A.F. Johnson

Tailored copolymers via coupled anionic and ring opening metathesis polymerization. Synthesis and polymerization of bicyclo[2.2.1]hept-5-ene-2,3-trans-bis(polystyrylcarboxylate)s

Abstract The preparation of polystyrene macromonomers containing a norbornene unit and their living ring opening metathesis polymerization (ROMP) to produce comb graft copolymers is described. The ROMP was initiated by the well defined Schrock initiators, Mo(CHR)(NAr)(OR′)2, where R is (CH3)3C or C6H5C(CH3)2, Ar is 2,6-diisopropylphenyl and R′ is (CH3)3C. Well characterized macromonomers and comb graft copolymers with polystyryl grafts with average degrees of polymerization (DPs) of 4, 7, and 9 were successfully produced. The graft copolymers exhibit single mode molecular weight distributions and narrow polydispersities. Attempts to prepare copolymers with longer polystyryl grafts gave products which exhibited bimodal molecular weight distributions in which one component of the distribution had the same retention time as that of the macromonomer, this observation is rationalized in terms of steric inhibition of the ROMP of such macromonomers.

Structural determination of substituted mercaptothiadiazoles using FT-Raman and FT-IR spectroscopy

Abstract The FT-Raman and FT-IR spectra of 2,5-dimercapto-1,3,4-thiadiazole (DMTD), 5-methyl-1,3,4-thiadiazole-2-thiol (MMTD) and 5-amino-1,3,4-thiadiazole-2-thiol (AMTD) are reported and vibrational assignments are made. The spectroscopic study reveals that the thiol groups of these molecules participate in a thiol-thone tautomeric equilibrium. DMTD exists mainly as a dithiol whereas MMTD and AMTD exist as thiones at ambient temperature.

Synthetic polyisoprenes studied by Fourier transform Raman spectroscopy

Abstract Fourier transform Raman spectra are presented for the cis -1,4 and trans -1,4 isomers of polyisoprenes Vibrational intensities are used to determine quantitatively the amounts of each isomer in the microstructure. Improvements over previous work are suggested for the quantitative assessment of 1,4 microstructure. Also, changes in the Raman spectrum due to oxidative degradation show that preferential oxidative degradation for the vinyl -3,4 units occurs. The α and β forms of trans -1,4 polyisoprene were studied the ν(CC) bands resolved were identified 4 cm −1 apart. A study of the copolymerization of methyl methacrylate with isoprene showed that the 1,4 form is the most favoured form produced on copolymerization. Accurate cis -1,4 and trans -1,4 microstructural information could not, however, be determined.

Critical assessment of vibrational and NMR spectroscopic techniques for the microstructure determination of polybutadienes

Abstract A critical assessment of infrared, Raman, and NMR (1H and 13C) spectroscopic techniques for the microstructure determination of polybutadienes and partially hydrogenated polybutadienes is presented. The polybutadienes analysed in this work were produced by anionic polymerisation methods. Measurements have been made on the polymers in the solid state and in solution as appropriate and three different analytical methods have been used to obtain the infrared data. The Raman and 13C NMR spectroscopic methods of analysis were found to agree quite closely with each other but it is considered that the infrared analyses give poor characterisation of the microstructure whatever the experimental procedure used. Raman spectroscopy is the recommended technique for the analysis of polybutadiene microstructures in the solid state or in solution because of its speed, accuracy and reproducibility.

Bulk polymerization of methyl methacrylate: Part I: some kinetic and modelling considerations for isothermal reactions

Abstract Kinetic studies of the bulk polymerization of methyl methacrylate have been carried out by differential scanning calorimetry (d.s.c.) and also by monitoring, gel permeation chromatography (g.p.c.). The residual monomer content in polymerizations was carried out in small thin-walled glass ampoules. Discrepancies have been found between the data acquired by the two experimental methods. These can be resolved by consideration of the measured temperature rise of the polymerizations (which can be up to 80 K above the bath temperature for a 5 g sample) carried out in the ampoules. Comparisons between the kinetic data obtained in these experiments with published data show that many of the reported kinetic constants for this polymerization are probably inaccurate because they were acquired under experimental conditions which may not have been isothermal. The implications of using inaccurate kinetic constants for the computer simulation of the high-conversion polymerization of methyl methacrylate are considered.

