Authors:N. Gupta, R. Srivastava, V. Choudhary, I. Varma, and S. Patnaik
Copolymers of vinyl acetate and ethylene were prepared by emulsion polymerization using ammonium persulphate and sodium metabisulphite as initiators in presence of cyclohexane. Several copolymer samples were prepared by changing initial pressure of ethylene from 100 to 250 psi. The copolymer composition was determined by 1H-NMR and thermogravimetric analysis in nitrogen atmosphere.
A series of PDPS/PDMS copolymers were synthesized through living anionic polymerization withn-butyllithium as an initiator. The changes of thermal property as a function of PDPS content were compared with respect to
different types of monomer sequence using differential scanning calorimetry and thermogravimtery. The results indicated that
the related variations of the thermal propertiesvs. the PDPS content and the monomer sequence provided independent operative control for preparing materials with desired thermal
properties. The thermal stability of these copolymers was dramatically improved with introducing PDPS segment. However, the
degree of these improvement pedended greatly on the monomer sequence in the copolymers.
Thermal characteristics of a new thiophene derivative, 2-(thiophen-3-yl-)ethyl octanoate (OTE), its homopolymer (POTE), and
copolymer with thiophene P(OTE-co-Th) were investigated via pyrolysis mass spectrometry. Thermal degradation of the copolymer
started by lose of side chains and thiophene involving products evolved almost in the same temperature range where PTh degradation
was detected, at slightly higher temperatures than PTh backbone decomposed during the pyrolysis of POTE. The extent of doping
and network structure decreased in the order POTE<P(OTE-co-Th)<PTh.
Authors:D. Radic, L. Tagle, A. Opazo, A. Godoy, and L. Gargallo
Poly(monoitaconates) containing octyl, decyl and dodecyl groups and random monoalkylitaconate-co-vinylpyrrolidone copolymers
were studied by thermogravimetric analysis. Copolymers of mono-n-octylitaconate (MOI), mono-n-decylitaconate (MDI), and mono-n-dodecylitaconate (MDoI), respectively, with N-vinyl-2-pyrrolidone (VP) of different compositions were studied by dynamic
thermogravimetric analysis. The thermal stability of the copolymers depends on the structure of the monoitaconate comonomer
and on the composition of the copolymer The kinetic analysis of the degradation data shows that the thermal decomposition
of these copolymers can be described by several kinetic orders depending on the copolymer and on the composition. The relative
thermal stability of the copolymers increases as the VP content increases and as the length of the side chain of the itaconate
increases, following the same trend as the flexibility of the copolymers in solution.
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.
Among widely available polymer-based packing materials, the most popular are non-polar styrene–divinylbenzene (ST-DVB) copolymers. As these materials are highly hydrophobic, they possess rather restriction and
Authors:Zbigniew Czech, Robert Pełech, Krzysztof Zych, and Jolanta Świderska
Methacrylate copolymers with their excellent physical, chemical, and mechanical properties are widely used in many applications such as raw materials for adhesives, polymeric films, paints, varnishes, and sealants
Authors:Stavroula G. Nanaki, George Z. Papageorgiou, and Dimitrios N. Bikiaris
cost and high quality [ 7 , 8 ] and this enables polyester production. Thus, only recently, papers dealing with polyesters based on 1,3-PD have been published [ 9 – 14 ].
Block copolymers consist of a most promising class of polymeric materials
The relationship between transition temperatures and copolymer composition was studied by DSC. Three types of copolymers were
studied: styrene-acrylonitrile (SAN), vinyl chloride-vinyl acetate (VC-VA), and ethylene vinyl acetate (EVA). SAN's and VC-VA's
are amorphous copolymers, whereas EVA's are semi-crystalline copolymers. The variation of the glass transitions and the crystalline
melting are discussed in this study.