Grafting kinetics for Poly(Bisphenol A-co-epichlorohydrin) glydiyl end-capped telechelics were studied.
Initial studies were conducted with Poly(Bisphenol A-co-epichlorohydrin) with a range of number average molecular weights (Mn) from 1075 to 6100. It is expected that MW will have a profound effect on the number of multiply-bound polymer chains grafted to the substrate. Preliminary results show an unexpected trend in the reaction kinetics for the series of epoxy-functionalized polymers.
Films were prepared by spin-casting the telechelic polymers from a 10% (wt/wt) THF solution onto hydroxylated silicon substrates. Thickness of the spin-cast film varied between 250-300 nm depending on the MW of the polymer. Films were annealed at 150 ˚C and removed at prescribed time intervals in order to follow the kinetics of the reaction.

Picture below shows that the processes of polymer grafting to the substrate can be segmented into two main regimes. During the first regime, deposition of the graft polymer is limited by the classical diffusion of the polymer chains to the interface. 
In this case, the grafting process is carried out from the melt so many chains are not limited by diffusion and must only undergo a reorientation within the first several mono-layers to expose the terminal functionalities to the reactive substrate. 
It is believed that this phenomenon extends the duration of the fast portion of the grafting kinetics leading to a more efficient anchoring process.  This process is relatively fast leading to the formation of a polymer layer through which additional polymer chains must diffuse in order to reaction with the substrate.  The formation of this polymer layer presents additional polymer chains being grafted with a potential barrier that has to be overcome to reach the surface reactive functionalities.  This is characteristic of the second, slower regime of the grafting process. 

The results seem to follow the classical description for the two regimes of the grafting process.  The grafting process plateaus for these systems around 300 min with no significant changes in thickness observed after 6 hours of grafting time. 
The most notable aspect of the results shown is the variation in the final thickness of the grafted polymer films.  The lowest MW (1075) telechelic yield the lowest film thickness (3.8 nm) which is what one would expect.  However, the variation in the final thickness of the remaining polymers films is unexpected.  The second lowest MW (1750) yield the greatest final thickness of about 5.8 nm.  The two highest MW ,4000 and 6100, give an intermediate film thickness of 5.2 and 4.5 nm, respectively.  This could imply that the lower MW telechelics adopt a brush-like confirmation at high grafting densities while the larger MW telechelic preferentially form loops on the substrate yielding a thinner grafted polymer film.

Picture below shows the water contact angle measurements for two of the films from the previous experiment.
Water contact angles (static) for the 1075 and 4000 MW telechelic are relatively indistinguishable with values of 74˚ and 76˚, respectively after 6 hours of grafting time.  These values are much greater than that reported in literature for an epoxy end-capped monolayer with a water contact angle of 52˚.

We also investigated the grafting process of the same telechelics in the melt from a polymer matrix. Sample preparation was similar to that previously mentioned with a few changes.  The substrate used in the following experiments was an aminopropyltrimethoxysilane functionalized silicon substrate. The thickness of the APS layer was consistent with 1 – 3 layers of the silane.  The polymer/telechelic mixture was spin-casted onto the APS-modified substrate from a 2% (wt/wt) THF solution with varying ratios of polymer to telechelic.  Samples were annealed in a vacuum oven at 150 ˚C for a prescribed amount of time. Picture below shows the kinetics for the various systems under investigation.

AFM images of the films compliment the increase in thickness by showing an increase in surface coverage as a function of time.

A control experiment was also conducted under the same conditions using the pure non-functionalized poly(bisphenol A-co-epichlorohydrin) polymer. From this control experiment, it was found that the matrix polymer undergoes an irreversible adsorption process under the grafting conditions. As shown in picture below, the matrix polymer thickness increases as a function of time.