Raman spectroscopic characterization of high-vinyl polybutadienes produced from anionic polymerization

Abstract High-vinyl polybutadienes have been prepared by anionic polymerization using n-butyllithium as initiator in cyclohexane solvent and complexing agents in order to change the mode of addition of monomer to (1,2)- or vinyl addition. The microstructure of these polymers was characterized by Raman spectroscopy using the Raman active carbon-carbon double bond stretching bands of vinyl, cis and trans structures at 1640, 1650 and 1664 cm −1 , respectively. Band areas were analysed with the aid of a curve analysis program and the data thus acquired used for subsequent calculations. The living-end concentration was determined from the number average molecular weight of the polymer obtained by gel permeation chromatography, which made it possible to calculate a more accurate value for the molar ratio, r , of the complexing agent to living polyanions than is possible by more conventional means. It has been observed that 1,2-dipiperidinoethane (DIPIP) is a very effective complexing agent for the control of polymer microstructure as is diglyme at 0°C but their effectiveness decreases with increasing temperature.

Preparation and characterization of poly(1,4-butadiene-b-1,2-butadiene)

Abstract Poly(1,4-butadiene-b-1,2-butadiene) diblock polymers have been prepared anionically by sequential addition of monomer using sec-butyllithium as initiator in cyclohexane. The first block is of low vinyl units and the second block is of high vinyl units in microstructure. 1,2-Dipiperidinoethane was used as complexing agent in order to change the mode of addition of butadiene from predominantly 1,4 to 1,2 addition. The diblock polymers were characterized using Raman spectroscopy, gel permeation chromatography (g.p.c.) and dynamic mechanical thermal analysis (d.m.t.a.). The increase in molecular weight after the second batch of monomer was added is confirmed by g.p.c. Raman spectroscopy shows the difference in microstructure of the two blocks. Phase separation has been found in two diblock samples through the observation of two Tg values arising from low and high vinyl blocks.

Polymerization of vinyl acetate using visible radiation and a dye-reducing agent sensitizer: 1. Pre-initiation and initiation reactions involving ethyl eosin and ascorbic acid☆

Abstract The ethyl eosin/ascorbic acid photosensitized polymerization of vinyl acetate in aqueous methanol using visible radiation has been shown to occur by a mechanism in which polymerization occurs after an induction period during which the dye colour fades completely. During this period the dye is excited by incident radiation and reacts with the reducing agent to form free radical species. These react with dissolved oxygen to produce hydrogen peroxide. It is shown that the polymerization of vinyl acetate is initiated by products of the reaction between ascorbic acid and hydrogen peroxide.

FT Raman spectroscopic study of the wavenumber region 2800-2630 cm−1 of selected organic compounds

Abstract A Raman spectroscopic study investigating the origin of a number of weak features observed in the Raman spectra of a comprehensive range of organic compounds in the wavenumber range 28002630 cm −1 has been undertaken. These bands have been found to be characteristic of (CH 3 C) groups in the wavenumber region 28002710 cm −1 , and of (CH 2 C) and (CHC) groups below 2710 cm −1 . In the wavenumber region 28002765 cm −1 , it is possible to distinguish between three different types of (CH 3 C) structural moieties, (CH 3 CMe 3 ), (CH 3 CMe 2 ) and (CH 3 CMe). Application of these observations to the Raman spectra of organic compounds provides new information on the extent of methyl branching in organic compounds.

Application of Raman Spectroscopy for Determining Residence Time Distributions in Extruder Reactors

The time that a polymeric material spends in the barrel of an extruder is known as its residence time. In an ideal plug flow reactor, all elements of the fluid travel at the same velocity, and the residence time of each fluid element is the same. However, the velocity profile developed in twin-screw extruders is nonideal because of back-mixing, as well as the slow exchange of bulk material to and from a polymer film on the barrel wall or screw surfaces. Consequently, a distribution of residence times is produced for the polymer, and this distribution is known as the exit age distribution or residence time distribution (RTD). The measurement of the RTD in an extruder usually involves a stimulus-response method. The extrusion process is subjected to a pulse input of a tracer at the feed port. The concentration of the tracer in the extrudate is then recorded as a function of time. A graphical plot of the tracer concentration against extrusion time produces the RTD curve. Some tracers which have been employed in the literature and the relevant property measured are given in Table I.