Polymer modifications

Polystyrene and ABS are the polymers that are most commonly modified with SBCs. SBS triblocks and SB diblocks with 30-40% styrene are often used in concentrations near 5% either as a toughener alone in combination with polybutadiene in high-impact polystyrene. In addition to the use of elastomeric 

a significant fraction of the more than 150 000 tons of high styrene content ( 60%) SBS polymers are also used in compounds with polystyrene for transparent film, cups, and trays. 

Hydrogenated SBCs are often used to modify polyolefins such as polypropylene, polybutylene and polyethylene. One of the unique characteristics of strongly phase-separated block copolymers such as high molecular weight ( 50 000) SEBS and SEPS is their response to shear in the melt. These polymers retain their phase-separated structure well above the Tg of the polystyrene because their order-disorder transition temperatures are above processing temperatures. This phase separation strongly inhibits flow in the absence of shear resulting in infinite viscosity at zero shear rates. The application of shear 

Whenever a polymer is formed in several stages, each subsequent stage is a kind of polymer modification. All cross-linking reactions (vulcanizations) of rubber would fall in this category, together with the molding of network polymers such as the phenol formaldehyde resins. However, the term polymer modification is used here to 

Sometimes several purposes can be served at once. Chlorination of natural rubber decreases the flammability of the polymer. At the same time, it raises the 7 so that the polymer can be used as a binder for traffic paints. Nitration of cellulose allows the native cotton to be plasticized and molded. Flammability is enhanced at the same time. This may be a disadvantage to makers of molded articles for decoration and apparel. However, the munitions manufacturer regards the flammability and propellant power of guncotton, cellulose nitrate, as its most important advantage. Most often a polymer modification is economically justifiable only when the original polymer occurs naturally or as a by-product. Sometimes modification is the only good way to make a material. A case in point is the photosensitive polymer polyvinyl cinnamate. 

An attempt to polymerize vinyl cinnamate would give a cross-linked network, since the functionality is 4. Even polyvinyl alcohol cannot be made directly, because the monomer is unknown (isomeric with acetaldehyde). Thus, it is necessary first to polymerize vinyl acetate, then to hydrolyze the polymer to the polyalcohol. Finally, the alcohol 

Introduce cross-linking Butyl rubber sites 

Increase flammability Decrease flammability Change mechanical properties 

It is often desirable to perform some kind of chemical modification to polymers once they have formed. Acetylation of cellulose, for example, represents the chemical modification of a naturally occurring polymer (see chapter 3) to give the technologically useful cellulose diacetate and triacetate polymers. Poly(vinyl alcohol) (PVA) is a well-known example of a polymer that can only be formed by chemical modification since vinyl alcohol monomer does not exist (except as its keto form, acetaldehyde). Instead, PVA is formed by hydrolysis of poly(vinyl acetate) (PVAc). Partly hydrolysed PVAc is, of course, simply a copolymer of VA and VAc. As another example, ethylene/vinyl chloride copolymers can be prepared by reductive elimination of chlorine from poly (vinyl chloride) (PVC). The driving force here is that, although ethylene and vinyl chloride can be copolymerised directly, the normal routes to these polymers give insufficient control over composition and sequence distribution. 

The microstructures of copolymers prepared by chemical modification are obviously amenable to study using exactly the same techniques that are applied to copolymers prepared by more normal routes. Here, part of the value of such studies is that they can impart information concerning the mechanism of the chemical modification reactions. Some examples of polymer modification are discussed in this section. 

Poly (vinyl alcohol-co-vinyl acetate) polymers are surface active species which can be used to stabilise latex and oil in water dispersions. In order to understand the properties of these materials, it is necessary that their sequence distributions are well characterised. A number of NMR studies on the microstructure of PVA/PVAc copolymers have been made [51-53] (see also chapter 3). Moritani and Fujiwara [51], for example, have used proton and carbon-13 NMR spectroscopy to extract dyad distributions for a range of copolymers with different degrees of deacetylation. Samples were prepared using one of three routes direct saponification of PVAc alcoholyis of PVAc using sodium methoxide and reacetylation of PVA. From the polymer composition and the dyad distribution, the parameter rj was calculated for each polymer as follows  

These results are in keeping with predictions of microstructure based on a kinetic model describing PVAc hydrolysis. In this model for acid- or base-catalysed saponification, the catalyst interacts strongly with free hydroxyl groups and this induces successive hydrolysis of nearest-neighbour acetyl groups, so leading to a blocky microstructure. 

