Surface Induced Homopolymerization

Combination of BP with 2-propanol or amines induces homopolymerization alone. The rate constants of BP 3 - isopropylamine and triethylamine are 2.95 10 and 2.42 1()9m-1s-1, respectively(22) whereas that of BP 3 - isooctane as a model of OPP is 1.0 lO M s l (24). Also hydrogen abstraction from 2-propanol(k=1.0 106 M s"1) (25) is much more efficient than that from aliphatic hydrocarbons. Even methanol is more reactive (k=2.8 10% - s - -) (25) than OPP towards BP 3. The aforementioned results and the finding that surface grafting does not occur in methanol are well interpreted by the following elementary reactions. 

Thermoplastic polymers will begin to soften with increasing temperature and thermally decompose into lower molecular weight fractions. It is probable that the more volatile, lower m.w. polymers will demonstrate greater tendency for chemical interaction with the metal surfaces. An increasing temperature gradient may also induce homopolymerization of low m.w. polymers. Interactions will also be influenced by atmospheric oxygen and hence in the tests which follow comparisons are made between air and inert gas exposure. 

In the absence of sensitizer, neither graft nor homopolymerization was induced by irradiation at 366nm. However, irradiation by a low pressure mercury lamp through a quartz plate(the glass plate(c) in Figure 1 was replaced by a quartz plate.) induces slow surface grafting sensitized by acetone. 

Electron beam irradiation was used for grafting of JV-phenyl-(3-amino-6-methyl-JV-allyloxycarbonyl)-JV -phenyl-(4-phenylamino)urea or JV-phenyl[3-amino-6-methyl-JV- (2-acryloyloxyethoxycarbonyl)]-jV -phenyl- (4-phenylamino)urea onto HOPE [229]. y-Radiation induced grafting of 2-hydroxy-4-(3-methacryloyloxy-2-hydroxypropoxy)benzophenone onto LDPE, HOPE or PP was performed in an air-free atmosphere and in the presence of cupric chloride (to prevent homopolymerization). Foils with chromophores located near the surface were formed [218]. 

Autoxidation, i.e. oxygen-induced curing, may take place both during copolymerization in the bulk phase and during homopolymerization of a surface monolayer. Two surfactants capable of undergoing autoxidation are shown in Figure 17.22. Surfactants that can undergo... 

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