Degradation of vinylidene chloride/methyl acrylate/phenylacetylene (VDC/MA/PA) terpolymers. Effect of internal unsaturation on the stability of Saran copolymers

The thermal degradation of vinylidene chloride/methyl acrylate/phenylacetylene (VDC/MA/PA) terpolymers containing a constant 9 wt % methyl acrylate and small but varying amounts of phenylacetylene has been examined in the solid phase and in bibenzyl solution. Thermally promoted degradative dehydrochlorination, largely uncomplicated by methyl chloride formation, readily occurs at temperatures approaching 200°C. Incorporation of phenylacetylene into the polymer structure greatly facilitates degradative dehydrochlorination. Indeed, the presence of phenylacetylene induces the formation of polyene segments during the polymerization so that all the terpolymers, even at very low phenylacetylene loading, are tan in color. The decreased stability of polymers containing internal unsaturation arises from an increased rate of initiation for the degradation reaction. The propagation rate is largely unaffected by the level of unsaturation initially present in the polymer. Thus random double bonds have been identified as the principal defect sites responsible for the facile degradation of Saran copolymers. Species which promote the degradation of Saran polymers probably do so by facilitating the introduction of double bonds into the structure. The ratio of hydrogen chloride to stilbene formed for degradation of the terpolymers in bibenzyl solution is ca. 35:1. This is strongly reminiscent of PVDC degradation and suggests that for degradation of either the homopolymer or Saran copolymers the chain-carrying allylic radical pair does not dissociate to any appreciable extent as dehydrochlorination occurs.     

Degradation of vinylidene chloride/phenylacetylene (VDC/PA) copolymers. Effect of internal unsaturation on poly(vinylidene chloride) stability

The thermal degradation of vinylidene chloride/phenylacetylene copolymers containing small but varying amounts of phenylacetylene has been examined in both the solid phase and in bibenzyl solution. Incorporation of phenylacetylene into the poly(vinylidene chloride) structure greatly facilitates degradative dehydrochlorination. Indeed, the presence of phenylacetylene promotes the formation of polyene segments during the polymerization process so that all the copolymers, even at very low phenylacetylene loading, are tan in color. The decreased stability of polymers containing interal unsaturation arises from an increased rate of initiation for degradative dehydrochlorination. The propagation rate is largely unaffected by the level of unsaturation initially present in the polymer. The ratio of hydrogen chloride to stilbene formed for degradation of these copolymers in bibenzyl solution is approximately 35:1. This suggests that the chlorine atom of the initially-formed radical pair preferentially abstracts an adjacent hydrogen atom rather than interacting with solvent, i.e., the chain-carrying radical pair does not dissociate appreciably as the unzipping dehydrochlorination occurs. Thus random double bonds introduced in a variety of ways may be identified as principal defect sites responsible for the initiation of the degradative dehydrochlorination of poly(vinylidene chloride). Species which promote the degradation of poly(vinylidene chloride) probably do so by facilitating the introduction of random double bonds into the structure.     

Preparation and characterization of novel thermal-stable vinylidene chloride–methyl acrylate–glycidyl methacrylate copolymer

A novel copolymer was synthesized by vinylidene chloride (VDC)/methyl acrylate (MA)/glycidyl methacrylate (GMA). The Fourier transform infrared (FTIR) and ¹H-nuclear magnetic resonance analyses indicated that the copolymer of VDC/MA/GMA (PVMG) was synthesized successfully. The influences of GMA on the molecular weight, melting point, and thermal stability of copolymer were investigated by gel permeation chromatograph, differential scanning calorimeter, thermogravimetric analysis–FTIR, respectively. The copolymerization eliminated the phenomenon of “double melting peaks” for poly(vinylidene chloride), and the melting point was reduced to 165°C. The GMA also enhanced the thermal stability of copolymer, which was proved by the increased decomposition temperature of copolymer. The existence of GMA caused the cross-linking of the copolymer, which contributed to the improvement of barrier performance of PVMG.     