The ability of NMR spectroscopy to distinguish between dyads, triads, and higher n-ad sequences in copolymers makes it an especially powerful tool for the polymer chemist interested in the fine details of molecular structure. In this chapter, we have seen that simple expressions derived from the relative abundances of various sequence types allow characterisation of the copolymer microstructure in terms of number-average sequence lengths, without any recourse to a statistical model. A more detailed examination of copolymer 

Impregnation of reactive species into a host polymer provides a method for polymer modification via a chemical reaction. TTiis work has been extended by showing that photolysis of W(CO)6 in polyethylene (PE) can lead to isomerization of the C=C double bonds, an interesting variation of Wrighton s work on catalytic alkene isomerization [40]. The method can be used to prepare iso-merized PE because the W(CO)e can be removed entirely after the isomerisation has taken place [5,41]. Ultraviolet photolysis of Fe(CO)5 in PE under a pressure of H2 leads to reduction of up to 80% of the C=C bonds [41], while photolysis under an atmosphere of O2 generates an oxide, most probably Fe203, within the PE matrix [41]. 

The effect of inorganic salts, for example sodium chloride, on the hydrolysis of chitosan in a microwave field was investigated by Li et al. [78]. The reactions were conducted in a domestic microwave oven. It was found that the molecular weight of the degraded chitosan obtained by microwave irradiation was considerably lower than that obtained by convectional heating. 

Microwave-assisted synthesis of a guar-g-polyactylamide (G-g-PAA) has also been reported [80]. The reactions were performed in a domestic microwave oven. Graft copolymerization of the guar gum (GG) with acrylamide (AA) under the action of microwave irradiation in the absence of any radical initiators and catalyst resulted in grafting yields comparable with redox (potassium persulfate-ascorbic acid) initiated by conventional heating but in a very short reaction time. Grafting efficiency up to 20% was further increased when initiators and catalyst were used under microwave irradiation conditions. Maximum grafting efficiency achieved under MW conditions was 66.66% in 0.22 min, compared with 49.12% in 90 min by the conventional method. 

The best results (degree of substitution) were obtained at 105 °C after irradiation for 2 h. 

In conclusion, polymer synthesis can benefit greatly from the unique features of modern microwave technology recently demonstrated in the large number of sue- 

The mode of action of microwave irradiation on chemical reactions is still under debate, and some research groups have proposed the existence of so-called non-thermal microwave effects, i.e. sudden acceleration of reaction rates which cannot be explained by the reaction temperatures observed. Recent critical reviews of both groups of theories have been published by Loupy et al. [86, 87], Nuchter et al. [88], and de la Hoz et al. [89]. 

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Polymer Modification. The introduction of functional groups on polysdanes using the alkah metal coupling of dichlorosilanes is extremely difficult to achieve. Some polymers and copolymers with 2-(3-cyclohexenyl)ethyl substituents on siUcon have been made, and these undergo hydrogen hahde addition to the carbon—carbon double bond (94,98). 

Etee-tadical reactions ate accompHshed using a variety of processes with different temperature requirements, eg, vinyl monomer polymerization and polymer modifications such as curing, cross-linking, and vis-breaking. Thus, the polymer industries ate offered many different, commercial, organic peroxides representing a broad range of decomposition temperatures, as shown in Table 17 (19,22,31). 

During emulsion polymerization, a high conversion of monomer to polymer produces cross-linked rubber which is insoluble. To obtain a high conversion in the polymerization reaction and a processable polymer, suitable polymer modification should be made. The use of sulphur moieties allows this goal to be reached [2]. Sulphur-modified polychloroprenes contain di- and polysulphide sequences in the polymer chains. After the polymerization reaches the desired degree, reaction is stopped by adding thiuram disulphide ... 

ADMET is quite possibly the most flexible transition-metal-catalyzed polymerization route known to date. With the introduction of new, functionality-tolerant robust catalysts, the primary limitation of this chemistry involves the synthesis and cost of the diene monomer that is used. ADMET gives the chemist a powerful tool for the synthesis of polymers not easily accessible via other means, and in this chapter, we designate the key elements of ADMET. We detail the synthetic techniques required to perform this reaction and discuss the wide range of properties observed from the variety of polymers that can be synthesized. For example, branched and functionalized polymers produced by this route provide excellent models (after quantitative hydrogenation) for the study of many large-volume commercial copolymers, and the synthesis of reactive carbosilane polymers provides a flexible route to solvent-resistant elastomers with variable properties. Telechelic oligomers can also be made which offer an excellent means for polymer modification or incorporation into block copolymers. All of these examples illustrate the versatility of ADMET. 

