Radical Polymerization Initiated from a Solid Substrate. 1. Theoretical Background

Abstract

From a survey of the literature on grafting free radical polymerization from solid surfaces we suggest kinetic schemes for the process. The system of differential equations in partial derivatives including the diffusion equation based on the classical theory of free radical polymerization and the assumption that surface-bonded free radicals terminate by (1) reactions with bulk free radicals and (2) chain transfer to solvent or monomer are introduced. Computer simulations performed using the equations have shown good agreement with the characteristic features of the grafting process. The rate of grafting is linearly proportional to the surface concentration of the initiator and decreases as the initiation rate in the bulk increases. It follows from the concentration profiles of the bulk free radicals that free radical concentration in the vicinity of the surface can be several times larger than that in the bulk. The concentration profile depends on the distance between two surfaces. For distances less than a critical distance of about 2 μm, the concentration profile of the bulk free radicals is homogeneous.

A versatile approach to develop porous hydrogels with a regular pore distribution and investigation of their physicomechanical properties

“…A solution of tert-butyl hydroperoxide (10.8 g, 0.12 mol) in diethyl ether (30 mL) was added dropwise to a suspension of N-(hydroxymethyl)acrylamide (10.1 g, 0.1 mol) in diethyl ether (25 mL) at 5-7 C. The mixture was stirred and a solution of H 2 SO 4 (2.94 g, 0.03 mol) in diethyl ether (20 mL) was added for 1 h at [14][15][16] C. After stirring for additional 3 h at [22][23][24][25] C, the organic phase was separated, washed in series with water, 5% aq Na 2 CO 3 , and water until pH 7. The organic phase was dried over MgSO 4 Polyacrylamide A solution of acrylamide (100 g) and 2-propanol (10 or 30 g) in water (890 or 870 mL, respectively) was degassed with argon.…”

“…13 It has been reported that peroxide groups immobilized on the surface of different mineral powders are widely used to initiate free radical polymerization from the solid surface. [13][14][15][16] A variety of polymeric [17][18][19] and low molecular weight peroxides 16,19,20 have been utilized for the initiation of grafting polymerization from the solid particulate surface, which results in the encapsulation of the powder particles because of the formation of a thin polymer layer on the dispersed surface. 21 The proposed approach is based on the formation of polyacrylamide (PAAm) hydrogels, with enhanced mechanical properties and regular pore distribution using silica particles with grafted polyacrylamide as a porogen and the subsequent leaching out of the particles.…”

Reversible addition–fragmentation chain‐transfer graft polymerization of styrene: Solid phases for organic and peptide synthesis

“…Minko et al 42 discussed the theoretical background of the radical polymerization initiated from a solid substrate in which the initiator is attached to a solid surface: after a specific grafting time, the grafting surface is completely covered by polymer coils. The subsequent grafting of new chains requires stretching of the coils until the maximum possible surface grafting is obtained.…”

Gradient and patterned polymer brushes by photoinitiated “grafting through” approach

“…This “grafting to” approach provides rather low grafting densities of grafted polymers. The so‐called “grafting from” approach consists of attachment of the initiator to the substrate surface and the successive propagation of polymerization from the surface 11–13. This method assures high grafting density with more than 100‐nm‐thick brushes.…”