Page 102 - Handbook of Adhesion Promoters

6.2 Selection of polyols and isocyanates 95

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0.5-3.6 wt% of 10-undecen-1-ol. A few hydroxyl groups improved adhesive properties
of the polymer.
The ethylene copolymers were synthesized for application as protective coatings for
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surface of stone monuments. An increased compatibility of the apolar polyethylene with
inorganic materials was obtained by introducing some oxygen and ester groups in the
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polymers by copolymerization with 10-undecen-1-ol and 7-methyl-1,6-octadiene. Ethyl-
ene/10-undecen-1-ol copolymer kept its protective efficiency because of its good stability
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on exposure to photooxidative degradation.
6.2 SELECTION OF POLYOLS AND ISOCYANATES

Polyurethane sealants made from a hydrophobic polyol had better hot water resistance
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than sealants made from polypropylene glycol diol. The PU sealant containing a hydro-
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phobic filler decreases the hot-water resistance during the prolonged immersion. The
adhesion promoters can enhance adhesion of a PU sealant to the substrate in a hot water,
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but they may increase water swelling, thus degrading its cohesion.
The adhesion properties of the PU elastomer were significantly enhanced in the pres-
ence of diethanol amine and 2-cyano-N,N-bis-hydroxyethyl acetamide used as chain
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extenders. The wetting and work of adhesion were also increased by chain extenders. 13
The increase in adhesion strength and wettability of the adhesive were more pronounced
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when the chain extender without side group (diethanol amine) was used.
Polyurethane acrylates modified by saturated alcohols were synthesized using satu-
rated alcohols, isophorone diisocyanate, 2-hydroxyethyl acrylate, and polycaprolactone
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triol. Acrylate modified with longer chain alcohol had better adhesion.
At lower NCO/OH ratios, the rigidity and stiffness of the adhesive bond increased
with increasing free NCO content, whereas beyond a critical free NCO content, high stiff-
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ness was responsible for the decrease in adhesion strength.
An increase in the hard segments content in the TPUs reduced the degree of phase
separation and the organization of their structure, resulting in less crystalline polymers
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having worse adhesion properties.
The formation during storage of by-products (uretdione, isocyanurate, and allophan-
ate) resulted in a higher cohesion of the moisture cured quasi-prepolymer, improving the
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adhesion properties of rubber and aluminum.
6.3 MODIFICATION OF POLYMERS BY MALEIC ANHYDRIDE

Carboxyl coatings are used for adhesion promotion, bio-immobilization, and surface reac-
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tions because of their reactivity towards nucleophilic groups and high wettability. The
plasma copolymerization of maleic anhydride and C H by atmospheric pressure dielec-
2
2
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tric barrier discharge can produce in situ such coatings. The layer synthesized at opti-
mized monomer flow rate and plasma power contains 5 at% of carboxyl groups (for
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structure see Figure 6.2).
An ethylene/5,7-dimethylocta-1,6-diene copolymer was modified with maleic anhy-
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dride via the Lewis acid-catalyzed Alder Ene reaction. Anhydride-grafted copolymers
show an improvement of adhesion as compared with the ethylene/diene copolymer pre-
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cursor or the commercial polyethylene.