuous network of PVC primaries which retards droplet contraction.