Degradation of vinylidene chloride/methyl acrylate copolymers in the presence of metal formates

Vinylidene chloride copolymers have a number of superior properties, most notably, a high barrier to the transport of oxygen and other small molecules. As a consequence, these materials have assumed a position of prominence in the packaging industry. At processing temperatures these copolymers tend to undergo degradative dehydrochlorination. The dehydrochlorination reaction is a typical chain process with distinct initiation, propagation, and termination phases. It has been demonstrated that initiation of degradation is strongly facilitated by the presence of unsaturation along the backbone. Such unsaturation may be introduced via interaction of the polymer with a variety of agents which might commonly be encountered during polymerization or processing. The presence of an unsaturated unit within the polymer generates an allylic dichloromethylene which may function as a major defect (labile) site for the initiation of degradation. The conversion of these dichloromethylene units into non-reactive groups would interrupt propagation of the dehydrochlorination reaction and lead to the stabilization of the copolymer. Potential stabilization in the presence of metal formates has been examined using a vinylidene chloride/methyl acrylate (five mole percent) copolymer and thermogravimetric techniques. The effect of the metal formate on the stability of the polymer reflects the relative halogenophilicity of the metal cation present. Metal formates (sodium, calcium, nickel(II) and to a lesser extent lead(II), cadmium, manganese(II) and magnesium) may be expected to be ineffective as stabilizers for vinylidene chloride copolymers. At the other extreme, metal formates which contain cations sufficiently acidic to actively strip chlorine from the polymer backbone, e.g., zinc formate, will function to enhance the degradation process. An effective carboxylate stabilizer must contain a metal cation sufficiently acidic to interact with allylic chlorine and to facilitate its displacement by the carboxylate anion. Copper(II) formate may possess the balance of cation acidity and carboxylate activity to function as an effective stabilizer for vinylidene chloride copolymers.     

Thermal degradation of vinylidene chloride/[4-(t-butoxycarbonyloxy)phenyl]methyl acrylate copolymers

Vinylidene chloride polymers containing comonomer units capable of consuming evolved hydrogen chloride to expose good radical-scavenging sites might be expected to display greater thermal stability than similar polymers containing simple alkyl acrylates as comonomer. Incorporation of a comonomer containing the phenyl t-butyl carbonate moiety into a vinylidene chloride polymer has the potential to afford a polymer with pendant groups which might interact with hydrogen chloride to expose phenolic groups. Copolymers of vinylidene chloride with [4-(t-butoxycarbonyloxy)phenyl]methyl acrylate have been prepared, characterized, and subjected to thermal degradation. The degradation has been characterized by thermal and spectroscopic techniques. The degradation of vinylidene chloride/[4-(t-butoxycarbonyloxy)phenyl]methyl acrylate copolymers is much more facile than the same process for similar copolymers containing either [4-(isobutoxycarbonyloxy)phenyl]methyl acrylate or methyl acrylate, a simple alkyl acrylate, as comonomer. During copolymer degradation, [4-(t-butoxycarbonyloxy) phenylmethyl acrylate units are apparently converted to acrylic acid units by extensive fragmentation of the sidechain. Thus, the phenyl t-butyl carbonate moiety does function as a labile acid-sensitive pendant group but its decomposition in this instance leads to the generation of a phenoxybenzyl carboxylate capable of further fragmentation.     

Synthesis and adsorption properties of colloid-imprinted mesoporous carbons using poly(vinylidene chloride-co-vinyl chloride) as a carbon precursor

A facile synthesis of micro- and mesoporous carbons has been proposed using colloidal silica nanoparticles with diameter of ∼24 nm and poly(vinylidene chloride-co-vinyl chloride) (Saran) as a carbon precursor. The resulting carbons possessed large specific surface area, ∼800 m²/g, and approximately the same volume of micro- and mesopores, each about 50% of the total pore volume. While the size of micropores was around 1 nm, the large and uniform spherical mesopores (about 24 nm) resemble the diameters of silica colloids used. Nitrogen adsorption measurements proved that these mesopores were interconnected and accessible. The well-developed microporosity was created mainly by decomposition of Saran copolymer during carbonization.     

Determination of gelation dose of a vinylidene chloride/acrylonitrile copolymer irradiated with gamma-rays by a spectrophotometric technique

The gelation dose of a vinylidene chloride (VDC)/acrylonitrile (AN) random copolymer irradiated with γ-rays in vacuum is first determined by conventional techniques, such as viscometry and solubility. The onset of gelation was determined to be 5.8 Mrad for this copolymer of composition 20% AN/80% VDC. The same gelation dose is also determined by a spectrophotometric method which is based on the recording of u.v.-vis spectra of solutions of this copolymer in THF. The advantages of this new technique for determination of gelation dose over the conventional methods are discussed.     

