Bonding styrene-acrylonitrile-copolymers

Impact Properties. Chemical Nature of the Rubber. If the rubber is too compatible with the matrix, it will dissolve in the rigid material and disperse on a molecular scale. Little or no reinforcement will occur since the rubber particles become smaller than the radius of the tip of a stress-induced propagating crack. However if it is highly incompatible, good adhesion between rubber and matrix cannot be obtained. For example polybutadiene rubber adheres poorly to a styrene/acrylonitrile copolymer, but a nitrile rubber adheres well to the SAN copolymer. If grafting techniques are used however, compatibility is less of a problem since the rubber is chemically bonded to the matrix. 

Thermoplastics are plastics which undergo a softening when heated to a particular temperature. This thermoplastic behaviour is a consequence of the absence of covalent bonds between the polymeric chains, which remain as practically independent units linked only by weak electrostatic forces (Figure 1.4(a)). Therefore, waste thermoplastics can be easily reprocessed by heating and forming into a new shape. From a commercial point of view, the most important thermoplastics are high density polyethylene (HDPE), low density polyethylene (LDPE), polypropylene (PP), polystyrene (PS), polyvinyl chloride (PVC), polyethylene tereph-thalate (PET), polyamide (PA), polymethyl methacrylate (PMMA), acrylonitrile-butadiene-styrene copolymer (ABS), and styrene-acrylonitrile copolymer (SAN). 

Figure 3.31. Oxygen uptake for polybutadiene rubber (PBR), grafted polybutadiene rubber (Graft), methacrylonitrile-butadiene-styrene resin (M A-B-S), acrylonitrile-butadiene-styrene (ABS), and styrene-acrylonitrile copolymer (SAN). Only the last polymer contains no double bonds. (Hirai, 1970.)...

As expected, there are some interesting blends that do not fit the classifications chosen for this chapter and will be summarized in this section. PHE/PVME blends were shown to be miscible with lest behavior observed [ 180]. Partial methylation or benzylation of the secondary hydroxyls of PHE lowered the position of the lest and thus reduced the inherent miscibihty [1140]. PHE was also shown to exhibit miscibility with poly(4-vinyl pyridine), presumably due to the hydrogen bonding potential expected from this combination [223]. The polyformal from the reaction product of tetramethyl Bisphenol S and methylene chloride was foimd to be miscible with styrene-acrylonitrile copolymers (24, 28 and 42 wt% AN) and also poly(vinyl chloride) [1141]. 

The CN bond stretching frequency was shifted to a higher value with an increase in the methacrylonitrile (MAN) content in the copolymers. There was no linear relationship between the CN frequency and the diad fraction of MAN-MAN linkages in the copolymer chain, as reported previously for styrene-acrylonitrile copolymers. Different methods for the copolymer sample preparation can cause differences in the shifts in the CN frequency. This suggests that the polymer morphology plays an important role. A study of blends of polymethacrylonitrile (PMAN) with polystyrene has shown that the CN frequency is shifted to a higher value with an increase of the PMAN composition of the blends. 

During World War II, several new synthetic elastomers were produced and new types of adhesives (mainly styrene-butadiene and acrylonitrile copolymers) were manufactured to produce adequate performance in joints produced with new difficult-to-bond substrates. Furthermore, formulations to work under extreme environmental conditions (high temperature, resistance to chemicals, improved resistance to ageing) were obtained using polychloroprene (Neoprene) adhesives. Most of those adhesives need vulcanization to perform properly. 

An appropriate formalism for Mark-Houwink-Sakurada (M-H-S) equations for copolymers and higher multispecies polymers has been developed, with specific equations for copolymers and terpolymers created by addition across single double bonds in the respective monomers. These relate intrinsic viscosity to both polymer MW and composition. Experimentally determined intrinsic viscosities were obtained for poly(styrene-acrylonitrile) in three solvents, DMF, THF, and MEK, and for poly(styrene-maleic anhydride-methyl methacrylate) in MEK as a function of MW and composition, where SEC/LALLS was used for MW characterization. Results demonstrate both the validity of the generalized equations for these systems and the limitations of the specific (numerical) expressions in particular solvents. 

In this paper a generalized approach is presented to the derivation of H-H-S equations for multispecies polymers created by addition polymerization across single double bonds in the monomers. The special cases of copolymers and terpolymers are derived. This development is combined with experimental results to evaluate the numerical parameters in the equations for poly(styrene-acrylonitrile ) (SAN) in three separate solvents and for poly(styrene-maleic anhydride-methyl methacrylate) (S/HA/MM) in a single solvent. The three solvents in the case of SAN are dimethyl formamide (DMF), tetrahydrofuran (THF), and methyl ethyl ketone (MEK) and the solvent for S/HA/HH is HER. 

The influence in the decomposition rate has been seen for example in the poly(styrene-co-acrylonitrile) copolymers. The elimination of HCN from the side chain of the polymer generates double bonds in the backbone. The decomposition of the polymer is significantly accelerated in this case, since the cleavage of the backbone in the p-position to the double bond is facilitated [17]. In other cases, such as in the copolymers of methylmethacrylate with acrylonitrile, the rate of decomposition is decreased around 220° C and the yield of monomer diminished [18]. 

Styrenic thermoplastics include polystyrene itself, acrylonitrile-butadiene-styrene (ABS) copolymers and plastic blends such as polyphenylene oxide/styrene. Most adhesives can be used to produce strong bonds with these plastics, but primers and solvents should be tested carefully for solvent attack or cracking. 

Butadiene and isoprene have two double bonds, and they polymerize to polymers with one double bond per monomeric unit. Hence, these polymers have a high degree of unsaturation. Natural rubber is a linear cis-polyisoprene from 1,4-addition. The corresponding trans structure is that of gutta-percha. Synthetic polybutadienes and polyisoprenes and their copolymers usually contain numerous short-chain side branches, resulting from 1,2-additions during the polymerization. Polymers and copolymers of butadiene and isoprene as well as copolymers of butadiene with styrene (GR-S or Buna-S) and copolymers of butadiene with acrylonitrile (GR-N, Buna-N or Perbunan) have been found to cross-link under irradiation. 

Another reason for copolymerization is to insert functional grouping in the polymer. A functional group is one that is easily reacted. For example, copolymerization of styrene with acrylonitrile, CH2=CH-CN, involves only the double bond, leaving the newly formed copolymer with the active functional group -CN, available for subsequent reaction. The copolymer might be reacted later with itself or another monomer to give a cross-linked thermoset. 

The chain transfer reaction played an important role, particularly because of abstraction of the active hydrogen at a-carbon from the allyl group. Moreover, unreacted double bonds were present in the copolymer obtained. The influence of chain transfer reaction could be diminished by applying multimonomers which do not contain allyl groups. This was shown in the example of copolymerization of multimethacrylate prepared by esterification of poly(2-hydroxyethyl methacrylate) with methacryloyl chloride. Copolymerization of the multimethacrylate with vinyl monomers such as styrene or acrylonitrile can be represented by the reaction ... 

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