The recent introduction of Fourier Transform Infrared (FTIR) spectrometers that are operable over the entire IR frequency range has revitalized the field of IR spectroscopy. IR studies of complex polymeric materials that were impossible, or at least extremely difficult using conventional dispersive spectrometers, are now readily accomplished. In this review of the application of FTIR to the study of polymeric materials, we initially present a brief critical comparison of the FTIR and dispersive spectrometers followed by a discussion of the results that have been published to date.

Fourier Transform Infrared Studies of Polymeric Materials

Spontaneous initiation in emulsion polymerization may be more important: than in the corresponding bulk free-radical polymerization. A methodology is derived for finding the locus of spontaneous polymerization in emulsion polymerization, through use of spin traps and catalysts which can accelerate decomposition of peroxides. Applying this to both styrene and chloroprene (chlorobutadiene), it is found that this generation occurs to some degree within all phases present. The rate of spontaneous initiation is relatively small in styrene emulsion polymerization but large in chloroprene. A means of including this effect in modeling rates and molecular weight distributions is derived, which also shows how rate parameters for the process may be obtained from experimental molecular weight distributions. This methodology is applied to these two monomers, with a series of seeded emulsion polymerizations using polystyrene host seeds for both. For styrene polymerization, the spontaneous initiation rate is low and varies with latex preparation; consistent values for this rate coefficient for a given latex are obtained by independent measurements involving two different techniques, thereby verifying the methodology. Applying this methodology to chloroprene, it is found that the effect of spontaneous initiation is much larger and probably arises from peroxides formed by exposure to oxygen. For chloroprene, spontaneous radical generation occurs both within the particles and in any monomer droplets present, with different chain-stopping mechanisms occurring in these two phases. It is a major influence on rates and molecular weight distributions, even in the presence of large amounts of added initiator; chain stoppage in droplets is largely by transfer to monomer, whereas chain stoppage within particles is by termination with short radicals formed by spontaneous initiation. Arrhenius parameters for the rate coefficient for transfer to monomer are obtained from the molecular weight distributions for the chloroprene system: k(tr)/dm(3) mol(-1) s(-1) = 10(4.3) exp(-30.9 kJ mol(-1)/RT).

Spontaneous polymerization in the emulsion polymerization of styrene and chlorobutadiene

Data relating to the vulcanization of mercaptan-grade polychloroprene (CR) by ZnO and MgO (alone or in combination) are examined Compounds were vulcanized through the isothermal heating of samples at 140°C in a laboratory press and at programmed rates in a differential scanning calorimeter The reaction was stopped at various points during the heating process The crosslink densities were determined via swelling Extractable ZnCl2 and MgCl2 were analyzed by atomic absorption spectrometry Three different crosslinking processes were identified The first crosslinking process involved the activation of the highly reactive tertiary allylic 1,2-units along the polymer chain, whereas the second and third crosslinking processes were attributed to the activation toward crosslinking of 3,4- and 1,4-units, respectively The crosslinking reactions of the 1,2-units comprised three distinct steps: isomerization (promoted by ZnO), dechlorination, and crosslinking ZnCl2 (which formed during compounding and upon crosslinking) promoted crosslinking, and its addition to formulations decreased but did not eliminate the induction period before crosslinking MgO retarded the crosslinking process by limiting the formation of ZnCl2 during mixing The results of the CR/ZnO system are discussed, and a modified cationic mechanism for crosslinking is proposed © 2007 Wiley Periodicals, Inc J Appl Polym Sci 2007

Vulcanization of polychloroprene rubber. I. A revised cationic mechanism for ZnO crosslinking

Markovian statistics and simplex algorithm for carbon-13 nuclear magnetic resonance spectra of ethylene-propylene copolymers

Five sphingoid bases, penasin A (1), penasin B (2), and a mixture of penasins C−E (3−5), were identified from a marine sponge Penares sp. as cytotoxic constituents. The structure of the common polar head part was assigned by analysis of the NMR data, whereas the structures of the long aliphatic chains including the locations of double bond(s) and a branched methyl group were determined by analysis of tandem FABMS and 13C NMR data together with the GC-MS analysis of ozonolysis products. The absolute configuration of the headgroup was defined for the mixture of 3−5 by the modified Mosher method. Penasins exhibit moderate cytotoxicity against HeLa and P388 cells.

Penasins A-E, long-chain cytotoxic sphingoid bases, from a marine sponge Penares sp.

13C NMR spectroscopy has proved to be a very powerful tool for the characterization of polychloroprene microstructure. We have identified and assigned the lines associated with diad and triad sequences involving the predominant trans-1,4 placement, together with other lines associated with cis-1,4, 1,2, isomerized 1,2, and 3,4 structural irregularities. Currently, we are performing 13C NMR, relaxation studies on the chloroprene polymers and will be presenting quantitative data in the near future.

13C NMR Characterization of Polychloroprene Microstructure I. Spectral Assignments

Spin relaxation, NOE, and quantitative measurements have been performed on chloroprene polymers prepared by free radical techniques in the range −150 to +90°C. 13C NMR has proved to be an ...

13C NMR Characterization of Polychloroprene Microstructure II. Relaxation, NOE, and Quantitative Measurements

Carbon-13 nuclear magnetic resonance (13C NMR) has been used rather extensively in the characterization of ethylene-propylene copolymers and terpolymers. Chemical shift assignments on these copolymers were first made by Carman and revised only slightly by him recently. Despite all the work that has been done to assign the lines in the 13C NMR spectrum to the various sequence structures in ethylene-propylene copolymers, ambiguity still remains in some of the assignments, such as the assignment of the Sαβ line. It still is not known whether it is attributable entirely to two propylenes with one of them inverted, to an ethylene sandwiched between two propylenes with one of them inverted, or to an equal population distribution of these two structures. Carman and coworkers state that inversion of propylene in their copolymers is certain, but because of the large error in the calculation, the degree of inversion can be between 10 and 40% of the propylene content. His suggestion is that the Sαβ line is ...

13C NMR Analysis of Carbon-13 Enriched Ethylene Copolymers with Propylene

Due to the facile free-radical polymerization of 2-chlorobutadiene-1,3 (chloroprene, CB), most experimental studies and commercial polymer preparations involve free-radical-initiated emulsion systems. From the reactivity ratios published in the literature and the calculated propagation rate of CB at 40°C, its rate is about 10 times faster than that of butadiene. Uniquely, among all the vinyl and diene monomers known, 2,3-dichlorobutadiene-1,3 (DCB) is more reactive than CB. Modification of the properties of polyCB through copolymerization is often relatively difficult. The comonomer most frequently used with CB is DCB, even though many other dienes and vinyl monomers have been tested. Copolymerization of DCB with CB modifies the polymer properties, as judged by evidence from increased crystallization resistance and the retention of building tack. The effect of DCB on the properties of the copolymer of CB and DCB is markedly influenced by the amount of comonomer present. Since no detailed studies ...

E. G. Brame

Papers

13C NMR Characterization of Polychloroprene Microstructure I. Spectral Assignments

13C NMR Characterization of Polychloroprene Microstructure II. Relaxation, NOE, and Quantitative Measurements

13C NMR Analysis of Carbon-13 Enriched Ethylene Copolymers with Propylene

13C NMR Characterization of Copolymers Of 2-Chlorobutadiene-1,3 and 2,3-Dichlorobutadiene-1,3