Simple preparation and catalytic activity of Pd particles dispersed mesoporous carbons from poly(VDC/MA) containing Pd and Y compounds

We report a simple preparation of Pd particles dispersed mesoporous carbons. The carbons were prepared by steam activation of carbonized vinylidene chloride/methyl acrylate copolymer (poly(VDC/MA)) containing yttrium acetylacetonate (Y(acac)(3)) and palladium acetylacetonate (Pd(acac)(2)). The resulting carbons consist of high contents of mesopore and uniformly dispersed fine Pd particles. We measured the catalytic activities of the carbons obtained for hydrogenation of methyl linoleate. The Pd particles dispersed in mesoporous activated carbons obtained from poly(VDC/MA) containing both Y(acac)(3) and Pd(acac)(2) showed high catalytic activities, compared with the microporous activated carbon obtained from poly(VDC/MA) containing only Pd(acac)(2). Especially Pd particles dispersed in mesoporous carbons exhibited excellent selectivity for hydrogenation of diene (methyl linoleate) to monoene (methyl oleate).     

Thermal decomposition of poly(vinylidene chloride) prepared in presence of oxygen

The thermal decomposition of poly(vinylidene chloride) was studied for samples prepared in the presence of oxygen. The products from both mass and aqueous suspension polymerizations show two modes of thermal decomposition. A rapid initial mode varies in rate and extent with the amount of oxygen present. A slower mode is unaffected by oxygen and in similar in rate to the polymer made in the absence of oxygen. The chief volatile products are phosgene and formaldehyde for the rapid decomposition and hydrogen chloride for the slow decomposition. The rapid decomposition is interpreted to be an unzipping reaction of a vinylidene chloride–oxygen alternating copolymer initiated by homolysis of a peroxide bond. The absence of significant amounts of hydrogen chloride during this stage of decomposition shows that none of the free radicals generated are capable of initiating a chain reaction that would unzip hydrogen chloride from the poly(vinylidene chloride) backbone. The presence of oxygen during the aqueous suspension polymerization correlates with the generation of hydrochloric acid in the aqueous phase. By analogy with the high temperature decomposition, the hydrochloric acid is believed to result primarily from the hydrolysis of phosgene produced by partial decomposition of the polyperoxide. Initiation of the decomposition is believed due to a reaction of the chain propagating radical.     

Study of the thermal dehydrochlorination of poly(vinylidene chloride) and poly(vinyl chloride) by ESR spectroscopy

The evidence for a radical elimination of hydrogen chloride during the thermal degradation of homopolymers and copolymers of vinylidene chloride is summarized and confirmed by an ESR spectroscopic study of the degradation residues. However, sufficient differences in the degradation characteristics exist between these polymers and those of vinyl chloride to suggest that a radical process alone is not sufficient. No evidence of a radical process can be obtained from an ESR spectroscopic analysis of the elimination. The paramagnetic character of the degraded polymer is attributed to the polyene structure produced on dehydrochlorination.     

Thermal degradation of vinylidene chloride/vinyl chloride copolymers in the presence of N-substituted maleimides

As a consequence of their excellent barrier properties vinyl chloride/vinylidene chloride copolymers have long been prominent in the flexible packaging market. While these polymers possess a number of superior characteristics, they tend to undergo thermally- induced degradative dehydrochlorination at process temperatures. This degradation must be controlled to permit processing of the polymers. Three series of N-substituted maleimides (N-alkyl-, N-aralkyl, and N-aryl) have been synthesized, characterized spectroscopically, and evaluated as potential stabilizers for a standard vinyl chloride/vinylidene chloride (85 mass%) copolymer. As surface blends with the polymer, these compounds are ineffective as stabilizers. However, significant stabilization may be achieved by pretreatment of the polymer with N-substituted maleimides. The most effective stabilization of the polymer is afforded by N-aralkyl- or N-arylmaleimides, most notably, N-benzylmaleimide and N-p-methoxyphenylmaleimide.     