Kirkpatrick J.P. and Preston D.T., Polymer modification with styrenic block copolymers, Elastomerics, 120, 30, 1988. 

Antony, P., Puskas, J.E., and Kontopoulou, M. The Rheological and Mechanical Properties of Blends Based on Polystyrene-Polyisobutylene-Polystyrene Triblock Copolymer and Polystyrene. Proceedings of MODEST, International Symposium on Polymer Modification, Degradation and Stabilization, Budapest, Hungary, 2002. 

Lewandowski, L.H., Polymer modification of paving asphalt binders. Rubber Chem. Technol., 67, 447, 1994. 

W.H. Starnes, Abstracts Second International Conference on Polymer Modification, Degradation and Stabilisation (MoDeStl), Budapest (2002). 

Deliberate production of (vinyl)polystyrene from (toluenesul-foxyethyl)polystyrene or (haloethyl)polystyrenes was best accomplished by quaternization with N,N-dimethylaminoethanol, followed by treatment with base beta-deprotonation is encouraged in the cyclic zwitterionic intermediate. Reaction was faster and cleaner than with other reagents recommended (64, 76, 77) for eliminations, such as alkoxide, diazabicycloundecene or quaternary ammonium hydroxide this new and efficient procedure may find application elsewhere. Hydrometallation or other additions to polymer-bound olefin may prove useful steps in future syntheses by polymer modification. 

Polyepichlorohydrin (PECH) is well known as a reactive elastomer. Displacement at the carbon-chlorine bond of PECH has been accomplished with a wide variety of nucleophilic reagents, for the purposes of polymer modification, grafting and crosslinking (1, 2). On the other hand, the PECH structure (1) is hardly optimal from the point of view of its reactivity as a substrate for nucleophilic... 

An important polymer modification reaction is the grafting to or from a polymer backbone by some chemical method to produce a branched structure Q). The characterization of the products of these reactions is often somewhat less well defined than block copolymers (2) due to the complexity of the mixture of products formed. It is therefore useful to prepare and characterize more well defined branched systems as models for the less well defined copolymers. The macromonomer method (3 ) allows for the preparation of more well defined copolymers than previously available. 

In addition, the polymer modification reactions leading to acidic and ionomeric functionalities are described in detail. The derived ion-containing block copolymers may aid in the correlation of chemical architecture with ionomer morphology and properties. 

Apparatus. Since all the polymer modification reactions presented in this paper involved gas consumption, an automated gas consumption measuring system was designed, fabricated and used to keep constant pressure and record continuously the consumption of gas in a batch type laboratory scale reactor. Process control, data acquisition, and analysis was carried out using a personal computer (IBM) and an interface device (Lab-master, Tecmar Inc.). 

It is important to note that the foregoing, biosynthetic-polymer modification is usually incomplete. In fact, only a fraction of the heparin precursor undergoes all of the transformations shown in Scheme 1. However, as the product of each enzymic reaction constitutes the specific substrate for the succeeding enzyme, the biosynthesis of heparin is not a random process. Thus, sulfation occurs preferentially in those regions of the chain where the amino sugar residues have been N-deacetylated and N-sulfated, and where D-glucuronic has been epimerized to L-iduronic acid.20... 

Meister JJ (ed) (2000) Polymer modification principles techniques and applications. CRC Press, 936... 

There also have been other reports of polymer-supported catalysts with incorporated boron moieties resulting from multistep polymer modification reactions to incorporate the boron moiety.76... 

Recently, nitrilases have been applied to polymer modification, specifically to the modification of polyacrylonitrile (PAN). Nearly 3 x 106 tons of PAN are produced per annum and used in the textile industry. However, there is a great need to improve moisture uptake, dyeability with ionic dyes, and feel of this acrylic fiber. The cyano moieties of PAN have been successfully modified to carboxylates with the commercial Cyanovacta nitrilase, thus enhancing the aforementioned properties of PAN [98]. Nitrilase action on the acrylic fabric was improved... 

D. Walt, F. Milanovich, S. Klainer 1986 Polymer modification of a fluorescent fiber optic pH sensor... 

Munkholm C., Walt D.R., Milanovich F.P., Klainer S.M., Polymer modification of fiber optic chemical sensors as a method of enhancing fluorescence signal for pEl measurement, Analytical Chemistry 1986 58 1427-1430. 

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