Thermal degradation of vinylidene chloride/4-vinylpyridine copolymers

Vinylidene chloride polymers are prominent in the barrier plastics packaging industry. They display good barrier to the transport of oxygen (to prevent spoilage of food items) and flavor and aroma constituents (to prevent 'scalping' on the supermarket shelf). However, these polymers undergo thermal dehydrochlorination during processing. This can lead to a variety of problems including the evolution of hydrogen chloride which must be scavenged to prevent its interaction with the metallic walls of process equipment. Such interaction leads to the formation of metal halides which act as Lewis acids to facilitate the degradation. A potentially effective means to capture hydrogen chloride generated might be to incorporate into the polymer a mild organic base. Accordingly, copolymers of vinylidene chloride and 4-vinylpyridine have been prepared and subjected to thermal aging. Results suggest that the pyridine moiety is sufficiently basic to actively promote dehydrochlorination in the vinylidene chloride segments of the polymer.     

Correlation of thermal degradation mechanisms: Polyacetylene and vinyl and vinylidene polymers

The thermal degradation of poly(vinyl bromide) (PVB), poly(vinyl chloride) (PVC), poly(vinyl alcohol) (PVA), poly(vinyl acetate) (PVAc), poly(vinyl fluoride) (PVF), poly(vinylidene chloride) (PVC₂), and poly(vinylidene fluoride) (PVF₂) has been studied by direct pyrolysis–mass spectrometry (DP-MS) and flash pyrolysis–gas chromatography–mass spectrometry techniques. Vinyl and vinylidene polymers exhibit two competitive thermal degradation processes: (1) HX elimination with formation of polyene sequences which undergo further moleculaar rearrangements, and (2) main-chain cleavage with formation of halogenated or oxigenated compounds. The overall thermal degradation process depends on the prevailing decomposition reaction in each polymer; therefore, different behaviors are observed. The thermal degradation of polyacetylene (PA) has also been studied and found important for the elucidation of the thermal decomposition mechanism of the title polymers.     

Dehydrochlorination of vinylidene chloride-vinyl chloride copolymer by aqueous sodium or potassium hydroxide solutions under two-phase conditions

The reaction of solid copolymer of vinylidene chloride and vinyl chloride with aqueous sodium or potassium hydroxide solutions in the presence of quaternary ammonium or phosphonium salts as phase transfer catalysts gave dehydrochlorinated products with chlorine-substituted polyene structure. Among the catalysts used tetrapropylammonium bromide was the best and potassium hydroxide was more active than sodium hydroxide. The activity of quaternary ammonium salts was discussed in terms of hydrophile–lipophile balance. The effects of temperature and the concentration of the bases and catalysts were investigated to obtain the optimum reaction condition. Treatment of the polymer films and solutions in tetrahydrofuran with aqueous bases under two-phase conditions also produced dehydrochlorinated films and powders.     

Crystallization kinetics for semicrystalline random copolymers of vinylidene chloride (VDC) with methyl acrylate (MA), and the effects on the internal morphology of the resin particles formed during synthesis

Isothermal crystallization kinetics for random copolymers of vinylidene chloride (VDC) with methyl acrylate (MA) is reported. Syntheses of many semicrystalline polymers follow heterogeneous reaction paths in which the macromolecule chains phase separate from the reaction mixtures. The internal particle morphology (the internal structure of the resin bead) from this type of reaction is granular and porous, as a result of the demixing processes accompanying polymer formation. Demixing in these polymers involves either liquid-liquid (L-L) phase separation followed by liquid-solid (L-S) transformation (crystallization) or L-S transformation alone. Crystallization (L-S transformation) must be an indispensable part of the process if a porous granular structure is to be expected. This is because L-S transformation is the most probable means by which the demixed structure can be stabilized against complete coalescence or agglomeration, which would lead to totally fused bead internal structure. This is particularly true if the glass transition temperature (T_g) is lower than the polymerization temperatures, as is the case with the VDC-MA copolymers. Copolymers that crystallize the fastest will have the finest (most porous) resin bead morphology. The result of this work is consistent with expectation. The homopolymer (PVDC) that crystallizes the fastest has the finest resin bead internal morphology. The copolymers show slower crystallization rates with increasing noncrystallizable MA content. Correspondingly, resin morphology measured by specific surface area decreased with increasing amounts of the noncrystallizable (MA) comonomer unit in the copolymer. This is clearly seen in SEM photographs of the internal bead structures of these copolymers. ©1995 John Wiley & Sons, Inc.     

Emulsion copolymerization of vinylidene chloride and methyl methacrylate. I. Effects of operating variables on the kinetic behavior

The effects of operating variables on the kinetic behavior of the emulsion copolymerization of vinylidene chloride (VDC) and methyl methacrylate (MMA) were examined at 50 °C with sodium lauryl sulfate as an emulsifier and potassium persulfate as an initiator, respectively. The number of polymer particles produced increased in proportion to the 1.0 power of the initial emulsifier concentration and to the 0.3 power of the initial initiator concentration and decreased with an increasing content of MMA in the initial monomer charge. The rate of copolymerization was proportional to the 0.4 power of the initial emulsifier concentration and to the 0.5 power of the initial initiator concentration and increased with an increasing content of MMA in the initial monomer charge. The molecular weight of copolymer produced decreased drastically with an increasing content of VDC in the initial monomer charge. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1275–1284, 2002     

THE EFFECT OF MONOMERS FEEDING METHODS ON EMULSION COPOLYMERIZATION OF VINYLIDENE CHLORIDE AND ACRYLATES

The emulsion copolymerization of vinylidene chloride (VDC) with methyl-methacrylate(MMA) and acrylonitrile (AN) was carried out by batch, seeded batch and semicontinuous pro-cesses,respectively. Significant differences were found in the physical and mechanical propertiesof the latexes and films, depending on the methods of monomer feeding. The results both intheory and experiments demonstrated that the copolymer composition and the length of the VDC sequences in the copolymer could be controlled by the modes of monomer feeding process.     

Film‐formation property of vinylidene chloride‐methyl methacrylate copolymer latex. II. Effect of latex storage temperature

Changes in the minimum film‐formation temperature (MFFT) of 91:9 wt % vinylidene chloride (VDC)‐methyl methacrylate (MMA) latex prepared by the seeded batch process during storage at 5, 20, and 40 °C were investigated. MFFT of the latex rose the fastest at 20 °C. Infrared absorption of fresh and stored latexes and wide‐angle X‐ray diffraction of powder polymers obtained by lyophilization of fresh and stored latexes indicated a much greater increase in polymer crystallinity during latex storage at 20 °C than at 5 and 40 °C. Observed increases in MFFT during latex storage correlated with increases in polymer crystallinity. Infrared absorption of polymer stored at 5–60 °C in the dry state, such as lyophilized polymer and coating film, indicated that a polymer crystallinity increase was greater during storage at higher temperatures. These results showed that crystallization behavior of 91:9 wt% VDC‐MMA copolymer latex differed from that of VDC‐MMA copolymer in the dry state. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 948–953, 2002     

Film‐formation property of vinylidene chloride‐methyl methacrylate copolymer latex. I. Effect of emulsion‐polymerization process

Changes in minimum film‐formation temperature (MFFT) during storage of latexes prepared from 91:9 wt % vinylidene chloride (VDC)‐methyl methacrylate (MMA) monomer mixture by seeded batch and seeded semicontinuous emulsion polymerization were investigated, with attention centered on polymer‐crystallization behavior during storage in the dispersed state. MFFT of latex prepared by the seeded batch process rose to 47 °C, whereas that of latex prepared by seeded semicontinuous process remained below 14 °C with storage at 20 °C for 12 weeks. Infrared absorption of latexes in the dispersed state and wide‐angle X‐ray diffraction of powder polymers obtained by lyophilization of fresh and stored latexes both indicated a much greater increase in polymer crystallinity during storage with latex prepared by the seeded batch process than with that prepared by the seeded semicontinuous process. Analysis of the copolymer composition drift calculated from reactivity ratios and ¹H NMR analysis indicated a wider sequence distribution and longer VDC sequences in polymer prepared by the seeded batch process than in polymer prepared by the seeded semicontinuous process. This explained the higher rate of crystallization during storage with latex prepared by the seeded batch process than with that prepared by the seeded semicontinuous process. Rising crystallinity during storage in the dispersed state is believed to have caused the MFFT rise. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 939–947, 2002